It has happened to us all.
You finally have a dinner date and you decide, in a fit of excitement, to call into service a pair of designer jeans you haven’t worn in a little while. However, try as you may to pour yourself into the expensive denim, you find, to your horror, that the jeans now resemble a corset, requiring violent sucking in of your abdominal region, flirting with hypoxia, before the buttons can eventually meet the holes to perform their intended job. Where can you ascribe blame for this scandalous state of affairs?
Are you genes to blame when your jeans don’t fit?Credit:Shutterstock
Over-indulgence over the festive period? Your increasingly desk-bound job? Above-inflation increases in your gym membership fees? Bankers? Or can you, as is seemingly fashionable, place the blame squarely at the feet of genetics? Are your genes to blame when your jeans don’t fit?
To answer this question, it is worthwhile considering some numbers:
a) an average-sized woman should consume around 2000 calories (8000 kilojoules) a day in order to survive, and an average-sized man 2500 calories; or around 750,000 – 900,000 calories a year;
b) while ageing from a youthful exuberant 20 years to a middle-aged 50, an average person will, depressingly, typically gain 15 kilograms in weight (some will of course gain little to no weight at all, while others will gain an awful lot more than 15 kilograms);
c) if you or I were like a giant chocolate bar complete with nutritional information stamped on our collar labels, our caloric content would be around 5000 calories per kilogram (give or take love handles/muffin-tops).
Because of c), the 15 kilograms of weight gained over 30 years is worth about 75,000 calories, or 2500 extra calories a year: a day’s ration of calories if you’re a man. If you did the necessary maths, you would find that an extra 7 calories a day for 30 years is all you would need to gain 15 kilograms in weight!
Are you kidding me? The question that emerges from these numbers is: ‘Why are we all not the size of houses?!’
The set point
We do tend to gain weight as we age.Credit:Jenny Evans
What is clear from data stretching back many decades is that mammals will robustly defend their bodyweight. The first data of this came not from humans, but from lab rats. Experiments done in the 1940s found that if a rat was left in a cage to its own devices and with sufficient food, it would grow at a certain rate. If the amount of food provided to the rat was reduced (i.e. if the rat was placed on a “diet”), the rat would lose weight, which was unsurprising. Once the amount of food that was provided went back to normal however, the rats rapidly began to gain back the weight, but interestingly, only back to the growth rate they were on before the “diet”, and then they carried on like the diet never happened.
When the food provided to the rats was changed to something very palatable, say high in sugar and fat, then the opposite was true, with their weight rapidly increasing. Once their food source was back to normal, the rats’ weight drifted back down to the previous trajectory. These experiments led to the so-called “set point” hypothesis, which proposed that all mammals in a stable environment will achieve a genetically determined trajectory of growth.
Data collected since those initial experiments shows that the same phenomenon occurs in humans. Despite all the holiday periods, the resulting diets, illnesses, pregnancies and life’s many other little surprises, only very unusually will anyone deviate more than 20 per cent in their adult body weight over a lifetime.
Yet, we do tend to gain weight as we age. Why? There are two major reasons. First, as we clear our twenties and go through our thirties and beyond, we begin to accumulate inefficiencies in our various organ systems, such that our metabolism begins to slow down. Second, on average, we move less as we get older. Yet, we don’t tend to eat that much less (if at all) as we age.
The strategy used by our brain to defend our bodyweight is straightforward, even while the underlying mechanisms are complex; that is, to influence food intake and energy expenditure. What I am not talking about here is the executive decision to go on a diet or to go to the gym. Those are conscious choices. Rather, the bodyweight defence strategy deployed by our brain is subconscious.
Imagine a typical festive season or some other vacation period, where there may have been a certain amount of overindulgence. Bacon and eggs every morning for breakfast you say? Sure! Desserts during both lunch and dinner? Why not! Eventually, and reluctantly, you have to get back to the real world and your normal day-to-day routine. Then comes that time in the day when you have to interact with food. Peering at a refrigerated supermarket shelf or perusing a menu in a restaurant, you may say, “Gosh, I don’t feel so hungry tonight, I might just have a salad”.
