A claim you hear on longevity podcasts

Does fasting cause muscle loss?

The claim checked: Fasting too much, or eating one meal a day, can contribute to muscle loss Hear it at 6:02

What do the studies say?

Leaning against

Six of ten studies found lean mass held up when people fasted for part of each day, half of them in people who also trained. Two found a drop in lean mass, and two found the same drop as ordinary calorie cutting. Most tested time-restricted eating, not one meal a day.

Computed from 10 studies that test this point, each judged by two readers, in full. 2 more studies are waiting for a full read and do not count yet.

What was said on the podcast?

“the longevity benefits associated with autophagy can have a downside when taking too far because prolonged or excessive suppression of these growth pathways can contribute to muscle loss.”
Mark Hyman, The Dr. Hyman Show · 5 Things You Think Are Extending Your Life (That Are Actually Doing Nothing) · 6:02 on YouTube
Episode check Fasting can cost you muscle, the episode says. In six of ten studies, it didn't. 5 claims checked against 79 studies · 1 chapter not checked yet See the whole episode →
The point checked Leaning against

Prolonged or frequent fasting, or eating one meal a day, can lead to loss of muscle (lean mass)

Agree 2

controlled trial · 2020 · landmark

“Appendicular lean mass (ALM) was decreased significantly in the TRE group (−0.64 kg; 95% CI, −0.89 kg to −0.39 kg; P < .001) but not in the CMT group (−0.17 kg; 95% CI, −0.41 kg to 0.07 kg; P = .16), and there was a significant difference between groups (−0.47 kg; 95% CI, −0.82 kg to −0.12 kg; P = .009).”

Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med
Who: Men and women aged 18-64 with BMI 27-43 living in the United States; body composition measured in an in-person subset near San Francisco
PMID 32986097

other primary study · 2020 · landmark

“Compared to the non-TRE group, the TRE group lost body weight, visceral fat, and lean mass (all p< 0.05: Figure 4).”

Time-Restricted Eating Effects on Body Composition and Metabolic Measures in Humans who are Overweight: A Feasibility Study. Obesity (Silver Spring)
Who: Adults with overweight or obesity (17F/3M, mean age 45.5 years, BMI 34.1 kg/m2) with a habitual eating window of 14 hours or more, Minnesota
PMID 32270927

Partly agree 2

controlled trial · 2016 · landmark

“When compared to a standard moderate calorie-restricted diet (-400 kcal/day), an ADF regimen produced similar changes in weight, fat mass, lean mass, lipids, and insulin sensitivity index (Si) at 8 weeks in adults with obesity.”

A randomized pilot study comparing zero-calorie alternate-day fasting to daily caloric restriction in adults with obesity. Obesity (Silver Spring)
Who: Adults with obesity (BMI >=30 kg/m2, age 18-55), non-smokers, without diabetes or CVD, Colorado
PMID 27569118

controlled trial · 2018

“We found that both ADF + DER and DER participants achieved a pooled mean weight loss of 11% over 16 weeks with an unanticipated finding of no group differences in weight loss or body composition including lean and fat mass changes.”

Randomized Trial of a High Protein, Partial Meal Replacement Program with or without Alternate Day Fasting: Similar Effects on Weight Loss, Retention Status, Nutritional, Metabolic, and Behavioral Outcomes. Nutrients
Who: Adults with overweight/obesity aged 25-60 years, BMI >27.0 kg/m2, without diabetes or other major disease, Adelaide, Australia
PMID 30142886

Disagree 6

controlled trial · 2013 · landmark

“Fat mass was reduced (P < 0.001) by 3.6 ± 0.7 kg, and fat free mass did not change, versus controls.”

Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutr J
Who: Normal weight and overweight men and women (BMI 20-29.9 kg/m2) aged 35-65 years, Chicago area
PMID 24215592

pooled analysis · 2020 · landmark

“There was no significant change in fat-free mass according to TRE ( Figure 4 C).”

Beneficial Effects of Time-Restricted Eating on Metabolic Diseases: A Systemic Review and Meta-Analysis. Nutrients
Who: Adults aged 20 years or older, healthy or with overweight/obesity, prediabetes, metabolic syndrome or NAFLD, in clinical trials of time-restricted eating
PMID 32365676

controlled trial · 2019 · landmark

“In the present investigation, adherence to TRF did not attenuate FFM accretion, skeletal muscle hypertrophy, or improvements in muscular performance.”

Time-restricted feeding plus resistance training in active females: a randomized trial. Am J Clin Nutr
Who: Healthy resistance-trained females aged 18-30 y with ≤33% body fat doing supervised progressive resistance training
PMID 31268131

Show 3 more Show fewer

controlled trial · 2020 · landmark

“TRF slightly increased leg fat mass by 2.5% compared with normal feeding; however, leg fat-free mass, an indicator of leg skeletal muscle mass, was unaffected by the intervention.”

Short-term time-restricted feeding is safe and feasible in non-obese healthy midlife and older adults. Geroscience
Who: Healthy non-obese (average BMI 24.7) midlife and older men and women aged 55-79, Boulder County, Colorado
PMID 31975053

controlled trial · 2021 · landmark

“These data support the use of TRE and concurrent exercise training as a short‐term dietary strategy for reducing fat mass and increasing lean mass in physically inactive and overweight or obese adults.”

Time-restricted eating and concurrent exercise training reduces fat mass and increases lean mass in overweight and obese adults. Physiol Rep
Who: Physically inactive adults aged 35-60 with overweight or obesity (BMI 25.0-34.9 kg/m2), mostly women (18 of 21), North Dakota
PMID 34042299

other primary study · 2020

“Furthermore, daily 16-h fasts do not impact the ability to retain lean mass and improve muscular strength over the course of four weeks in recreationally active populations who resistance train.”

Four Weeks of Time-Restricted Feeding Combined with Resistance Training Does Not Differentially Influence Measures of Body Composition, Muscle Performance, Resting Energy Expenditure, and Blood Biomarkers. Nutrients
Who: Recreationally active men aged 18-35 years who resistance trained 2-4 times per week
PMID 32316561

What else was said but not tested?

  • mTOR is activated by protein and resistance training and signals the body to build and maintain muscle

More on food and fasting

All checked claims · How we check a claim

How Precis checks a claim · Report an error

The Precis Weekly

Get each new check by email.

One email a week with the claims and episodes we checked, what the studies found and the minute each claim was said.

Free. Unsubscribe anytime.