Why intermittent fasting may not be the magic bullet for weight loss
The last 15 months haven’t been kind to our bodies. A more sedentary lifestyle and the pursuit of something to salve the fear of the deadly pandemic raging around the globe has pushed us to the biscuit tin and takeaway delivery apps. In the first three months of the pandemic, Brits reportedly saw body weight increase by between 1.6 and 6.5lbs.
Recognising the potential damage that could cause, and preparing for society reopening, we’ve started to take action. Six in 10 of us have made at least one change to our diet in the past year to get healthier, according to a survey for the British Nutrition Foundation. Some of us will have turned to one of the most popular fad diets of the last decade: intermittent fasting, hailed for health benefits as well as its ability to shift pounds.
But there’s increasing uncertainty about whether it works.
New academic research shows that alternate-day intermittent fasting may not be all that effective. Switching between a day of normal eating and then a day of fasting has less ability to reduce fat than a “traditional” diet where calorie intake is restricted daily. Rather than stopping eating entirely for days on end, you’d lose more weight if you simply cut down on the calories every day a little bit.
James Betts of the University of Bath first conceived of his study a decade ago. “It’s been interesting to see fasting become more popular with the public and more studies appear in the scientific journal, but the whole time missing that question of whether the benefits of fasting are just due to losing weight,” he says. “We wanted to know if there are any particular benefits of fasting,” he says. He admits that the notion of calorie restriction triggering changes in the body’s metabolism, which is often cited as one of its benefits, was plausible in theory – and one he thought would be borne out in the results. But it wasn’t. “Any diet is a diet,” he says.
The principle of intermittent fasting is simple: you restrict your calorie intake, usually to 500 or 600 calories a day for a certain proportion of time – most popularly, two days a week – then eat as normal the remaining five. However, there are plenty of alternatives from alternate-day fasting, where you have zero calories pass your lips on certain days, to diets like the 16:8, where you don’t eat for a significant portion of the day. “It’s like buying a car: you can go from an SUV to a sports car,” says Duane Mellor, a dietitian.
The idea is that your calorie intake drops, stimulating your body to survive on less and replicating the way our forebears survived in hunter-gatherer mode. In theory, intermittent fasting is meant to change your hormone levels to stimulate weight loss, reduce insulin levels and release norepinephrine, a fat-burning hormone.
The diet method is also seen as more achievable than others because you’re only banning yourself from the food you like for a short period of time, rather than feeling miserable about avoiding your favourite foods all the time. It’s even been digitised by Noom, an app that purportedly helps you keep track of calorie-restricted days and coaches you through the intermittent fasting journey.
John Gaskell is one of those who has turned to intermittent fasting to try and shift the lockdown weight. The 42-year-old from Crosby has previously had success with water fasting (where you only drink water), but found it unsustainable. He now uses the 20:4 intermittent fasting plan, eating in a four-hour window every day. “Do I miss a latte? Of course I do,” he says. “Do I miss chocolate biscuits with the coffee? Of course I do. But with a bit of discipline I will enjoy them in the future, of course I will.” After a month of dieting, he’s lost 11lb and is now down to 17st 5lb.
“Studies of different weight-loss diets have shown that there is no diet that outperforms all the others and so it’s down to what works for an individual,” says Bridget Benelam of the British Nutrition Foundation. “For intermittent fasting to work, you have to stick closely to the calorie limits on the ‘fasting days’ and not go overboard on the ‘non-fasting’ days or you won’t get the calorie deficit needed for weight loss.”
“There is interesting mechanism stuff in the research, and good science in there showing energy intake is a bit lower in those under continuous restriction than intermittent restrictions,” says Mellor. “But you’re looking at weight loss in people who don’t really need to lose weight.” Betts and colleagues’ intermittent fasting was tested on those who are already lean individuals – with a cohort of those classed as overweight still waiting to report data.
While Benelam points out that the study was only carried out over a period of three weeks, longer term studies comparing different types of diets have found they all have similar results when compared over the course of a year. “The success of any diet is down to whether you can stick with it and different approaches work for different people,” she says.
“There’s nothing magic, and we didn’t think there was anything magic about intermittent fasting,” adds Mellor. “It’s just one way of achieving energy restriction.” Intermittent fasting’s various flavours, he says, are all about finding a tolerable way for individuals to decide on when and how to cut back. “There are some theories that you might reset your microbiome,” he says, “but the biggest effect is you’re only eating for eight hours a day so when you’re watching the cookery programme you can’t eat those biscuits.”
It seems, therefore, that the secret trick thought to unlock the body into burning the pounds actually is the oldest trick in the book: by consuming fewer calories than normal, you lose weight. Nothing more, nothing less.
But if intermittent fasting is perhaps not for everyone – and not as effective as first thought – then is there one best way to shift the lockdown pounds? “The simple answer is no: it all involves a change that can stick,” says Mellor. “That’s the goal. How you get to that goal will vary for some people.”