Why are we fat?

Recently I read an article about the science of obesity, which I found very interesting ^1. The fact is, we don’t know what causes obesity. People get fat because they eat more than they “need” but why do they do that? Because they can’t control their impulses and are greedy? This is the “energy balance” theory. Or because their bodies are too good at storing fat (or more exactly their bodies trigger a hormonal response that renders what they eat into storage as fat) and therefore they eat to compensate? This is the “endocrine hypothesis”)

The second hypothesis was actually conceived before the first, – by German scientists before WW2 and the first by American scientists after it. The German scientists’ work became unpopular and remained unread after the war, as German science lapsed (most good German scientists had either emigrated or were dead).

“Everyone” knew in the 60’s and 70’s that carbohydrate restriction worked, in that people lost more weight quicker. The Atkins diet was formulated in 1972. It was the conventional wisdom when I trained – insulin was the stuff that enabled sugars to enter the cells and also promoted fat storage. Without insulin you got very thin, the body had to use other very inefficient and dangerous biochemical pathways to get energy and eventually you died. So when insulin was in short supply or didn’t work you cut down the sugar in your diet.  We told everybody they had to only eat a certain amount of carbohydrate each day, so no sugar, very little starchy foods, and you could eat a lot of fat. If they stuck to that, some did manage to control their weight and their diabetes was controlled to some extent.

After WW2 American scientists formulated the theory that the basis of obesity was psychological – you ate more because you lacked the ability to control your eating (and therefore got fat). And this theory became popular despite scientists realizing by now that insulin was crucial to fat metabolism as well as sugar, and that if insulin worked extra-specially well or you had a lot of it, you would get fat. This could well have been an adaptive advantage to populations in times of food famine.

There has never been any evidence that the endocrine theory – that insulin works too well in some people  – is untrue, and we know that the overeating theory (too much energy intake makes you fat) is a dead end because people cannot in fact control their weight.  Neither in fact has been conclusively proved but one theory is at least as good as the other. We certainly know that low carb diets are much better at initiating weight loss for type 2 diabetics than the conventional diets (which I never really understood!) but it has always been assumed that this is irrelevant because over the long term most people revert to “over-eating” and regain weight.

So the American hypothesis of energy balance took over completely, and the German theory was forgotten. Experts in the 70’s pointed out that eating all this fat (which you had to do if you were to get enough calories) was very bad for your cholesterol and your heart.  And the rest is history. Sugars were counted as “empty calories” and despite Dr Yudkin’s efforts ²,  (he wrote “Pure White and Deadly” in 1972 and was pilloried for his efforts), sugars were available for food companies to make more and more sweet drinks, and carbohydrates were used as a cheap source of calories for poor people so that food companies were able to make more and more “low fat” but tasty cheap meals, often with extra sugar added. And lo and behold, population body weights have rocketed in America and in the rest of the developed world, and type 2 diabetes, which develops when you overload the body with calories, has become a modern day plague.

The writer of the article, Gary Taubes, went to to say that he is trying to right the wrongs of previous science and has founded the “Nutrition Science Initiative (NuSI.org)” to improve scientific understanding. Let’s hope this organisation succeeds in finding out the cause of the current epidemic of obesity and the best way of combating it.

           Following on from that, I have recently become interested in the “Primal” or “Paleo” diets. (I am not too sure of the difference, so people are welcome to enlighten me). But both seem to come from the hypothesis that Paleolithic people were thin, and they had low carbohydrate intakes because their diet consisted of meat (from hunting) and naturally occurring protein rich foods such as fruits and vegetables.  It must have been a high protein, moderate fat, and relatively low carb diet.  It was only later with the discovery and spread of agriculture that grains were used, bringing rice, bread, and so on, enabling more people to have calorie rich diets, (and live a more sedentary life), so the theory goes.  Our modern diets are high carb; therefore if we could stick to a high protein, high fat but low carb diet, we ought to be thinner, and possibly fitter.

 So there is some justification for this “Paleo” diet in terms of the scientific ideas above, although if you read some of the blogs of people following these diets, a very large number of them seem to supplement their diets with extra vitamins, nutrients, oils and so on, as if by every tree in those far off times there needed to be a vitamin bush with bottles of “extras” hanging from it! If the diet means anything it should mean that the diet is self sufficient without added nutrients, otherwise we couldn’t have survived.

