Can the right foods really boost your metabolism?

It’s the Holy Grail of weight loss: a way to eat yourself thin with foods that melt away fat by boosting your metabolism. Green tea, spices, chilli and coffee are all claimed to contain compounds that kick-start your body into shedding fat. But is it true?

Celebrities such as Gwyneth Paltrow, a well-known fan of green tea, seem to think so, as do millions of people keen to find a shortcut to losing weight. A search for the terms ‘weight loss’ and ‘teenager’ and ‘green tea’ on YouTube, for example, throws up an incredible (and worrying) 27,000 results – many of which are promotional videos for green tea brands. At the same time, media reports and health and wellbeing websites depict ‘metabolic enhancers’ such as green tea and chillies as an easy way to fight flab. “Turn up your body’s fat burn with these healthy foods,” urges one website. “Chilli peppers can boost metabolic rate by as much as 50 per cent,” declares the headline in a popular national newspaper.

But leading metabolism scientists say the claims simply aren’t true. While there is some evidence to show certain foods contain compounds that boost metabolism, the experts say the effect of consuming these foods is too small to cause weight loss.

The science bit
So what is metabolism? According to Professor James Timmons, a metabolism expert from Loughborough University’s School of Sport, Exercise and Health Sciences, it describes all the chemical processes in our bodies that keep us functioning, such as breathing and digestion. The minimum amount of energy we need for this is called our basal metabolic rate (BMR). “A ‘slow metabolism’ is more accurately described as a low BMR,” Professor Timmons explains on the NHS Choices website.

BMR accounts for 40-70 per cent of our body’s energy needs and varies according to age, gender, body size, genes and lifestyle. For example, BMR tends to decrease with age because muscles use up more energy than fat, and we generally lose muscle as we get older. This doesn’t mean a slow metabolism is to blame for being overweight. “In fact, the opposite appears to be true,” Professor Timmons says. “Overweight people may actually have a faster metabolism than their leaner counterparts, as a larger body size requires more energy to keep it running.”

Some crash diets can slow down BMR by forcing the body to break down muscle to use for energy – which makes it easier to pile on the pounds after resuming normal eating. But nothing we eat can do the reverse and speed up our metabolism to the point of slimming down. “There are no foods that, when eaten in excess, help you to lose weight,” says Naveed Sattar, professor of metabolic medicine at the University of Glasgow.

Hollow promises
There is evidence that certain foods can boost metabolism to some extent, says Dr Thomas Barber, associate professor in clinical endocrinology and lead researcher at the Human Metabolism Research Unit, run by University Hospitals Coventry, Warwickshire NHS Trust and Warwick Medical School. All food ‘boosts’ our metabolism for two to three hours after we eat it, and some foods have a bigger effect than others. “It is known that chilli-based food can have a more pronounced effect on metabolism after a meal than other foods due to molecules chillies contain called capsaicins,” says Dr Barber. But utilising that metabolic effect to lose weight? “It’s unlikely,” he says. “To make it even remotely possible you’d have to consume large amounts of chilli, for example, which wouldn’t be advisable.”

There is also some evidence that green tea can boost metabolism by activating what’s known as brown adipose tissue – the type of body fat that burns calories rather than storing them. But again, Dr Barber says the effect of that metabolic boost is minimal: “I don’t believe it’s significant enough to lead to weight loss.” And what about the claims that drinking lots of caffeine can help melt away pounds? “You absolutely shouldn’t use caffeine as a means of boosting your metabolism,” he says emphatically. “Caffeine can stimulate the cardiovascular system and increase heart rate – in excess, it can lead to palpitations and heart arrhythmias… Caffeine can never be advocated for weight loss.”

What’s the verdict?
Many factors affect weight and metabolism, from genetic disposition to thyroid function. But there’s no solid evidence to prove anything you eat or drink can speed up metabolism to the point of helping you slim down. According to Professor Sattar, a high quality, balanced diet containing lots of fibre is the only way to manage your weight. Emerging evidence indicates that insoluble fibre (found in wholemeal bread, bran, cereals, nuts and seeds) is particularly effective for weight management. Still, there’s no quick fix. ”If there was a magic food solution for weight loss, we’d know it by now – but there isn’t,” he says.

Too good to be true
News media and the internet are awash with claims that specific foods have magical fat-busting powers. Here are just a few wild claims that have no basis in fact:

•  “Calcium-rich foods have slimming superpowers”
•  “The good news is there are specific foods loaded with quality calories that can be the perfect answer to melting fat away from your mid-section permanently”
•  “Drinking one or two glasses of green vegetable juices daily helps melt away fat. It may not make sense to you, but it works!”
•  “Tea can reset your internal thermometer to increase fat burn by up to 10 per cent without exercising or dieting”
•  “Seven metabolism-boosting foods to snack yourself SKINNY”