Fat, Fate, and Disease : Why we are losing the war against obesity and chronic disease (7 page)

There is more than one perspective on body shape. Throughout much of human history, body fat has been recognized as a sign of health and also as an indicator of social position. Venus figurines found in archaeological sites across Europe, and dating from between 20,000 and 35,000 years ago, depict very rotund female figures, and it is believed that these were probably Palaeolithic fertility symbols.

The singer and actress Jessica Simpson focused on some contemporary issues concerning fat in her documentary series
The Price of Beauty
. Is it a sign of beauty for a woman to be fat and, if so, how fat? In some parts of Africa young women are fed on high-fat foods until they become grossly obese, as this is thought to show that they are healthy and ready for marriage. Young women in rural Mauritania are sent to ‘fattening farms’ where they are beaten if they do not consume extraordinary amounts of fat-dense food. It is estimated
that up to 20 per cent of young girls in rural Mauritania are subjected to this practice, known as
leblouh
. A typical diet for a six-year-old girl will include two cups of butter and 20 litres of camel’s milk—every day. Some girls choke to death from being force-fed.

Similar practices occur in Uganda where young women are fattened up for two months prior to marriage—they are made to drink a jug of camel’s milk every two hours and can put on up to 80 pounds. The presence of stretch marks on the abdomen is regarded as an essential beauty sign. Less extreme but similar practices are known in other parts of Africa. The strange thing is that while some body fat is essential for reproduction, gross obesity is associated with infertility.

These seem awful examples to people from developed countries. But in many highly developed societies, from the time of the Buddha in about 400
BC
to contemporary life in cities in Asia, to be fat is seen as a sign of accomplishment, affluence, and social status. But then again, Western society has at times gone to extremes the other way. Why is it that the contemporary fashion industry promotes emaciated, gaunt, seemingly under-nourished skeletal figures as symbols of elegance and beauty? Not only is this an unrealistic physique in health terms, but thousands of girls have been harmed by the pressure to emulate this body image, which has led to eating disorders such as anorexia and bulimia and also—again—to infertility. None of these examples seems to make much biological sense.

Humans are designed to have some body fat. Even the fittest of individuals needs some fat to provide the energy reserves necessary for coping with normal life. But while good nutrition is clearly a sign of health and thus fertility, we now live in a very different world where excess body fat is associated with disease. At the centre of the crisis is the dramatic change in the number of people suffering from diabetes and cardiovascular disease. In this chapter we will explain why this has happened.

The amounts of fat in our bodies change throughout our lives. We described the striking observation that the fattest babies in the animal
kingdom are human babies. We suggested that this gives the baby a fuel store, which is needed because the human brain grows most rapidly in the first two years after birth. Infants gradually get thinner up to the age of about three, then they start putting on body fat again until about six years of age (at least in modern societies). We will come back to the importance of this childhood weight gain later.

Nearly all of us tend to put on a little weight in middle age, partly because we exercise less, and partly because the ageing process affects some of our control systems, especially the accuracy of the body’s fat controller. But in between these two time points—the other five ages of man in Shakespeare’s terms—we should remain reasonably thin and with a stable level of body fat. But observation of contemporary societies reveals something else: most of us just go on getting fatter as we get older.

How do we measure fatness? There are several ways. The most sophisticated use X-ray or magnetic resonance scanners to calculate the amount of fat, muscle, and bone as a per centage of total body weight. A typical healthy male might be about 13–17 per cent fat and a typical healthy female 20–21 per cent, because women have some additional fat deposited on their hips and in their breasts. But such techniques are restricted largely to medical research; most estimates of fatness (also called adiposity) are made simply by measuring height and weight.

The most widely used measure for adults is the body mass index (BMI). This is calculated as the weight of the individual (in kilograms) divided by their height (in metres) squared. For Western adults a BMI less than 18.5 kg/m
²
is regarded as too thin; a normal BMI is between 18.5 and 24.9 kg/m
²
. The term ‘overweight’ is restricted technically to those having a BMI between 25 and 30 and the term ‘obese’ to those with a BMI over 30 kg/m
²
. But these
categories differ between populations. In Asian populations, a higher disease risk can be seen even at BMIs as low as 22 kg/m
²
.

The BMI and these definitions are those used in international comparisons so we will use them in this book. The BMI, however, has serious limitations. As it relies only on height and weight it cannot separate out the amount of fat, muscle, and bone. A very fit rugby player, perhaps a first row prop forward, may have lots of muscle and little fat. But because he weighs more than average his BMI may be close to 30 even though he is in fact perfectly healthy.

Before 1980, the percentage of people who were overweight was much lower, although even then we knew that it was increasing. But now the problem has spiralled massively upwards, so that the proportion of overweight and obese people in Asian populations has more than doubled: 50 per cent or more of the population can now be classified as overweight. The problem is even more acute in developing countries. In Brazil the obesity rate nearly doubled in women and tripled in men between 1975 and 2003. Similar effects have been observed in India, with a doubling over ten years, and in China, where it has tripled even though the absolute rate still remains low. In developing countries the rise in obesity is faster than in the West and is particularly striking in urban areas.

The World Health Organization projects that by 2015, 2.3 billion adults worldwide will be overweight and more than 700 million will be obese. Almost a third of teenagers are now overweight in the United States and one-quarter are clinically obese. The effect is occurring earlier and earlier in our lives too. Now the fat of middle age is spilling over into childhood, adolescence, and young adult life.

The statistics for non-communicable diseases associated with obesity are even more worrying. They account for 36 million deaths per year, nearly two-thirds of all deaths globally, from whatever cause. In China it is estimated that there are over 100 million diabetics.
And diabetes and cardiovascular disease are setting in earlier and earlier in our lives. In urban parts of India, as many as 20 per cent of 30-year-olds have diabetes.

