Fasting and Lean Mass Over 45: Short Trials, Small Differences

That is the picture from a scoping review in Advances in Nutrition. A scoping review maps the evidence on a question rather than pooling it into one verdict. This one covered 20 randomized controlled trials with 1,653 participants. About 64% were women, and most had overweight or obesity.

Muscle matters because it declines naturally with age, and strength falls faster than muscle mass. Low muscle mass is linked to frailty, reduced mobility and loss of independence. That raises a fair worry: could a diet that cuts calories also strip away muscle in people who are already losing it?

The authors, led by Santero and colleagues, searched three databases for trials published from 2000 to early 2025. Eligible trials enrolled adults aged 45 and older. Fasting had to last at least four weeks. Body composition had to be measured with validated methods. People with diseases that cause muscle loss were excluded.

The trials compared intermittent fasting with a habitual diet or with continuous calorie restriction, meaning eating a little less every day. Regimens included alternate-day fasting, alternate-day modified fasting (a very low-calorie day instead of a full fast) and time-restricted eating, which limits food to a daily window.

Over the periods studied, commonly 12 weeks or less, differences between groups in total fat-free mass were generally small. Fat-free mass is everything in the body that is not fat, including muscle, organs, bone and water.

Intermittent fasting reduced fat mass, body weight and waist circumference by amounts comparable to continuous calorie restriction. Compared with a habitual diet, reductions in weight and fat mass were reported more consistently with fasting. Alternate-day approaches were often linked to those reductions.

The authors are clear about the limits. Most studies used dual-energy X-ray absorptiometry or bioelectrical impedance, which measure total lean mass. Those results may not reflect changes in skeletal muscle itself. Strength, physical performance and quality of life were rarely assessed.

Evidence on insulin-related outcomes, protein intake and combining fasting with exercise was limited and varied between trials. The authors also point to a lack of data on adults aged 70 and older.

In their words, the current evidence does not permit definitive conclusions on whether intermittent fasting preserves fat-free mass, especially over the long term in older people. So the review offers reassurance on short-term lean mass, not proof of muscle safety.

The authors call for longer, high-quality trials that measure muscle health and function with standardized methods.

Two-Year Fish Oil Trial Finds No Memory or Brain-Shrinkage Benefit Detailed Data Confirm Personalized mRNA Melanoma Vaccine Cut Recurrence Risk 42% Blood Signatures of Fitness Linked to Lower Death Risk in UK Biobank Change in AI Face Age Between Photos Linked to Cancer Survival Untreated Sleep Apnea Linked to 69% Faster Cognitive Decline Over 10 Years Over 80 Nutrition Experts Urge White House to Release Ultra-Processed Food Definition Beetroot Juice and Postmenopausal Heart Oxygen Balance After Hard Exercise: A Small Trial Topical Urolithin A Lowered Eye Wrinkle Depth in Randomized Studies Short Breathing Exercises Blunted Heart Rate and Anxiety Under Stress Aerobic and Resistance Training Ended Up Equal for Type 2 Diabetes Plant and Dairy Protein Shakes Left Blood Chemistry Alike in Adults Over 50 Intensity Relative to Your Own Fitness Better Explained Fitness in Midlife Women Blood Flow Restriction Training Showed No Overall Advantage for Artery Health Cigarette Smoke Disrupts Eye Cell Mitochondria, Pointing to Macular Degeneration Risk Ultra-Processed Food Intake Leaves Distinct Blood Fat and Metabolite Signatures Gut-Made Kidney Toxins Linked to Tiny Brain Bleeds in Mice and Patients Flo App Survey of 17,494 Women Finds Gaps in Perimenopause Knowledge New Aging Framework Names Epigenetic Change the Dominant Driver of Aging Exercise Helps Blood Cancer Patients During Treatment, but Diet Evidence Lags Review: Protein Supplements Often Unnecessary Outside the Lab for Active Adults Ear Vagus Nerve Stimulation Linked to Less Inflammation After Surgery Fasting and Lean Mass Over 45: Short Trials, Small Differences Fragmented Sleep Tracked by Wrist Monitors Linked to More Brain Amyloid at Autopsy Blood Test for p-tau217 Predicted Decline Over 12 Years Steady Aerobic Exercise Raised Fitness on Average in Heart Disease Patients Rising Arterial Stiffness Linked to Progression of Heart-Kidney-Metabolic Disease Brain-Wide Gene Therapy Restored Memory in Alzheimer's and Old Mice Men With Heart and Metabolic Disease Show Faster Epigenetic Aging AI Spotted Heart Disease From Face and Tongue Photos in Small Test