Why We Eat (Too Much) Page 5
Figure 1.5 The weight set-point
Unfortunately, the weight set-point is not always set at a healthy weight. If you suffer with obesity then your set-point is probably the cause of this. If you consciously try and lose weight by traditional means (i.e. eating less and moving more with no change to the quality of the food you eat), your powerful negative feedback mechanism will force your weight back up. It becomes a struggle of wills between your conscious desire to be a particular weight and your brain’s subconscious power to regain its desired weight set-point. Invariably – but unfortunately for all dieters – biology always wins. It may take a week or a month or a year or even several years, but your subconscious brain will eventually haul your weight back to where it wants it to be.
The weight set-point theory, plus negative feedback to control your weight at that set-point, fits in with both sensible biological models and with what patients tell us of their experiences with obesity. They feel trapped, not in control. They can lose weight but will always regain it as the subconscious brain wins the battle of wills. If, by losing weight on a diet, you send signals of probable future famine to the brain, then not only will you regain the weight you lost, but invariably your set-point will edge upwards and you will end up heavier than before you started dieting.
Summary
The secret of successful and sustainable weight loss is to understand how our bodies regulate our body weight set-point. It is not as simple as energy in and energy out. Now that we know that the set-point is the master controller of our weight, we need to find out how our brains calculate where it is set. Various factors in our environment, our history and our family background determine our individual set-point – whether it will be set as slim, obese or somewhere in between.
Later chapters will discuss how to identify the signals (in the type of foods we eat and the way we live) that control our weight set-point. Once we understand these signals, our weight set-point, and therefore our weight, will finally be under our control.
TWO
The Sacred Cow
How Genetics, Epigenetics and Our Food Control Our Weight Set-Point
I was sitting at a dusty roadside tea shop in rural India, daydreaming and watching the sun go down, when I noticed that the traffic had come to a complete standstill. The chaotic weaving of lorries, cars, bikes and tuk-tuks had ceased. Normally when this happens there follows a cacophony of horns as the source of the roadblock is abused, even if the jam happens to be caused by an accident. But this time there was unusual silence and I wondered what was going on. Five minutes passed and the traffic started up again, but at a slower pace than before. Then, calmly walking in the opposite direction to the traffic, in the middle of the road, I saw the source of the traffic jam, a cow, sacred and revered by Hindus.fn1
The animal looked fairly bedraggled in the heat and noise, but what made me curious was its size. I knew that it would have been very well fed by its owner, who had placed colourful garlands around its neck, but despite this it seemed slim and wiry compared to the cattle that I was used to seeing in the drizzly green fields of England. The cows that I remembered were double the size and the discrepancy puzzled me. Why would well-fed Indian cows remain slim, compared to the same animals in my country?
The answer to this question is quite simple, but can lead to a better understanding of the factors in play with regard to humans: how our environment and our genetics determine our weight set-point. And when we truly understand this concept, we can beat obesity.
Imagine that you are a cattle farmer and you want to maximize your profits. How can you make your farm and your herd better than your neighbour’s? How can you make your cattle grow bigger so that you can make greater profits when they are sold? The first and obvious answer would be to ensure that there is a plentiful food supply in both summer (grass) and winter (hay). This would surely optimize their size. All the cattle would be well nourished. But hang on, aren’t the slim sacred cows in India well fed all year round? So maybe the obvious answer is not the correct one.
There are two common strategies used by farmers to make their cows grow larger than non-farm, or wild, cows. When these practices are applied to human populations, you’ve guessed it, obesity results. Here is why.
Drive-Through for Cows
The first strategy is not to feed the cows what they would normally eat and what generations of cows have eaten for millennia, i.e. grass. If you change the food that the cows are given from grass to a mixture of grains and vegetable oils, then you have a good chance of fattening them up so that they are worth much more when you come to sell them. We know that this happens quite regularly on commercial farms. Cows that consume a diet including grains, such as maize and soy, mixed with oils such as palm oil, will gain weight considerably faster than those grazing on grass.
To optimize weight gain even further and faster, farms introduced feeding lots so that the animals are confined to a pen and cannot really do anything but eat the corn or oil feed that is right in front of their noses for hours on end, for months at a time. The present-day human equivalent would be a kind of fast-food drive-through (with use of all the car’s entertainment systems banned – but free food), where the car does not actually drive through but stays by the serving window. The recipients would be so bored that they would continue to eat the tasty high-carb, oily foods passing in front of them throughout the day, every day. Imagine being stuck in this situation for the decade that you were growing and you can imagine what would happen to your waistline.
It’s not just cows that will grow bigger in response to a change in their diet. We know from studies of rodents that if you want them to grow faster, and fatter, you cannot do this by just feeding them more of their natural food (called chow). It is not the amount of food that will alter their weight set-point, it is the quality of the food. If a rodent is given high-calorie, high-fat foods (called ‘canteen food’ by the scientists), its weight set-point will be raised.1
So feeding cows a high-calorie grain-and-oil mix, and detaining them in a pen, makes them grow faster. This is not really rocket science, but the point is that this type of change in diet, towards more grain- and oil-based foods, when mimicked in the human population, causes a similar change in size – people will get bigger and fatter. It’s the same with all mammals. On the whole, we are no different in our metabolic biology to those farm cows and lab mice and rats.
