Christopher Snowdon

Ignore the latest fad theory. The ‘secret’ of weight loss is to eat fewer calories than you burn

Ignore the latest fad theory. The 'secret' of weight loss is to eat fewer calories than you burn
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Before I got sidetracked by bogus obesity predictions, I was discussing the equally bogus controversy about whether physical inactivity is linked to obesity.

It's now fashionable to argue that exercising doesn't help you lose weight. As I mentioned in my previous blog post, this is the line taken by Dr Jason Fung, a Toronto-based kidney specialist who runs something called Intensive Dietary Management. He reckons that people are exercising more than ever and yet are becoming fatter and fatter. But, as I argued, it's simply not true that we're exercising more as a population.

Now let's look at the effect of exercise on individuals. Fung – who coined the term 'Calorie Reducation as Primary', or CRaP, to describe 'current obesity thinking' – is unequivocal. In a series of blog posts entitled 'The Myth about about Exercise', he writes: 'There are many benefits to regular exercise. Weight loss, though, is not one of the benefits' (italics in the original).

He cites three studies which found that burning off a certain number of calories did not result in a commensurate loss of body weight. He rightly attributes this to a degree of compensatory eating. In other words, exercise creates appetite which can lead to more calories being consumed.

But, in making this point, he downplays the conclusions of the studies themselves, all of which also make it clear that the participants who exercised lost a significant amount of weight.

The first of these studies concluded that 'physical activity expressed as energy expended per week is positively related to reductions in total adiposity'. The second found that people who exercised most intensively did not lose more weight than people who trained less intensively, but the crucial fact remains that all the subjects who trained lost more weight than those who didn't. All exercise groups had a significant reduction in waist circumference. Similarly, the third study concluded that 'supervised exercise, with equivalent energy expenditure, results in clinically significant weight loss'.

By the time he gets to his third 'Myth of Exercise' post, Fung has almost given up on his claim that 'there is no measurable association between obesity and physical activity' and is instead arguing that exercise is merely less effective than dietary change.

He cites a 2007 study involving people who exercised for around 45 minutes a day. After a year, their body mass index (BMI) had dropped by 0.5 and 0.6 (for men and women respectively) while the BMI of the control group either rose or stayed the same. Moreover, those who exercised the most lost the most weight.

Fung views this amount of weight loss as trivial, saying: 'Colour me unimpressed. Exercise is just not that effective for weight loss.' That's a matter of opinion, but it's rather different to claiming that weight loss is not one of the benefits of exercise.

As the killer blow, Fung discusses marathon running, which he evidently sees as the ultimate test of the exercise/weight loss hypothesis. He relishes the chance to talk about a 1989 study of people who were training for one:

Endless chub rub (chafing between the inner thighs). Miles upon miles on the dreadmill.  But so worth it, right?  Average body fat loss for men …  5 pounds.  Average weight loss for women ... zero.

What Fung doesn't mention is that this study was not aimed at achieving weight loss and there is no evidence that the participants wanted or needed to lose weight.

The men had a healthy average BMI of 23.4 before they started training and the women were a slender 21.1. Both groups consumed significantly more calories while training, mainly from carbohydrates, and both groups actually did lose weight. The men lost an average of 2.7 kg and the women lost 0.9 kg, though the latter was not statistically significant. Both groups also lost fat as a percentage of body weight (from 16.6 to 13.4 per cent for men and from 24.9 to 23.6 per cent for women) although there were were too few participants for these results to reach statistical significance.

The literature on physical activity is very large and Fung is entitled to select any part of it to make his case, but if these studies debunk the claim that exercise helps people lose weight then you can only wonder what the rest of the literature says.

Unsurprisingly, other studies make the case for physical activity even more convincingly. Listing a few in chronological order:

• A randomised control trial published in 2000 found that 'weight loss induced by increased daily physical activity without caloric restriction substantially reduces obesity'.

• A 2003 study from the US found that 'moderate-intensity exercise sustained for 16 months is effective for weight management in young adults.'

• A 2004 study of overweight women from Singapore found that an eight-week exercise programme 'significantly reduced body weight, body mass index, percentage body fat and waist circumference'.

• A 2005 review concluded that 'Regular exercise can markedly reduce body weight and fat mass without dietary caloric restriction in overweight individuals.'

• A 2009 study of middle-aged women found that 'body mass, body composition, waist circumference, and high-density lipoprotein cholesterol changed favorably' after a 30 minute, five days a week exercise routine.

• A 2009 study of younger women found that physical activity was 'associated with a reduction in long-term weight gain, and greater duration is associated with less weight gain'. Moreover, it found that 'sedentary behavior independently predicted weight gain.'

• A 2012 study found that a moderate-intensity exercise programme reduced BMI by 2.4 per cent amongst post-menopausal women, rising to 10.8 per cent if combined with a reduced calorie, low-fat diet.

• A 2013 study from the US concluded that 'supervised exercise, with equivalent energy expenditure, results in clinically significant weight loss'.

I could cite many more studies (and have before) but there is no point in labouring a point that should be obvious: if you burn off calories they cannot turn into body fat.

The simple, unavoidable fact of human physiology is that you can't lose weight without creating a calorie deficit. Whether you do this by eating less, moving more or a combination of the two is a matter of preference. Some people may find it too difficult to change their diet while others may find it too difficult, or too time consuming, to start exercising. Some find it easy to cut out alcohol or sugar, while others find it easier to play more sport.

Since nobody denies that physical activity has health benefits that extend beyond weight management, it could be argued that a calorie burned is better than a calorie foregone, but the crucial thing is to eat fewer calories than you burn. If your preference is for radical dietary change then by all means make your case – but don't let your interest in 'calories in' blind you to the importance of 'calories out'.