Interpreting claims about weight loss

You might be surprised to learn that makers of dietary supplements rarely carry out clinical trials. That's part of the reason why there's little scientific evidence to show that weight-loss supplements work.

For example, raspberry ketone is marketed as a clinically proven weight-loss product. That claim is supported by one clinical trial.

The trial included 70 adults with obesity. All were placed on a restricted diet and exercise program. They were then randomly assigned to receive either a placebo or a supplement containing raspberry ketone, caffeine, bitter orange, ginger and garlic root extract.

The 45 people who completed the trial all lost weight:

• The average weight loss in the supplement group was 4.2 pounds (1.9 kilograms).
• The average weight loss in the placebo group was 0.9 pounds (0.4 kilograms).

While these results are intriguing, the fact that the trial was small and lasted only eight weeks means the results can't be reliably generalized to real-world situations. And importantly, a short trial like this may miss side effects that only become apparent with long-term use.

In addition, the trial used a supplement that contained multiple ingredients. So it's impossible to tell which ingredient was responsible for the weight loss.

Ideally these initial results would be tested in a much longer trial involving hundreds of participants with careful monitoring for side effects. Results from such a trial would allow for an informed decision about the safety and effectiveness of such a product.

Until such trial data is more readily available, claims regarding dietary supplements and weight loss should be treated with caution.