The Reason Why Diets Don't Work

Dear Dr Adam,

I’ve tried every diet under the sun, but the results are always short-lived. Why don’t diets work for me, and is there a sustainable solution?

Meera, Guildford

Dear Meera,

Well, that’s the six million-dollar question!

The answer to why diets don’t tend to work in the long-run, not just for you, but for everyone, is two-fold. First of all, by definition, a diet is finite. It gets you from A to B. So your baseline might be overweight and you want to get to a lower weight – what often happens at B is there’s no maintenance or appreciation of what state you’re in at this point. Behaviourally, people naturally go back to habits predating point A.

The other thing people don’t appreciate, particularly with fad-type diets, is that when you’re at a rapidly changing energy balance, your body responds to that. Your body becomes more efficient, driving up energy intake and driving down energy expenditure in order to compensate for that lack of energy. Energy balance is dynamic in the sense that it maintains body weight very well.

So you have two things going on: the diet is designed to get you to a finite point, and that journey creates a physiological response so that when you reach that point you are primed to go back to the start.

In a purely simplistic view, let’s say you go from A to B by creating an energy deficit of 500 calories a day and that might help you achieve, say, a stone and a half weight loss in six weeks. Now, you might be a stone and a half lighter than at A, but if you then went back to the same diet at B, you’d be in an energy surplus. You’d have to consume 500 calories less than what got you there in the first place and maintain that over the long term because you’re now at a new equilibrium.

People often miss that. They think they’ve followed the diet to get them this far and that’s job done.

In scientific research, weight regain after diets is probably underestimated. Studies that get published tend to be of positive outcomes – even those that look at people in the long-term – so you tend not to see the failed weight loss studies in the literature. When you do a study where you’re purposely looking at weight maintenance, that study will possibly either have an intervention to help participants maintain their end weight, or, just the fact that they’re in that study tends to accrue people who are better at maintaining their weight. They’re better at controlling what they’re eating and they’re motivated to do so because they’re conscious of the fact they’re being observed.

“The weight loss industry is very lucrative because success is based on failure”

But not only do people on diets tend to regain the weight they’ve lost, they often overshoot their original weight. There are physiological reasons for that, too. It’s because this drive of restoration of lost tissue involves mechanisms designed to help you survive with the deficit next time this happens. Next time, you’ll have more stores of energy to cope with the deficit and you end up fatter than you were before, so you’ll have to do something more extreme just to get back to B again.

It’s great as an industry. The weight loss industry is very lucrative because success is based on failure. In theory, losing weight is easy, I could just make something up – anything that gets you to consciously look at what you’re eating and bring about a beneficial behaviour change – if someone is motivated to do it, it’ll work, but the challenge is always maintenance.

I suppose the recent success of things like low carbohydrate diets or intermittent fasting is because people have typically followed them for weight loss in the beginning, but it’s a regime they can maintain already. Intermittent fasting, for instance – from the very early stages and continually, whether it’s 5:2 or any other form – simply gets people who are overconsuming to eat less food.

Even if you eat more food on non-fast days, it’s not enough to tip the balance on the days you do fast. So the metabolic advantage is in there, but it’s not exploited because what you’ve done is just adapted to a change in fuel state. The metabolic advantage is more about what intermittent fasting is doing: periods of high, periods of low, rather than continuous periods of low.

If you’ve not tried intermittent fasting before, I’d encourage you to learn more as it does seem to be proving successful for a lot of people. I’ve written extensively about intermittent fasting in a dedicated email course for Form, which you can sign up to free-of-charge here.

To have your nutrition questions answered by Dr Adam Collins, please email hello@formnutrition.com