Fat, Fate, and Disease : Why we are losing the war against obesity and chronic disease (8 page)

And so we evolved largely with a metabolism designed around a kind of high-fibre, low-glycaemic-index diet. There were times of year when there was perhaps more access to fat in the game hunted—which provided a welcome high-energy storage form of fuel. When that happened the hunter-gatherers would gorge themselves to store up excess fuel for harder times. Even in more recent historical times, the Plains Indians of North America were
known to engage in this kind of gorging behaviour after mass buffalo kills at a time of the year when the animals were well-fed and relatively fat. It seems that we, like other species, evolved to be able to store fat when food supplies are in excess so that we can cope better in hard times.

Over the last 10,000 years our lives have changed considerably, but our biology has changed much less. Evolutionary change is generally a slow process. Starting about 10,000 years ago in the Middle East, we invented agriculture and learnt how to herd goats, sheep, and cattle. These skills also developed independently in other parts of the world. Agriculture and animal husbandry gradually changed what we ate. For example, with the domestication of cattle in some parts of the world, we started to drink cow’s milk. In those places we developed the enzymes needed to break down milk sugar (lactose) in the gut. However, in Asia, the Americas, and large parts of Africa, where cows were not farmed for milk, a tolerance of lactose never evolved. Many people from these regions still cannot consume cow’s milk without becoming sick.

But while the development of agriculture produced a big change, it was small compared to the changes in our diets over the past 200 years. The industrial revolution brought with it an agricultural revolution, which gave us a greater dependence on large-scale farming of grain, corn, sugar cane, and beet. The industrial revolution also saw the dawn of the modern food-processing industry. Food changed from being composed of simple natural ingredients to increasingly processed and refined products. Salt, sugar, and fats were added to improve taste and preserve the food. The food industry grew as cities expanded, so that fewer and fewer people across the planet could grow their own food. The relationship between food as it was sold and its original ingredients became more remote. In the 1860s,
Emperor Louis Napoleon III of France offered a prize for the development of a substitute for butter suitable for use by the armed forces and the lower social classes (don’t ask what went into the winning recipe), and since then synthetic spreads and cooking oils have become a common part of our diet. For many years some processed foods have contained trans-fats, which were a direct result of the processing of the ingredients. Corn oil and corn starch became nearly universal ingredients, and so fructose and omega-6 fatty acid levels in foods started to rise.

Then along came the fast food industry, the soft drink industry, our expanded intake of confectionary and alcohol—all excess calories that are easier to turn into fat than energy. And the cheapest foods now are often those that are most calorie-dense—so the more impoverished people in our societies eat less balanced diets than those who are better off.

Technology has changed our lives in other ways too, of course. Few of us now hunt or fish to feed ourselves or wander the forests in search of tubers and seeds. Fewer and fewer of us even walk to a shop to buy our food—we are more likely to drive or to take a bus or train, or just to pick up the phone or order online. Manual work is increasingly replaced by machines. Leisure is spent in front of a computer or television, rather than walking or playing a game or a sport outside. Our children are more likely to be driven to school than to walk or ride a bike.

Of course we do not know how much energy our hunter-gatherer ancestors expended each day—some anthropologists think that it was much more than we do now; others are less certain. The estimates are based on hunter-gatherer communities which still exist, but they have changed their lifestyles over the last 10,000 years too, and many of them are not free of modern influences. But if we look at more recent times, the situation is clearer. Most of us expend much less energy in living our lives than our great-grandparents did a century ago. Studies in countries such as Japan
show a direct correlation between the number of motor cars and the number of people who are obese. Other studies find the same correlations with the average number of hours spent watching television. While it is tempting to draw a cause and effect relationship, there is considerable debate about this. Would increasing exercise at a population level reduce the rate of obesity? Logic suggests that it would, although the size of the effect may be much smaller than might be expected—for reasons which will become apparent.

We have grown up eating three meals every day with one or two snacks in between them. It was somewhat different in Victorian times, as many people had large meals at breakfast and in the evening but little for lunch. But as we now live and work in heated buildings and need to metabolize very little to keep warm, and as many of us spend our working days and leisure time sitting and being transported about the world by mechanical means, we can see how easily a mismatch between what we eat and how we burn it up can occur.

