It’ll take more than a soup-and-shakes diet plan to tackle obesity in the UK

If the government really wants a healthier nation, it needs to address the twin scourges of processed foods and food poverty

It seems fitting that a government lacking in substance is now urging the nation to lose some of its own. At the end of July it launched its anti-obesity strategy, boosted by evidence that Covid-19 hits overweight people hardest. Today saw a more targeted soup-and-shakes weight-loss plan aimed at people with type 2 diabetes.

Common to both initiatives is the advice to exercise more and eat less. It seems as pure and virtuous as Mom and apple pie (well, maybe minus the pie). But as a strategy for weight loss it has a basic and fatal flaw: it doesn’t work.

I learned this through bitter experience. Several years ago I carefully cut back on my eating, and sure enough, the kilos fell away. So did my sanity. Feeling hungry most of the time had made me grumpy, irritable – and obsessed by the next meal. I was leaner but meaner.

When I hit my target weight I was careful not to go back to old habits. So it was deeply disturbing when I could not stop my lost weight piling back on with a vengeance. Twelve months later I was at least as heavy as I had been before. Anecdote is not evidence, of course. But my case is an example of a well-established fact: the vast majority put back on all the weight they lose when dieting, or even more.

The reasons for this are complicated, but the basic principles are clear enough. The simple energy-in-energy-out model treats the body as though it were a machine, always burning its fuel in the exact same way. Instead, nature favours organisms that can adjust their energy expenditure in accordance with what is available.

The human body is such a homeostatic, self-regulating system. Deprive it of calories and it starts to burn fewer of them, and tries to horde away any excess as fat. So all the time the dieter is congratulating themselves on their weight loss, their body is wondering what the hell is going on, and doing all it can to reverse it.

Evidence is mounting that body weight is not determined purely by calorie intake. How we metabolise our food depends on what kind of food it is, not just how much energy it contains. We don’t yet know exactly what makes a difference, but we have lots of evidence that people get fatter when they eat more highly processed foods, especially refined carbohydrates. They are also slimmer when they eat more home-cooked meals. So a serious anti-obesity strategy would require the government to take on the food industry’s promotion of highly processed foods.

The apparent success of the soup-and-shakes strategy in trials is no vindication of old-school calorie-counting. It’s not just that the trials were highly controlled and participants had serious health conditions and so were highly motivated. More importantly, the success heralded was in remission of type 2 diabetes, not weight loss. While 35.6% of participants were in remission after two years, only 11.4% had maintained a 15kg weight loss. Since the results after two years were significantly worse than those after one, we don’t yet know whether even these gains are sustainable. The study is encouraging for diabetes treatment, but it is not even close to being evidence that sustainable weight loss is achievable for most people.

We should be less obsessed by weight in itself anyway. I’ve seen meta-studies that suggest all-cause mortality is lowest in people who are actually slightly overweight. Even a recent Lancet study, which suggested the officially healthy body mass index of 25 was indeed optimal for health, still showed that increases in risk are minor for the moderately chubby.

Government calls to reduce our weight assume we can control what in reality we can merely influence. The most we can control is the kinds and amounts of food we eat, how much we exercise, whether we smoke and how heavily we drink. If you do that and are a little overweight, you are going to be much healthier than a couch potato who stays slim through endless cans of diet Coke and cigarettes.

If the government wants to help people to eat better, its main priority should be ending what is often called food poverty – more accurately described as poverty, full stop. The poorer you are, the more likely you are to be overweight, almost certainly because of the way poverty limits your food choices. If people cannot afford good food, or the fuel to cook from scratch at home, telling them to eat less and better is pointless.

Of course we should all try to take responsibility for our own health. But we can be responsible only for what we have the power to do. That is limited not just by basic biology, but by what is on our shop shelves and in our wallets. Tackling those problems requires controls on business and greater redistribution of wealth. The government rejects both on ideologic grounds, and instead promotes dieting and personal responsibility, preferring flawed common sense to the evidence.