If someone asked you what you thought was the most fundamental, the most essential, the most important health challenge that we face as modern human beings living in industrialised countries, what would you tell them?

Take a moment. Shift your gaze away from this text, and think about it.

When we read or hear something about health and nutrition in the news, on websites, on blogs, on social media, or even in books, the information we encounter is almost always biased and directed  in some way. It is also always restricted in scope. In fact, it is usually very restricted in scope. All this is perfectly natural and expected: whenever we sit down to write, it is usually about something in particular, something specific, some topic we want to address or explore. It’s hard to think of circumstances where this would not be the case.

Moreover, basically everybody who writes anything, does so in order to be read, and therefore naturally attempts to appeal as much as possible to their readership, both in content and in style. But maybe the most influential factor is that we have grown accustomed to information packets, to bite-size bullets of information: quick-to-read, quick-to-scroll-through, and quick-to-either-share-or-forget. And this has above everything else shaped the way information is being presented by all those people out there trying to appeal to more readers. Little can be done to counter this tendency. It’s just how it is at this time.

As a consequence, for all these reasons, we are—the whole world is—migrating away from the mindset that encourages inquiry into the global, the general, the underlying aspects of things. Instead, we are migrating towards an evermore concentrated, focused, laser-beam approach to basically everything. This is true in all fields of study and inquiry to some extent. In matters of nutrition, it is particularly noticeable, and the reason is surely at least in part because we tend to be at the same time very interested and highly sensitive to advice about what we should or should not eat. We take such advice very personally, and often react strongly to it.

Our relationship to food is very deep because it is so constant and continuous, so intimately related to our survival. This relationship starts when we come out of our mother’s womb, and persists throughout each day, every day of our life, until this life of ours itself comes to an end. What in addition makes this relationship so close and so intense is that if we don’t drink or eat, usually even for a few hours, we get headaches and stomach aches, we get light headed, weak, and unable to concentrate and function, we get grumpy and irritable. It is very clear and naturally understandable that we therefore tend to be—that we are—very sensitive to advice about what to eat, but immensely more so to advice about what not to eat, especially if we happen to eat those foods about which the advice is given.

Hence the movement to superficial, non-contentious, bite size bullets of information: ‘blueberries are excellent: they are low in sugar and full of antioxidants’; ‘avocados are amazing: they are not only full of healthy fats but they are also alkalising’; ‘hydrogenated vegetable oils are very bad: they are full of toxic trans fatty acids.’

But what about the essential, the fundamental, the underlying aspects of things?

You have had more than a few minutes to think about it. What would you say, then, to this question of what is most fundamental to the health, to what constitutes the most fundamental health challenge we face? I would say it’s digestion.

Digestion is where everything about us begins and ends. It is in and through the digestive system that we absorb all the nutrients from our food and excrete all solid wastes. It is through the digestive system that we absorb all the constituents of everything that we call body, and excrete all that is toxic, be it produced from the environment or from within through healthy digestive and metabolic processes. Do you find this sufficient to illustrate why digestion is so fundamental? For me it is. But we can go a lot further.

Evolutionary considerations, arguments, and observational evidence, are always useful, and usually very powerful in guiding clear thinking about matters of health. One of the main questions that has and continues to preoccupy evolutionary biologists is that of the growth of the human brain. In this, one of the most compelling ideas put forward to explain its evolutionary history is called The Expensive Tissue Hypothesis. I plan to, in the future, devote much more time to it. But I must refer to it here because of its relevance to digestion.

The Expensive Tissue Hypothesis is based on the fact that there is a strict minimum to the amount of calories any animal requires to survive, the observation that the brain is the most metabolically expensive organ in the body, and the conclusion that it would be very hard for any large complex animal to sustain two systems as energetically expensive as the brain. Because the gut is the second most metabolically expensive, and because both the brain and gut together account for a disproportionately large fraction of the body’s caloric needs, an increase in the size of the brain would necessarily be at the expense of that of the gut, and vice versa. It simply would not be possible to sustain both a large brain and a large gut. And thus, the growth of the brain would have to be accompanied by a shrinking of the digestive system. This is what is observed.

However, it is important to emphasize that it is the shrinking of the digestive system that allowed for the growth of the brain; not the growth of the brain that precipitated the shrinking of the gut. The growth of the brain would only be possible with a surpluss of calories for it to growth and have its increased activity sustained. It is even more important to emphasize that this evolution was the unintended consequence of a shift from a high-fibre, nutrient-poor, plant-based diet, to one consisting mainly of low-fibre, nutrient-rich, animal-based foods.

Male mountain gorilla of the berengei berengei subspecies of eastern gorillas in Ruanda (Source: Time). As you can see from the chest muscle definition, this adult male’s bodyfat is low. The huge bulging belly that is apparent when they are seated and relaxed is the consequence of having it hold the very long gut required to process each day approximately 20 kg of fibrous roots, leaves, and stocks of the plants they eat.

It is very interesting—and it is surely related to this evolutionary history—that the gut has by far the largest number of nerve endings, second only to the central nervous system. Moreover, unlike other organs and systems of the body, all of which are entirely controlled by the brain, it is the only one with directive nervous signalling to the brain. Because of this, it is the only organ with a direct influence on the brain. Thus, besides the physical implications, some of which we’ll explore soon, it is quite literally the case that a happy gut means a happy brain. And conversely, a sad, unhappy, depressed brain is very likely to be caused by a dysfunctional gut.

It is a sick, dysfunctional, damaged gut that is the primary characteristic underlying states of disease. This is why I would say that it is a sick, dysfunctional, damaged gut that is the most fundamental health challenge we face today as modern human beings.

I know this might leave you hanging. Especially because we have not yet made any reference to the title. But I promise, we’ll pick up from here next time.

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