Evolution of the human diet

 

It was only in the 1900s that humans began to consume vegetable oils, which are very high in unsaturated fats. Before this time, our predecessors used animal fats.

 

Going back to our evolutionary past, the big divergence in human evolution occurred some 2.6 million years ago, when they began consuming meat, fat and bone marrow from animals (r). This gave humans a distinct advantage over other hominids as they could now survive on animals and plants. This gave them greater flexibility in a changing environment (the climate was cooling and the Earth began its path through a number of ice ages – this lead to a scarcity of plant food as forests gave way to savannahs, but there still remained plenty of animals) and ultimately enabled modern man to outlive their other hominid brethren. This sudden increase in nutrition and calories allowed the human brain to begin developing. It become larger.

 

Then around 790 thousand years ago, man discovered fire. This enabled man to cook their meat (and sometimes vegetables), which made most nutrients more bioavailable and drastically increase the calories available from food. It freed our digestive system from a lot of the hard work in breaking down the raw material. These increase in energy availability and nutrition is what ultimately propelled our brains to their current form. Bain power quickly became our most dangerous weapon….and our biggest liability. It demanded a lot of energy.

 

To facilitate a growing brain a lot of changes occurred. Ultimately the growing brain lead to a shrinking gut, which meant highly nutrient dense foods with high bio-availability had to be consumed. The only source of food available to do this was meat, particularly cooked meat. Humans become obligate meat eaters.

 

From 2.6 million years ago to 790 thousand years ago, roughly 1.8 million years, the human body and mind adapted to better process raw meat. This occurred via natural evolutionary process i.e. natural selection. Those humans that were better at surviving with the meat lived longer and had more children. The selective advantage of better meat digestion lived on. This continued until our bodies were selectively better at digesting meat rather than plant matter. The same thing happened again when fire began to be used. Those that started to lose their ability to digest raw meat were at an advantage in that their body was freed of resources and energy required to keep those systems in place. Since that time our bodies have adapted to preferentially consume cooked meat, the only living organism on this planet to have done so.

 

The switch from plant matter to meat is evidenced most obviously by humans’ cecum. In humans, the cecum is a short pouch between the small and large intestine that absorbs fluid and salts after digestion in the small intestine. This is vastly different to our pre-meat ancestors and the other great apes, whose cecum is much more developed. The role of the cecum for them is to take all the fibre from plant matter and ferment it into saturated short chain fatty acids. The result is that the largest component in their diets would ultimately be fat (~60%), with 25% protein and only 15% being carbohydrates (r).

 

Importantly, this system of using fat for energy was maintained for humans when they switched to meat as their primary source of food. Red meat, the kind that our human ancestors would have had access to regularly, is relatively high in saturated fat and almost devoid of carbohydrates. Their bodies maintained the adaptation to successfully exist off fat. These are the same bodies that we have today.

 

To put that in perspective, the first hominids, from which we descended, had bodies that preferentially used saturated fats as a fuel source (from the break down of plant fibre into short chain fatty acids). Thus, the use of saturated fat as fuel has been a conserved mechanism for roughly 6,000,000 years.

We’ve only had ‘vegetable’ oils in our diets for at most the last 110 years and only to any great quantity in the last 60.