Dairy Science & Technology · Foundations · also Nutrition, Food and Nutrition, Dairy Nutrition
Nutrient needs, the place of milk in diets across life stages, lactose intolerance and milk allergy, and dairy in public health programmes.
In the exams: ICAR AICE subject 37 Unit 6; GATE XL-U Section 1 (nutrition); ICAR AIEEA-PG group 18 Unit I
Milk is the first food of every mammal and, for people in most of the world, a food eaten throughout life. A glass of cow milk supplies high-quality protein, calcium, phosphorus, potassium, iodine, riboflavin and vitamin B12 for little energy; cheese and yoghurt concentrate or transform these nutrients; and dairy foods carry saturated fat, lactose and allergenic proteins that some people must limit or avoid. A dairy technologist designs, formulates, fortifies and labels these foods, so must understand what the body needs, what milk provides, and what the evidence does and does not show about dairy and health.
This manual covers the human nutrition a dairy degree requires. It begins with the macronutrients and energy requirements and the reference values used to set nutrient targets. It explains how protein quality is measured, from biological value to the digestible indispensable amino acid score, and why milk proteins rank highly. It treats calcium, vitamin D and bone health; the place of milk in the diets of infants, children, adults and older people; lactose intolerance and cow's milk protein allergy, two conditions that are often confused; and the debate over dairy fat and cardiovascular disease, with an honest account of its limits. It ends with dairy in programmes against malnutrition, including school milk and fortification, and with the international rules for nutrition labelling and claims.
Examinations in dairy and food technology ask this material directly: Atwater factors and energy calculations, definitions of reference intakes, protein quality indices, causes and management of lactose intolerance, the difference between intolerance and allergy, and the conditions for nutrient content claims. Examples are taken from dietary guidance and programmes in many countries; national reference values differ and are described as ranges, not as a single standard.
The macronutrients are the nutrients needed in large amounts: carbohydrates, proteins and fats, with water and, in many classifications, dietary fibre. They supply energy and the building blocks of the body. Energy is measured in kilojoules (kJ) or kilocalories (kcal); 1 kcal = 4.184 kJ. The energy available from food is calculated with the Atwater general factors: about 17 kJ (4 kcal) per gram of protein, 17 kJ (4 kcal) per gram of available carbohydrate, 37 kJ (9 kcal) per gram of fat and 29 kJ (7 kcal) per gram of alcohol. Some labelling systems give lower factors for fibre and polyols.
These factors give the energy of milk products directly. Cow milk with 3.3% protein, 3.6% fat and 4.8% lactose provides per 100 mL about 3.3 × 4 + 3.6 × 9 + 4.8 × 4 = 64.8 kcal, or about 270 kJ; skimmed milk, with almost no fat, about 35 kcal. More than half of the energy of whole milk comes from fat, while in skimmed milk most comes from lactose and protein. Cheddar-type cheese, with about 25% protein and 33% fat, provides around 400 kcal per 100 g.
Carbohydrates supply glucose, the preferred fuel of the brain. The carbohydrate of milk is lactose, a disaccharide of glucose and galactose. International guidance distinguishes free sugars, those added to foods plus those in honey, syrups and fruit juices, from sugars naturally present in intact fruit and in milk; the World Health Organization recommends that free sugars provide less than 10% of energy, and ideally less than 5%. Lactose in plain milk is not a free sugar, but sugar added to flavoured milks, yoghurts and desserts is.
Proteins supply amino acids for building and repairing tissue, enzymes, hormones and antibodies. Nine amino acids are indispensable (essential) because the body cannot make them in sufficient amounts and they must come from food. Protein needs are expressed per kilogram of body weight. The joint FAO/WHO/UNU expert report of 2007 set a safe level of intake for healthy adults of 0.83 g of good-quality protein per kilogram per day, which covers the needs of nearly all adults; needs per kilogram are higher in infancy, childhood, pregnancy and lactation, and several expert groups recommend more, about 1.0 to 1.2 g/kg, for older adults.
Fats supply energy, essential fatty acids (linoleic and α-linolenic acids), and the fat-soluble vitamins A, D, E and K, and they carry flavour. Fats are classified by their fatty acids: saturated, monounsaturated, polyunsaturated and trans. Milk fat is roughly two thirds saturated fatty acids, with smaller amounts of monounsaturated, mainly oleic acid, and a few per cent of polyunsaturated and naturally occurring trans fatty acids. WHO guidance recommends limiting saturated fat to less than 10% of energy and trans fat to less than 1%, and keeping total fat roughly within 15 to 30% of energy, with national guidance varying in its upper limit.
Dietary fibre, the non-digestible carbohydrate of plant foods, is absent from milk, although some dairy products are formulated with added fibres such as inulin. Water is the largest dietary component of milk, which contributes meaningfully to the fluid intake of children and older people.
Energy requirement is the energy intake needed to balance energy expenditure in a healthy person of a given age, sex, size and level of physical activity, plus the needs of growth, pregnancy and lactation. Total energy expenditure has three main components: the basal metabolic rate (BMR), the energy used at complete rest to maintain body functions, which accounts for most of the expenditure in sedentary people; the thermic effect of food, about 10% of intake; and physical activity, the most variable part.
Expert committees estimate BMR from equations based on age, sex and body weight, such as those adopted by FAO/WHO/UNU, and multiply it by a physical activity level (PAL) to give total expenditure. The 2004 FAO/WHO/UNU report described lifestyles with PAL values of about 1.40 to 1.69 as sedentary or light, 1.70 to 1.99 as active or moderately active, and 2.00 to 2.40 as vigorous. For example, a woman with a BMR of 5.6 MJ per day and a PAL of 1.6 expends about 9.0 MJ (2,140 kcal) per day.
