When it comes to weight loss, buyer beware.

If you are dieting, cleansing, popping diet pills, injecting vitamin B or entering a weight loss program, use the old adage: “If it seems too good to be true, it is too good to be true.”

Many commercial weight loss providers feed off people’s desperation and trick them with false claims such as “lose 40 pounds in four weeks,” according to two obesity doctors who recently wrote a warning in the Canadian Medical Association Journal.

It is widely agreed that the best way to lose weight is gradually, using techniques such as eating healthy, nutritious food and exercising regularly. Be wary of vitamin B injections, diets that promise fast and dramatic weight loss and “magic” herbal supplements, warned the doctors. They called for the government to begin regulating weight-loss programs and clinics.

In Canada, 59 per cent of adults are overweight and 23 per cent are obese, according to a survey done in 2005 by Statistics Canada.