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Study finds pitfalls of intermittent fasting

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Intermittent fasting is gaining popularity as a weight management tool, but a new study shows it may not be any more effective than other methods and, more worrying, potentially leads to muscle loss.

The small (116 participants) 12-week study into the effects of 16:8-hour time-restricted eating (TRE) on weight loss and metabolic risk markers found intermittent fasting was not more effective for weight loss than eating regularly throughout the day.

A 16:8 fasting method usually involves eating only during an eight-hour window each day and fasting for the remaining 16 hours

Muscle loss a problem for fasters

Of the weight that was lost in the fasting group, approximately 65 per cent came from lean mass loss. Lean mass includes muscle and excludes fat mass. Typically, lean mass loss accounts for just 20-30 per cent of weight loss, the researchers say.

Reduced appendicular lean mass, specifically, can lead to ‘weakness, disability and impaired life quality’, they warn.

And, in previous studies, significant lean mass loss has been correlated with weight regain.

Lead author Dylan Lowe says the muscle loss may be down to the fasting participants consuming less protein, due to skipping breakfast.

Other health markers unaffected by fasting

As well no significant difference in weight loss, when comparing the fasting and non-fasting groups, the researchers found there was little difference in body composition, metabolic and health markers such as fat mass, fasting insulin, HbA1C or blood lipids. The latter finding contradicts previous studies.

“Our results are consistent with a prior study demonstrating that a recommendation to skip breakfast does not affect weight outcomes in patients trying to lose weight but, contradict previous reports describing the beneficial effects of TRE on weight loss and other metabolic risk markers,” Dr Lowe, et al, says.

The study had some limitations, so further investigation is needed to see if the results can be replicated. The researchers suggest further studies should examine the effects of protein intake and timing of fasting on appendicular lean mass loss.

The research was published in JAMA Internal Medicine.

First published: Oct 2020

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