Energy balance determines body weight. When intake persistently exceeds expenditure, the excess is stored as fat; when it falls short, body tissue is used. Both undernutrition and overweight now coexist in many countries, often in the same communities and households, a situation called the double burden of malnutrition. Milk and dairy foods appear on both sides: as energy- and nutrient-dense foods that help underweight children grow, and, in their high-fat and sweetened forms, as possible contributors to excess energy intake.
Nutrient reference values translate scientific knowledge of requirements into numbers for planning diets, assessing intakes and labelling foods. Different bodies use different names, but the concepts are shared. Requirements vary between individuals, and for most nutrients they are assumed to follow a roughly normal distribution. The estimated average requirement (EAR, called the average requirement by the European Food Safety Authority) is the intake that meets the needs of half the healthy individuals in a group. The recommended dietary allowance (RDA), called the recommended nutrient intake (RNI) by FAO/WHO and the population reference intake (PRI) in Europe, is set at the EAR plus two standard deviations, so that it covers the needs of about 97 to 98% of individuals.
Where evidence is insufficient to set an average requirement, an adequate intake (AI) is given, based on the observed intakes of apparently healthy groups. The tolerable upper intake level (UL) is the highest daily intake unlikely to cause adverse effects in almost all people; it matters for fortified foods and supplements, especially for vitamin A, vitamin D, iron, zinc, iodine and calcium. For energy, no safety margin is added, because eating above one's requirement leads to weight gain; energy reference values are set at the average requirement.
Reference values are set separately for age groups, for men and women, and for pregnancy and lactation. They apply to healthy people and to average intakes over time, not to single days, and they do not cover the needs of people with disease.
Reference values for the same nutrient differ between expert bodies, sometimes widely. Calcium is a clear example. For adults aged about 19 to 50 years, FAO/WHO and the United States and Canada recommend about 1,000 mg per day; European reference values are in a similar range; the United Kingdom's reference nutrient intake is 700 mg; and recommendations in some Asian countries are lower still. Recommendations for adolescents are generally higher, around 1,000 to 1,300 mg, because of the rapid gain of bone mass. For vitamin D, recommendations for adults range from about 10 to 20 µg (400 to 800 IU) per day.
The differences arise because committees use different evidence, choose different criteria of adequacy (for example, calcium balance, bone density or fracture risk), make different assumptions about absorption and sun exposure, and apply different safety margins. Body size and typical diets differ, too. None of these values is wrong; each is a judgement under uncertainty. A dairy technologist formulating a product for several markets must therefore check the reference values and labelling rules in each, rather than assume that one set applies everywhere.
Reference values are used in different ways for different purposes. For assessing the diet of a group, the proportion of people with usual intakes below the EAR estimates the prevalence of inadequate intake; comparing intakes with the RDA overestimates inadequacy, because by definition most people need less than the RDA. For an individual, an intake at or above the RDA is very likely adequate, and an intake below the EAR is likely inadequate, but day-to-day variation means that several days of records are needed. For planning, diets for groups are designed so that few people fall below the EAR and few exceed the UL.
Nutrient density, the amount of a nutrient per unit of energy, helps judge which foods contribute most. Milk is highly nutrient-dense for calcium, riboflavin, vitamin B12 and iodine relative to its energy: 250 mL of semi-skimmed milk supplies about 300 mg of calcium for about 120 kcal, roughly a third of the adult calcium recommendation used in many countries. Food-based dietary guidelines turn nutrient targets into advice on foods, often recommending two to three servings of milk or dairy products a day, or placing dairy within a group of protein foods; the advice varies between countries in amount, preferred fat level and the place given to plant-based alternatives.
On food labels, reference values are simplified into single nutrient reference values (NRVs), used to express content as a percentage. Codex Alimentarius sets NRVs for labelling, for example 1,000 mg for calcium, and many countries adopt them or set their own.
Protein quality describes how well a dietary protein meets the body's needs for indispensable amino acids and nitrogen. It depends on two things: the amino acid composition and the digestibility. Several measures have been used.
Biological value (BV) is the percentage of absorbed nitrogen that is retained in the body: BV = (nitrogen retained / nitrogen absorbed) × 100. Whole egg protein, with a BV near 100, was long used as a reference; milk proteins also have high values, and cereal proteins much lower ones. Net protein utilisation (NPU) is the percentage of ingested nitrogen retained, which equals BV multiplied by digestibility. The protein efficiency ratio (PER) is the weight gain of growing rats divided by the protein they eat, usually measured over four weeks; casein is the reference protein, and results are commonly adjusted so that casein scores 2.5. PER was used for decades in labelling in some countries, but it reflects the needs of fast-growing rats, which need more sulfur amino acids than humans, and it is not proportional, so a protein with a PER of 2 is not twice as good as one of 1.
The chemical score, or amino acid score, compares the content of each indispensable amino acid in a protein with that in a reference pattern; the lowest ratio, for the limiting amino acid, is the score. Lysine is limiting in most cereals; methionine and cysteine in many legumes.
In 1991 an FAO/WHO expert consultation adopted the protein digestibility-corrected amino acid score (PDCAAS): the amino acid score of the limiting amino acid, multiplied by the true faecal digestibility of the protein, with any value above 1.0 truncated to 1.0. Milk proteins, egg and soy isolates all score 1.0 under PDCAAS, which therefore cannot distinguish among high-quality proteins.
