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 The 60 healthy people in the four-week study were not overweight.
Researchers randomly assigned them to either stick to their usual
eating habits or switch to alternate day fasting, with 12 hours of
unrestricted food followed by 36 hours of no food.
With alternate-day fasting, people reduced weekly calories by 37% on
average and shed an average of 3.5 kilograms (7.7 pounds). That
compares with an average calorie reduction of 8.2% and an average
weight loss of 0.2 kilograms (0.44 pounds) without this diet.
"We do not recommend this as a general nutrition scheme for
everybody, because this is a harsh intervention of which we do not
know the long-term effects," said Frank Madeo, senior author of the
study and a researcher at the University of Graz in Austria.
"We feel that it is a good regime for some months for obese people
to cut weight," Madeo said by email.
To ensure that people assigned to alternate day fasting didn't eat
on fasting days, researchers asked them to wear continuous glucose
monitors. Spikes in blood glucose levels might mean people had a
snack. Researchers also asked participants to fill in food diaries
documenting their fasting days.
After 4 weeks of alternate day fasting, people had more lean muscle
and less body fat, lower cholesterol levels and improved heart
health - all things that can happen with a wide variety of exercise
and nutrition programs.
To get a sense of the safety of alternate day fasting, researchers
looked at a separate group of 30 people who had been eating this way
for at least 6 months, comparing them to healthy people who had not
been fasting.
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They didn't find any meaningful negative side effects.
One limitation of the study is that researchers didn't test the diet
in people who needed to lose weight. They also didn't have any
long-term safety data, and many health problems associated with
extreme dieting like malnutrition and brittle bones can take much
longer than 6 months to develop.
"The 'starvation mode' the body goes into during alternate day
fasting may have some benefits," said Susan Roberts, a senior
scientist at the USDA Nutrition Center at Tufts University who
wasn't involved in the study.
For example, fasting can improve the body's ability to use the
hormone insulin to transform sugars into energy, a process that can
help reduce blood sugar and prevent diabetes, Roberts said by email.
But there isn't enough safety information about alternate day
fasting to recommend it as a regular way of eating to maintain a
healthy weight or for weight loss, Roberts said.
"My preferred option to be honest is not to recommend alternate day
fasting per se but to use occasional daily fasting as a toolbox
option that some people may find helpful," Roberts said. "A small
percentage of people wanting to lose weight may find it helpful, but
we don't yet know the long-term safety to recommend it with
comfort."
SOURCE: http://bit.ly/341MXUZ Cell Metabolism, online August 27,
2019.
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