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Does Michael Mosley's intermittent fasting diet really work?

Intermittent-fasting advocate Michael Mosley. Photo/Joe Sarah

Like the Mosley intermittent fasting diet, attempts to lose weight by periodically going hungry can often have the opposite effect.

QUESTIONMichael Mosley’s 5:2 intermittent-fasting eating plan is sometimes called a diet. It seems to have some medical support, but I can’t find any serious research on it. Is intermittent fasting likely to follow the same pattern as other energy-restricted diets, as you outlined in the June 16 issue?

ANSWERWhether you try to reduce your body size through intermittent fasting or a standard energy-restricted diet, the same issue remains – are humans actually able to consciously control their body weight? Weight set-point theory would say no.

Decades of research suggests that although we can lose weight in the short term, it is invariably regained within two to five years, and for as many as half of dieters, more weight is regained than was originally lost.

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US obesity and neuroscience researcher Stephan Guyenet says there is no evidence to suggest intermittent fasting – cutting normal calorie intake by about three-quarters for two days in seven, say – is more effective for weight loss than daily portion control for the average person. “Another way of putting it is that neither strategy is very effective for weight loss,” says Guyenet.

He points to a 2016 study published in the journal Nutrients that compared intermittent fasting with standard energy-restricted diets and found they were as good as each other at producing weight loss.

Read more: Crash diet or smart choice? 5:2 creator Michael Mosley explains new rapid weight loss theory

The difficulty we have tricking our body into downsizing itself comes down to neuroscience, he writes in his book The Hungry Brain. Weight set-point theory, which explains why repeated dieting is unsuccessful at producing long-term change in body weight or shape, was developed in the 1980s.

The theory supposes that we have an inbuilt control system that dictates how much fat we carry and we can’t consciously or permanently change our weight because our subconscious will drive us to regain it.

Researcher Stephan Guyenet. Photo/Adam Roe

It’s a bit like someone else having the remote control for your television. You can try to manually change channels, but the remote’s invisible force keeps switching it back.

The central controller of our weight is thought to be located in the hypothalamus, which receives feedback from around the body on fat and activity levels. The hypothalamus then influences our eating habits and energy expenditure to maintain our weight set-point.

The controller does this by increasing hunger (as every dieter knows, the more weight they lose, the more persistent hunger becomes), increasing food reward value (making high-energy foods more appealing) and by slowing our metabolic rate. Within days of starting a self-imposed famine, the body adapts to conserve energy by slowing the metabolism down, making weight loss increasingly difficult.

Wellington broadcaster Simon Morton had been on a low-glycaemic diet for the sake of his health. After he did an interview with exercise- and diet-book author Michael Mosley, he decided to try intermittent fasting. “Intermittent fasting was a way of getting the weight down even further.”

However, Morton gave it up within a year after finding hunger was affecting his mood and therefore his family. “It became hard on my family because I would get a bit ‘hangry’.

“It was sort of total irritability associated with feeling hungry that would manifest as grumpiness. This void in my stomach would create a void in my sense of humour and my ability to tolerate things.”

Along with the stomach and other grumbles, hunger can cause loss of energy, lethargy, sleepiness, headaches, light-headedness and difficulty focusing and concentrating.

At a population-health level, the effect of intermittent fasting isn’t known. Fasting proponents espouse its potential for improved glycaemic control and longevity. But the jury is still out over whether it is increasing rates of eating disorders, an unfortunate and not altogether unexpected outcome of many energy-restricted diets.

This article was first published in the September 15, 2018 issue of the New Zealand Listener.