In 2013 an FAO expert consultation recommended a new method, the digestible indispensable amino acid score (DIAAS). DIAAS uses the true ileal digestibility of each indispensable amino acid, measured at the end of the small intestine, because amino acids that reach the colon are fermented by bacteria and are not absorbed for protein use. For each amino acid, the digestible content per gram of protein is divided by its content in a reference pattern, and the lowest ratio, expressed as a percentage, is the DIAAS. Values are not truncated, so proteins with more than enough of every amino acid score above 100. Three reference patterns are used: for infants up to 6 months, for young children from 6 months to 3 years, and for older children, adolescents and adults. The consultation proposed that proteins with a DIAAS of 100 or more could support claims of excellent or high quality, those of 75 to 99 claims of good quality, and those below 75 no quality claim.
Milk proteins have DIAAS values above 100 in most published studies; whole cereals are much lower, limited by lysine; and legume proteins lie between. Data are still limited, because ileal digestibility is measured in growing pigs or by invasive human methods, and values depend on processing.
Protein quality matters most where diets depend on one staple food or where needs are high: infants, young children, pregnant and lactating women, older people, and those recovering from illness. In a mixed diet, the amino acids from different foods add together. Milk proteins are rich in lysine and in the branched-chain amino acids, especially leucine, so a small amount of milk complements cereal-based diets, raising the overall score of a meal; a meal of maize or wheat with milk has a better amino acid balance than either alone. This is one reason why milk powder is used in blended foods, therapeutic foods for malnourished children and food aid.
The two families of milk proteins differ. Caseins, about 80% of cow milk protein, clot in the stomach and are digested slowly, releasing amino acids over several hours. Whey proteins, about 20%, stay soluble, are digested quickly and are especially rich in leucine and cysteine. These differences are used in sports and clinical nutrition, where whey proteins are given to stimulate muscle protein synthesis after exercise or in older people at risk of sarcopenia.
Processing can reduce quality. Severe heating with reducing sugars, as in Maillard browning of milk powders during long, warm storage, binds the ε-amino group of lysine and makes it unavailable, lowering the quality of the protein even though the amino acid analysis after acid hydrolysis may not show the loss. Measurements of available lysine or of furosine detect this damage. The protein quality of infant formulas and therapeutic foods is therefore protected by careful heat treatment and storage.
Calcium is the most abundant mineral in the body; about 99% of it is in bones and teeth as hydroxyapatite, a calcium phosphate. The remaining 1% in blood and soft tissues controls muscle contraction, nerve conduction, blood clotting and cell signalling, and its concentration in blood is held within narrow limits by parathyroid hormone, calcitonin and vitamin D. When intake is low, bone is broken down to maintain blood calcium, so a long-term shortfall shows up as low bone mass rather than low blood calcium.
Milk and dairy products are the main sources of calcium in the diets of many populations: cow milk contains about 1.2 g per litre, hard cheeses about 0.7 to 1.2 g per 100 g, and yoghurt about the same per serving as milk. Fractional absorption of calcium from milk is about 30% in adults, similar to the absorption from most other foods and supplements. Oxalate, as in spinach, and phytate, as in unrefined cereals and legumes, bind calcium and reduce its absorption, so that some vegetables rich in calcium supply much less of it than their content suggests, while low-oxalate greens such as kale and bok choy are well absorbed. Calcium-set tofu, small fish eaten with their bones, and fortified foods are other sources. In populations that consume little dairy, calcium intakes are often well below the reference values.
Milk also supplies phosphorus, magnesium, potassium, protein and, where fortified, vitamin D, all of which contribute to bone health.
Vitamin D is formed in the skin from 7-dehydrocholesterol by ultraviolet B light, and obtained in the diet as cholecalciferol (D3) from animal foods and ergocalciferol (D2) from fungi and fortified foods. It is converted in the liver to 25-hydroxyvitamin D, whose blood concentration is the standard measure of vitamin D status, and in the kidney to 1,25-dihydroxyvitamin D, the active hormone that increases intestinal absorption of calcium and phosphate. Severe deficiency causes rickets in children, with soft, deformed bones, and osteomalacia in adults.
Few foods are naturally rich in vitamin D; oily fish and egg yolk are the main ones. Unfortified milk contains very little. Skin synthesis depends on latitude, season, time of day, skin pigmentation, clothing, age and sunscreen use; at high latitudes little or no vitamin D is made in winter. Vitamin D deficiency is therefore common in many regions, including in sunny countries where people cover the skin or stay indoors, and among older people, people with dark skin living at high latitudes, and exclusively breastfed infants not given supplements.
For these reasons many countries fortify milk, margarine, plant-based drinks or other staples with vitamin D, either by law or voluntarily, and recommend supplements for infants and older people. Fortification of fluid milk is long established in North America and in the Nordic countries; elsewhere it is voluntary or absent. Fortification levels are set nationally with the upper intake level in mind, because excess vitamin D causes hypercalcaemia.
Bone mass increases through childhood and adolescence and reaches its peak in early adulthood, around the third decade. Peak bone mass is largely determined by genetics but is also influenced by calcium and protein intake, vitamin D status, physical activity and hormones. After middle age, bone is lost, especially in women after menopause. Osteoporosis, defined by the World Health Organization as a bone mineral density at least 2.5 standard deviations below the young adult mean (a T-score of −2.5 or less), greatly raises the risk of fractures of the hip, spine and wrist.
