Updated: Aug 1, 2022
There is no specific human diet. There are many types of foods that one can eat to reach the same endpoint as the body is truly flexible.
Hippocrates reportedly noted, 2500 years ago, let food be thy medicine and medicine be thy food. It's true and there is a reason. To a significant degree, the body ages due to chronic inflammatory damage. Chronic inflammation is driven by your diet.
This inflammation arises from the immune cells in the gut wall. Diet influences the intestinal bacterial colony, which in turn affects your gut wall's neuro-immune system. Thus what you eat plays a significant part in dictating the amount of chronic inflammation in your body. As you will see later, some foods promote inflammation while others actively suppress it.
We are a super-organism sharing space with a bacterial colony and their genes. Some of the bacteria influence how the body manages various foods. We may share many common genes as humans, but our microbiomes make people uniquely different.
So what to eat ?
Our knowledge of how our ancestors lived weakens as we go back in time. We have to draw ideas from rare and limited evidence from these ancient periods. But anthropologists have constructed a picture based upon information obtained from multiple scientific disciplines. As we get closer to modern times, the evidence improves. We have meaningful information for the last 100,000 years and accurate information for the last 10-20,000.
There are libraries dedicated to research exploring, and arguing about our past. Yet, there is one clear and obvious truth. Humans have managed to colonise almost every land-based habitat on the planet. We have survived in places as diverse as tropical rainforests, dry savannah plains, and the frozen north. The only reason we have been able to do so is that we are adaptable in our dietary and to a lesser extent nutritional needs. We are omnivores and perhaps, to use a new word, flexivores. Omnivorous in that we are able to eat anything and flexivorous in that we can eat whatever is around us right now to sustain us.
Changes in environment and circumstances led to human innovation and evolution. This included novel ways to access food.
Our ancestors moved from foraging for plants and hunting wild animals to domesticating those plants and animals. Modern animals, grains, vegetables, fruits, and nuts have been developed through careful breeding and cultivation from their wild varieties evolving into those that we find in our stores today. Our predecessors took food that was difficult to eat and enhanced it over many hundreds, indeed a few thousand years, making it palatable. They made the procurement of food efficient. Farming made it local and more reliable. The domestication of herd animals like sheep and goats who would stick together and could be moved from place to place supporting nomadic tribes with a constant food source were critical to our evolution.
The population was able to grow and this evolution of food sources allowed them to spend time on other things like technological advancement and ultimately scholarly pursuits rather than spending most of their life trying to get enough food to survive.
Let's not drown in detail, but three facts dispel certain myths and point to the complexity and diversity of the food debate.
For two million years, we have survived on a mixture of plant and animal-based foods. Recent evidence shows that even groups living in the arctic wastelands fermented or grew vegetable matter in the belly of seal carcasses. Even there, where vegetation is minimal, people developed techniques to grow and eat plants.
The Regulatory Genes
The distribution of the enzyme lactase, the chemical that breaks down lactose or milk sugar, is patchy around the world. Most ethnic groups lose the enzyme and the ability to digest dairy products at weaning. But some groups across many diverse regions retain this enzyme into adulthood, allowing them to utilise milk products throughout life. These populations are those that maintained the herding of domesticated animals as a lifestyle. Equally, there are many regions of the world where this enzyme disappeared in communities where the use of milk products did not persist in adult life. The driver of the presence of the enzyme is a lifestyle. In other words, different peoples have evolved in recent history (10,000 years) to survive in specific environments, and this is an excellent example of that. Environment and lifestyle drives evolution.
Another interesting example is found in the distribution of another digestive enzyme, salivary amylase. It breaks down starch, which is just glucose (sugar) in another form. Why is it in the mouth when all other digestive enzymes are in the small intestine? Because if you chew tubers, which are highly fibrous root vegetables containing a considerable amount of starch, you need the starch without all that fibre. If you chew and digest the starch in your mouth, you can spit out the fibre. Salivary amylase occurs in all of us. Still, there are significant variations amongst different groups in the quantity of salivary amylase related to the number of tubers they consume around the world. Societies that have traditionally survived on a diet with very high tuber intake have more copies of the enzyme’s gene and make more salivary amylase than communities that eat fewer tubers. Again a relatively recent evolutionary change in specific groups of people driven by the environment.
These are two well-documented examples of enzymes, but geneticists recognise many more subtle differences between populations. These differences are related to genes that we call regulatory genes which control the turning on and off of other genes. Returning to the lactase gene, your tribe might have the gene present in their DNA, but you may also have the gene that tells the body to turn off the lactase gene when you are weaned. Thus you possess the gene for lactase, however it is silenced at the end of infancy, and the individual then becomes lactose intolerant. There are thousands of such genes, and we are just beginning to figure them out.
So you have to be very careful when extrapolating information about diet from one part of the world to another. A good example is the China Study. This impressive work, beautifully conducted, may turn out to be relevant in China. However, the findings may not apply to other populations unless they are of Chinese descent. Why? Because in many regions of China, the community does not have the lactase gene expressed, and they are lactose intolerant. That is not the case in Northern Europe, where people strongly express the gene and are lactose tolerant into adulthood. So possibly, some of the claims made about the dangers of dairy may be regionally relevant but not necessarily applicable to all people.
Up to this point, I have been talking about human genes. However, we are a super-organism sharing space with a bacterial colony and their genes. This fact is of significant importance. A hundred trillion bacteria weighing 3.5 lbs live in and on us. They contain millions of genes as compared to our 24,000 genes. People around the world have very different bacterial colonies which co-evolved with that population. Some of the bacteria influence how the body manages various foods. We may share many common genes as humans, but our microbiomes make people uniquely different. If you're interested, read the section on the Microbiota.
The bottom line is that we evolved to make use of the foods available in our local environment. Some of these evolutionary changes are "recent" and continue. The dialogue probably needs to change from what is our ancestral diet to what are the ideal foods for our time and ethnic group? Although ancestral diets do give us guidance the debate needs to consider our individual needs, our society as a whole, along with our planet and its limited and finite resources.
The take-home message is that there is no specific human diet. There are many types of foods that one can eat to reach the same endpoint as the body is truly flexible. We can say that there are diets that may well work better for you, depending upon where your ancestors came from. Some of us do well on dairy, and some do not. However, a highly processed, high sugar, high refined carb, and low fibre diet is not a good diet for anyone.