6 1GT Tuesday October 13 2020 | the times

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dementia. One of the new report’s

co-authors, Dr Ethan Weiss, says he

had been a keen intermittent faster for

seven years, but was so surprised by

the results that he has abandoned it.

Intermittent fasting has been found

wanting before. In 2017 researchers at

the University of Illinois at Chicago

assigned 100 overweight people to one

of three regimens: traditional everyday

calorie-reduction, alternate-day

fasting and not dieting. At the end

of the 12-month study, both diet

groups had lost weight. However,

the fasters lost no more than the

conventional calorie-cutters. So much

for boosted weight loss through

accelerated metabolic rates.

But why the muscle loss? Weiss’s

study found that, overall, the fasting

participants walked about 2,500 fewer

steps each day than those in the

control group. Something similar was

found by a Nottingham University

study published in the journal Appetite

last month. Investigators followed

14 men on an intermittent fasting

regimen, measuring their levels of

exercise and energy intake on the day

before a fast day, the fast day itself and

the day afterwards.

Their normal calorie consumption

rose by 6 per cent the day before

fasting, and by 14 per cent on the day

after fasting. Exercise levels fell, so

that the men burnt on average

health

Intermittent

fasting: why

it could be

bad for you

It began with the 5:2 regimen, and now

stop-go dieting is a way of life for many.

As a new study suggests it could do

harm, John Naish looks at the evidence

I

Is it all over for intermittent

fasting, one of the world’s most

popular weight-loss methods?

The much touted regimen

involves severely limiting

calories on certain days of the

week or for specified hours

during the day. Popular among

the variations are the 5:2 (five days

eating normally, two days fasting) and

the 16:8 (a daily eight-hour window for

eating, with 16 hours’ abstinence).

Whatever the model, the basic

weight-loss premise is that you take in

fewer calories than you burn overall.

A promised bonus is that intermittent

fasting may help to reduce your

appetite by slowing your metabolism,

making self-denial easier.

Garnish this with the fact that you

feel starved for only part of the time

rather than all the time, as with

conventional diets, and it’s small

wonder that we’ve swallowed the

promises hook, line and shrinker, with

intermittent dieting becoming the

world’s most googled diet.

Yet now comes a stark warning that

such regimens could have a serious

health cost. Not only do they bring

modest benefits, they may rob you of

vital muscle mass, researchers warned

last month in the highly reputed

journal JAMA Internal Medicine.

The three-month study, led by

investigators at the University of

California, San Francisco, followed

more than 100 obese or overweight

people who followed the 16:8 regimen

or stuck with normal three-meal-a-day

patterns. Overall the intermittent

fasters lost on average only slightly

more than the control group — about

2.2lb — but they did lose a seriously

high amount of muscle fibre. Some

lost 65 per cent of their lean mass,

whereas when people generally shed

weight, they lose about 25 per cent.

Many studies show that too much

muscle loss is particularly dangerous

from midlife onwards, significantly

raising the risk of debilitating

age-related diseases such as

osteoporosis, type 2 diabetes and

Many see

it as a

miracle

diet, but

it’s not