Why weight loss supplements don't work, according to GSK

By Lorraine Heller

15-May-2008 - A petition seeking to classify all weight loss claims as drug claims highlights the major ingredients used in weight loss supplements, and maintains that these are not sufficiently substantiated, that they are ineffective, or that they are linked to adverse effects.

Filed by drug company GlaxoSmithKline (GSK) together with the American Dietetic Association and a number of obesity organizations, the petition aims to eliminate the weight loss category from the dietary supplement market.

In the third in a series of articles on the issue, NutraIngredients-USA.com examines the ingredients highlighted by the petition, which include bitter orange, chromium, guar gum, hoodia, garcinia, CLA, pyruvate and chitosan.

The slimming ingredients market can be divided into five groups based on the mechanisms of action: increasing energy expenditure; modulating carbohydrate metabolism; increasing satiety or suppressing appetite; increasing fat oxidation or reducing fat synthesis; and blocking dietary fat absorption.

Below is what the GSK petition claims about different ingredients in these categories. All references to studies can be found in the original petition (click here).

Increasing energy expenditure

Bitter orange

Bitter orange has gained in profile since ephedra was banned by the Food and Drug Administration in 2004 as it contains similar compounds and has been favored by dietary supplement manufacturers as an ephedra substitute.

The active ingredient in bitter orange is believed to be synephrine - a sympathomimetic amine that is structurally similar to epinephrine.

According to the petition, there is "little evidence" that bitter orange is effective in weight loss. The petition cites two studies in support of this.

In addition, the petitioners claim that bitter orange may have adverse effects similar to ephedra, including increased heart rate, blood pressure, and the risk of cardiac complications.

Modulating carbohydrate metabolism

Chromium

Chromium picolinate is a naturally occurring derivative of tryptophan that is thought to promote weight loss by optimizing insulin signaling.

The petition states that "insufficient evidence exists" to support the effectiveness of chromium, and many studies yielded "inconsistent results," were "poorly designed," and reported benefits that were refuted by other reports.

"The results of other studies, including three randomized clinical trials, did not show any differences in weight loss between treatment and control groups."

Increasing satiety or suppressing appetite

Guar gum

Guar gum is a dietary fiber derived from the Indian cluster bean. Soluble fiber is believed to absorb water within the gut, thereby causing increased satiety and lower caloric intake.

"The efficacy of this supplement was assessed in a meta-analysis of 20 double-blind, placebo-controlled randomized clinical trials. That meta-analysis indicated that guar gum is 'not effective' in reducing body weight. The consistency of the results among the individual trials confirmed the overall conclusion of this meta-analysis. Other studies have reported adverse gastrointestinal events associated with guar gum," states the petition.
Hoodia

An extract from the South African plant Hoodia gordonii, licensed by drug firm Phytopharm, is thought to cause neurons within the satiety center of the hypothalamus to fire rapidly and thereby suppress appetite.

The petition states: "While certain animal studies involving [this extract] have been published, there does not appear to be any publications in peer-reviewed journals involving human trials with Hoodia extract. As a result, there is no credible scientific support for the efficacy of weight loss supplements containing Hoodia extracts."


Increasing fat oxidation or reducing fat synthesis

Garcinia

Hydroxycitric acid (HCA) is contained within extracts of the fruit rind of Garcinia cambogia, a tree species native to India.

"HCA has been shown to inhibit citrate cleavage enzyme and suppress fatty acid synthesis. Nevertheless, clinical data to suggest that HCA may help in weight loss are 'inconsistent' and most of the clinical studies are 'confounded by methodological flaws'," writes the petition.

"Where there has been a randomized, double blind clinical trial involving HCA, it found no significantly greater weight loss in the treatment group than in the placebo group."

CLA

Conjugated Linolenic Acid, or CLA, is a group of linoleic acid derivatives produced by bacteria in the gut of ruminant animals and believed to inhibit lipoprotein lipase, an enzyme that breaks down fat for absorption.

"Data from human studies involving CLA are 'equivocal and uncompelling'," writes the petition. "Several studies have found no changes in body weight or BMI."

"Moreover, based on an analysis of the results from 13 randomized, controlled trials, investigators reported that there is little evidence to suggest that CLA helps reduce body weight. The authors of this study also reported that CLA may promote liver hypertrophy and insulin resistance, and therefore, may have adverse effects."

Pyruvate
This three carbon ketoacid is created in the body during glycolysis. Pyruvate
is believed to manipulate fat metabolism by increasing fat oxidation and decreasing carbohydrate oxidation.
"Some studies have reportedly shown positive results with pyruvate but they had small sample sizes with short treatment periods, and patients greatly restricted their caloric intake during the study period. On the other hand, two double blind randomized clinical trials involving patients with a BMI greater than 25 found no significantly greater effects on weight reduction than were seen with placebo," states the petition.

The results of these 'rigorous clinical trials' have led investigators to conclude that the case for pyruvate as an aid to weight loss is 'weak', it added.

Blocking dietary fat absorption

Chitosan

Chitosan is a cationic polysaccharide derived from chitin harvested from the
exoskeleton of crustaceans .

The petition states: "Several studies involving well-designed, randomized controlled trials have failed to show any differences in weight loss.' Moreover, to the very limited extent that other studies may suggest efficacy for chitosan, investigators found 'serious methodological limitations of the clinical evidence' and results that were 'conflicting and short-term' and based on 'poorly designed studies'."

"One report declared that 'claims that chitosan is a fat-trapping weight-loss aid are not merely unsubstantiated, they are false.' Thus, there is also 'considerable doubt' that chitosan is effective in reducing body weight in humans."

More weight loss focus

In further articles in this series, NutraIngredients-USA.com will examine industry's response to the petition. We will also provide an overview of the weight loss market, and the drug-supplement conflict.