Trials in children show that extra calcium or dairy increases bone mineral accrual modestly, though the effect may not persist after supplementation stops. In older adults, combined calcium and vitamin D supplements reduce fractures in people who are deficient, such as frail older people living in institutions, but the effect is small or absent in community-dwelling adults who are not deficient. Observational studies of milk intake and hip fracture give inconsistent results, with some cohorts showing no protective association and some countries with high milk intakes also having high fracture rates, a pattern that is confounded by differences in body size, longevity, genetics and activity.
The honest conclusion is that adequate calcium, vitamin D and protein are necessary for bone health throughout life, that dairy foods are an efficient way for many people to obtain them, and that dairy is not a guarantee against osteoporosis, nor is it irreplaceable where other sources supply the same nutrients. Claims on dairy products about bone health must reflect this evidence and the rules of each market.
Breast milk is the ideal food for infants. The World Health Organization and UNICEF recommend exclusive breastfeeding for the first six months of life, followed by appropriate complementary foods with continued breastfeeding up to two years of age or beyond. Human milk differs from cow milk: it has less protein (about 0.9 to 1.2 g per 100 mL in mature milk compared with about 3.3 g), a higher whey-to-casein ratio, more lactose, a different fatty acid profile, oligosaccharides that feed beneficial gut bacteria, and protective factors such as secretory IgA, lactoferrin and lysozyme.
When an infant is not breastfed, infant formula is the only suitable substitute. Most formulas are made from modified cow milk, adjusted in protein content and whey-to-casein ratio, with vegetable oils replacing much of the milk fat, added lactose, and added vitamins, minerals and other nutrients to meet the composition set by the Codex standard for infant formula and by national rules. Formulas based on goat milk, soy protein or protein hydrolysates exist for particular needs.
Unmodified cow milk is not recommended as the main drink before 12 months of age. It provides too much protein and minerals, raising the renal solute load; it is low in iron, and the iron it contains is poorly absorbed; it is low in vitamin C and essential fatty acids; and in young infants it can cause small losses of blood from the intestine. Together these increase the risk of iron-deficiency anaemia. Small amounts of cow milk in complementary foods, and yoghurt and cheese, are generally accepted from around six months.
After the first year, milk and dairy foods are valuable sources of energy, protein, calcium and other nutrients for young children, whose stomachs are small and whose needs per kilogram are high. Many national guidelines advise whole milk for children from one to two years and allow lower-fat milk from about two years, while others recommend whole milk for longer or leave the choice to families; very high intakes, above about half a litre to 700 mL a day, are discouraged in young children because they displace iron-rich foods.
In low-income settings, studies have associated milk and other animal-source foods with better linear growth of children, and milk is often given to undernourished children. In high-income settings, the concern shifts to sweetened milk drinks and desserts, which add free sugars, and to replacing water and milk with sugary beverages. Plain milk and water are the drinks most guidelines recommend for children.
Adolescence is the period of most rapid bone mineral accrual; about a quarter or more of adult bone mineral is laid down in the two years around the growth spurt. Calcium recommendations are highest at this age, yet milk intake commonly falls during adolescence, especially in girls, as soft drinks replace it. For adolescents who do not consume dairy, attention to other calcium sources, or fortified alternatives, is needed. School-based programmes, described in a later chapter, are one way societies have tried to sustain dairy intake in children.
For adults, dairy foods are one of several ways to meet needs for protein, calcium, iodine, riboflavin and vitamin B12. Food-based dietary guidelines in many countries in Europe, the Americas, Oceania and parts of Asia recommend two to three servings of dairy a day, often preferring lower-fat and unsweetened forms; others include dairy among protein foods or give smaller amounts; and a growing number mention fortified plant-based alternatives. Fermented products such as yoghurt and cheese suit many lactose-intolerant adults. In pregnancy and lactation, needs for protein, calcium, iodine and several vitamins rise, and milk is a convenient source, although unpasteurised milk and some soft cheeses are avoided because of the risk of listeriosis.
Iodine deserves mention. In many countries milk is a major dietary source of iodine, largely from iodine supplements in cattle feed and from iodine-based sanitisers used on teats and equipment; its concentration varies widely with farming practice and season. Shifts from milk to unfortified plant drinks can lower iodine intake, a concern in pregnancy.
Older people often eat less, while their protein needs per kilogram rise because muscle becomes less responsive to protein, a condition called anabolic resistance. Loss of muscle mass and function, sarcopenia, raises the risk of falls, frailty and disability. Expert groups recommend protein intakes of about 1.0 to 1.2 g/kg/day for healthy older adults, with more for those who are ill, spread over meals with about 25 to 30 g of high-quality protein at each. Milk proteins, and whey in particular because of its leucine content, are well suited; soft dairy foods also help those with chewing or swallowing difficulties.
Lactose is digested in the small intestine by the enzyme lactase-phlorizin hydrolase (lactase), on the brush border of the intestinal cells, into glucose and galactose, which are absorbed. In most mammals, including most humans, lactase activity falls after weaning to a low level; this is lactase non-persistence, also called primary hypolactasia. In some human populations, lactase activity continues into adulthood, a trait called lactase persistence. It is caused by genetic variants in a regulatory region upstream of the lactase gene; different variants arose independently in northern Europe, in pastoralist groups of East Africa and in the Middle East, and spread because milk drinking gave a nutritional advantage to dairying peoples.
As a result, the prevalence of lactase persistence varies greatly around the world: high, often above 80 to 90%, in north-western Europe, intermediate in southern Europe, parts of South Asia, the Middle East and some pastoralist populations of Africa, and low, often below 10 to 20%, in East Asia, much of sub-Saharan Africa and among Indigenous peoples of the Americas and Oceania. Overall, about two thirds of the world's adults are thought to be lactase non-persistent.
