AN APPETITE FOR EVIDENCE WOULD SERVE DIETERS WELL
Weight-loss products are often marketed with anecdote more than with science
Universal agreement when it comes to nutritional issues is rare, but virtually everyone agrees that obesity is undesirable. There is no agreement, though, on how to attack the problem.
Infomercials, newspapers and magazines tout a host of supplements guaranteed to “burn fat” or “rev up metabolism.”
Bookstore shelves sag under the weight of diet books and researchers duke it out over the effects of intermittent fasting and the role of different dietary components in the pages of peerreviewed journals.
What does it all add up to for the consumer? Mostly confusion.
But some of that can be dispelled just by asking a simple question: “Is there evidence?”
When it comes to dietary supplements for weight control, the answer is: precious little.
A typical newspaper ad sings the praises of a product that “curbs hunger,” “burns calories instead of storing them” and “increases heat production by the body, leading to weight loss.”
The heat is due to chili powder and the changes in metabolism are attributed to the inclusion of epigallocatechin gallate, or EGCG, a compound found in green tea leaves. There is actually
some evidence that EGCG at a dose of 200 to 300 milligrams a day can increase the oxidation of fats leading to an expenditure of about 80 calories — an insignificant amount.
Unfortunately, there is also evidence that EGCG can cause kidney and liver problems. It is all a question of the dose. The CBC’s excellent program Marketplace undertook an investigation of green tea extracts after a couple of Canadian consumers developed liver damage, and turned up over 60 documented such cases in the peer-reviewed literature.
How much EGCG there is in supplements is generally a matter of some mystery, but toxic effects are possible even at 400 mg. The important point, however, is that there are no studies demonstrating that the particular product featuring chili powder and EGCG being advertised leads to weight loss.
An anecdote that an unidentified woman went from Size 12 to a Size 6 in six months and fit her wedding dress of 37 years ago does not constitute evidence.
Evidence comes from peerreviewed studies. But even in this case, the evidence may not be of practical significance to people.
A number of newspapers reported on a weight control study with headlines like “Can eating at the same time of day enable you to burn off more fat?” Yes, it can, if you are a mouse on a high-fat diet!
Researchers hypothesized that the body clock could have an impact on metabolism and designed an experiment comparing mice with an unlimited access to a high-fat diet with mice that had access to the same diet at set times during each day.
The mice on the fixed eating schedule put on less weight even though their calorie consumption was about the same. An interesting finding, but mice aren’t people and extrapolation of the findings to humans is unrealistic. While this study does not provide evidence that eating only at set meal times is conducive to weight loss, it can, however, raise that prospect.
David Zinczenko, who serves as the ABC television network’s nutrition and wellness editor (despite having no background in science), has ideas along these lines.
In his book The 8-Hour Diet, Zinczenko claims the human body is designed for periods of eating and then periods of fasting, and that consuming calories over an eight-hour period and then fasting for a 16 hours each day leads to weight loss.
The hook for this regimen is that there are no restricted foods; anything can be eaten over the eight-hour period.
But when Zinczenko’s recommendations for foods that should be eaten are examined, it is clear that calorie restriction is a player. As far as evidence for the 8-Hour diet goes, there isn’t any.
Michael Mosley, author of The FastDiet, also makes a case for intermittent fasting.
Mosley graduated from medical school, but became more interested in presenting science on television than practising medicine. He has become an outstanding journalist, hosting a variety of programs including the BBC’s excellent Trust Me I’m a Doctor.
In his FastDiet, he recounts his own experience, bolstered with theories drawn from the scientific literature, that consuming roughly 2,000 calories per day for five days a week, and fasting at a level of 500 calories a day for two days, not only leads to weight loss, but also to improved insulin sensitivity. Attention-grabbing, but in need of evidence from properly designed studies.
Unfortunately, where we do have plenty of evidence is in the failure of any kind of diet in the long run.
The fact is that the majority of dieters end up regaining more weight than they lose. Still, they do not lose their appetite for the next scheme that comes along, be it the clay, tissue paper or tapeworm diet — don’t ask. joe.schwarcz@mcgill.ca Joe Schwarcz is director of McGill University’s office for science and society (mcgill.ca/oss). He hosts the Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 p.m. to 4 p.m.