Big Fat Lies?

Burn more fat and you’ll spare carbohydrate, lose weight and ultimately ride faster — that’s the theory. But does it work in practice? Michelle Arthurs-Brennan investigates.

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You’re full of fat. No offence. We all are. Even a lean athlete has around 100,000 calories of the stuff stored away, predominantly nestled under the skin and within muscles. When we ride, it’s carbohydrates — of which the body can store just 2,000 calories’ worth — we guzzle, in the form of drinks, bars and gels. It’s hardly surprising, then, that cyclists have long been looking for ways to make the body shovel more fat into the fuelling furnace. But despite all the hype around fat-burning, can we really access this near-limitless fuel source to ride further and faster? Let’s have a go at separating the facts from the wishful thinking…

Your body’s nutritional requirements can be broadly split into three macronutrients: carbohydrate, fat and protein. Carbohydrate is broken down into glucose for immediate use and any excess is converted into glycogen to be stored in the muscles and liver for later use. Converting carbs into energy requires less oxygen, compared to metabolising fat, so when you’re exercising at around 70 per cent of your max heart rate (or above), your body is fuelling almost entirely on carbs.

On longer rides, topping up with carbs is essential. Failing to do so means ‘bonking’ or ‘hitting the wall’ — remember, we store only around 2,000kcal of carbs, enough for two to three hours of riding. You have enough fat, meanwhile, to fuel several days of low-intensity riding (no, we don’t advise putting that to the test). Fat-fuelled riding is slow riding; above a moderate pace, you rely on carbs.

The last of the big three is protein, which crucially supplies muscle protein synthesis — the building and repair of muscle. Protein can be used as a fuel, but the body only resorts to this when other sources are low.