I don’t feel so hungry tonight.
Why not? Did you have a sudden attack of “will-power”? No, the signals in your brain are simply making you feel “not hungry”. “Why can’t I feel like that a little more often?” many of you will undoubtedly be thinking.
More than almost anything however, your brain absolutely hates it when you lose any weight. Because how much fat you are carrying is essentially how long you would last without food, your brain equates weight loss to a reduced chance of survival.
So when you lose even a kilogram, your body begins to fight back, making it rapidly more and more difficult (or so it seems) to shift each additional gram. Your body also makes you feel more hungry, driving you to eat more.
Keeping in mind that just a pesky 7 extra calories a day makes such a surprisingly large impact over a lifetime, eventually, the depressing phenomenon familiar to dieters the world over occurs; where after a couple of months, all of the weight you fought to lose has somehow grimly clawed its way back. This is, of course, what most will be familiar with as “yo-yo” dieting, where you lose weight (yay!) then you regain the weight (boo!) and the cycle, depressingly, repeats itself interminably. Although it might seem as if you are gaining more weight than you had lost, this is seldom the case, and your weight will typically go back to where it was before you began your diet i.e. your set point. Considering at any given point in time, nearly 20 per cent of you reading this will be on some sort of “diet”, there are a lot of depressed people about due to this pattern.
Illustration: John Shakespeare Credit:ss
Today, 60 per cent of us are carrying too much fat, making obesity one of the greatest public health challenges of the 21st century. It is a modern problem, with the prevalence of obesity having tripled in many countries in the world since the 1980s. According to the latest health report from the Organisation for Economic Co-operation and Development, more than 30 per cent of adults in the US, New Zealand and Mexico, and more that 25 per cent in the UK, Australia, Canada, Chile, and South Africa are obese. Within the European Union nearly 150 million adults and 15 million children are considered obese. The problem is not with obesity itself per se, but with the accompanied increased risk to a whole host of nasty diseases, including type 2 diabetes, heart disease, high blood pressure and certain types of cancer.
So how can we explain this rapid worldwide increase of bodyweight? Have our genes changed? Have we suddenly evolved?
Clearly not. These dramatic changes have occurred over the past 30 years, against a constant gene pool and well within the lifetime of many of you reading this. This would put the smoking gun in the guilty hands of “environmental changes”, an all-encompassing term used to describe changes in lifestyle, diet and working practices. Sadly, no matter how much one doth protest, the ONLY way you can gain weight, is if you eat MORE than you burn. It is simple physics.
Let me say this very clearly; the reason we have become more obese as a species is because we eat too much and don’t move enough. Therefore, the only way to become less obese, is to eat less and move more. There we have the cause and cure for the obesity epidemic. We all know this.
That being said, hidden in this simple statement is oft over-looked complexity that is well worth further exploration.
The question of HOW we have become obese is one of physics. The question of WHY we have become obese requires examination of why some people eat more than others, why some people are more metabolically efficient and why some people burn more energy. It is in these latter questions that the biological variation lies.
Our biology, how we are put together, how our organs work, how the cells that characterise our organs function, how the molecules and proteins that form our cells interact, begins with our genes. So to understand biological variation, it is inescapable that we first need to understand variation in genetic heritability.
What surprises most people is that the heritability of weight is actually close to that of height. No one would dispute the fact that height is genetically determined: tall parents = tall children.
It is also well known that skeletons and written records show that human beings today are inches taller than humans just a century or two ago. For example, soldiers around the age of 20 who enlisted in the army during World War I were on average 168cm (5’6”), while today’s average for young men is 178cm (5’10”). Why have we become taller as a species? Change in diet, environment, and lifestyle.
It is the same argument with bodyweight, except that the changes have happened over a far shorter period of time. We are now more obese as a species compared to 30 years ago because of changes to our diet, environment, and lifestyle. But it does not change the fact that if our parents are overweight and/or a certain shape, we are very much more likely to be overweight and/or be that shape.