Lactose malabsorption, the incomplete absorption of lactose, follows from low lactase. Secondary lactase deficiency is a temporary loss of lactase due to damage to the small-intestinal lining, as in gastroenteritis, coeliac disease or chemotherapy; it resolves as the gut heals. Congenital lactase deficiency, present from birth, is very rare.
Not everyone who malabsorbs lactose has symptoms. Lactose intolerance is the occurrence of symptoms after lactose intake in a person with malabsorption. Undigested lactose passes into the colon, where it draws water by osmosis and is fermented by bacteria into short-chain fatty acids and gases, hydrogen, carbon dioxide and in some people methane. The result can be abdominal pain, bloating, flatulence, borborygmi and loose stools, usually from half an hour to a few hours after eating. Symptoms depend on the dose of lactose, whether it is eaten with other food, the rate of gastric emptying, the colonic bacteria, and the individual's sensitivity; anxiety about milk can itself produce symptoms in blinded studies.
The hydrogen breath test is the common clinical test: after a dose of lactose, typically 25 to 50 g, a rise in breath hydrogen above baseline of about 20 parts per million or more indicates malabsorption. The lactose tolerance test measures the rise in blood glucose after a lactose dose; a small rise indicates poor digestion. Genetic tests identify known lactase persistence variants but do not diagnose secondary deficiency, and the relevant variants differ between populations. Many people diagnose themselves, and self-reported lactose intolerance is often not confirmed by testing, which can lead to unnecessary avoidance of dairy and lower intakes of calcium and other nutrients.
Lactose intolerance is not an allergy. It involves no immune reaction, is not dangerous, and depends on the amount of lactose; cow's milk protein allergy, described next, is an immune reaction to milk proteins that can be severe even with traces.
Most people with lactose malabsorption do not need to avoid dairy foods entirely. Controlled studies summarised by a United States National Institutes of Health consensus conference in 2010 found that most adults with lactose malabsorption can tolerate about 12 g of lactose, the amount in about a cup (240 mL) of milk, taken in one dose with little or no increase in symptoms, and more if it is spread through the day and taken with meals. Regular intake may also improve tolerance through adaptation of the colonic bacteria.
Dairy foods differ greatly in lactose. Milk contains about 4.5 to 5% lactose. Yoghurt contains somewhat less, and it is better tolerated than its lactose content suggests because its live bacteria supply β-galactosidase that digests lactose in the intestine; this benefit is recognised in an authorised health claim in the European Union for live yoghurt cultures. Hard and long-ripened cheeses, such as Cheddar-type, Parmesan-type and Emmental-type cheeses, contain very little lactose, typically below 0.1 g per 100 g, because most of the lactose leaves with the whey and the rest is fermented during ripening. Butter contains little. Soft fresh cheeses, ice cream and milk powders contain more.
Lactose-free and reduced-lactose milks are made by adding lactase to milk, before or after heat treatment, which hydrolyses lactose to glucose and galactose and makes the milk taste sweeter; ultrafiltration may be used first to remove part of the lactose and keep the sweetness and energy close to those of ordinary milk. The maximum lactose allowed for a 'lactose-free' claim differs between countries, commonly 0.01 to 0.1 g per 100 g or mL. Lactase enzyme tablets or drops taken with dairy foods are another option.
Cow's milk protein allergy (CMPA) is an adverse immune reaction to one or more milk proteins. It is one of the most common food allergies of infancy; estimates of its prevalence in young children in high-income countries range from about 0.5 to 3%, depending on how it is diagnosed, and fewer data exist elsewhere. It usually appears in the first year of life, often when cow milk formula is introduced, and most children outgrow it: many by three years of age and most by school age, though IgE-mediated allergy tends to persist longer and occasionally into adulthood.
There are two main mechanisms. IgE-mediated allergy develops when the immune system produces immunoglobulin E antibodies against milk proteins; on re-exposure, the antibodies on mast cells trigger the release of histamine and other mediators within minutes to two hours, causing hives, swelling, vomiting, wheezing and, in severe cases, anaphylaxis, a life-threatening reaction. Non-IgE-mediated allergy involves cell-mediated reactions, with delayed symptoms hours or days later, mainly in the gut: vomiting, diarrhoea, blood in the stools, poor growth, and eczema; food protein-induced enterocolitis syndrome (FPIES) and allergic proctocolitis are forms of it.
All the major milk proteins can be allergenic. The caseins, especially αs1-casein, and the whey proteins β-lactoglobulin and α-lactalbumin are the main allergens. Because these proteins are similar in the milks of related ruminants, more than 90% of children allergic to cow milk also react to goat and sheep milk, which are therefore not suitable substitutes. Milks of more distant species, such as camel and donkey, cross-react less but are not routinely recommended.
Diagnosis starts with a careful history of the symptoms, their timing and their relation to milk intake, and a physical examination. For suspected IgE-mediated allergy, skin prick tests and blood tests for milk-specific IgE show sensitisation; higher levels make allergy more likely, but sensitisation alone does not prove clinical allergy. For non-IgE-mediated allergy there is no reliable laboratory test.
The definitive test is the oral food challenge: milk is removed from the diet for a period, usually two to four weeks, to see whether symptoms resolve, and is then reintroduced under medical supervision to see whether they return. The double-blind, placebo-controlled food challenge is the reference standard in research. Challenges with a risk of severe reactions are performed in hospital.
