Muscle mass won't burn up a bad diet
- SA US study of diet and exercise has challenged the prevailing thinking on the most effective ways to lose weight. Maggie Fox reports
- February 03, 2007
READERS of every women's magazine know that the best way to lose weight is to combine healthy eating with some form of exercise. That way, by exercising as well as cutting out the cream cakes, you put on a bit of muscle too, and muscle cells burn still more calories just by existing - right?
Well, maybe not so right, at least if the findings of a surprising new US study are anything to go by. The findings suggest that dieting and exercising are equally good at helping to lose weight - contradicting many of the popular tenets of the multi-billion dollar diet and fitness industry.
Tests on overweight people show that a calorie is just a calorie, whether lost by dieting or by running, say the researchers.
Some of the results are not so surprising. They found there is no way to selectively lose belly fat, for instance, or trim thighs, which is what experts have thought for some time. Doing lots of sit-ups is not going to shift the fat from your stomach rather than your hips (although it will firm your stomach muscles).
But what is surprising is that the study has added to evidence that adding muscle mass does not somehow boost metabolism and help dieters take off even more weight.
"It's all about the calories,'' says Eric Ravussin of the Pennington Biomedical Research Centre, Louisiana State University. "So long as the energy deficit is the same, body weight, fat weight, and abdominal fat will all decrease in the same way.''
Ravussin says the study, published in the Journal of Clinical Endocrinology & Metabolism (doi:10.1210/jc.2006-2184), is one of the few done under controlled conditions that can actually demonstrate what happens to the human body while dieting and exercising.
Ravussin's team has been testing volunteers for another reason - to see if taking in fewer calories helps people live longer. Strict diets have been shown to help animals from worms to dogs live longer, but it takes longer to study monkeys and humans. They tested 24 people, split into two groups.
One group of 12 people was put on a diet that cut the calories in their food by 25 per cent compared to their normal intake. The other group was put on a less restrictive diet that cut the calories in their food by just 12.5 per cent. But they were also put on an exercise regime calculated to burn the equivalent of the other 12.5 per cent of calories - so the two groups were effectively faced with the same net reduction in available energy.
Ten other volunteers acted as controls. All food was provided by the university in measured portions for most of the study. After six months of follow-up, during which the exercisers were exercising five times a week, the volunteers in both groups lost about 10 per cent of their body weight, 24 per cent of their fat mass, and 27 per cent of their abdominal visceral fat. Visceral fat is packed in between the internal organs and is considered the most dangerous type of fat, linked with heart disease and diabetes.
The distribution of the fat on the body was not altered by either approach - helping prove that there is no such thing as "spot reducing'', Ravussin says in a telephone interview. This suggests that "individuals are genetically programmed for fat storage in a particular pattern and that this programming cannot easily be overcome'', he added.
Ravussin has published other studies that also dispute the idea that exercise builds muscle that helps people lose weight. "If anything, highly trained people are highly efficient, so they burn fewer calories at rest,'' Ravussin says.
Dieting alone also did not appear to cause the volunteers to lose muscle mass along with fat, Ravussin's team found. "There is a concept that if you exercise, you are going to lose less of your muscle,'' he says. But his team found no evidence this is true.
Ravussin believes exercise is crucial to health, however. "For overall health, an appropriate program of diet and exercise is still the best,'' he says.
His team found some small suggestion that cutting 25 per cent of calories by either diet or diet and exercise might extend life. "We found that two of the biomarkers of ageing were improved - core temperature was 0.4 to 0.5 degrees celsius less,'' he says. "Insulin, which has been shown to be a biomarker of ageing, was reduced.'' That finding was published in the Journal of the American Medical Association last April (2006;5;295(13):1577-8).
Australian experts say the latest study was well-conducted, but its conclusions have to be treated with caution because, with 24 participants, its sample size was extremely small.
Exercise physiologist Chris Tzar, director of the Lifestyle Clinic at the University of NSW, says that in addition, while the nutritional aspects of the trial were well-conducted, other shortcomings meant significant questions remained unanswered. Subjects were allowed to pick their own favoured form of exercise, and the researchers did not factor in the possibility that intensity of exercise altered the effect it had on the body - as research conducted in Sydney by Tzar's own unit recently found.
To investigate the impact of exercise it would also have been more useful to compare the dieting group which did no exercise to a group which had its calories also cut by the same 25 per cent, but which did exercise on top of that.
"The hypothesis has been previously that if you diet only, a lot of the weight loss you experience will be lean tissue and fluid rather than fat,'' Tzar says. "This is the first study to suggest that's not entirely the case. But it was conducted under unique circumstances which may not correlate to real life.'' Tzar also emphasises there are many other reasons to exercise, apart from weight loss. In short, it's good for you and reduces the risk of umpteen different conditions, from cardiovascular disease to cancer.
He thinks the researchers missed an opportunity by not also testing the study subjects for markers that would show what effect exercise had on general health. For example, they could have tested participants before and after the study for blood cholesterol, insulin resistance, and markers for cardiovascular disease.
"Even if the data (comparing exercise and diet) were correct, exercise has been shown to mitigate the health risks associated with obesity,'' Tzar adds.
