Proteins are large molecules made from smaller units called amino acids. There are twenty amino acids commonly found in both plant and animal proteins. There are generally considered to be eight amino acids that the body cannot make itself which need to be obtained from the food we eat. These are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Infants additionally need food sources of histidine and possibly taurine. Proteins are necessary for maintaining tissues and for sustaining growth. They are also used to make hormones and other physiologically active substances.
Protein Requirements
Experts are still not entirely sure how much protein we need and estimates have been revised often in recent years. The national and international organisations which advise on nutrient requirements suggest standards which are calculated to meet or exceed the requirements of practically everyone in the population. They take into account individual variation and so the levels have a wide inbuilt safety margin. The recommendations below are based on the complete digestibility of milk or egg protein. Since protein from plant sources may be slightly less digestible, the UK's Department of Health recommends that vegetarians and vegans multiply the above figures by a factor of 1.1.
The UK Reference Nutrient Intakes (RNI) for protein are as follows: (The RNI is a daily amount that is enough or more than enough for 97% of people. The RNI is similar to the Recommended Daily Amount used previously in the UK.)
Type of person (Amounts Required)
· 0-12 months (12.5-14.9g/day)
· 1-3 years (14.50g/day)
· 4-10 years (19.7-28.3g/day)
· 11-14 yrs (boys) (42.1g/day)
· 11-14 yrs (girls) (41.2g/day)
· 15-18 yrs (boys) (55.2g/day)
· 15-18 (girls) (45g/day)
· 19-50 yrs (55.5g/day)
· 50+ yrs (53.3g/day)
· 19-50 yrs (45g/day)
· 50 + yrs (46.5g/day)
· During pregnancy (extra 6g/day)
· Breast feeding 0-6mths (extra 11g day)
· Breast feeding 6+ mths (extra 8g/day)
The US Recommended Dietary Allowances introduced in 1989 are similar to the UK values.
Vegan Sources of Protein
The foods which commonly supply the most protein in a vegan diet are pulses (peas, beans, lentils, soya products), grains (wheat, oats, rice, barley, buckwheat, millet, pasta, bread), nuts (brazils, hazels, almonds, cashews) and seeds (sunflower, pumpkin, sesame). The chart on the following page lists plant foods providing 10g of protein which should give an indication of the amounts of foods that should be eaten on a daily basis. Examples of amounts of foods providing 10g of protein
Type of food (Quantity)
· Peanuts (39g)
· Almonds (47g)
· Brazil Nuts (50g)
· Hazel Nuts (71g)
· Soya flour (24g)
· Whole lentils dried & boiled (114g)
· Chickpeas dried & boiled (119g)
· Kidney beans dried & boiled (119g)
· Wholemeal bread (95g)
· Wholemeal spaghetti boiled (213g)
· Brown rice boiled (385g)
· Pumpkin seeds (41g)
· Sunflower seeds (51g)
· Sesame seeds (55g)
Are Plant Proteins Second Class Citizens?
No, certainly not! Nutritionists once believed that plant proteins were of a poorer quality than animal proteins. And even now plant proteins are sometimes called 'second class' proteins whilst animal proteins are elevated to the 'first class' department. This belief centred on early research on the poor laboratory rat which showed that giving extra amino acids of weanling rats reared on a plant-protein diet improved their growth. The same was assumed to be true for humans. However, the parameters of the experiments were set in such a way that differences in the quality of plant and animal proteins were exaggerated. Also, rats and humans have different nutritional requirements, since weanling rats grow at a much faster rate, relatively, than human infants and therefore need more protein. A comparison of rat and human milk makes the difference quite clear: protein comprises only 7% of the calorie content of human milk, while rat milk contains 20% protein. If weanling rats were fed only human milk, they would not thrive. These tests over-estimated the value of some animal proteins while under-estimating the value of some vegetable proteins and The World Health Organisation has now abandoned this inadequate method of assessing the value of proteins to the human body.
Protein Combining. Is It Necessary?
No, it really isn't necessary! Research on laboratory rats also led to the misleading theory of protein combining (2). Protein combining has unfortunately gained momentum over the years. It was based on the idea that complementary protein foods with different limiting amino acids, such as beans and grains, should be eaten at each meal in order to enhance the availability of amino acids.
