There is probably not a day that goes by that you are not exposed to an advertisement for a weight-loss product. But do they really help the way they say they do?

Two studies presented at the 2010 International Conference on Obesity found 18 different weight loss supplements ineffective at helping people to lose weight, despite being marketed with scientific-sounding tags like fat magnets and carb-blockers. Zero for 18 is not a good track record. Each study tested nine different supplements.

In the U.S. alone, people spend over $1.6 billion a year on weight loss supplements. The two studies suggest they'd be better off buying lottery tickets.

The first study was a German clinical trial that tested supplements found in many German pharmacies: L-carnitine, polyglucosamine, cabbage powder, guarana seed, powder, bean extract, Konjac extract, fiber pills, sodium alginate (seaweed) extract, and selected plant extracts.

The second study was a British review of published clinical trials of Ephedra, chromium picolinate, bitter orange, conjugated linoleic acid (CLA), calcium, guar gum, glucomannan, chitosan, and green tea.

The German study was a two-month, randomized trial. Researchers bought the products, repackaged them and rewrote the information inserts to eliminate the product name. 189 obese or overweight middle-aged adults were then given either one of the nine supplements or fake pills. Some products came with dietary information, which was also provided to the trial subjects.

Over two months, the fake pills worked just as well as the commercially-marketed weight-loss products did, which is to say, they were not very effective.

Weight loss did occur: an average of 1.2 kg for those getting the fake pills and from 1 to 2 kg for those getting a weight loss product. But there was no statistically significant difference between the weight loss from taking a particular product and that from taking the fake pills.

Apparently, they were all fake pills, even those that were not supposed to be fake.

Likewise, the British study found no evidence in the literature that any of the nine products it looked at were an adequate treatment to reduce body weight.

In the U.S. alone, people spend over $1.6 billion a year on weight loss supplements. The two studies suggest they'd be better off buying lottery tickets.

When people lose weight, it's usually because of changes in their behavior. In certain situations, doctors may prescribe medications that help people to lose weight, but these are prescription medications. Even then, changes in behavior are key to keeping weight that's been lost from coming back.

Anyone who wants to lose weight should speak to their doctor as part of the process. Even if you don't have the best of relationships with your doctor, can they possibly do worse than 0 for 18?

The two studies were presented at the 2010 International Conference on Obesity. The conference was held July 11-15 in Stockholm, Sweden.