Your shape is largely determined by where fat sits in your body. This is not meant to depress you, but close your eyes for just one moment and reflect upon the shape of your parents. Does your mum have a big bum and a skinny upper body? Does your dad have a big tummy and skinny legs? Who do you look like? Who do your siblings look like? While the absolute amount of fat may differ; you may have a bigger bum or a smaller tummy say; the chances are very high indeed that you will have the shape of one of your parents.
In truth, everything about us; our looks, our shape and size, our character, our intelligence, our athleticism, our risk of mental illness, even our risk of getting into a car accident, along with a million other traits, all have a genetic and an environmental component. It is very rarely, if at all, 100 per cent genetic or 100 per cent environmental. The real difficulty is in determining the relative contribution of each and, crucially, how they interact with each other.
The dessert stomach
Why is it so difficult to say no to dessert? Credit:Shutterstock
Given the importance that eating enough has in keeping us alive, our brain has evolved strategies to make sure that it also feels “good” or rewarding to eat; the “oooooooo” factor. This is easily illustrated by the all too familiar “dessert stomach”, when you are out for a meal. It is almost certain that by the end of the main course, you would have fulfilled your metabolic needs for the day. Yet when the dessert menu arrives, you order the chocolate cake, tarte tatin or creme brulee. Why is it specific to desserts?
Flashback to 50,000 years ago on the Serengeti, and you are dragging an antelope back to the village. Let us just say it has cost you, metabolically speaking, 2000 calories to stalk, chase and bring down the antelope. When you get back to the village, you would clearly have to consume at least 2000 calories to recoup your expenditure. But there is no guarantee that you would successfully get an antelope the next time out, so if you ONLY ate to your metabolic need, you wouldn’t survive very long. That is when the hedonic part of the brain, which governs the feeling of reward (the ‘oooooooo’ factor) kicks in, driving you to eat more.
But how do you get past the mechanical difficulty of a stomach packed full with 2000 calories of venison? Your brain becomes more picky, it begins to crave foods that are more calorically dense and more calorically available, which are going to be foods high in free sugars and fat. What foods are high in free sugars and fat? Desserts.
Your dessert stomach is an evolutionary holdover from your days in the Serengeti, to make sure that even when full, you were still craving the right types of foods to ensure you were able to maximise your caloric intake at every meal, because there was never a guarantee of when the next meal would arrive. It kept us alive in regular feast-famine cycles, but has become toxic for many of us in the feast-feast environment of today.
'Beer belly' or 'wine wobble'?
Pure alcohol contains almost the same amount of calories as fat, and is no more or less calorific whatever drink it happens to be in.Credit:Shutterstock
When it comes to alcohol and weight gain, the term “beer belly” is misleading. The majority of calories from drinking don’t come from the carbs, they come from the alcohol. Pure alcohol, at 7 calories per gram, contains almost the same amount of calories as fat (9 calories per gram), and is no more or less calorific whatever drink it happens to be in; whether it is beer, wine, gin or whiskey. So, a 175ml glass of wine, with an alcohol content of 13 per cent, contains nearly 160 calories, while a whole bottle will be around 700 calories.
Gene Eating by Dr Giles Yeo, published by Hachette Australia.
A standard 330ml bottle of beer with 5 per cent alcohol contains 140 calories. Compare this to 140 calories found in a can of Coca Cola. Very few people would consume six cans of cola in one sitting, whereas many would think nothing of drinking a six-pack of beer. In addition, there are many alcoholic drinks, mixers or alcopops for instance, that are also high in sugar, jacking up the calorie content even further.
And the denouement is that the more you drink, the more disinhibited you become, and the less you will care about what and how much you are consuming. Any spare calories you don’t use immediately will then be converted in to fat. Where you put your fat depends on your own personal biology. On average, men are more likely to store theirs in visceral fat that sits around their belly (hence beer belly), while women will tend to store it underneath their skin as subcutaneous fat. So it’s just less obvious in a woman … although perhaps we could coin the term “wine wobble”, or perhaps “champagne chin”?
This is an edited extract from Gene Eating by Dr Giles Yeo published by Hachette Australia on December 27 (RRP $32.99).
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