A warm bowl of pasta, a fluffy white bread roll, or a bag of generously salted chips – these starchy delights are the stuff of dreams. It’s no wonder many of us couldn’t fathom giving up carbs for good.
However, a new study by the University of Surrey has found that spending just one day without carbs has similar effects on the body to eating very little food, as what happens when following intermittent fasting.
Intermittent fasting, also known as time-restricted eating, involves alternating between periods of normal eating and stretches of significantly reduced calorie intake. These fasting windows can last for specific hours each day or span entire days during the week.
While this approach has been linked to a range of health benefits, eating fewer than 800 calories a day – as recommended twice a week on the popular 5:2 diet – can feel like a tough ask for some.
The good news? This new research suggests you may not have to slash your calories so drastically on fasting days – simply cutting out carbs might offer similar fat-burning benefits.
“What we’re interested in is not necessarily about weight loss, but the metabolic effect of this dietary intervention,” Dr Adam Collins, co-author of the study and Associate Professor of Nutrition at the University of Surrey, told BBC Science Focus.
“The issue that people have, irrespective of their weight, is one of metabolic disturbance, which leads to insulin resistance, type 2 diabetes and cardiovascular disease. These are the things that put burdens on people’s health and ultimately increase their risk of premature death.”
To investigate the effect of carbs on metabolic health, the scientists recruited 12 adults, aged 20 to 65, who were considered overweight or obese.
The participants followed three diets, each one for a period of 36 hours – one full day plus two nights’ sleep – with a five-day break in between each dieting day. The three diets were:
- A normal diet
- A low-carb diet, with the same calorie intake as the normal diet
- A low-carb diet, but this time, low-calorie too
The morning after each of the diet days, the scientists took measurements to see how the participants had responded to the diets.
They found that, regardless of how many calories the participants consumed, eating a low-carb diet encouraged their bodies to burn fat for energy – just like on a fasting diet.
“The body is designed to use carbohydrates for energy when you’ve got carbohydrates – for example, after a meal – and then to use fat in between meals and overnight,” said Collins.
But, he explained, if we eat too much and too often, our bodies rarely switch to burning fat for energy, and we end up with “metabolic mismanagement” – with fat accumulating around our waists, inside our organs, and in our blood vessels.
Having periods of intermittent fasting – or reducing carb intake, as this study showed – seems to help the body “clear the decks,” he said, and start clearing that fat away.
Some people follow low carbohydrates all the time, but Collins said this might impair their body’s ability to process glucose in the long run. Not to mention, pasta is delicious – so giving it up completely can be difficult.
But alternating between low-carb days and regular eating days seems to improve metabolic health – while also being a more manageable dietary pattern for the carb-lovers among us.
“No food is a sin,” said Collins. “Carbohydrates aren’t bad. Fat isn’t bad. It’s all about everything in moderation.”
Read more:
- The secret super carb: How 'resistance starch' can transform your gut health
- Why fasting is a surefire way to lose weight (and keep it off)
- This 3-day-a-week diet could be a vital weight loss strategy, say scientists
About our expert:
Dr Adam Collins is an Associate Professor of Nutrition at the University of Surrey's School of Biosciences. He has been a qualified nutritionist for more than 20 years and is a programme leader for BSc and MSc nutrition at Surrey. His current research includes exercise intensity and energy balance, intermittent fasting, meal timing and composition – specifically, the use of carbohydrate manipulation for metabolic health.
