‘When you talk about ‘burning fat’, you’re talking about the oxidation of body fat; the breakdown of lipids into fatty acids to use them as fuel,” says Bethan Crouse, a performance nutritionist from Loughborough University. It’s the process that needs to occur for someone to lose weight or go through “body recomposition”; losing fat and gaining muscle.
Regular exercise can increase rates of fat oxidation, Crouse says. (When we work out at low-moderate intensity, fat provides the majority of the fuel for working muscles. As intensity increases, this will shift more towards carbohydrates.) However, she says, “There’s not necessarily a food that burns fat.” For a food to oxidise fat, consuming it would have to “replicate the effects of exercise”.
Where does she think the idea that green tea burns fat comes from then?
“Caffeine – which is found in green tea – in relatively high doses has, in some circumstances, been shown to increase fat oxidation,” Crouse says. It activates the fight-or-flight response, increasing the release of hormones such as adrenaline and noradrenaline that mobilise energy stores.
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However, she says, “It’s a very small amount, and the research isn’t great – it’s definitely not something that you’d recommend relying on if somebody is trying to change their body composition.”
That’s especially true since, even if we’re exercising extensively and oxidising lots of fat, if we’re in an energy surplus and consuming more calories than we’re expending, our body mass will not decrease. “You can absolutely burn fatty acids instead of carbohydrates, but still not lose body mass,” Crouse says.
Her tips for anyone trying to lose fat? Avoid falling for hype around superfoods or supplements. “There are a lot of big, bold claims out there,” she says. Instead, increase exercise and gently decrease the number of calories you consume.