Proteins in foods have a distinctive pattern, being higher in some amino acids and lower in others. For many years the quality of a protein reflected its amino acid pattern and was measured against the protein in a hen's egg which counted as 100%. By this method, in each protein the amino acid furthest below the standard reference is known as the limiting amino acid. This is not necessarily the one present in the lowest absolute amount but the one present in the lowest proportion compared to protein in a hen's egg! In most grains and seeds, the limiting amino acid is lysine, while in most pulses it is methionine. Tryptophan is the limiting amino acid in corn (maize), and in beef it is methionine. Although each food has a limiting amino acid, most foods have all amino acids in adequate amounts for human health.
Even vegetarians are sometimes advised to combine vegetable proteins with dairy foods. This advice is now very old fashioned. Protein combining may reduce the amount of protein required to keep the body in positive protein balance but several human studies have indicated that this is neither necessary nor even always the case. Diets based solely on plant foods easily supply the recommended amounts of all the indispensable amino acids, and protein combining at each meal is unnecessary. Soya protein is actually equivalent in biological value to animal protein.
Protein - Too Much of a Good Thing?
Studies show that vegan diets provide the ideal amounts of protein recommended by the World Health Organisation and by the UK's Department of Health. On the other hand, many omnivores eat more protein than guidelines recommend and this may have disadvantages for their health. Excessive protein consumption may be associated with health risks. Kidney function can be compromised by too much protein in older people and in patients with kidney disease; also, a high protein intake may adversely affect calcium balance and contribute to mineral loss from bone. The Office of Population Censuses and Surveys 1990 survey of British adults (3) showed that average protein intakes are 84g/day for men and 64g/day for women which are higher than recommended,
Different types of dietary protein may have differing effects on cholesterol and fats in the bloodstream. Greater hormonal responses resulted in a meal derived from casein (milk) than from soya beans. This suggests that milk protein leads to higher levels of cholesterol and fats in the blood. These, in turn, are risk factors for coronary heart disease.
A survey of 620 women in Singapore revealed that, among pre-menopausal women, those who regularly ate soya protein and soya products in general had about half the normal risk of developing breast cancer. In contrast, the consumption of red meat and animal protein was linked with an increased risk of breast cancer in pre-menopausal women.
Diets rich in meat protein lead to more uric acid in the urine, and a general increase in urine acidity. because of the acidity, the uric acid does not easily dissolve and can form into kidney stones.
Is there Enough Protein for Growing Children?
Children's over-riding nutritional need is for energy rather than protein per se. As long as children's energy needs are being met they will thrive on a diet in which protein is available from a mixture of plant foods. Infants and children reared on a varied vegan diet obtain adequate protein and energy, and are healthy and grow normally. Although they tend to be of lighter build than omnivore children they are within the normal ranges for height and weight. Regular consumption of suitably-prepared high-energy foods, such as grains, pulses and nuts, with smaller amounts of bulky, less energy-dense fruits and vegetables, will ensure a satisfactory intake of protein and energy. There have been only two recent reports of protein and/or Calorie malnutrition in infants reared by vegan parents on a vegan diet, and these were due to over-dilution or inadequate variety of weaning foods. Other published cases of protein and energy deficiency in infants given alternative diets involved restrictive macrobiotic or fruitarian regimes, or dietary limitations imposed by non-vegan parents for perceived health reasons.
Further Details
For more details on protein and the vegan diet in general see Vegan Nutrition by Gill Langley. This book is the most comprehensive survey of scientific research on vegan diets. It is ideal for vegans, would-be vegans and health care professionals. It includes highlighted key points, easy-to-follow tables and chapter summaries.
(1) Food & Agriculture Organization/World Health Organization/United Nations University (1985). Energy & protein requirements. WHO Technical Report Series 724. Geneva: WHO.
(2) Lappé, F.M. (1976). Diet for a Small Planet. New York: Ballantine Books.
(3) Millward, D.J., Newsholme, E.A., Pellett, P.L. & Uauy, R. (1992). Amino acid scoring in health and disease. In: Protein-Energy Interactions - Proceedings of a workshop held by the International Dietary Energy Consultancy Group. Switzerland: IDECG.