Protein is one of the essential macro-nutrients, with the human body unable to make at least eight of the amino acids that make up proteins. Whether two others should be classified as essential is disputed, and may depend on the age of the subject. The requirement for these essential amino acids could theoretically be achieved with about 6g per day of them in exactly the right proportions. In addition, there is a requirement for around 50g of protein of less specific composition. Until recently, the way these requirements were achieved using different sources of protein was not realised to be of any great significance, as long as the quantity of the essential amino acids was adequate, but more recent evidence suggests that other factors are also important to health.
In practice, the total protein needed could be found in a single source of meat protein, or two carefully chosen sources of vegetable protein. No single plant source (except soya) is able to provide all of the essential amino acids in adequate quantities, but vegetarians have no problems achieving the requirement for essential amino acids with a rudimentary knowledge of which vegetable sources of protein complement each other.
It is becoming apparent through several large scale studies in different parts of the world, looking at the statistical relationship between diet and health risks, that the particular sources of protein used, and the quantity of protein consumed has significant effects on major health risks.
There is some concern about high intake of animal proteins, as several studies have shown this may increase the risk of some cancers including those of the breast and kidney. Other studies have shown that a low carbohydrate, low protein diet (and exercise programs resulting in a similar effects on physique) lowers both cardiovascular and cancer mortality. On the other hand, increased vegetable protein in the diet has an association with lower cancer rates.
Whey protein is the most balanced of proteins in terms of the amino acid profile, and has some highly beneficial effects, including an increase in a key endogenous antioxidant in the body, glutathione. It is believed that this is one of the reasons that whey protein has well-established anti-carcinogenic effects.
Soy intake causes measurable benefits to cholesterol levels and is quite strongly protective against cardiovascular risk. However, this is believed to be a whole food effect caused by a synergy of different nutrients, as neither soy protein on its own nor other components of soy have demonstrated the benefits that the whole food does.
Based on the totality of research published to date, it is safest to avoid over-dependence on animal protein, by including a moderate amount of whey protein and vegetable protein in the diet. The evidence available suggests that such a course of action reduces the risks of serious disease significantly, with a likely increase in life expectancy. Any such benefits are likely to increase in significance with age.
Liam Roche is a science writer who writes a lifestyle and health blog at http://rochehealth.com/news which deals with the influence of diet, exercise, mental and social activities on health.