Weight loss supplements: marketing gimmicks or scientifically proven products?
New products with new promises for quick fixes swamp the market almost daily. These range from appetite suppressants to absorption blockers and metabolic influencers. Some even promise weight loss without any modification in exercising or eating habits.
In an effort to shed some light on the jungle of marketing slogans, and to separate the "wheat" of effective supplements from the "chaff" of marketing gimmicks, we took a deeper look at the various available natural or herbal weight loss supplements, their proposed actions and the existing clinical evidence supporting possible claims. The following information was presented at the recent World Obesity & Weight Loss Conference held September 13-14 in Washington, D.C.
(A word on methodology: Our conclusions are based on Internet and database research, combined with the responses of manufacturers to our inquiries on scientific data.)
Weight Loss Mechanism: Fat Burning/Thermogenesis
The resting metabolic rate accounts for 60-70% of the total daily energy expenditure. It can be influenced in two possible ways: by increasing the rate of fat degradation, or by stimulating the sympathetic nervous system. It is a mechanism used by many weight loss ingredients, among them ephedra, which has been banned because of safety concerns.
The proposed action of caffeine, contained in coffee, cocoa, kola nut, yerba mate, guarana and tea, is that it prolongs the fat-burning process following exercise. Indeed, scientific evidence for this action exists, especially in combination with other substances or with a low-calorie-diet and exercise. However, in placebo-controlled, double-blind randomized studies, caffeine alone could not be shown to have any significant effect on the weight of volunteers.
Green tea polyphenols are supposed to inhibit noradrenaline degradation, as well as fat digestion and uptake; another part of their proposed action is stimulation of fat degradation in the liver. Among the polyphenols, epigalocatechin gallate (EGCG) specifically has been proven in randomized, double-blind, placebo-controlled studies to reduce weight and waist circumference in moderately obese men. EGCG also affects satiety and glucose production in the liver, making it a promising anti-obesity agent. Hydroxycitric Acid (HCA), contained in Garcinia cambogia, is another promising anti-obesity agent with encouraging clinical data. Its proposed action is the inhibition of citrate cleavage enzyme, which leads to suppression of de novo fatty acid synthesis and food intake. In combination with Gymnema sylvestre extract, the effects of HCA on weight loss are even more pronounced.
Forskolin, derived from the ayurvedic plant Coleus forskohilii, enhances lean body mass and stimulates fat loss. Both these effects could be proven in in vitro and preliminary randomized, double-blind, placebo-controlled studies, with even more weight loss achieved in combination with low-calorie diets.
New on the weight loss scene, is a new ingredient called 7-oxo dehydroepi-androsterone (7-oxo DHEA), which is a naturally occurring metabolite whose proposed action is increasing the rate of fat catabolism and mitochondrial oxidation by inducing the activation of fattyacyl-CoA oxydase and the formation of liver mitochondrial glycerol-3-phosphate dehydrogenase. Again; especially in conjunction with exercise and reduced-calories diets, significant weight loss could be shown in randomized, double-blind, placebo-controlled studies.
Contained in beef and dairy products, conjugated linoleic acid (CLA) is another relatively new weight loss ingredient. CLA has been proven in randomized, double-blind, placebo-controlled studies to influence fat metabolism toward the reduction of stored fat.
Weight Loss Mechanism: Protein Breakdown Inhibition
Inhibition of protein degradation shifts catabolism towards degradation of fat storage molecules, which promotes an increase in lean body mass and a decrease in the storage fat. A metabolite of leucine, hydroxy-methylbutyrate (HMB), is proposed to induce weight loss via this mechanism. However, to date, only two randomized, double-blind, placebo-controlled clinical studies have been conducted, so further study is necessary in order to make a claim.
Weight Loss Mechanism: Fat Absorption Blocking
By binding to fat molecules taken up with food, weight loss ingredients using this mechanism are supposed to reduce fat absorption via the intestine. Uncleaved triglycerides are simply excreted and don't end up on the hips.
Chitosan, one candidate for this mechanism, has not been proven so far to aid in weight loss. It contains amino polysaccharides derived from the powdered shells of marine crustaceans. So far, evidence of the proposed action could only be shown in animal studies. And although other good human studies exist, the results were either not statistically significant or inconclusive because of low numbers of participants and/or other methodological flaws.
Weight Loss Mechanism: Mood Regulation
It has been proposed that many people compensate for stress and frustration by eating, and that mild depression is a possible trigger for obesity. The weight gain resulting from this behavior supposedly leads to even more depression, creating a vicious cycle. It is thought that mood lightening substances could possibly break this cycle.
Although there are many candidates for this proposed action--natural substances like St. John's Wort, ginkgo biloba, and rhodiola rosea--so far, evidence for their effectiveness as weight loss agents has yet to be provided.
Weight Loss Mechanism: Appetite Suppression
There are two ways of curbing the urge to eat--by physically inducing a feeling of fullness or by deceiving the hypothalamus with fake information about high blood glucose levels, therefore suppressing hunger.
A feeling of fullness is, of course, induced by dietary fibers in the food. Examples for these are beta-glucan, inulin, psyllium, pectin, glucomannan and galactomannan. Clinical and epidemiological studies show varying effects for the different fibers. One randomized, double-blind, placebo-controlled study exists for glucomannan, showing significant effects compared to placebo. However, more studies are still needed in order to substantiate a claim.
5-hydroxytryptophan (5-HTP), an extract from Griffonia simplicifolia, influences the brain serotonin levels to curb carbohydrate cravings in dieting persons. Its efficacy has been proven in randomized, double-blind, placebo-controlled studies, but drug-nutrient interactions are possible if taken in combination with a selective serotonin reuptake inhibitor (SSRI).
For another active working on the same principle, pine seed extract from seeds of Pinus koraiensis seems promising for weight loss. Although clinical studies using the randomized, double-blind, placebo-controlled design have yet to be conducted, data from other studies are encouraging.
As for the most famous appetite suppressant--hoodia gordonii extract P57--its efficacy has been proven in preclinical and small clinical studies so far. Further studies are expected to be published in the near future.
Dr. Joerg Gruenwald is president and Irene Wohlfahrt is scientific consultant of analyze & realize ag, a specialized product development, research, and consulting company for nutraceuticals, herbal medicines, and functional food. Dr. Gruenwald is also author of the PDR for Herbal Medicines. Both authors can be reached at analyze & realize ag, Waldseeweg 6, 13467 Berlin, Germany; 49-30-40008100, Fax: 49-30-40008500; E-mail: firstname.lastname@example.org, email@example.com; Website: www.analyze-realize.com.
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|Author:||Gruenwald, Joerg; Wohlfahrt, Irene|
|Date:||Nov 1, 2005|
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