However does it really fit with what we know about hominids from Paleolithic times, that is 2.6 million years ago, to the end of the Pleistocene around 10,000 BP?  We know from large numbers of Paleolithic carvings that obesity was well established, and possibly admired, at that time.  Obesity was certainly not invented with agriculture. It has been around for much, much longer than that, and is likely to be as human a characteristic as is our walking on two legs.

No, I don’t go much on the prehistoric explanation people give for the success of the “Paleo” diets.  Another theory which, like the German theory above, has not taken off despite never having been disproved is the aquatic ape theory,³  and this is the one I find much more attractive in explaining obesity. According to this theory, long before Paleolithic times, about 5 million years ago, at the time of the split between chimps and us, a group of hominids took a trip to the beach. They got good at fishing and diving and adapted to living in water. There they had a plentiful supply of fish, shellfish, small arthropods and other protein rich foods – and very little carbohydrate. There was another big advantage to this diet and this was that such a diet contains just the right balance of omega 3 and omega 6 fatty acids needed for optimum brain development.  Subcutaneous fat developed in these hominids and was useful for temperature control (they also lost their hair because wet hair is a very poor insulator), and buoyancy.  And it is possible that this source of rich protein and fat was the catalyst needed for the brain to grow so much bigger than it did in the apes that stayed in the trees.

Yes, fat was good then, as it is now. Human babies are much, much fatter than chimp babies, and women are often fatter than men because they have to provide the fat for babies in milk.  There is nothing much wrong with “the right sort of fat”. Excessive obesity is another matter altogether and may well be caused by the excessive carbohydrate intake many people have now with fructose rich drinks and carbohydrate loaded meals.

         Unfortunately there is a catch in all this. In those very far off days, early humans could take what they wanted from the environment. Just imagine all that naturally occurring food all around them – they could just pick it.  But nowadays there are so many more mouths to feed and we have to grow nearly all of it. If low carb is what at least some of us should be eating, how are we going to feed ourselves? Getting protein from livestock or even fish farming is very energy intensive, appropriates over 30% of all ice-free land, uses up vast amounts of freshwater and contributes to climate change, as well as reducing biodiversity. This is reflected in the fact that high protein, low carb diets are very expensive and completely unaffordable for many people, so that they are forced to eat high carb meals.

         We know that not everyone will put on weight even when offered large calorie meals. Some cannot physically take it in, or will vomit, while others will put the extra weight on as muscle rather than fat. People’s metabolism varies tremendously and it depends very much on our genes.  But those who have the “endocrine disorder”, according to the German theory, will need to eat far fewer carbs if they are not to succumb to obesity and diabetes. We don’t know what percentage of people will put on weight when offered unlimited supplies of a high carb diet, but even if it is as low as 50% that still leaves an awful lot of people consuming too much, and many of these will get diabetes. There are 7 billion people in the world today, many of whom are suffering from poor nutrition, and while many scientists say that the world can sustain food supplies for all these people, with the right distribution and economic systems, what if the population rises to 9 billion as many think it will?  Certainly we would have to stop eating so much meat, and fish farming is also non-sustainable in energy terms.⁴

         People who gladly eat high protein, low carb diets now, will find such foods totally out of their reach financially, as the world population rises, maybe in the next two decades, and they will have to go back to eating carbs, and getting fat again with all the consequences for our health, and costs for our economies in treating the effects.

         Many scientists are feeling as if Malthus is coming back to revisit us. The solution now, as it was in his day, has to be to use our ingenuity, this time to develop novel plant protein products and to innovate to improve food preservation and waste reduction.⁵ There are some pointers – scientists from the Netherlands have recently produced “meat” by cloning cells in laboratories. But can we really provide enough protein this way in the time scale that would be needed?  It doesn’t seem as if we are trying very hard.

References

¹The science of obesity: what do we really know about what makes us fat?  Gary Taubes BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f1050 (Published 16 April 2013)

²John Yudkin  Pure, White, and Deadly: 1972, re-issued by Penguin 2012 with an enthusiastic introduction (doi:10.1136/bmj.e8612).

³Aquatic Ape Theory,  Elaine Morgan “The Descent of woman”, “The Aquatic Ape Hypothesis: Most Credible Theory of Human Evolution” (Independent voices) [Kindle Edition]

⁴Aiking, H., Future Protein Supply, Trends in Food Science & Technology

22 (2011) 112-120 (original manuscript), doi:10.1016/j.tifs.2010.04.005

⁵Mark Post, Professor of Vascular Physiology and Tissue Engineering at Maastricht

University