Supplements

In clinical trials of prescription-strength orlistat (120 mg, Xenical), participants lost approximately 2.9 kg more than placebo over one year in a meta-analysis of 17 randomised controlled trials. The 4-year XENDOS trial showed 2.8 kg additional weight loss versus placebo plus lifestyle changes, and a 37% reduction in progression to type 2 diabetes. The OTC dose (60 mg) has less evidence than the prescription strength but uses the same mechanism at half the dose.

In a systematic review and meta-analysis of 12 randomised controlled trials, berberine significantly decreased body weight by a mean of 2.07 kg, BMI by 0.47 kg/m², and waist circumference by 1.08 cm compared to placebo. Significant improvements in fasting blood glucose, LDL cholesterol, total cholesterol, and triglycerides were also observed. Most trials were short (8–12 weeks) and relatively small. Many were conducted in China, with methodological quality varying.

A meta-analysis published in the American Journal of Clinical Nutrition found that high-protein diets produced significantly more fat loss and lean mass preservation compared to standard protein diets during calorie restriction. Recommended intake for weight loss is approximately 1.2–1.6 g of protein per kg of body weight per day. Protein supplements help reach these targets when dietary sources alone are insufficient. The evidence is stronger for the high-protein dietary strategy than for protein supplements specifically.

In a meta-analysis, caffeine intake was associated with approximately 0.4–0.5 kg additional weight loss in short-term trials. The effect is real but small and temporary. Tolerance to the thermogenic effect develops quickly — within 1–2 weeks of daily regular use, the metabolic boost largely disappears. Most commercial 'fat burner' supplements rely heavily on caffeine for any observed effect. Long-term sustained weight loss from caffeine alone has not been demonstrated.

The evidence is mixed — two meta-analyses reach different conclusions. A 2023 meta-analysis of 6 randomised controlled trials in overweight and obese adults found that psyllium taken before meals (about 10.8g/day for about 5 months) produced an average of 2.1 kg more weight loss than placebo, with reductions in BMI and waist circumference too. However, a broader 2020 meta-analysis of 22 randomised controlled trials in general adults found no statistically significant effect on weight (-0.28 kg, not significant). The positive findings come specifically from trials that dosed psyllium before meals and studied people who were already overweight — general use may show less benefit.

A 2023 network meta-analysis of 111 randomised controlled trials found that chitosan produced 1.70 kg more weight loss than placebo — moderate certainty evidence. This was consistent with an older Cochrane review of 15 randomised controlled trials (1,219 participants) which found 1.7 kg more weight loss than placebo. The evidence is reasonably consistent, but the magnitude of effect is modest.

A 2023 network meta-analysis of 111 randomised controlled trials found that nigella sativa produced an average of 2.09 kg more weight loss than placebo — moderate certainty evidence. This is a meaningful and consistent finding relative to many supplements in this review. Effects on blood sugar and cholesterol may be an additional benefit for some people.

A 2023 network meta-analysis of 111 randomised controlled trials found that spirulina produced 1.77 kg more weight loss than placebo — and notably, this was rated as HIGH certainty evidence, which is unusual for supplement research. Spirulina was one of only two supplements in the analysis to reach this level of evidence certainty. Additional benefits on cholesterol and blood pressure have also been reported in trials.

A 2023 network meta-analysis of 111 randomised controlled trials found that curcumin produced 0.82 kg more weight loss than placebo — moderate certainty evidence. This is a modest effect. Additional benefits on blood sugar and cholesterol have also been shown in trials, which may be more relevant for some people than the weight loss effect alone. The results are consistent across studies, but the magnitude is small.

The evidence varies by fibre type. Psyllium has conflicting meta-analyses (see its separate entry). Glucomannan does not show statistically significant weight loss in the primary meta-analysis. Inulin and other prebiotic fibres have emerging evidence on gut microbiome effects, but the weight loss data in humans is limited. Overall, soluble fibre supplements may produce small weight reductions through increased satiety, but the effect size is modest and depends on which type is used and how it is taken. Fibre supplements work best as part of a broader dietary approach rather than as a standalone weight loss tool.

A double-blind placebo-controlled trial of 88 mg/day saffron extract (Satiereal) in 60 mildly overweight women over 8 weeks found a significant reduction in snacking frequency (–55% vs. –28% placebo) and significant weight reduction in the saffron group. A 2022 meta-analysis of 25 RCTs found improvements in body weight, BMI, and waist circumference alongside cardiometabolic markers including blood sugar and cholesterol. Effects are modest and most pronounced in people who eat in response to stress or emotions. Evidence is stronger for appetite reduction than for direct fat loss.

A systematic review and meta-analysis of 8 randomised controlled trials found a non-statistically significant weight loss vs. placebo (mean difference –0.22 kg; 95% confidence interval –0.62 to +0.19 kg). There was high heterogeneity across trials (I²=65%), meaning results were inconsistent. Some individual trials showed modest benefit; most showed minimal effect. On the available RCT evidence, glucomannan does not demonstrate statistically significant weight loss.

