Plants can be incredibly beneficial for human health but they can also be incredibly destructive. Plants do not want to be eaten and use behaviour, physical and chemical defenses, to survive predation. This includes the handful of plants that humans eat. It is estimated that there are more than 250,000 plant species in the world yet most of us would consume fewer than 100 different types in a year, depending on commercial availability. Some are used in small doses for medicinal use and for nutrition and energy as vegetable foods. Humans are not raw food vegetarians by nature nor by anatomy. There is much confusion about the foods that humans should eat.
The structure of an animal’s gastrointestinal tract indicates the main foods it eats. Although some animals are classified as specialist feeders, such as the great apes, almost all will eat a variety of foods from plants and insects to birds and other animals, depending on availability, season, health, and so on. Each animal will, however ‘prefer’ a particular class of food to which their digestive processes are most adapted (great apes prefer stems, leaves, fruits and shrubs but eat insects and grubs associated with these). Humans eat all types of foods: plant, flesh, insect, milk and eggs. We are omnivores genetically adapted to using tools to cut and pound our foods, and fire to cook our foods. This is what makes the human diet unique and our gastrointestinal tract so complex.
We have a gastrointestinal tract from our mouths to our anuses, averaging about 5 metres in length when alive and between 7.5 to 8.5 metres when stretched out without the effect of muscle tone. Our small intestine is between 6 to 7 metres long while our colon is about 1.5 metres long, without muscle tone. In general, carnivores have intestinal tracts that are three to six times their body length, while some hind-gut herbivores such as rabbits have intestinal tracts 10 to 12 times their body length. Humans are neither of these.
The uniqueness of the human gastrointestinal tract is confusing. You could argue that humans are naturally carnivores or herbivores. Our dentition, jaw shape, cheeks and starch peptide enzymes from our mouth indicate herbivore come omnivore. It must be remembered however that humans have used tools to cut animal flesh for probably 3 million years and we probably have been cooking flesh foods for more than 1 million years (theorised on Homo erectus’ ability to move away from Africa into new environments) and our physiology has adapted to this.
Carnivores have a capacious single-chambered stomach which can be as much as 60 per cent of the total digestive tract in large carnivores. Large carnivores kill about once a week, and a large stomach allows these animals to quickly gorge themselves and digest while resting. Humans, like small carnivores, also have a simple, single-chambered stomach. Traditional Australian aboriginal hunter-gatherers varied their eating from three to four times a day to once a week.
Carnivores keep their gastric pH around 1-2 even when food is present. This is necessary to breakdown raw protein and to kill dangerous bacteria often found in decaying flesh foods. Human enzymes and pH are mid-range to assist cooked and dissected foods. We more quickly digest cooked flesh foods than cooked vegetables. You may have noticed when you vomit up a meal even more than an hour after eating, only undigested vegetables are visible not chunks of meat.
Herbivorous animals that predominantly consume high cellulose plants must ferment (digest by bacterial enzyme action) their food. They are classified as either foregut fermenters (ruminants) or hindgut fermenters. The foregut fermenters have a four-compartment stomach which ferments their food before uptake in the small intestine. Hindgut fermenters have convoluted stomachs which partially break down their food, pass it quickly through a moderate small intestine to a fermenting chamber called a caecum. The caecum connects the small intestine to the ascending colon. These animals uptake most of their nutrients in an extensive colon. The caecum is large in hind-gut fermenters while it is small to non-existent with a vermiform appendix in carnivores. Humans have a non-existent caecum and vermiform appendix. Humans are neither a fore-gut nor hind-gut fermenter.
So what does this tell us? The muscular-skeletal structure of our bodies allows us to move reasonably well but not exceptionally well (we are not a large animal, we don’t run as fast, nor swim as well, nor balance, nor are as strong as many animals), we are however, exceptionally well adapted to handle and use tools. In the same understanding, our gastrointestinal tract allows us to eat a wide variety of all types of foods not exceptionally well. Our gastrointestinal tract is however, exceptionally well adapted to digesting foods we eat by cutting, pounding, grinding, fermenting, cooking and soaking them.
If your immune system is functioning normally, eat a wide variety of foods, prepare them with care and enjoy their taste, texture, smell and nourishment. If your immune system is not functioning normally, you will probably have to change your diet to accommodate for this—but this is the subject another blog.