High fat, Low carb

Ten years ago you couldn’t move without nudging into someone living, and certainly breathing, the Atkins diet. Many perceived it as a foody fad and it fell out of fashion. But proponents of high-fat, low-carb living, like TV chef Tom Kerridge, have spawned a revival. It’s been given a further shove by professor Tim Noakes and his book, The Real Meal Revolution, who explains how his life changed on this diet.

“I remember running and running but I felt terrible and I put on weight,” Noakes tells us. “It’s then I discovered I’m insulin sensitive and had diabetes, meaning if you metabolise too many carbs, it can be highly toxic. The only solution is cutting carbs.”

Noakes sees the irony as, in his book Lore of Running, he promotes high carb use. “Though, I still advised some athletes in the 1980s to train on a high-fat diet,” he says. “The person who benefitted most was Paula Newby-Fraser who won eight World Championships. She said that was the best advice she received in her career.”

An increasing number of athletes are now switching to high fat. Typically, when it comes to dietary strategies there are grey areas, but the overarching idea is to switch the body from metabolising glycogen (carb stores) to fats. As fats in your diet are more satiating, you eat less and burn more, so become leaner. Evidence of its tri benefits are equivocal. One study found that a group of cyclists who followed a low-carb, high-fat diet for two weeks extended their time-toexhaustion period. However, they didn’t improve in high-intensity tests.

This is key. Ultimately, carbohydrates are king when it comes to intense efforts. They’re burnt quicker than fats – vital for working muscles. Research suggests that when training at 50% of maximal aerobic capacity, 45-55% of calories come from fat. This drops to about 10-30% when training at 75% of maximum, and zero when you’re practically blind through exertion. As intensity increases, a greater proportion of energy comes via glucose. A 50% carb diet leaves 1,000 calories of readily available energy compared to 2,000 on a 60-70% carb diet. That’s the strong argument to top up with carbs.

“That doesn’t mean a high-fat diet doesn’t have its benefits,” counters nutritionist Judith Haudum, who formerly worked with the BMC Racing cycling team. “We had athletes on high-fat diets during the off-season when training intensity was lower.” There’s certainly research that suggests this diet’s more beneficial at cutting weight compared to a high-carb diet on the same calorie count. There’s also a case for ultra-triathletes consuming a highfat diet, since they compete at a lower intensity.”

As for what constitutes a low-carb, high-fat diet, it’s when carb intake is less than 25% of daily calorie count and fat intake is greater than 60%.