Many parents bemoan the fact that children just do not seem to engage in as much physical activity at school as they did when they were children themselves. It is true that in the UK, for example, many local education authorities have sold off fields where children could engage in sport or just run around. Very often they are valuable pieces of real estate and the cash helps to balance the books of the local council. In addition, the number of children who walk or cycle to school is far lower than it used to be. Parents worry about traffic or potential molestation by paedophiles or just that, if their children are making their own way home from school, it is hard to know exactly what they might get up to on the way. There is no doubting the
seriousness of the road traffic accident worry and very few Western cities have adequate cycle lanes or paths which would allow children to go to and from school in relative safety. The statistics, however, do not bear out the worry about other threats—it seems that children are no more likely to be murdered, abducted, or sexually assaulted today than they were a generation ago.

But of course children don’t need acres of space in order to exercise. What about good old-fashioned physical education lessons? These still take place in many schools and are prescribed in most curricula. They were never the most popular lessons among many children. Now they are deeply unfashionable with some groups, who effectively refuse to participate. The difference in perception occurs in the early puberty years when boys and girls tend to separate in their attitudes. If there is a training element which seems linked to sporting or other prowess, the activity can often be sold to the boys in the class, but for the girls the concept of changing into unappealing or revealing sports kit and then getting hot and sweaty is not alluring.

But what about life outside school? Recent studies suggest that this too may be important, although the reliability of such studies is uncertain. There are often very big differences between what people say they do and what they actually do, as measured by using electronic monitoring equipment. Nevertheless it is sobering to note that some researchers found that children who undertook a high level of physical activity at school were far less likely to be physically active at home. In contrast, those children who appeared to do relatively little physical exercise at school were more likely to go out to play football or join dance classes outside school hours. So in the end the net effect may be the same for both groups.

This is not to say that children do not differ in the overall amounts of physical activity in which they engage over the course
of a week and that possibly this may link to how well they control their appetites and body weight. But what these studies do suggest is that the setting for physical activity is established relatively early in the lives of our children. If we force them to do more exercise in one setting—say at school—will they do less in another? Once again we get the feeling that merely focusing on exercise levels in children is not the whole answer. Exercise may help but it may also be too late to produce a permanent change, at least in some people. One of our major themes pops up again—people vary.

The energy that we expend in deliberate physical activity is only part of the story. Jogging or weightlifting is all very well and certainly burns up calories, but recent research suggests a surprising way in which we also use calories. Ever noticed that the nervous, twitchy child in the class, who is always fidgeting and shifting in his or her seat, dropping things on the floor and picking them up, is also likely to be the thin child? They are not going anywhere or doing anything very useful but they are burning up a lot of energy in the process. This type of apparently minor activity uses a lot of energy every day, but once again it balances out. If we exercise in the gym on the way home from work, we will probably fidget less later when we are 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.

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 effective, at least in the short term—but there is the rub. For some reason people who restrict themselves to such diets lose weight for a period of time, but then they inevitably pile back on the pounds. It is as if an individual’s metabolism has been set to achieve a certain body weight, and while it will allow the body to deviate from this over a short period of time if the person decides to consume a different diet, it will not allow the body weight to fall by too much for too long even though being overweight may be associated in the long term with poor health.

As we progress through this book we will add other layers of complexity to the story. If we do not view the full picture in proper perspective we will never find the right solutions. We started from the immediate problem—something very much in the foreground of the picture—that although we have to eat too much and exercise too little to become obese, dieting and exercise do not restore healthy
body weight in everybody. People are different. Two people may live in exactly the same way but one becomes fat and the other does not; one gets diabetes while the other continues to control their blood glucose very well. In this chapter we have added the evolutionary perspective to our picture. It helps us to get a clearer idea of how our fundamental biological processes contribute to the problems we now face. But still the picture is far from complete. We will have to keep filling it in if we are to come up with some effective solutions.