''Exercise can make us eat more,'' says David Driscoll. ''What's not clear is whether this is because our bodies are demanding the extra fuel or because we think we deserve it.
It's a message that has become louder during the past few years: exercise doesn't work for weight loss.
There was the 2009 Time magazine cover story, ''The myth about exercise'', featuring a photo of a woman pounding a treadmill, her eyes trained on a cream-topped cupcake. It symbolised the story's thrust: research suggesting exercise won't help weight loss because it makes us eat more to make up for the kilojoules we burn. The theme is repeated in a new book, Big Fat Lies, in which author David Gillespie, a lawyer, describes exercise for weight loss as ''pointless''. But is it really true?
No, David Driscoll says. He's not a lawyer but an exercise physiologist and sports dietitian who thinks exercise deniers, like climate change deniers, don't tell the whole story. Instead, they cherry-pick the evidence that suits their message.
It's not hard to find research showing exercise does shift weight, especially when combined with a leaner diet, says Driscoll, a member of Sports Dietitians Australia. But when studies find little or no weight-loss benefit from exercise, this might have more to do with behaviour than biology.
''Exercise can make us eat more,'' he says. ''What's not clear is whether this is because our bodies are demanding the extra fuel or because we think we deserve it. In studies where people do consume more kilojoules after exercise, we need to establish if it's because of real hunger or because they feel they need a reward for working out. We need to establish this - it's well known that eating isn't always related to hunger.''
If you're in the ''I need a reward'' camp - and you wouldn't be alone - knowing more about how many kilojoules you have burned can help.
If you're doing a cardio class at the gym at a moderate intensity, for instance, you're probably burning eight kilojoules to 12 kilojoules a minute. Over a period of 45 minutes, that adds up to 360 kilojoules to 540 kilojoules. Based on that, Driscoll says, it makes sense to settle for a small reward - two squares of chocolate. Not the whole bar.
''Timing an exercise class before a meal is another strategy - you'll be eating anyway and less likely to overcompensate,'' he says.
''Another problem is that some people do a 45-minute gym class and think it means they can do nothing for the rest of the day, but 45 minutes isn't enough.''
One way of putting this into perspective is that the level of physical activity we would have done a century ago just to get through the day would seem like an extreme sport compared with what most of us do now.
When research finds little weight loss from exercise, Driscoll believes it's also important to look at how much fat is shed, not just weight. In some studies, people might not lose much weight but they may lose fat and gain muscle - and muscle weighs more than fat.
As for a shining example that diet and exercise do work, there's the US National Weight Control Registry, a project tracking the progress of 10,000 people who have lost an average of 30 kilos and kept it off for more than five years. Guess what? Ninety-eight per cent of these losers report that they changed their diet in some way to lose weight - and 94 per cent increased their physical activity.
So, is the exercise-is-useless message dangerous? ''It's irresponsible - but it's also a message that some people want to hear and it appeals to people who don't like exercise,'' Driscoll says.
''But I don't think it will make people who are already exercising stop. And in the unlikely event that exercise turned out not to work and actually caused weight gain, the health benefits of physical activity are so great, they would offset the problem of a little extra weight.''
Paula Goodyer blogs at smh.com.au/chewonthis