Misdiagnosis is common in both directions. Colic, reflux and eczema have many causes, and labelling an infant allergic without a challenge can lead to unnecessary restriction of diet and use of expensive special formulas. On the other hand, unrecognised allergy causes continued symptoms and poor growth. Professional guidelines from paediatric and allergy societies in several regions give algorithms for diagnosis and management, which differ in detail.
Management is strict avoidance of cow milk protein, with a nutritionally adequate substitute. Breastfeeding is continued; in some infants with symptoms while breastfed, the mother may be advised to remove dairy from her own diet, with calcium and vitamin D supplements. For formula-fed infants, an extensively hydrolysed formula, in which milk proteins are broken down into small peptides, is the usual first choice and is tolerated by most allergic infants. An amino acid-based formula is used for severe or complex cases and for infants who react to extensively hydrolysed formula. Soy-based formula may be considered in some guidelines for infants over six months without soy allergy, and hydrolysed rice-protein formulas are used in some countries. Partially hydrolysed formulas, marketed for other purposes, are not suitable for treating allergy.
Tolerance is checked periodically by supervised reintroduction. Many children tolerate extensively heated milk, as in baked goods, before they tolerate fresh milk, because heat changes the shape of some allergenic regions of the proteins; stepwise 'milk ladders' are used under medical guidance for non-IgE allergy in some regions.
For the dairy industry, milk is one of the major food allergens that must be declared on labels under the Codex General Standard for the Labelling of Prepackaged Foods and the laws of most countries, including when milk derivatives such as casein, whey, lactose or butter are used in non-dairy foods. Allergen management in mixed plants, the cleaning and verification of lines shared between dairy and dairy-free products, and the correct use of precautionary labels such as 'may contain milk' protect allergic consumers. Lactose-free milk is not suitable for people with milk allergy, because it still contains milk proteins; this confusion is common and dangerous.
Cardiovascular disease, chiefly coronary heart disease and stroke, is the leading cause of death worldwide. Its main modifiable causes include high blood pressure, raised low-density lipoprotein (LDL) cholesterol, smoking, diabetes, obesity and physical inactivity. The diet–heart hypothesis, developed from the 1950s, holds that diets high in saturated fat raise LDL cholesterol and so raise the risk of coronary disease.
The first link is well established. Controlled feeding trials show that saturated fatty acids, especially lauric (12:0), myristic (14:0) and palmitic (16:0) acids, raise LDL cholesterol compared with unsaturated fatty acids or carbohydrates, while stearic acid (18:0) has little effect. Trans fatty acids raise LDL cholesterol and lower high-density lipoprotein (HDL) cholesterol. LDL cholesterol is a causal factor in atherosclerosis, supported by genetic, epidemiological and trial evidence.
Milk fat is about two thirds saturated, with substantial amounts of myristic and palmitic acids, so on its fatty acid composition alone it would be expected to raise LDL cholesterol. Butter does so in feeding trials when it replaces unsaturated oils. Dietary cholesterol, about 14 mg per 100 mL in whole milk and more in butter and cheese, has a smaller and more variable effect on blood cholesterol than saturated fat. Systematic reviews of randomised trials, such as a Cochrane review updated in 2020, find that reducing saturated fat intake for at least two years reduces combined cardiovascular events, with the greatest benefit when saturated fat is replaced by polyunsaturated fat rather than by refined carbohydrate.
Dairy foods are not just their fatty acids. Studies over the past two decades have found that the effect of dairy fat on blood lipids depends on the food that carries it, the so-called food matrix. In controlled trials, cheese raises LDL cholesterol less than butter with the same amount of fat, possibly because its calcium binds fatty acids and increases their excretion in faeces, because of the milk fat globule membrane, which is largely retained in cheese and lost in butter, or because of fermentation. Dairy foods also supply calcium, potassium, magnesium and proteins, which may lower blood pressure, and fermented products contain bacteria and their metabolites.
Prospective cohort studies, combined in meta-analyses, generally find that total dairy intake is not associated with higher risk of coronary heart disease and is associated with a modestly lower risk of stroke and of type 2 diabetes, with yoghurt and cheese often showing neutral or inverse associations. Associations for whole-fat and low-fat dairy are often similar, which does not support the strong preference for low-fat dairy based on fatty acid composition alone. Ruminant trans fatty acids, present at a few per cent of milk fat, have not shown the adverse associations of industrial trans fats at usual intakes, although they raise LDL cholesterol at high experimental doses. Claimed benefits of conjugated linoleic acid for human health have not been established.
Interpreting this evidence requires care. Observational studies show association, not causation; dairy consumers may differ from non-consumers in income, education, smoking, physical activity and other diet, and adjustment cannot remove all confounding. Dietary intake is measured imperfectly, usually by questionnaires once or a few times. The comparison matters: dairy fat may look neutral compared with the average of what people would otherwise eat, which in many diets is refined carbohydrate, yet harmful compared with unsaturated plant oils, nuts or fish. Products and habits differ between countries, so results from one population may not transfer to another. Long-term randomised trials of dairy foods with hard outcomes such as heart attacks and deaths have not been done and may never be. Much research on dairy and health is funded by the dairy industry, which does not make it wrong but makes independent replication important.
National dietary guidance reflects these uncertainties in different ways. Many guidelines, for example in North America and much of Europe, continue to advise lower-fat dairy products to keep saturated fat below about 10% of energy. Others place less emphasis on fat content and more on whole foods and dietary patterns, while still advising limits on butter and cream. Cardiovascular and diabetes organisations differ in their wording. Sodium in cheese and added sugar in flavoured milk and yoghurt are separate concerns.