So why do so many people now get fat and suffer the direct and indirect consequences of obesity? The simple answer is that the way we live our lives has changed dramatically in at least three ways—what we eat, what we do, and how we live our lives. We need to dissect out each of these differences. In doing so we will expose the problems of some widely held assumptions and some rather naive thinking.

Our starting point is human evolution. In our book
Mismatch
we explained that our biology has been shaped over more than 100,000 years by selection and other evolutionary processes. These matched our biology to our world, but of course this was a very different world from the one we now inhabit. It is in the nature of evolutionary processes that they set the range of biological responses that we can make to an environmental change. But that range has limits. We cannot cope with an environmental change which is too large or beyond our ancestral experience. If our ancestors did not experience certain environmental conditions, they could not have undergone selection to leave us with a biology which allows us to cope with them now.

A good example concerns the level of oxygen in the air. All our early ancestors lived at altitudes below about 3,500 m. So it is not surprising that in general human beings can cope with altitudes up to that level. It takes some of us a few days before we are comfortable if we go from sea level to a mountain resort at 3,500 m, but most of us can do it. However, no human society can survive successfully above about 4,000 m. Very fit individuals may be able to climb higher than this, even without oxygen—for example, to work in mines at 4,500 m in the Andes for a short period of time—but even then, these individuals
will have to descend to lower altitudes before too long. Human fertility also falls off dramatically with altitude, so we clearly never evolved to colonize these lofty regions of the planet. One way of putting this is to say that we are just not ‘designed’ to live at these high altitudes—but evolution has no design or purpose, and does not imply that a designer exists. But contrast humans with the bar-headed goose which can fly at 10,000 m—needless to say without oxygen tanks. So some species have evolved to be adapted to life at great heights and low oxygen levels, but we are not one of them.

We find it very useful to take this evolutionary perspective in order to understand why the changes in what we eat, what we do, and how we live our lives have had such dramatic consequences. Diet and lifestyle are important aspects of the environment which we have made and now inhabit.

The most common explanation for the rise in obesity is that we have adopted a lifestyle in which we eat far too much of the wrong kinds of food and are too lazy to take physical exercise—we are guilty of the sins of gluttony and sloth. Some public health experts try to make us feel guilty about this. There is of course a degree of truth in their charge because it is not possible to become obese without taking on board more energy from the food we eat than we expend through basal metabolism, growth, physical activity, and even reproduction.

But there is much more to the story than that. We need to unpack it, to see what is involved. First, it is true that modern diets, especially in the developed world, often contain high levels of sugars or carbohydrates which are highly refined—such as in white bread, sweet drinks, and polished rice—and these foods release their carbohydrates into the bloodstream very rapidly. They push up blood glucose levels quickly, and are consequently called ‘high glycaemic index’ foods. The high levels of glucose in the bloodstream are more than the body can easily use as an immediate fuel source, so they push up the blood levels of insulin; the excess fuel is taken up by adipose and other tissues to be stored as fat. This is a
simple and highly effective strategy, which evolved in most animals including even some insects, whereby fat storage provides a depot of energy which can be used later.

Got too much on your plate? Well, gobble it up anyway and stash some away for later; you never know when your next meal is going to come along. This biology is widespread. Laboratory animals fed on high-glycaemic-index foods get fat. So do cats, dogs, and other pets, such as budgerigars and gerbils. Animals do not get fat in the wild, however, except those which lay down extra fat before going into hibernation. So there must be something unnatural about the fat family dog. It is strange that so many scientists still stick to the view that because obesity runs in families, inherited genetic effects must hold the key—but how do they explain that often the dog in these families is obese too?

There are other unfortunate things about modern Western diets. For example they contain relatively low levels of fibre, especially if they have a high refined carbohydrate content. Fibre is useful because it retains nutrients in the gut and so delays their absorption. Hence a given caloric load in a meal that contains high fibre produces a lower level of blood glucose over a longer period of time than one which does not.

Then of course there is the fat content of the food we consume. Many modern foods contain high levels of saturated fats in meat, eggs, and dairy produce. Snacks such as biscuits, chocolates, cakes, and crisps often have a high fat content too. Unfortunately, because we eat them between meals, they tend to alter the body’s metabolism in favour of fat deposition. And modern processed food sometimes contains different fats, such as trans-fats, which in the past we only ate in tiny quantities because we had not invented the industrial processes for producing them.

Modern Western diets are unbalanced in other respects too. Even the trace nutrients that we need in our diet, such as iron and zinc, folic acid and vitamins, are sometimes not present in high enough
concentrations to keep us healthy. Vegetarians can be deficient in vitamin B12, which is found primarily in meat—this is a major problem in some ethnic groups in India which have very strict vegetarian diets.

We are a generalist species, in other words one which can survive on a wide range of diets. Otherwise we would not have been able to inhabit the globe in the way that we do, from the Tropics to the Arctic regions. The Inuit eat large quantities of meat, yet many people in India are strict vegetarians. But this does not take away from the fact that it is the balance of nutrients as well as their absolute amounts in our diet which is so important to our health.

And so, now that we can see how the components of the modern diet fit into the story, we return to our evolutionary perspective.

While there is still room for some speculation and it is dangerous to generalize because our ancestors lived in so many different ways, there is a general consensus about the kinds of diet our predecessors had. The diets of hunter-gatherers in our Palaeolithic past 100,000 years ago contained very few simple carbohydrates, let alone sugars other than perhaps from wild honey and the fructose in fruits. The meat content in their diets may have been high but it was usually lean meat, because the animals that were hunted for food ran around even more than their early human predators. The balance of the diet was made up of a higher proportion of vegetables, roots, nuts, and seeds than most people consume today, even in developing countries.