Vegetarianism

Professor Robert Pickard

Emeritus Professor of Neurobiology at the University of Cardiff

 

The ancestor of all the primates was a carnivorous tree shrew and human primates have progressively added plant material to their diet over a 7-million-year period. Currently, humans are classified as omnivores and one-third of their balanced diet is normally derived from foods of animal origin and two-thirds are normally derived from foods of plant origin. Humans thrive when they eat a little bit of everything and not too much of any one thing.

 The hallmarks of the omnivore can be seen in the dentition; the simple gut structure; the gut ecosystem; the adaptability and range of the digestive enzymes; and the requirement for essential nutrients that are usually provided by both animal and plant products. Unlike dedicated herbivores, we have no mechanism for the degradation of cellulose, the key molecule that differentiates plants from animals. Animal products, such as red meat with liver, provide humans with the full range of amino acids, fats, minerals and vitamins; all in forms so chemically suited to human digestion and absorption that there is usually little or no faecal waste. This is not surprising, since cows, sheep and pigs share 80% of their genes with humans.

 As we age beyond 60 years, our ability to make certain molecules diminishes, as does our absorption efficiency. Animal products, with their high nutrient densities, are particularly helpful at this time: a biological insurance. If we can’t make it, there’s a very good chance that a cow can. Plant products, such as broccoli with peas, nuts and yeast, provide humans with non-digestible fibre, most of the required amino acids, most of the required fats, most of the minerals and vitamins, notably vitamin C. In addition, plant foods provide carbohydrates, which are largely absorbed as sugars, and pharmacologically active phytonutrients, such as glucosinolates and salicylates.

 Sugars are vilified, unjustifiably, in the popular press because overconsumption is allowed to obscure their true nutritional significance. Sugars are the best source of energy for humans. Glucose is the major source of energy for the brain. DNA, required in most human cells, is constructed from a molecular variant of the sugar, ribose.

 Most vegetarians construct a healthy, balanced diet by supplementing plant foods with eggs, fish, dairy produce and a source of iron. Even extreme vegetarians, vegans, can still construct a healthy, balanced diet by supplementing plant foods with iron and vitamin B¹²  sources but this is more difficult and requires more awareness on the part of the eater. There is no biological justification for choosing to restrict one’s diet only to foods of plant origin but a vegetarian may have many other reasons for taking this course of action.