A dairy technologist should be able to present this evidence honestly to colleagues, customers and the public: dairy foods can be part of healthy diets; the effect of dairy fat depends on the food and on what it replaces; and neither claims that dairy fat is harmful in every form nor claims that it is protective are supported by conclusive evidence.
Malnutrition includes undernutrition, micronutrient deficiencies, and overweight and obesity. In children, undernutrition is measured against the WHO Child Growth Standards: stunting is a height-for-age more than two standard deviations below the median, reflecting chronic undernutrition and infection; wasting is a weight-for-height more than two standard deviations below the median, reflecting acute undernutrition; and underweight is a low weight-for-age. Joint estimates by UNICEF, WHO and the World Bank put the number of stunted children under five at around 150 million in the early 2020s, most of them in South Asia and sub-Saharan Africa. Deficiencies of iron, vitamin A, iodine and zinc, sometimes called hidden hunger, affect far more people. At the same time, overweight is rising among children and adults in every region.
Milk can help on several fronts. It supplies high-quality protein, minerals and vitamins in a form children accept, and studies in low-income countries have associated milk or dairy intake with better linear growth, although the size of the effect varies and depends on the rest of the diet and the burden of infection. Livestock development programmes that help households keep dairy animals can improve both income and child nutrition, but the benefits are not automatic: income from milk sales may not be spent on children's food, and the work burden often falls on women.
Severe acute malnutrition is treated with therapeutic foods built on milk. The WHO protocol for inpatient care uses F-75, a low-protein, low-sodium milk-based formula for the stabilisation phase, and F-100 for rehabilitation. Ready-to-use therapeutic food (RUTF), an energy-dense paste of peanut, sugar, oil, vitamins, minerals and milk powder, allows most children to be treated at home; the international specification requires that at least half of its protein comes from milk products, although formulations with less milk are being tested.
School milk programmes give milk or dairy products to children at school, free or subsidised. They have a long history: national programmes began in several European countries and North America in the first half of the twentieth century, and today programmes of many sizes run in countries across Asia, Africa, Latin America, Europe and Oceania. The Food and Agriculture Organization promotes World School Milk Day each year on the last Wednesday of September.
Programmes aim to improve children's nutrition and health, and often also school attendance, and to support local dairy farmers by creating a steady market. Their design varies: the product may be fresh pasteurised milk, UHT milk, milk powder reconstituted at school, flavoured milk, yoghurt or fortified milk; it may be bought from local cooperatives or imported; and it may be targeted at the poorest areas or given to all. Key practical questions are safety, especially the cold chain for fresh milk and the hygiene of reconstitution; cost per child; the sugar content of flavoured products; acceptability; and reliable delivery during school terms. Several food safety incidents linked to school milk have shown the importance of supplier approval and testing.
Evaluations show benefits for nutrient intakes and, in some studies, for growth, micronutrient status and attendance, but results vary with the starting nutritional status of the children, the amount given and the quality of implementation. Programmes linked to local dairy development have been described as a way to build national dairy sectors as well as feeding children.
Food fortification is the addition of micronutrients to foods to prevent or correct deficiencies in a population. Guidelines published by WHO and FAO in 2006 distinguish mass fortification of widely eaten staples, targeted fortification of foods for particular groups such as infants or schoolchildren, and market-driven voluntary fortification by manufacturers. Fortification may be mandatory or voluntary under national law, and levels are set so that the most exposed consumers do not exceed upper intake levels while the least exposed still benefit.
Milk is a suitable vehicle for some nutrients. Vitamins A and D are fat-soluble; vitamin A is largely removed with the fat when skimmed or low-fat milk is made, so many countries require or allow restoration of vitamin A in such milks, and several fortify milk with vitamin D. These vitamins are added as stable emulsified concentrates before homogenisation and are reasonably stable through pasteurisation and UHT treatment, although vitamin A is sensitive to light. Losses during processing and storage must be allowed for, and levels are checked by analysis.
Iron is the most difficult nutrient to add to milk. Soluble iron salts catalyse fat oxidation, giving metallic and oxidised flavours, and bind to casein; insoluble forms are better tolerated but less absorbed. Encapsulated iron salts, iron chelates such as ferrous bisglycinate, and micronised ferric pyrophosphate are used, and the calcium in milk somewhat reduces iron absorption. Milk powders for young children, growing-up milks and fortified school milks often carry iron, zinc, iodine and vitamins. Iodine and folic acid are also added in some programmes. Every fortification programme needs quality control at the plant, monitoring of the population's status and periodic review.
Nutrition labelling informs consumers of the nutrient content of foods. The international reference is the Codex Alimentarius Guidelines on Nutrition Labelling, which most national rules follow in structure. Where nutrition labelling is applied, the Codex guidelines list energy, protein, available carbohydrate, fat, saturated fat, sodium and total sugars as the nutrients to be declared, with any other nutrient for which a claim is made. Values are given per 100 g or 100 mL, and may also be given per serving, with the number of servings in the package. Many jurisdictions make the nutrition declaration mandatory on most prepackaged foods.
Declared values are average values, derived from analysis of the product or calculated from the known composition of ingredients, and must stay within tolerances set by national authorities over the shelf life. Rounding rules are specified. For dairy products, natural variation of milk composition by season and region, losses of vitamins in storage, and the conversion of nitrogen to protein with a factor of 6.38 all affect declared values. Energy is calculated with conversion factors set in the rules, usually the Atwater-type factors.
