Although the use of some herbal and dietary supplements show statistically greater weight loss than placebo, it is not sufficient to benefit health, according to the joint findings of two systematic reviews, which are the first to comprehensively include all available herbal and dietary supplements for weight loss for over 15 years.
"There is currently insufficient evidence to recommend any of the supplements we included in our reviews for weight loss," stressed lead author Erica Bessell, a PhD candidate from the University of Sydney in Australia.
She added that some products with promising results warrant further investigation in well-conducted randomized controlled trials (RCTs) to determine their efficacy and safety. But, overall, she would like to see a reduction in the number of products on the market without evidence to support their efficacy, "because, as we found, many of the products currently marketed for weight loss just do not work."
"Herbal and dietary supplements might seem like a quick-fix solution to weight problems, but people need to be aware of how little we actually know about them," she told Medscape Medical News in an interview. "We would recommend that people trying to lose weight should save their money and seek out evidence-based care instead," she emphasized. The research was presented as two posters at this year's online European Congress on Obesity (ECO).
Herbal and Dietary Supplement Industry Booming
Supplements for weight loss are growing in popularity, sustaining a rapidly expanding business sector globally. In the United States, the herbal and dietary supplements industry was estimated to be worth USD $41 billion in 2020, with 15% of Americans having tried a weight loss supplement in their efforts to shed pounds.
In light of this, Bessell said it is increasingly important to ensure supplements are efficacious and safe: "The popularity of these products underscores the urgency of conducting larger, more rigorous studies to have reasonable assurance of their safety and effectiveness for weight loss." Commenting on the study and the wider issues related to the surge in uptake of herbal and dietary supplements, Susan Arentz, PhD, said the evidence is similar to that for other complex interventions that people attempt for weight-loss, including for example exercise, in that it is heterogeneous and low quality.
"One outstanding limitation for herbal medicine was the failure of trialists to validate the contents of interventions. Given the chemical variability of plants grown and harvested in different conditions, and the presence of pharmaceuticals and heavy metals found in some supplements ... future investigations of standardized herbal supplements and RCTs of higher methodological quality are needed," remarked Arentz, a board member of the Australasian Integrative Medicine Association and researcher at Western Sydney University, Australia.
"Also, further RCTs are warranted due to the consumer preferences for natural treatments, especially in health settings with predominant use of traditional medicines and practices," said Arentz.
One Review for Herbal Supplements, One for Organic Compounds
To accommodate the large number of trials investigating supplements for weight loss, the researchers conducted two systematic reviews, together representing 121 randomized placebo-controlled trials. One of the reviews investigated herbal supplements, and the other examined supplements with isolated organic compounds for example, specific fibers or lipids.
Many of the included trials had been published in the last decade and had not been previously included in an up-to-date systematic review. Bessell added that many studies often had a small sample size or were poorly designed, with insufficient information on the composition of supplements, and often featured little data on long-term effectiveness. The two reviews primarily analyzed efficacy, not safety, because many of the studies did not report adverse effects.
The first review, published last year in Diabetes, Obesity and Metabolism, looked at 54 placebo-controlled randomized trials up to August 2018 on the effect of herbal supplements on weight loss. Participants included 4331 individuals aged 16 years or older who were overweight or obese. To be clinically meaningful, a weight loss of at least 2.5 kg was required over a period of, most often, 12 weeks or less.
Herbal supplements included in the analysis included green tea; Garcinia cambogia and mangosteen (tropical fruits); white kidney bean; ephedra (a stimulant that increases metabolism); African mango; yerba mate (herbal tea made from the leaves and twigs of the Ilex paraguariensis plant); veld grape (commonly used in Indian traditional medicine); licorice root; and East Indian Globe Thistle (used in Ayurvedic medicine).
The second review analyzed 67 randomized trials up to December 2019 that compared the effect of dietary supplements containing naturally occurring isolated organic compounds to placebo for weight loss in 5194 individuals aged 16 years or older who were overweight or obese.
Meta-analyses were conducted for chitosan, glucomannan, conjugated linoleic acid, and fructans comparing the mean weight difference post-intervention between participants receiving the dietary supplement or placebo.
No Clinically Significant Results
Commenting on the overall results, Bessell said: "Though most supplements were safe for use in the short-term, very few were found to produce clinically meaningful weight loss. Those that were found to result in clinically meaningful weight loss had only been investigated in one or two trials, so need more research."
The first review on herbal supplements found that only Phaseolus vulgaris (white kidney bean) resulted in significant weight loss compared to placebo, with an average weight difference of 1.61 kg (3.5 lb). The result was not clinically meaningful, however.
For isolated organic compounds, significant weight differences compared to placebo were seen for chitosan, with a mean difference of 1.84 kg (4 lb), glucomannan at 1.27 kg (2.8 lb), and conjugated linoleic acid at 1.08 kg (2.4lb).Again, none of these findings met the criteria for clinical significance (weight loss of 2.5 kg [5.5 lb] or more).
In addition, some combination preparations containing African mango, veld grape, East Indian Globe Thistle, and mangosteen showed promising results with a mean weight difference of 1.85 kg (4 lb), but were investigated in three or fewer trials, often with poor research methodology or reporting, and the findings should be interpreted with caution, the researchers noted.
Other dietary supplements, including modified cellulose — a plant fiber that expands in the stomach to induce a feeling of fullness — and blood orange juice extract, also showed encouraging results but were only investigated in one trial and need more evidence before they can be recommended for weight loss, Bessell added.
She pointed out that some supplements are banned in some countries, such as ephedra (an extract from the plant Ephedra sinica). "This supplement is already banned in many countries because of the risk of serious adverse effects. The possibility of drug interactions may also be present with some other supplements, so health professionals and consumers should be aware of this."
The isolated organic compounds supplements review will be published in the International Journal of Obesity to coincide with the ECO 2021 conference.
Bessell has declared no relevant conflicts of interests. Arentz reviewed the systematic review of RCTs of herbal medicine supplements for weight loss published in Diabetes, Obesity and Metabolism.
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