Comprehensive Data Review Returns Insufficient Evidence for Using Herbal, Dietary Supplements for Weight Loss

Patrick Campbell

Two studies examining RCTs of herbal and dietary supplements found none of these supplements provided a clinically meaningful reduction in body weight among patients with overweight or obesity.

A pair of studies examining data from more than 120 randomized placebo-controlled trials of herbal and dietary supplements for weight loss has concluded there is “insufficient evidence” for supporting use in assisting weight loss.

Presented as part of the European Association for the Study of Obesity’s 28th European Congress on Obesity, the studies' results demonstrate that, even among trials showing weight loss, any observed reductions were not significant enough to benefit health and also noted a need for reform among trials in the space.

"Our rigorous assessment of the best available evidence finds that there is insufficient evidence to recommend these supplements for weight loss. Even though most supplements appear safe for short term consumption, they are not going to provide weight loss that is clinically meaningful,” said Erica Bessell, a practicing dietitian, PhD candidate from the University of Sydney in Australia, and lead investigator of both studies, in a statement.

To provide clinicians and patients with an updated overview of data related to complementary medicines, Bessell and a team of colleagues from institutions in Australia sought to conduct a comprehensive review of data related to use of these supplements. The first study, Bessell and team designed as a systematic review and meta-analysis of randomized placebo-controlled trials of herbal medicines of adults with overweight or obesity and no specific comorbidities. The second study was designed as a systematic review and meta-analysis of randomized placebo-controlled trials of dietary supplements in a similar patient population.

Of note, a supplement needed to be examined in at least 4 trials for inclusion in either study. Additionally, a weight difference of 2.5 kilograms or more was considered the threshold for clinically significant weight loss.

When examining herbal supplements, a search of Medline, Embase, Cinahl, and Web of Science databases from inception through August 2018 yielded 54 trials meeting criteria for inclusion.

In their analyses, investigators found Phaseolus vulgaris was the only supplement, when used as a single agent, that resulted in statistically significant weight loss compared to placebo (-1.61 kg; 95% CI, -1.96 to -1.26), but this weight loss failed to reach the threshold for clinical significance. No effect on weight loss was observed when assessing use of Camellia sinensis (-0.27 kg; 95% CI, -0.73 to 0.18) or Garcinia cambogia (0.04 kg; 95% CI -0.33 to +0.41).

Additionally, investigators noted statistically, but not clinically, significant differences were observed for combination preparations containing Phaseolus vulgaris (-1.85 kg; 95% CI, -3.24 to -0.46), Camellia sinensis (-1.63 kg; 95% CI, -2.41 to -0.85), or Ephedra sinica (-0.58 kg; 95% CI -0.78 to -0.37).

When examining dietary supplements, a search of Medline, Embase, Cinahl, and Web of Science databases from inception through December yielded 66 trials meeting criteria for inclusion.

In their analyses, investigators noted statistically significant weight differences compared to placebo were observed for chitosan (-1.84 kg; 95% CI, -2.79 to -0.88; p <0.01; Figure 1), glucomannan (-1.27 kg; 95% CI, -2.45 to -0.09; P=.04), and conjugated linoleic acid (-1.08 kg; 95% CI, -1.61 to -0.55; P <0.01), but none of these met the threshold for clinical significance.

In the aforementioned statement, Bessell underlined the importance of further research and patient education related to supplements.

"Very few high-quality studies have been done on some supplements with little data on long-term effectiveness. What's more, many trials are small and poorly designed, and some don't report on the composition of the supplements being investigated. The tremendous growth in the industry and popularity of these products underscores the urgency for conducting larger more rigorous studies to have reasonable assurance of their safety and effectiveness for weight loss,” added Bessell.

These studies, “Effectiveness of dietary supplements for weight loss: a systematic review and meta-analysis of randomized placebo-controlled trials,” and “Effectiveness of herbal medicines for weight loss: a systematic review and meta-analysis of randomized placebo-controlled trials,” were presented at the 28th European Congress on Obesity.