Effective fat burners act like a hyperdrive for your metabolism - pop a pill and your body’s ability to burn calories kicks into warp speed. “Fat loss supplements do three things: increase fat oxidation during rest and exercise, boost your body’s ability to metabolise fat – convert it to energy – and produce heat in your body to hike up your energy expenditure, which is called thermogenesis,” says sports nutritionist Aaron Deere (opens in new tab). They're big promises, so the Men's Fitness team went to investigate how true they are.
Which ones work?
Caffeine delivers on all of the above points, while antioxidants called catechins in green tea can increase fat-burning conditions by 4.7%. Research into the South American herb yerba mate, used to make a type of tea, has shown it ticks the fat-burning boxes due to its high caffeine content.
“Some supps might have shown beneficial effects on animals or cells in a test tube but that doesn’t necessarily mean they translate to humans,” says Deere. Manufacturers don’t always have to provide rigorous evidence for their claims, so be vigilant. The natural amino acid-derived carnitine and forskolin, which is produced by the Indian coleus plant, are both involved in fat oxidation but evidence for their benefits in supplement form is thin on the ground.
How much is enough?
Before you stock up on green teabags and whack on the kettle, it’s important to realise you’d need to chug down a paddling pool’s worth to get any noticeable benefits. For green tea evidence indicates that you need at least 8.6g a day, which works out at a minimum of nine cups. Concentrated green tea extract comes in powder, capsule or pill form and is a far easier way to consume the fat-burning catechins.
How much is too much?
Caffeine works, but fat-burning isn’t its only effect. “To increase energy expenditure you need a high daily dose of 8mg per kilogram of bodyweight,” says Deere. For an 80kg man, that’s a little over eight Starbucks short Americanos in a day. “But for those sensitive to caffeine it’s been linked with anxiety, insomnia, an upset stomach and muscle tremors.” Green tea contains caffeine too, although in smaller amounts, but too much of it can also stunt the absorption of iron from food, which reduces energy production.
Joel Snape, associate editor: “Do fat burners work? Yes, but so do lots of other things if you want to get lean – and if you’re chugging NitroCut (or whatever) alongside fizzy pop and cupcakes, you’re going to hit a sticking point sooner or later. The best advice, as usual, is *read the label* and *don’t overdo it*. Think of them like a secret weapon: something to break out after the progress you can make with sensible eating and a solid training programme has stalled.”
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