Assessing the science behind weight loss supplements

When it comes to weight, America has a problem. According to the National Institutes of Health (NIH), more than one-third (35.7 percent) of adults are considered to be obese. That number represents a significant public health issue when you consider that obesity is a risk factor for a number of diseases, including metabolic and cardiovascular diseases, such as Type 2 diabetes, dyslipidemia, atherosclerosis, hypertension and stroke; and for cancer, including cancers of the colon, breast, kidney and digestive tract. It's also a risk factor for other diseases, including arthritis, sleep apnea, gallstones and gout; and for affective disorders, including low self-esteem.

With so many negative issues associated with obesity, experts say it is in the public's interest for Americans to lose that excess weight. But the only proven way to do so is to move more, eat less and to choose healthier foods. However, in a society where fast food is usually plentiful and where many have sedentary lifestyles, doing so may be easier said than done.

This is where weight loss pills -- prescription or over-the-counter dietary supplements -- enter the fray. While they may have different ingredients and compositions, they all have one thing in common: They are not a magic bullet. The best of these supplements may provide a modest boost in your weight loss efforts. The worst of them may make you wish being overweight was your only health concern.

There are plenty of companies that want to prey upon people's desire to both lose weight and for a quick fix to accomplish that. Among other things, these companies advertise supplements with claims that have not been verified or tested by a reputable independent organization. Manufacturers don't have to seek FDA approval before putting dietary supplements on the market, and many are not afraid to make exaggerated claims about the efficacy of their products, adding only an easy-to-miss disclaimer revealing that those claims have not been verified by the FDA. One very popular claim is that these supplements mean you don't have to diet or exercise, but the very fine print usually tells a different story, which is that participants used a combination of diet and/or exercise as well as the product.

Because diet pills come and go, and because there are many experts who question whether regulation of dietary supplements is effective, it is impossible for us to choose a Best Reviewed diet pill. Instead, we have assembled the science and safety profiles for each type, and gathered specifics on their ingredients. These include fat burning supplements, carbohydrate blockers, appetite suppressants, and prescription diet pills.

We turned to the scientific community and government agencies for information presented in this guide. We reviewed the results of clinical trials on individual supplements that were published by the National Institutes of Health (NIH), Centers for Disease Control, the U.S. Food and Drug Administration, the Natural Medicines Comprehensive Database and medical journals. We were careful to take studies that were sponsored by the very companies that make the weight loss supplement with a grain of salt -- especially if they were highly positive and came to very different conclusions from earlier, non-affiliated studies -- preferring to rely on the meta-analysis of a wide variety of studies by respected research institutes. We did not consider information presented by websites or organizations with no scientific accreditation.

One last caveat: The information in this Buyer's Guide is targeted toward U.S. residents only; other countries may have different facts, figures and regulations. In addition, if you're really serious about losing weight and getting healthy, first try the tried-and-true combination of a healthy diet and exercise. We cover weight loss programs in a separate report, and our discussion of how to pick a diet for your specific lifestyles may help you find one you can stick to for the long term. Experts also note that exercise is an important component of healthy, maintainable weight loss, and our fitness category includes reports on treadmills, elliptical trainers, exercise bikes and more. All of these offer exercise equipment options for any budget and any level of fitness.

Types of Diet Pills

  • Some studies show mild weight loss
  • Generally safe when taken at low doses for short periods of time
  • Potential for serious side effects
  • Some are dangerous
  • Can make you feel anxious and jittery
  • Insufficient reliable evidence to recommend their use

Thermogenics don't necessarily burn fat as their marketing name -- fat burners -- suggests. What little help they do offer is a result of stimulating the sympathetic nervous system to increase the amount of energy your body expends while at rest. The sympathetic nervous system is the part of our nervous system responsible for the "fight or flight" response, which increases heart rate and blood pressure. If thermogenics are taken in large amounts or for extended periods, these heart rate and blood-pressure increases can have serious side effects, including strokes, irregular heart rhythms and even heart attacks. Science doesn't show that these risks are worth the nominal weight loss that these products may produce, and the risks increase when two or more ingredients are combined. This brings up two points of caution when using thermogenics:

1)     Watch out for products that contain multiple ingredients, as those formulations carry increased risk of serious side effects.

2)     Be aware of how much of one active ingredient you're taking -- such as caffeine, which is found in guarana and green tea -- so you can avoid an overdose. 

  • Initial studies look promising
  • Minimal side effects
  • Could keep you from having to completely eliminate carbohydrates
  • Insufficient evidence to recommend
  • Can cause some gastrointestinal upset

Carbohydrate blockers work as their name suggests, by blocking the absorption of carbohydrates in the body. White kidney bean extract (Phaseolus vulgaris) decreases the calories absorbed from carbohydrates, so it could potentially allow you to eat carbs while losing weight. Initial studies are promising: Weight loss averaged 4 to 8 pounds with minimal side effects.

  • Minimal side effects
  • Insufficient weight loss proof
  • Not good for those allergic to shellfish
  • May interfere with medications

Fat blockers work as their name suggests by blocking the absorption of fat in the intestines. Chitosan is one of the more well-known ingredients that perform this function, and it is made from the shells of crustaceans. The lesser known alginate is found in brown algae. Neither has been proven as a weight loss aid. Further research is needed, but if the data continues to come in the way they have in the majority of studies, neither chitosan nor alginate will be recommended for use in weight loss. Also, because they interfere with fat absorption, they can potentially interfere with the absorption of medications. Lastly, chitosan should be avoided if you have an allergy to shellfish.

  • Some have been used for centuries
  • Insufficient evidence to recommend their use
  • Potential serious side effects, such as esophageal or intestinal obstructions and liver damage.

Appetite suppressants curb your hunger; if you eat less, you'll lose weight. However, of the ingredients that we studied, there wasn't sufficient evidence to recommend their use. The most interesting are caralluma and hoodia, which have been used for centuries by indigenous tribesmen to suppress appetite, but further research is needed to see if they can be proven clinically effective. Some appetite suppressants have the potential for serious side effects: Hydroxycitric acid (HCA) has the potential to cause liver damage; glucomannan and guar gum if taken in large amounts and without water can potentially cause esophageal and intestinal obstructions; and the use of 5-hydroxytryptophan (5-HTP) has been associated with a condition that affects blood cells and muscles called eosinophilia myalgia syndrome (EMS). It is recommended that use of 5-HTP be avoided until further research is completed.

  • Used under doctor supervision
  • Overseen by Food and Drug Administration
  • Proven modest weight loss
  • Various side effects
  • Not many choices
  • Can be expensive

Prescription drugs could be the gold standard (if there was one) of the diet pill industry. Regulated by the Food and Drug Administration (FDA), companies are required to prove that their weight loss products either produce weight loss that is greater than 5 percent (compared to people taking a placebo) or help more than 35 percent of the population achieve greater than 5 percent weight loss; in addition, lipid, glycaemia and blood pressure profiles must improve. These requirements have made the options available limited. The few options available are associated with 3 percent to 5 percent loss of bodyweight over six months to one year and improved cardiovascular benchmarks, such as blood pressure.

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