Once the food supply to a human population is changed to ‘canteen’-type food, then many of that population will become obese. One of the interesting factors in this dietary change that I have noticed over the years is the real difficulty for most of the population to be able to purchase ‘normal’ fresh food (i.e. food that is not processed). When you leave the office in search of a healthy lunch, it can be very tricky to find foods that haven’t been manipulated or changed into high-calorie food replacements. The Western high street is like a food desert – natural foods only exist in rare, difficult to find, oases. The mirage of real food is around, but it doesn’t really exist.
Survival of the Fattest
Now we are ready for the second strategy that farmers can use to make their herd bigger and more profitable than their neighbour’s. In every herd of cattle there are individual differences between animals. They are obviously not all identical. These individual differences (called heterogeneity in medical jargon) are very important for the survival of species. If some of the species are taller or shorter, or bigger or smaller, or faster or slower, the individuals at the extremes of the spectrum may be more likely to survive unexpected changes in the environment. For example, if there was a famine, the cows that were carrying more energy reserves (fat) before the start of the famine would be more likely to survive. Because more cows with a tendency to carry extra weight had survived the famine, the next generation of cows would be more likely to become fatter compared to the previous generation. In other words, this is an example of Charles Darwin’s theory of natural selection or survival of
the fittest (or, in this case, fattest).
Farmers can use the differences in characteristics between cows within a herd to make all the cows bigger and fatter by an artificially induced natural selection (or, more succinctly, unnatural selection, because it is not the natural environment that is selecting the next generation but the farmer). For instance, they will select those cows that put down fat deposits within their muscles to give the eventual meat the tasty marbling effect that you may know from a rib-eye steak. Obviously, this type of fatty meat is more valuable to the farmer. When full grown, the cows with these characteristics will be selected by the farmer for breeding the next generation; the ones that do not grow so big or so fat will not be selected and their ‘slim’ genes will be lost to the next generation of cows. If they continue with this unnatural selection generation after generation, then within ten generations the farmers who have used this method will have a herd of cows that grow much faster, are bigger and have more fatty muscle marbling, compared to the farmers who just concentrated on looking after, and feeding, their herd. This method of manipulating the gene pool of the herd to make them more likely to exhibit characteristics that are valuable to the farmer is known as selective breeding. It is the reason that, of the 1.4 billion cows on Earth, there are now over 1,000 different breeds, exhibiting favourable individual characteristics for the farmer.
Who Can Grow the Biggest Cow?
What can dietary manipulation and selective breeding in cows tell us about the human obesity crisis? Let us imagine three pens of cattle next to each other. The cattle from each pen are from three separate farms and each farm employs different farming practices:
In the first pen the cattle are fed only grass and hay
The second pen has cattle fed on canteen foods (corn and palm oil)
The third pen contains cattle fed on canteen foods, but these cattle have also been subject to over ten generations of selective breeding to encourage rapid growth of fat-containing muscle.
How will the different pens compare?
Pen 1: Grass-Fed
The grass-fed cows will look similar to the sacred cow that I saw blocking the traffic in India – not much extra fat. As there was no selective breeding, there would be more differences between the cows, with some being bigger and some smaller, but most would be normal sized.
Pen 2: Corn-Fed
The corn-oil-fed cows would, on average, be significantly larger than the neighbouring grass-fed cows. Their weight set-point would be raised by their change in diet. However, as with Pen 1 cows, there will have been no selective breeding, so there would still be a significant difference in characteristics within this herd. Some of the cows at the lower end of their herd’s size spectrum could easily be unrecognizably different if placed in Pen 1, despite eating a completely different diet throughout their lives.
Pen 3: Selective Breeding + Corn-Fed
The selectively bred and corn-fed cows would look massive compared to Pen 1’s cows and would be much larger on average than Pen 2’s. However, the larger cows in Pen 2 would not look out of place in Pen 3 despite never having been selectively bred (these are the cows that would have been chosen for selective breeding if it had happened in their farm).
If the differences between the cows in the three different pens were transferable to human characteristics, what would that tell us about the obesity crisis and who is affected?
It would suggest that if a group of humans were in an environment where they only consumed natural types of foods, then they would not really suffer significantly with an obesity problem. We’ll call this Group 1 Humans.
If the humans were exposed to canteen-type food (i.e. grain/oil-based food with a high-calorie density), then this group would on average be much bigger and more obese than those groups that were eating natural foods. We’ll call this Group 2 Humans.
Finally, if the group of humans had been selected to favour survival (and reproduction) of the biggest and most obese, and had also been fed canteen-type food, then they would on average be the biggest of the groups: Group 3 Humans.
