Many of us will have tried to trim our waistlines by counting calories and hitting the gym, but only for all our efforts to be met with little to no success. So what's going wrong?
Well, losing weight has surprisingly little to do with how much we're eating, or how many hours spent exercising. That's according to Dr Andrew Jenkinson, a consultant in bariatric surgery at University College London Hospital and author of the books Why We Eat (Too Much) and How to Eat (And Still Lose Weight).
He argues instead of calorie counting and endless gym work, it's much more effective (and easier) to lose weight by eating foods that better manage your levels of the hormone leptin.
How exactly does leptin work? What food should we actually have on our plates? And is there an easy way to fight cravings? Jenkinson answered all of this and much much more during a recent chat with us.
BBC Science Focus: How big is the problem of obesity globally?
AJ: I think there's a massive problem in the Western world that's going to probably contribute to bankrupting the healthcare systems. In America, a third of people, are morbidly obese, as in obese to up to a level that's affecting their health.
In Europe, it’s around about a quarter. Massive proportions of these people have type 2 diabetes, high blood pressure, sleep apnea, joint problems and an increased risk of cancer.
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For the first time ever, we're seeing life expectancy decrease because of obesity. We've got new treatments on board, such as injections, but these treatments are massively expensive.
If you roll them out to millions and millions and millions of people, and those people then just become dependent on them. So, obesity is a massive economic and health problem that needs to be addressed.
Obesity is not caused because there is suddenly a lot of tasty high-calorie food available to a population. It comes about because that food acts in a way that is similar to a drug that blocks normal weight regulation pathways.
Wild animals have very similar pathways, but we don’t see a pride of lions becoming morbidly obese and not being able to move around because suddenly there are too many antelope to eat.
So the issue is with our hormones?
Yes. Leptin is a hormone [the so-called 'satiety hormone'] that works to regulate wild animals’ weights and it should work in humans in the same way.
The level of leptin acts as a signal to the weight control centre in our brain – a little area called the hypothalamus. This hormone is the ultimate control of where our weight is – when the brain senses leptin, it reduces our appetite and increases our metabolism.
It's a hormone that actually comes from fat cells. And the fatter we get, the more leptin we produce, which should decrease our appetite and ramp up metabolism.
However, particular types of food can block the leptin signal. We all know that sugar, refined carbohydrates and processed foods cause obesity. But we think that’s because they've got too many calories in them and are too tasty. It's not. It's because they increase our levels of insulin, and insulin blocks leptin. It's as simple as that.
Once you lose control of leptin, your brain can no longer gauge how fat or thin you are. You may be clearly visibly overweight, but your brain can't sense that and is actually sending you signals saying you’re underweight.
It's like if you were driving a car and you suddenly see that the fuel gauge is empty. You panic and pull over to get fuel, but as you fill up you release the tank is already full – it's not the petrol that's the problem, but the fuel gauge. A similar thing happens to your body when leptin is blocked.
What role does the concept of calories play in weight loss?
We need calories to live. A calorie is a unit of energy that’s stored in plants. Basically, plants store carbohydrates and energy in a cellular matrix.
We use that energy to heat our bodies, make our hearts beat, move around etc. But the interesting thing is that 70 per cent of the energy we consume we burn at rest. This is called the basal metabolism and covers things like your immune system, body heat and heart rate.
The thing that's slightly misunderstood by people who are totally focused on calories is that the body can get rid of calories very easily. It can switch up our basal metabolism by 600 or 700 kilocalories per day. That’s the same as you’d burn doing a 10k run or take on by eating a large three-course meal.
It can also switch it down. If we go on a low-calorie diet, within a couple of weeks we adapt to it by switching our metabolism down, and so weight loss stops.
However, when you look at the calories we consume, a lot of us are overeating. We should be putting on a hell of a lot more weight than we are. But our bodies try to fight this by increasing our basal metabolism. It's why there's a Western epidemic of high blood pressure – our bodies increase our blood pressure to expend more energy.
Why do some people seem to find it more difficult to lose weight than others?
It comes down to an idea called the weight set point, or weight anchor. If you imagine you were a ship attached to an anchor, you can't really sail away from the area you're anchored to. It's the same with your weight anchor.
Your weight anchor might be set to the 'overweight' or even 'obese' area. You can try to sail away from it by thrashing yourself in a gym or going on a low-calorie diet, but the weight control centre in your brain will pull you back to where it wants you to be.
This is your weight set point. It's determined by a number of things that you can change, but also one thing that you can't change – your genes.
We all know people who are naturally slim and can eat whatever junk they want, and they don't tend to put on weight. But a quarter to a third of the population have genes that means they have a propensity to put on weight if they are exposed to the Western diet.
This is due to the availability of sugar, refined carbohydrates, processed foods, fructose, vegetable oils etc. Things are there when we go to a supermarket. Basically everything has got them in apart from the fresh vegetable section.
This is where there’s a misunderstanding from doctors and nutritionists. They say you've got to count your calories. That's a load of rubbish – it's all about what the food does to you as a drug.
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So what should we be eating?
We need to remember that it's not about dieting, but diet. Dieting implies a short-term calorie restriction. But if you understand what different foods do to your body as a drug, you will lose weight. Avoid sugar, refined carbohydrates and vegetable oils, which have detrimental effects on insulin.
Switch them out for home-prepared foods and without any effort, your weight set point will shift downwards. You'll lose a decent amount of weight – much more than if you just exercised regularly. You don't have to be hangry. You don't have to be irritable.
You can easily swap out the toxic snacks you may mindlessly eat while watching TV in the evening with a plate of vegetables sprinkled with a bit of salt, for instance. It's all about identifying bad habits and changing them into good ones.
At first, you may find you get cravings when you give up sugar or chocolate. But you can overcome this by 'crave surfing'. This is simply becoming aware a craving is there – rather than ignore it, concentrate on it. You can notice this craving more intense and then watch it come down again. There will be waves of these cravings, but each one will become shallower and shallower.
What role does exercise have to play in weight loss?
If you can afford to go to the gym for an hour and a half and do very vigorous activity, you'll expend maybe a thousand calories a day. Do that six days a week and that can have an effect on your weight.
But, unless we're an athlete, most of us won't be able to manage this. And the recommendation of half an hour’s exercise, three or four times a week isn't going to have any significant effect on your weight – you might lose two kilograms in a whole year.
Just as our metabolism becomes more efficient if we go on a diet and restrict calories, it also becomes more efficient if we use up a lot of energy in the gym.
If we go to the gym and do a half hour’s exercise and we expend, 400 kilocalories, for instance, we're going to get quite hungry. And unless we have an iron will, we will consume those 400 extra calories. Even if we don't consume those calories, we’ll simply burn 400 fewer calories when we sleep. The metabolism is in control.
The way of trumping this effect is to do both calorie restriction and vigorous activity, a double whammy. Our metabolisms can't readjust more than about 600 or 700 kilocalories per day. So, if you manage to lose over 1,000, you will start to lose weight. But that's extremely difficult, you’d be absolutely shattered and hungry.
This interview has been edited for clarity and length.
About our expert, Dr Andrew Jenkinson
Andrew is a consultant in bariatric (weight loss) and general surgery at University College London Hospital.
He is also the author of the books Why We Eat (Too Much) and How to Eat (And Still Lose Weight).
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