Spices and Herbs for Weight Loss: What the Human Evidence Actually Shows

Hoping cumin, ginger or a shake of cayenne will help you lose weight? No spice or herb has been shown to cause meaningful weight loss in people, and nothing here suggests any spice treats or prevents obesity. The NIH Office of Dietary Supplements (ODS) says little is known about whether weight-loss supplements work,¹ and the National Center for Complementary and Integrative Health (NCCIH) says none of the ones it lists, including green tea extracts, Chinese herbs and bitter orange, has been shown to be effective.² A few kitchen spices do have small human trials behind them, mostly of capsules or extracts given to people who were overweight or had type 2 diabetes. If you’re thinking about a weight-loss supplement, especially if you have a health condition or take medicines, talk to a doctor first.

At a glance

Supplements are not the same as spices in food

Almost all the human research below tested capsules or extracts at fixed doses, not the amounts that end up in a curry or a pot of chili. Unlike drugs, dietary supplements don’t need FDA review or approval before they’re sold,¹ and NCCIH warns that the FDA has found weight-loss products tainted with prescription drug ingredients.² A result for one supplement in a trial tells you nothing certain about a different product on a shelf, or about a spice in your cooking.

Chili peppers and capsaicin

Capsaicinoids give chili peppers their heat, and capsaicin is the most abundant and best studied of them. The ODS says they’ve been proposed to fight obesity by raising energy expenditure and fat burning (lipid oxidation), but that most of the research has looked at how much people eat and how hungry they feel.¹

• Appetite and intake. A meta-analysis of eight randomized, placebo-controlled trials, with 191 participants of normal weight or moderately overweight, found that capsaicinoids cut energy intake by an average of 74 kcal per meal.¹ Body weight wasn’t measured, so the ODS says you can’t put a number on what that cut does to weight. Other research the ODS cites suggests capsaicin makes people feel fuller partly by causing gastrointestinal distress.
• Body weight. A 2017 trial gave 77 overweight adults 2 mg or 4 mg of capsaicinoids a day for 12 weeks. The calorie cuts didn’t significantly change body weight at 6 or 12 weeks.¹
• Safety. At 4 mg a day, capsaicinoid supplements can cause gastrointestinal distress, and they might raise serum insulin and lower HDL cholesterol. Otherwise, the ODS says they appear safe.¹

A popular claim says capsaicin turns white body fat into brown fat that the body burns easily. The capsaicin section of the ODS fact sheet doesn’t mention brown fat, and we found no human evidence for the claim. See cayenne pepper and chili powder.

Cumin

A 2018 systematic review and meta-analysis pooled seven randomized controlled trials of cumin, with data from 412 people who were overweight, had type 2 diabetes, or both. Compared with controls, cumin was linked to lower body weight (−1.74 kg), BMI (−0.67 kg/m²) and fasting blood glucose (−17.82 mg/dL).³ The authors note that the changes were tied to the participants’ clinical condition and to study quality. The abstract doesn’t say what form or dose of cumin was given, or for how long, so the result doesn’t show that cumin in everyday cooking helps you lose weight. We couldn’t trace the claim that cumin works by speeding up metabolism to any source we reviewed. See cumin uses.

Ginger

A meta-analysis of 14 randomized controlled trials, with 473 overweight or obese subjects, found that ginger supplements lowered body weight, waist-to-hip ratio, fasting glucose and insulin resistance and raised HDL cholesterol. They didn’t change BMI, insulin, triglycerides, or total and LDL cholesterol.⁴ The abstract we could read doesn’t give the size of the weight change. We couldn’t trace claims that ginger lowers the stress hormone cortisol and so prevents belly fat to any source we reviewed. See cooking with ginger.

Cardamom and cinnamon

• Cardamom. A 2025 meta-analysis of eight studies found that cardamom supplements lowered serum insulin but had no significant effect on fasting blood glucose, weight or BMI.⁵
• Cinnamon. NCCIH says it’s unclear whether cinnamon supplements help with diabetes or weight loss. Most cinnamon sold in North America is cassia, and NCCIH notes that long-term use of cassia could be a problem for sensitive people, such as those with liver disease.⁶ See cassia cinnamon.

Garcinia and kokum

Garcinia cambogia, sold as a weight-loss supplement, has fruit pulp and rind high in hydroxycitric acid (HCA). The ODS says the evidence on whether it works for weight loss is conflicting, and its effect on body weight is still uncertain. It also records 10 reported cases of liver toxicity, including one death and two liver transplants.¹ Kokum is a different species, Garcinia indica, and the ODS findings are about G. cambogia supplements, not kokum rind used in cooking. See kokum.

Fennel seed

Fennel has an old medical reputation. PROSEA notes that Hippocrates and Dioscorides mentioned it as a diuretic.⁸ Today the European Medicines Agency accepts sweet fennel medicines for mild spasmodic digestive complaints including bloating and gas, for minor menstrual cramps, and as an expectorant in coughs with colds. It bases this on traditional use and notes that clinical trials are limited.⁷ Weight loss isn’t on that list. We found no systematic review showing that fennel suppresses appetite, cuts fat storage, or leads to weight loss. See fennel seed.

Rosemary

Rosemary is now classified as Salvia rosmarinus, in the mint family. We found no NIH summary or systematic review of human trials on rosemary and body weight. We couldn’t trace claims that it suppresses appetite, or that its carnosic acid stops fat cells forming in people, to human evidence.

Seaweed

Seaweeds like kelp, nori, kombu and wakame are among the best food sources of iodine, though the amount varies a lot between species.⁹ For weight, the most studied compound is fucoxanthin, a carotenoid found in brown seaweed and other algae. The ODS reports only one clinical trial of a fucoxanthin supplement for weight loss, of a product combining brown seaweed extract with pomegranate-seed oil. It says more research is needed, and notes that fucoxanthin’s safety hasn’t been thoroughly tested in humans.¹

The bottom line

Cook with these spices because they make food taste good. The best human evidence points to small effects from concentrated supplements in specific groups, and in the one longer capsaicin trial the ODS describes, eating slightly less didn’t add up to significant weight loss.¹ If you’re thinking about a weight-loss supplement, talk to a health care provider first.

Related

• Herbs for inflammation: what the evidence shows
• Cumin, too much cumin
• Ginger, turmeric
• Cinnamon, cardamom, kokum
• Fennel seed, rosemary