Percentages of nutrient reference values (NRVs) are often shown alongside amounts. Front-of-pack nutrition labels summarise the information more simply, and their designs differ widely: colour-coded traffic lights, graded summary scores such as Nutri-Score and the Health Star Rating, and black warning octagons for nutrients in excess used in several Latin American countries. Under some schemes, cheeses and sweetened dairy products receive warnings or low scores because of their fat, sodium or sugar, a frequent subject of debate between regulators and the dairy industry.
A nutrition claim is any statement suggesting that a food has particular nutritional properties. Codex Guidelines for Use of Nutrition and Health Claims set the general framework, and national rules supply the exact conditions. A nutrient content claim describes the level of a nutrient: 'low fat', 'high in protein', 'source of calcium'. Under the Codex conditions, for example, a 'source' claim for a vitamin or mineral requires at least 15% of the NRV per 100 g for solids, or 7.5% per 100 mL for liquids, or 5% per 100 kcal, or 15% per serving; a 'high' claim requires twice the 'source' value. 'Low fat' requires no more than 3 g of fat per 100 g for solids or 1.5 g per 100 mL for liquids, and 'fat free' no more than 0.5 g. National thresholds can differ and must be checked.
A worked example: semi-skimmed milk with 120 mg of calcium per 100 mL contains 12% of the Codex calcium NRV of 1,000 mg per 100 mL, which exceeds the 7.5% needed for a 'source of calcium' claim for a liquid but not the 15% needed for 'high in calcium' per 100 mL; a 250 mL serving, however, provides 300 mg, or 30% of the NRV, which meets the 'high' level on a per-serving basis where that basis is permitted.
A comparative claim compares a food with a reference food, such as 'reduced fat' or 'light'. Codex requires a relative difference of at least 25% in the nutrient, and a meaningful absolute difference, with the comparison stated. Claims about lactose, such as 'lactose-free' or 'low lactose', and about added sugars, such as 'no added sugar', have their own conditions, which vary by country.
A health claim states or implies a relationship between a food or one of its constituents and health. Codex distinguishes nutrient function claims, which describe the physiological role of a nutrient, such as 'calcium aids in the development of strong bones and teeth'; other function claims, describing a specific beneficial effect of a food or constituent; and reduction of disease risk claims, which relate a food or constituent to a reduced risk of a disease, such as osteoporosis. Codex requires that health claims be based on current, relevant scientific substantiation, generally from well-designed human studies, that the food contain a meaningful amount of the constituent, and that the claim be consistent with national health policy.
Countries regulate health claims in different ways. Some, such as the European Union, approve each claim individually after scientific assessment and publish a list of permitted wordings; many claims about probiotics have been rejected there for lack of evidence of a beneficial effect in the general population. Others allow claims based on a list of approved diet–disease relationships, or require notification and substantiation by the company. Claims about dairy foods that have been authorised in some jurisdictions include those relating calcium and vitamin D to normal bones, and live yoghurt cultures to improved lactose digestion.
A dairy technologist preparing a label must therefore check the product's analysis against the claim conditions of each market, use only permitted wordings, avoid implying that the food prevents or cures disease where that is prohibited, and keep the evidence on file. Misleading claims, and claims on foods that are high in fat, sugar or salt where nutrient profiles forbid them, are common causes of enforcement action and product recalls.
Calculate the energy and nutrient content of every product you study, from the composition table and the Atwater factors, and compare it with reference values for a child, an adult and an older person. Learn to distinguish lactose intolerance from milk allergy without hesitation, because examiners, customers and parents confuse them. Read the Codex guidelines on nutrition labelling and claims, then check whether real labels on milk, yoghurt and cheese meet their conditions; that exercise teaches more than memorising thresholds.
A product developer or regulatory officer five years into the job formulates reduced-fat, reduced-sugar, high-protein and lactose-free products, designs fortification premixes and calculates overages for vitamin losses, prepares nutrition panels and checks claims against the rules of each export market, and answers consumer questions about lactose, allergy and fat. Typical decisions: whether a new yoghurt qualifies as a source of protein or high in calcium, how much lactase and time are needed for a lactose-free claim, and how to handle allergen cross-contact on a shared line.
A technical or regulatory director with 25 years' experience sets the nutrition strategy of a dairy business: reformulation targets for sugar, salt and saturated fat, the company's position on front-of-pack labelling schemes, investment in lactose-free and high-protein ranges, and participation in school milk and fortification programmes. They brief executives and regulators on the evidence about dairy fat and health, which requires presenting its limits honestly, and they decide which health claims are worth the cost of substantiation in each market.
A professor or research leader designs and reviews nutrition studies on dairy: protein digestion and DIAAS measurement, calcium absorption, dairy matrix effects on lipids, lactose tolerance in different populations, and the effects of school milk on child growth. Independent, well-designed trials and transparent reporting of funding are central to the credibility of the field. They advise expert committees on reference values and claims, and teach students to read the epidemiology critically rather than selectively, whichever way the results happen to point.
National reference values, fortification levels, school milk rules and claim conditions are described in outline and through Codex; exact values for any country must be read from its current regulations. Clinical nutrition (enteral and parenteral feeding, disease-specific diets), sports nutrition, the gut microbiome, and evidence on dairy and cancer, acne or body weight are not covered. Prevalence figures for lactose malabsorption and milk allergy are approximate and come mainly from high-income countries; data for many regions are sparse. Infant formula technology is left to infant-nutritional-dairy-products, and probiotics to probiotics-functional-dairy.
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