Dorian Yates Slender

Caffeine· evidence: Strong

Caffeine is one of the best-supported performance aids, with consistent research showing it can improve endurance, strength and alertness. The doses used in research are usually 3–6 mg per kg of body weight, taken about an hour before exercise.

The catch is the dose: it adds to any coffee, tea or energy drinks you already have, and it can disrupt sleep if taken later in the day. There is no authorised health claim for caffeine and sports performance in the UK.

Typical dose: Research doses are 3–6 mg per kg of body weight

Safety: High caffeine content. Not recommended for children or pregnant or breastfeeding women. Healthy adults should keep total caffeine from all sources to no more than 400 mg a day and 200 mg at a time. Avoid late in the day and do not combine with other caffeine products.

Research we looked at:
Guest NS et al. (2021). International Society of Sports Nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr 18:1.
EFSA NDA Panel (2015). Scientific opinion on the safety of caffeine. EFSA Journal 13(5):4102.

Chitosan· evidence: Limited

Chitosan is a fibre made from the shells of crustaceans such as shrimp and crab. It is sold on the idea that it binds dietary fat in the gut. A Cochrane review found a small effect on weight in the trials, but the better-quality trials showed little or no effect, and the amount of fat bound appears too small to matter.

There is an authorised GB claim for chitosan and blood cholesterol, but only when a product provides 3 g of chitosan a day. We make no weight-loss claims for chitosan.

Typical dose: Weight-loss products usually give 1–3 g a day before meals

Safety: Made from shellfish: not suitable if you have a shellfish allergy, or for vegans and vegetarians. Can cause wind, bloating and constipation. It may reduce absorption of fat-soluble vitamins (A, D, E, K) and some medicines, so take them at least 4 hours apart. Speak to your GP if you take warfarin or other medication. Not for pregnancy or breastfeeding.

Research we looked at:
Jull AB et al. (2008). Chitosan for overweight or obesity. Cochrane Database Syst Rev (3):CD003892.
EFSA NDA Panel (2011). Scientific opinion on the substantiation of health claims related to chitosan and maintenance of normal blood LDL-cholesterol concentrations. EFSA Journal 9(6):2214.

L-carnitine (incl. L-carnitine L-tartrate)· evidence: Limited

L-carnitine helps carry fats into cells to be used for energy. Your body makes its own, and meat and dairy supply more, so healthy people eating a normal diet are not short of it. Taking extra does not appear to raise the amount in muscle much, which is one reason it does not act as a 'fat burner'.

Reviews of the trials report a small average drop in weight (around 1 kg) compared with placebo, mostly in older or overweight people, often alongside a diet. There is little evidence of a meaningful effect on fat loss in healthy, active people with a normal diet. Small studies of L-carnitine L-tartrate have looked at muscle soreness after exercise, with mixed results.

There is no authorised health claim for L-carnitine, so we make no claims about its effects. Fat loss comes from a sustained calorie deficit, not from this ingredient.

Typical dose: Studies have typically used 1–3 g a day; liquids and capsules usually give 0.5–3 g per serving

Safety: Usually well tolerated at up to about 2 g a day. Higher doses can cause stomach upset, diarrhoea and a 'fishy' body odour. Speak to your GP first if you take thyroid medication or warfarin, have kidney disease, or have had seizures. Not recommended in pregnancy or breastfeeding without medical advice.

Research we looked at:
Pooyandjoo M et al. (2016). The effect of (L-)carnitine on weight loss in adults: a systematic review and meta-analysis of randomized controlled trials. Obes Rev 17(10):970–976.
Talenezhad N et al. (2020). Effects of L-carnitine supplementation on weight loss and body composition: a systematic review and meta-analysis of 37 randomized controlled clinical trials with dose-response analysis. Clin Nutr ESPEN 37:9–23.
EFSA NDA Panel (2011). Scientific opinion on the substantiation of health claims related to L-carnitine. EFSA Journal 9(6):2212.

Chromium· evidence: Limited

Chromium is a trace mineral needed in tiny amounts. Most people get enough from foods such as meat, wholegrains, broccoli and nuts, and true deficiency is rare.

Chromium supplements, especially chromium picolinate, are often sold for appetite, cravings or weight loss. Reviews of the trials have found the effect on body weight to be very small and of doubtful practical value. There is no good evidence that extra chromium helps people who are not short of it.

We make no claims about weight loss or blood sugar conditions. If you have diabetes or take medicine for blood sugar, speak to your GP before taking chromium.

Typical dose: The NRV is 40 µg a day; supplements usually give 50–200 µg

Safety: The NHS says 10 mg or less a day of chromium from supplements is unlikely to cause harm; most products give far less. Speak to your GP first if you have diabetes or take blood sugar medication, or if you have kidney or liver disease.

Research we looked at:
NHS. Vitamins and minerals: others (chromium) (nhs.uk).
Onakpoya I et al. (2013). Chromium supplementation in overweight and obesity: a systematic review and meta-analysis of randomized clinical trials. Obes Rev 14(6):496–507.
EFSA NDA Panel (2014). Scientific opinion on dietary reference values for chromium. EFSA Journal 12(10):3845.