Something to contemplate: What if a species suddenly (in relative terms) developed technology which allowed it to grow food, rather than having to find it and/or chase after it? What if it learned a way to manipulate and "enhance" the calorie-poor grown food to make it more calorific and filling? What if it began to eat less of the calorie, fat and protein rich animal-sourced food that used to be available to it and replaced this with refined carbohydrate-rich plant matter?
What I have outlined above is a large and far-reaching change to the evolution-linked diet of a species. By evolution-linked I mean the diet that the species had adapted to over an evolutionarily-significant time period i.e. hundreds of thousands to millions of years. It's not credible to argue that we could safely make this enormous transition without the requisite change to our biology. And there just hasn't been enough time to allow that to happen.
I have been running a diet experiment on myself for the past seven years. My views on human diet have not come about as a direct result of this but my personal experience has certainly influenced my thinking on the subject.
I was incredulous when I first heard about the Atkins diet. I'd never heard of anything like it. How could one possibly eat copious amounts of fat and protein without getting fatigued, constipated, obese; or in some other way damaged? I was also, however, intrigued. I read a little about the general principles of the diet. I bought and skim-read the Atkins books then began the diet. Friends and family were concerned that it may cause some kind of long-term harm. I wasn't worried. I was enjoying the food, it seemed to suit my digestion and metabolism, and I was losing two kilos per week.
I have not, of course, stuck to the diet rigidly for seven years. Cravings for carbohydrate, particularly bread and potatoes, sometimes arise. And when I start to eat those kinds of foods I just want to eat more of them. My weight goes up during holiday periods when I am poor at regulating what I eat. But I can always use the diet to get my weight down again in short order. I am heavier now than I was after my initial couple of months on the diet but not by a great deal. My weight is under control and I am in good health. I don't exercise.
My personal experience of this kind of ketogenic diet would, of course, be classed as anecdotal. That is fair. It is not scientific evidence and I use it only to illustrate my personal interest in the subject. I have fed (sic) that interest by reading various articles and books about ketogenic diets. I recently read "The Diet Delusion" by Gary Taubes. I now have a much clearer understanding of how ketogenic diets work and how the current dreadful state of half-truth and misinformation about human diet has emerged.
The evidence is still incomplete and many lost years of vitally important research and studies still remain to be made up for. But the outline is clear: fat is not bad for you; eating copious refined carbohydrates causes the body to store fat; obese people are not fat because the eat too much - they eat a lot because they are fat; refined carbohydrates appear to be addictive and abuse of these substances can lead to diabetes, heart disease and cancer.
I think that an important part of the reason we have held to the completely unproven notion that fat is bad for us, is a puritanical one. Fat just seems like it should be bad. It can be found in lots of delicious but somehow 'sinful' foods. It also seems logical that fatty substances should block up our arteries in the same way that they can block up our drains. But this 'common-sense' notion is wrong. Our drains do not process fat poured into them whereas our bodies are complex homeostatic mechanisms, finely tuned to process and distribute the nutrients presented to them in the most efficient manner possible. But it's unfair to blame people for these misapprehensions when the patched-together 'fat hypothesis' has be fed to us as fact for decades.
Some doctors actually think that ketosis is bad for you. This makes no sense because it ignores the evolutionary perspective. Human beings have been 'in ketosis' for millions of years. The 'ketone bodies' produced in the body and used by the brain when very little carbohydrate is consumed, are a very efficient fuel and probably the one we have evolved to use, rather than the glucose fuel our brains have increasingly utilised over the last century. I wonder (as an aside) which fuel our brains run most efficiently on.
We are also being fleeced by marketing gimmicks such as 'Low GI'. The Glycaemic Index of a food could be a very useful metric if it actually factored in all the variables. One of the most mind-boggling omissions in the Glycaemic Index scheme is the effect of fructose. Bizarrely fructose, known affectionately as 'fruit sugar', is excluded because it passes directly to the liver and is metabolised there rather than passing into the bloodstream in the way that glucose does. Fructose therefore has a negligible effect on 'blood sugar', allowing marketeers to sell it as a 'Low GI' health product. This, I think, borders on criminal. Consumers naturally make the association with 'healthy stuff' like fruit and buy the product. But fructose appears in fruit and veg only in relatively small quantities. An apple, for example, is far more nutritionally complex than a spoonful of high-fructose corn syrup and the body will, therefore, metabolise the fructose content more slowly and less harmfully. High fructose diets can, in the longer term, induce high blood sugar, high insulin levels and insulin resistance. The 'table sugar' we are probably most used to consuming (the white/brown sugar you put in your tea) is known technically as sucrose and is derived from 50% fructose/50% glucose - it's all bad.
This is a vast subject and I am just highlighting a few examples of how we have this wrong. The 'fat bad/carbohydrate good/sugar indifferent' dogma is decades out of date. And it is just that: a dogma. Too many professional reputations and company fortunes have been staked on it to pull back now. Government health agencies are going to look pretty stupid too.
I have have no particular desire to eat animals. It is fair to call it corpse-food. But my body is the result of an evolutionary process which has come to utilise this matter in a very efficient way. There are, of course, ways to eat healthy quantities of fat and protein without eating dead animals. But we must accept that we need those nutrients and that we cannot live on poor vegetable matter and starchy stodge alone.
We are not omnivorous in the sense that our early ancestors might have been. Our evolutionary path brought us to a point where we had the advantage of large brains in the process of hunting and killing abundant prey. The 'symbiosis' with our prey shaped our diets and our metabolisms to a point where we could derive optimal benefit from the nutrients. Large brains also aided in the process of foraging and discovery of useful 'gathered' foods such as shellfish and, occasionally, nuts and berries. No large quantities of carbohydrate of any kind and virtually no refined carbohydrates whatsoever were available until the advent of agriculture.
I am not 'on a diet'. I eat the food I eat because I enjoy it and because my body requires it. As I write this my brain is running on ketone bodies so please feel free to highlight any errors in my facts, spelling or grammar to use as examples of glucose-deprivation-induced dementia.