Whether you practice 18:6 intermittent fasting or a full 48-hour fast, studies show that fasting can improve stress resistance and longevity while also lowering your risk of chronic diseases such as cancer and obesity. Exactly why longevity doctor, Peter Attia, M.D., once fully subscribed to the practice.
In his fasting era, Attia was known to do a seven-day water-only fast once a quarter, and a three-day water-only fast once a month.
He was even featured in National Geographic’s documentary Limitless, where he coached Chris Hemsworth through a four-day fast in the name of a longer lifespan and better health.
However, during a recent interview with celebrity trainer and nutrition influencer Thomas DeLauer, Attia stated that he has changed his mind about fasting.
“While there are some advantages to [fasting], it is very difficult to measure what is going on cellularly,” says Attia.
Those benefits also come with a huge downside, decreasing muscle mass, which is why Attia hasn’t done a multi-day fast since 2020. “Today, I just don’t feel that that trade-off is worthwhile, at least at the extreme level that I was doing.”
What happened to Peter Attia?
Attia was losing muscle mass while fasting regularly, both monthly and quarterly. “Over three years, I probably lost around ten pounds of lean mass,” he stated.
One review concluded that a major downside of fasting is the accompanying loss of muscle. If there is a way to make up for this loss, Attia hasn’t found it.
“As much as you try to exercise during those fasting periods like I did, you are just not going to be able to maintain lean mass,” he said.
As you get older, you need to maintain your muscle mass. Even if you do not fast, beginning at age 30, you can lose three to eight percent of your muscle mass per decade.
Muscle loss slows down your metabolism and decreases your strength and functional ability to complete daily tasks with ease.
Is it good to keep fast?
During fasting, a person loses weight on the scale, but their body composition deteriorates: they lose lean mass (muscle) while body fat remains constant or even increases,” wrote Peter in his book Outlive.
That is why Attia sees fasting as a “tool” that should only be used by the best candidates. That person is either someone with a lot of muscle to spare or someone who has more than 35% body fat and can tolerate losing a little muscle because they have so much fat to lose.
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