Information about Weight Loss Diet Supplements

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Google "diet supplements" and you'll get about 13 million search results, most from companies selling products that promise to cure your weight problem—in as little as a week. Their proprietary formulas, which can cost $40 a bottle and up, are often touted as "all natural," "healthy" and "proven to work" with "no side effects." But weight loss is neither quick nor easy. Nothing "melts fat away," and certain diet pills can have serious side effects.

Dietary supplements do not have to be tested for safety or effectiveness, nor do they have to list warnings or contraindications. And the FDA can pull them from the market only after there's proven evidence of harm. That's what happened with ephedra, which the FDA finally banned in 2004—but only after serious problems and even deaths were reported. Since then, ephedra-like substances, including synephrine (in bitter orange) and dimethylamylamine (DMAA; sometimes listed as geranium oil), have taken its place and may not be any safer.

In April 2013, the FDA reported that the agency will use all tools at its disposal to remove dietary supplements containing DMAA from the market. This stimulant can elevate blood pressure and cause serious cardiovascular problems, including shortness of breath and heart attack. Until the last of these products are discontinued, the FDA is warning consumers to avoid supplements that contain DMAA.

More cause for alarm: Some weight loss products have been found to contain undeclared pharmaceuticals, which can be harmful if not used properly. In recent years, the FDA has warned about dozens of diet supplements, many from China, that were tainted with drugs, including amphetamine-like chemicals, tranquilizers, antidepressants, prescription diuretics and anti-seizure medications.

Keep in mind that if a diet product does work, it's likely to have other effects that may not be so desirable. Some ingredients (such as chaste tree, daidzen and dong quai) can affect levels of some hormones. And diet aids, even if "natural," may interact with medications.

Bottom line: Below are some common ingredients in diet aids. At best, there's slim evidence for a couple of them. Don't expect such supplements to help you lose much weight. Even if some do cause you to lose a few pounds, none are proven to sustain weight loss, which is key. Prescription diet pills have a lousy track record, too.

Weight loss supplements contain a mind-numbing list of substances touted to burn fat, boost metabolism, suppress appetite, control sugar cravings and increase energy. Some claim to help you lose weight by elevating your mood or helping you overcome a genetic predisposition to obesity. A few ingredients have been tested in controlled studies, with inconsistent results. But most have no convincing scientific support behind them or have not been tested at all.

Here's a rundown of some popular ingredients in weight loss supplements.

  • Caffeine. Diet pills often contain substances, such as green tea, guarana and yerba mate, that claim to have "natural" stimulant properties. But what you're really getting is caffeine or caffeine-related substances. Caffeine may temporarily boost calorie burning, but this does not mean you will lose much weight. First, the effects are small and temporary. Second, tolerance to caffeine tends to develop with regular use. Moreover, if a diet pill does boost metabolism, then it can also boost heart rate and blood pressure and have other potentially undesirable effects.
  • Capsaicin. Some research suggests that capsaicin and related substances in chili peppers can briefly speed metabolism, increase fat burning and suppress hunger. However, the studies tend to be small, short and poorly designed and have had inconsistent results. There’s no evidence that such supplements lead to significant and lasting weight loss.
  • Conjugated linoleic acid (CLA). Studies on CLA, a fatty acid in dairy and meat, have yielded mixed results. A 2010 report from Health Canada (which acts like the FDA) said there is insufficient evidence that they help with weight loss. Potential adverse effects include increased inflammation, decreased HDL ("good”" cholesterol and reduced insulin sensitivity. CLA has been shown to cause liver damage in animal studies. It’s not clear which formulations (there are many) are riskier.
  • Chitosan. This fiber-like substance, derived from crustacean shells, is said to block fat absorption in the intestines. A 2008 review from the Cochrane Collaboration concluded that though there is some evidence that chitosan may help in the short term, studies have had mixed results and most are of poor quality. Better-quality trials have found no clinically meaningful effect on weight. Plus, there are potential risks. If it does block some fat, it may also reduce absorption of fat-soluble vitamins (A, D, E, K), as well as calcium, iron and magnesium. People with shellfish allergies should not take chitosan.
  • Diuretics. Some ingredients, such as green coffee, cherry stalk and wild pansy, act as diuretics, which increase urination. This may lead to small initial weight loss, but it's only water loss, and the weight comes back as soon as you rehydrate. Diuretics do not cause fat loss.
  • Food extracts, such as broccoli, spinach, blueberries, garlic, sprouts, tomatoes and soybeans. DecaSlim and Lipovox, for instance, contain "10 Super Foods" that can, it's claimed, help you lose "10 pounds in 10 days." These ingredients have no known weight-loss benefits and are typically present in such small amounts that they likely have no significant effect on anything. Papaya and pineapple are sometimes included, too, presumably for their digestive enzymes, though these have nothing to do with weight loss either.
  • Fiber. Fiber does help fill you up, so you are more likely to eat less. But the amounts in diet supplements tend to be quite small. If you want to supplement your diet with more bulk-forming fiber, generic psyllium is a good (and cheaper) choice.
  • Green tea extract. Besides caffeine, green tea contains polyphenols called catechins, which may promote calorie and fat burning. A 2009 review found that catechins decreased weight and helped keep it off. But not all studies confirm the benefits. The effects of green tea extracts may vary from person to person, and if there is weight loss, it's likely to be small at best.
  • Herbal laxatives. Cascara, senna, rhubarb root, buckthorn and aloe (often in "dieter's teas") are promoted for quick weight loss, under the mistaken notion that they expel undigested food and thus calories. In fact, these ingredients simply stimulate your bowels and have little or no effect on absorption of food. Any weight loss is due to expulsion of water and body waste—and is temporary. Chronic use may lead to dependency, decreased bowel function, dehydration and electrolyte imbalance; some deaths have been reported from laxative abuse.

Adapted from The University of California, Berkeley Wellness Letter (February 2012)

Publication Review By: the Editorial Staff at

Published: 19 Jan 2012

Last Modified: 09 Feb 2016