A Cochrane systematic review found a small, statistically significant weight loss of approximately 0.95 kg vs. placebo. This is clinically insignificant for most people. The effect appears caffeine-dependent and is not demonstrated with decaffeinated preparations. Most effects are short-term and modest.

A systematic review found a statistically significant but very small reduction in body fat of approximately 0.05 kg per week vs. placebo. Over 6 months this equates to roughly 1.3 kg of fat mass reduction — very modest. Results are inconsistent across trials, and many studies have industry funding. The effect is on body fat specifically, not necessarily total body weight.

A Cochrane review of 9 randomised controlled trials (622 participants) found that chromium picolinate produced 1.1 kg more weight loss than placebo. However, the authors noted that the effect did not correlate with dose (which would be expected if chromium was truly the cause), the quality of the evidence was rated as low, and the clinical significance — whether a 1.1 kg difference actually matters for health — was described as 'debatable.' The evidence is real but the effect is small.

The evidence base is limited. A review by the NIH Office of Dietary Supplements found only limited clinical evidence supporting potential short-term (under 12 weeks) weight loss effects. The available trials are generally small, short, and of low methodological quality. There is more consistent — though still modest — evidence for effects on blood sugar levels and blood pressure. Green coffee bean extract should not be counted on as a reliable weight loss strategy based on current evidence.

A meta-analysis of 9 randomised controlled trials (911 participants) found that l-carnitine produced 1.33 kg more weight loss than placebo, with a small BMI reduction of 0.47 kg/m². The effect was statistically significant but modest. The results were fairly consistent across studies, but the average trial length was short (under 6 months). Whether these effects persist long-term is unclear.

Research reviewed by the NIH Office of Dietary Supplements shows that capsaicin modestly increases energy expenditure — by roughly 50 kilocalories per day. This is the equivalent of walking about 10 minutes. By itself, this is not a meaningful amount for weight loss. Most individual trials show statistically significant but clinically small effects. Capsaicin works better as one component of a broader weight management approach than as a standalone treatment.

Several small randomised controlled trials (primarily from Cangiano et al., 1991–1998) showed meaningful weight loss with 750–900 mg/day: in a 12-week trial, participants lost an average of 5 kg (11 lbs) vs. 1.1 kg on placebo, largely by spontaneously reducing calorie intake — especially carbohydrates. A lower-dose study (100 mg/day in physically fit adults) found approximately 0.8 kg fat mass reduction vs. a small gain in placebo. The trial evidence is promising but largely from small, older studies. Larger, more recent independent trials are lacking. The effect on carbohydrate cravings is one of the more distinct findings.

A randomised controlled trial of 52 adults under chronic stress (600 mg/day KSM-66 ashwagandha, 8 weeks) found a 3.0% reduction in body weight and 2.9% reduction in BMI, compared to 1.5% weight reduction and 1.4% BMI reduction with placebo. Serum cortisol significantly decreased; food cravings and emotional eating scores also improved. A broader set of trials confirms the cortisol-lowering and stress-reducing effects (including a 27% reduction in perceived stress in one trial). The weight/body composition effects are modest and most relevant for people who overeat in response to stress. Ashwagandha is not a weight loss drug — it's better understood as a stress-management supplement with a secondary effect on weight in stress-affected individuals.

A 2020 meta-analysis of 8 randomised controlled trials found borderline statistically significant weight loss of 1.34 kg vs. placebo (p=0.03). However, when only the most rigorous trials are analysed, the effect is no longer statistically significant. A 2025 scoping review of 14 studies concluded that all 14 failed to demonstrate clinically significant weight or BMI reduction. The marketing claims for garcinia cambogia are substantially stronger than the evidence supports.

There are no published randomised controlled trials evaluating raspberry ketones alone for weight loss in humans. The evidence base consists of animal studies and one short-term human study that combined raspberry ketones with multiple other substances (caffeine, capsaicin, garlic, and ginger) — making it impossible to know which ingredient, if any, was responsible for any effect. The NIH and FDA do not consider raspberry ketones to be an effective weight loss supplement based on available human evidence.

IMPORTANT CONTEXT: The most-cited recent ACV weight loss study (Abou-Khalil et al., BMJ Nutrition Prevention & Health, 2024) was retracted by BMJ Group in September 2025 due to concerns about statistical analysis, data reliability, and lack of trial registration. A 2025 meta-analysis of 10 randomised controlled trials (861 participants) found that ACV reduced body weight and BMI, but with 'substantial heterogeneity' — meaning the results varied widely between studies, which reduces confidence in the conclusion. Most trials are small (under 50 participants), short (4–12 weeks), and from limited geographic regions. Expert opinion from Stanford and Harvard: the current evidence is limited and inconsistent.