So, is the farmed-cow model a good one to unpick the causes of human obesity? Let’s look at the evidence in humans.
Hadza Hunters
It is very difficult to find a population of humans that still eats the same food as its distant ancestors did millennia ago. We know that there has been a massive shift in the type of foods available to ‘Western’ populations since the industrial food revolution of the last hundred years (more on this in chapters 7 and 8). However, the food that humans were accustomed to eating started to change around 20,000 years ago with the advent of agriculture, so we need to go back even further to the time when our ancestors ate only what they hunted and collected. Learning about the lives of hunter-gatherer populations is essential in order to understand who we are now, and how we reacted to our changed environment. There are a very select few nomadic, hunter-gatherer tribes remaining in the world today, among them isolated rainforest tribes in the Amazon, the Pygmies of the Congo jungle, the Bushmen of the Namibian desert and the Hadza people of the savannahs of Tanzania.
As part of my research for this book I was lucky enough to spend time with a Hadza tribe to gain first-hand knowledge of these unique people who represent humanity in its oldest and most untarnished form. The tribe that I got to know consisted of several family groups. The Hadza are a pure hunter-gatherer people and are proud of their culture and heritage. Visits from Western researchers do not dilute their lifestyle and they do not like to accept gifts or money; they prefer any funds and resources to be used to protect their land and their way of life from encroachment by farmers. You will not be surprised to learn that the Hadza tribe do not suffer with an obesity problem. They consume meat, berries, fruits, tubers (like sweet potato), and their favourite food is natural honey straight from the hive. These are the foods that they have been consuming for 150,000 years and they see no reason to change their lifestyle. They probably wonder why people would grow food like farmers do, when one can take it for free (in their case, directly from the savannah).
When you analyse the weights and sizes of individuals in the hunter-gatherer tribes you find a pattern common to all animal species which are consuming the natural foods that they were evolved to eat (just like the cows in Pen 1). Some of the population are underweight and a few are bigger than normal and overweight, but the majority (80 per cent) are within the normal weight and size range.2 They have what statisticians would call a normal, or symmetrical, distribution to the size of their population. (See fact box below.)
Figure 2.1 Frequency of underweight, normal-weight and overweight people in hunter-gatherer tribes
This distribution of body types is the same for all types of animals living on natural foodstuffs, from chimps to lions to cows. Even when there is an abundance of natural foods available to these animals, you don’t see the population becoming obese. This suggests that high-calorie availability will not affect weight, as long as those calories come from natural foods.
FACT BOX: WHAT IS A HEALTHY WEIGHT?
Doctors and scientists commonly use a term called the Body Mass Index (BMI) to calculate whether someone is underweight, overweight, obese or in the normal weight range. They cannot rely on weight alone as body size depends on both weight and height. For example, a 70kg (11 stone) woman who is 5ft 7in tall will have a normal BMI and a 70kg woman who is 5ft 2in will have a BMI in the overweight range.
BMI is calculated by dividing a person’s weight in kilograms by their height in metres squared. BMI = kg/m2. The normal healthy range of BMI is 18–25kg/m2. Someone is underweight if their BMI is less than 18 kg/m2; overweight if their BMI is 25–30kg/m2. Obesity is diagnosed if someone has a BMI of over 30kg/m2. A BMI of over 40kg/m2 is termed morbid obesity (‘morbid’ means ‘diseased’ in medical language).
BMI is an important predictor of health. The higher the BMI (above the healthy range), the greater the risk of developing Type 2 diabetes, high blood press
ure, high cholesterol (all of which cause heart disease) and cancer. People with a BMI of 38kg/m2 or over will die on average seven years earlier than those in the healthy range.3
However, the BMI calculation can be an inaccurate predictor of disease risk if it fails to take into account someone’s build. A bodybuilder (imagine Arnold Schwarzenegger in his prime) carries extremely heavy muscles and may have a very small amount of fat, but if you calculated his BMI he would invariably fall into the obese category (because muscle is so heavy). BMI is only accurate in someone who has a normal build (and this has not been defined). For instance, people of Asian descent have, on average, less muscle mass and therefore their BMI under-predicts their obesity risk. In their case a BMI of 28kg/m2 is defined as obese.
So don’t worry so much if you are a well-built person who is in the overweight BMI range – your weight is probably healthy … but do worry if you have a slim build and are in the overweight BMI range – you may already be at risk of obesity.
Farming Communities
What would happen to the Hadza tribe that I visited if the land that they relied on for their natural foods was taken over, and they were forced to become farmers? We know from fossil evidence at the time of the advent of farming that within a few generations the Hadza would probably become sicker and their height would decrease. The quality of their diet would suffer as they consumed more grains and had less food variety. But what about their weight? Well, if we look at the weights of early farming populations we can see that although most are still remarkably fit, many more of those populations are now overweight rather than underweight and a small number are now on the borderline of obesity.4 In fact, if we look at the population weight curve we can see that some seem to be more affected by the change in the environment than others.