Journal Title (Medline/Pubmed accepted abbreviation): Int. J. Sport Nutr. Exerc. Metab.
Page numbers: 139-154
This review summarizes popular weight loss supplements and the current scientific studies evaluating their effectiveness.
1) Products designed to decrease the absorption of fat and/or carbohydrates:
a) Phaseolus vulgaris
- a compound that inhibits the enzyme that digests starch. Two studies were performed. One showed no difference, the other showed greater improvements in weight loss with the supplement compared to the placebo.
- fiber from the shells of crustaceans (ex. lobster). It is hypothesized to bind fat, making it unavailable to fat-digesting enzymes, and thereby unable to be taken up by cells in the small intestine. Collectively, most studies show only a slight benefit for those who want to lose weight or prevent gaining fat mass.
2) Stimulants: products designed to increase metabolism and thereby burn more energy
- Caffeine stimulates the central nervous system which can increase the amount of total energy produced, thereby reducing the amount of energy (i.e. fat) stored. Due to the tolerance to caffeine that is developed, most studies do not support that caffeine is an effective weight loss supplement.
(also known as ma huang)- a compound found in the Ephedra
plants that increases the release of adrenaline and stimulates the same receptors. This results in an increase in heart rate, blood pressure, and alertness. It is also thought to reduce appetite. Several studies have shown ephedra to be effective in promoting weight loss, but it also leads to a stress on the cardiovascular system (for example, it raises blood pressure).
Due to the dangerous, potentially deadly side effects of ephedra, it is banned in most sports and in most countries. Although ephedra as a plant is banned in the United States, companies are allowed to use extracted ephedrine compounds. Additionally, within many countries where ephedra is banned, consumers can buy it online.
The combination of caffeine and ephedra has been assessed in two studies, showing that the combination encouraged weight loss greater than a placebo. However, side effects were more severe than either supplement alone. Because of the danger to the cardiovascular system, combining caffeine and ephedra is not recommended.
c) Green tea
- The two main ingredients in green tea that are hypothesized to aid in weight loss are caffeine and catechins (especially epigallocatechin gallate, EGCG). The catechins are thought to modulate fat metabolism, increase thermogenesis and EGCG specifically is thought to prolong the action of norepinephrine. Several studies have shown that green tea can increase the rate of fat burning, can help people lose weight in combination with a low calorie diet, and help maintain weight after weight loss.
d) Bitter orange
- Bitter orange also contains compounds that stimulate the central nervous system. Bitter orange has not been studied as extensively as the other ingredients listed here and, when it is studied, it is often in combination with other ingredients, so its benefits for weight loss are currently not well established. Moreover, it is thought to exhibit negative side effects including increased blood pressure and heart rate. Bitter orange is not recommended at this time for weight loss until more research can support its use.
3) Nutrient partitioning- substances marketed to change the metabolism of carbohydrates, fats, or proteins, thereby changing the storage of energy in the body.
- Adequate calcium intake is required for optimal fat metabolism.
- High calcium intake may lead to the formation of calcium-fatty acid complexes that increase the amount of fat in the feces.
- Increased calcium intake has not been shown to promote weight loss, but it may help prevent normal, age-related weight gain.
b) Conjugated linoleic acid (CLA)
- A lot of attention has focused on the ability of CLA to promote a strong, lean physique. However there is not a lot of evidence supporting this claim. There may be differences between the efficacy of CLA molecules that have slightly different chemical structures (isomers). Additionally, the person (age, gender) or the dose of CLA could lead to positive or no outcomes. More research is needed to tease out the effective factors that lead to the enhancement of body composition with CLA.
c) Chromium picolinate
– Chromium is a mineral that is essential to our diet. Supplements have purported to increase muscle mass while reducing fat loss, but evidence is lacking.
4. Appetite suppressants
a) Soluble fiber
- Fiber may contribute to a feeling of fullness by binding water and perhaps other mechanisms. Against controls, guar gum and glucomannan supplements have resulted in weight loss.
b) Hoodia gordonri
has been promoted for weight loss but there is currently no scientific evidence of its efficacy.
Many weight loss supplements combine ingredients, which can lead to dangerous side effects. Side effects often vary depending on the individual, so do not assume a product is safe because a trusted store/website sells it or you know someone has used it, and never try a new supplement the day of competition.
There is not significance evidence that any weight loss supplement is effective at promoting weight loss and keeping the weight off, but many studies are short (14 wks or less) and do not follow up with participants. A healthy lifestyle including a healthy diet and exercise is recommended for athletes and non-athletes to achieve and maintain their ideal weight.