Free Fat, Fate, and Disease : Why we are losing the war against obesity and chronic disease by Mark Hanson Peter Gluckman Page B

sitting in front of the computer.
    Once again our biology seems designed to defeat weight loss. But of course this is the wrong way of looking at it. Our biology has evolved to do just that—to keep our body weight fairly constant regardless of what our level of activity actually is by adjusting a range of processes which consume energy. Indeed there are aspects of our biology designed to favour laying down energy reserves. This is because in our evolutionary past obesity was rare and there was always an advantage in storing those excess calories for a rainy day. We are left with this fundamental property of our biology. Metabolic processes which were useful 10,000 years ago are one reason why we are in trouble now.
Short lives
    How long do we think our Palaeolithic ancestors lived? We don’t know precisely, but fossil records give us some clues. On average their lifespan might have been as little as 30 years from birth, but this figure is heavily influenced by the high rate of infant mortality. Probably only about half the babies born survived, most dying soon after birth or at weaning, with others perishing in childhood. It may be that, provided they lived beyond childhood, there was a reasonable chance of their living to a much older age. Once again, however, it is clear that average life expectancy has changed dramatically in more recent times. In France in 1800 a man had a life expectancy at birth of about 30; in 1900 this was 45, in 1950 about 64, and now he can expect to live until about 78 (longer for a woman). The same trends, albeit with different baselines, have been observed in the USA, the UK, and many other developed countries. And many developing countries have seen major changes in life expectancy too—for example, in India there was on average a 13 per cent increase in life expectancy in men in the last 25 years of the 20th century.
    If we now live longer lives than we did in our evolutionary past, then health problems which evolution was never able to filter out will emerge in later life. Indeed this is one of the most fundamental principles of evolutionary biology—selection pressures are strongest in the period up to when reproductive capacity is maximal. This is because in the end evolution is driven by successful reproduction. Ageing is a process whereby repair mechanisms, needed to protect the individual up to the age of reproduction, are overwhelmed by the accumulated damage from toxins, solar and cosmic radiation, and other factors. Once reproduction is over, the evolutionary pressures to repair cells are greatly reduced. So we can expect that as we age, the pressures of metabolic overload induced by changed diets and exercise patterns are more likely to be exposed in the form of obesity and chronic disease—for example diabetes and vascular damage,which lead to heart disease and stroke. The risk of mutation increases, and as DNA repair processes wane, cancer becomes more likely.
    From the evolutionary point of view extreme fatness would have been rare, but in contrast a moderate level of body fat is good for survival, for reproduction, and even for defence against infection. But because our Palaeolithic ancestors lived shorter lives, the diabetes of today’s middle-aged obese person was not a problem they faced. So at its simplest it is the concatenation of longer lives and different lifestyles today, mismatched to our evolved fundamental biology, which is associated with the current increased level of diabetes and cardiovascular disease.
    The consequence of this argument is that, if only we could restore our diets and behaviour to those for which our evolution suits us, we would stay slim and be incredibly healthy. Reducing the glycaemic index of foods is partly the basis of the Atkins diet (there is another component of it relating to appetite control which we will return to later) and there are many other dietary fads and supplements which purport to be as effective. Some of them are indeed