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Fitness & Health

15th Jul 2019

Intermittent fasting no good for weight loss, study says

Intermittent fasting is a hugely popular dietary trend, but scientists are adamant it offers no advantage in terms of athletic performance

Alex Roberts

It’s a hugely popular dietary trend, but not one that has much use for powering your workouts

Scientists are generally in agreement that intermittent fasting isn’t a wise strategy for boosting athletic performance. That’s not to say it has no merit whatsoever, but in the context of training is best left alone.

What is intermittent fasting?

Scientists define intermittent fasting as “the idea of abstaining from eating food for a certain period during a day and consuming calories ad lib during the eating hours.”

In other words, you’d consume all your food within a restricted window and then fast for the remainder of the day. Numerous celebrities have cottoned on to the idea, from England rugby player Danny Cipriani to Avengers star Chris Hemsworth.

Chris Hemsworth has previously been a proponent of intermittent fasting (Photo: Getty Images)

Why doesn’t it benefit athletic performance?

It’s worth noting that humans have always fasted. Everyone does. You fast when you sleep, and eat when you’re awake. Hence ‘breaking your fast’ with food when you wake up.

In the context of athletic performance, researchers recently published a wide-ranging review of all studies involving intermittent fasting.

A 2012 study discovered that fasting impaired finish times, speed and power output in people undergoing sprint tests. Scientists say this is likely because high-intensity exercise depends on carbohydrate availability.

Yes – carbs are useful and are not the devil like many would have you know. For example, cyclists in the Tour De France take on an enormous level of carbs each day to power their pursuits. This couldn’t be the case if they seriously cut back on food.

Where could intermittent fasting be used?

It should be said that training for athletic performance and training to lose weight are two distinct goals. Carbs and calories are your friend if you’re trying to set a new PB, but you may need a different outlook if you’re looking to lose weight.

Intermittent fasting has the potential to work for weight loss, but mainly insofar as you’re restricting calorie intake. As you may be aware, weight loss generally occurs when you’re in a calorie deficit.

Will you consume fewer calories if you only eat between certain hours? Yes. But do you necessarily need to follow strict timings to achieve this? Not really. Getting into a calorie deficit could prove as easy as reducing the portion size of each meal you’re currently eating.

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