More than two-thirds of adults are overweight or obese, and about half of these are trying to lose weight. So it’s not surprising that products claiming easy weight loss solutions get attention.

More than two-thirds of adults are overweight or obese, and about half of these are trying to lose weight. So it’s not surprising that products claiming easy weight loss solutions get attention. According to the National Institutes of Health, Americans spend more than $2 billion a year on weight loss dietary supplements. These supplements promise to help people lose weight a variety of ways, including reducing calorie absorption, reducing appetite, increasing metabolism or burning body fat. Unfortunately, there is little proof to back up these claims.

Dietary supplements are usually a mix of common ingredients, such as herbs, other plant material, fiber, caffeine and minerals. Because dietary supplements are not classified as drugs, the FDA does not approve their safety or effectiveness. The manufacturer alone is responsible for making sure the product is safe and that any claims are true. The “proof” offered often results from very small, poorly controlled studies. Following are five popular weight loss supplements and the truth behind the claims.

1. Raspberry ketone

What it is: The chemical found in red raspberries responsible for the raspberry’s distinct flavor and smell. A synthetic version of this is sold as a weight loss supplement.

The claim: It alters fat metabolism by causing cells to break down fat more effectively and increases a hormone that is believed to be related to weight loss.

What the science says: Tests, done only with lab rats, have shown little to no effect on weight.

Potential side effects: Raspberry ketone is generally considered safe, but there are no long-term or human studies. The supplement chemically resembles a stimulant, so increased blood pressure, increased heart rate and jitteriness may be concerns.

2. Matcha green tea powder

What it is: A powder made from specially grown and harvested green tea leaves. Before harvesting, the plant is placed in the shade for a few weeks, which increases the concentration of theanine and caffeine.

The claim: It increases metabolism and improves the body’s fat-burning capabilities.

What the science says: There are no studies with matcha and weight loss. Six studies using green tea found possible modest effects on body weight, but the results varied widely.

Potential side effects: The caffeine may increase heart rate and blood pressure, and the tea itself may cause constipation, abdominal discomfort and potential liver damage.

3. Garcinia cambogia

What it is: Extract from a small green tropical fruit that contains a large amount of hydroxycitric acid (HCA).

The claim: HCA interferes with fatty acid production, reduces fat storage in cells and helps reduce appetite and cravings.

What the science says: Several short-term human clinical trials revealed little to no effect on body weight.

Potential side effects: Concerns include headache, nausea, upper respiratory tract symptoms, gastrointestinal distress and liver damage.

4. Caffeine

What it is: Concentrated caffeine in pill form.

The claim: It increases the metabolic rate and speeds up weight loss.

What the science says: Studies show that 100 milligrams of caffeine (about the amount in one cup of instant coffee) will increase the average metabolic rate by about nine calories per hour during a three-hour period. So consuming 400 milligrams could potentially burn about 100 extra calories.

Potential side effects: There are multiple safety concerns for consuming more than 400 milligrams of caffeine in a day, including insomnia, tremors, dizziness, tachycardia, jitteriness and vomiting.

5. Hydroxycut

What it is: Billed as America’s bestselling weight loss supplement brand, this supplement is mostly caffeine, along with various plant extracts.

The claim: It leads to weight loss, increased energy and a higher metabolic rate.

What the science says: There have not been any independent studies on the effectiveness of this product, only those done by the company. There is no data available concerning the long-term effectiveness.

Potential side effects: The list includes anxiety, jitteriness, tremors, nausea, diarrhea and irritability. Dietary supplements for weight loss can be expensive, and they generally don’t work. Their safety isn’t proven, so there is always risk in using them. Lifestyle changes, such as eating better and getting more exercise, take longer to deliver weight loss results, but you’ll be better off in the long run. Anita Marlay, R.D., L.D., is a dietitian in the Cardiopulmonary Rehab department at Lake Regional Health System in Osage Beach, Mo.