Alternate-day Fasting Cuts Body Fat But Also Reduces Muscle

Nov 28 2025

New investigation shows that while 4 weeks of alternate-day fasting tin quickly trim assemblage weight and fat, it besides leads to a measurable nonaccomplishment of muscle, and adding a whey macromolecule shingle during fasting days isn’t capable to extremity it.

Study: Effects of Four Weeks of Alternate-Day Fasting pinch aliases Without Protein Supplementation - A Randomized Controlled Trial. Image credit: Pormezz/Shutterstock.com

In a caller study published successful Nutrients, researchers investigated nan effect of short-term alternate-day fasting (ADF) pinch aliases without macromolecule supplementation connected wellness and assemblage composition.

Around 44 % and 16 % of adults worldwide are overweight and obese, respectively. In Singapore, nan corresponding estimates are astir 41 % and 14 %. Several weight nonaccomplishment strategies person been introduced to combat obesity, pinch intermittent fasting gaining important liking owed to its imaginable benefits connected metabolic and cardiovascular health, arsenic good arsenic lipid profiles. It involves alternating betwixt fasting and feeding periods, pinch fasting periods lasting 16 to 20 hours/day.

ADF, a type of intermittent fasting, involves alternating betwixt feeding and fasting days each 24 hours. However, ADF includes a azygous mini repast of ~400 to 600 kcal during fasting days alternatively than extended regular fasting windows. Some grounds suggests that ADF decreases assemblage mass, fat mass, assemblage wide scale (BMI), cholesterin levels, humor unit (BP), and triglyceride levels. Despite nan benefits of ADF, musculus nonaccomplishment remains a peculiar concern, and whether macromolecule supplementation prevents musculus nonaccomplishment remains unclear.

Study creation compares ADF pinch and without macromolecule intake

In nan coming study, researchers investigated whether short-term ADF has beneficial effects connected assemblage creation and whether higher macromolecule intake preserves musculus during weight loss. Asian males aged 21 to 35 years pinch a BMI > 23 kg/m2 who did not fume aliases usage baccy were enrolled successful Study 1. Individuals taking semipermanent medications, those pinch a wellness information that mightiness beryllium aggravated by fasting, aliases those incapable to meet nan fare and beingness activity requirements were excluded.

Participants were subjected to a four-week ADF protocol that began astatine 12 AM, alternating betwixt fasting and feeding days successful 24-hour cycles. On fasting days, only h2o aliases zero-calorie beverages and a mini repast of 400 to 600 kcal were allowed betwixt 12:00 and 2:00 PM. On feeding days, free intake of foods and beverages was permitted. Body creation was assessed earlier and aft involution utilizing bioelectrical impedance analysis.

Resting BP and fasting humor glucose (FBG) were measured weekly. Physical activity levels were assessed utilizing nan Global Physical Activity Questionnaire, administered each week. A dietary grounds was besides maintained connected immoderate 2 days of fasting each week. Furthermore, nan squad conducted a randomized controlled proceedings (Study 2) to analyse whether expanding macromolecule intake would thief sphere musculus during weight loss.

Study 2 besides enrolled young Asian males aged 21 to 35 pinch a BMI > 23 kg/m2 for a four-week ADF, but participants were assigned to a power aliases macromolecule group. The macromolecule group consumed a 25 g whey macromolecule supplement (125 kcal) during nan fasting days. Besides nan macromolecule supplementation connected fasting days for nan macromolecule group, nan remainder of nan proceedings was identical to Study 1, including dietary records, GPAQ, wellness assessments, and laboratory measurements.

ADF lowers weight and fat but reduces musculus too

Study 1 enrolled 20 participants successful February and March 2017, while Study 2 recruited 26 subjects from January to March 2018. Seven individuals from Study 1 and 2 from nan macromolecule group were mislaid to follow-up. As such, nan last analytic sample consisted of 37 participants, pinch an mean property of 25 years and a BMI of 26.7 kg/m². During days of fasting, Study 1 subjects consumed an mean of 525 kcal, of which 38 %, 37 %, and 25 % were from carbohydrates, fat, and protein, respectively.

The macromolecule group consumed 495 kcal connected fasting days, of which 34 %, 26 %, and 40 % were from carbohydrates, fat, and protein, respectively. The power group consumed 533 kcal, pinch corresponding estimates of 46 %, 33 %, and 22 %, respectively. Hydration position earlier and aft involution remained accordant successful some studies. Since nary relationship effects were observed betwixt nan macromolecule and power groups, information from Study 1 and Study 2 were mixed for analysis.

All assemblage creation measures post-intervention showed important reductions, including assemblage mass, fat mass, and fat-free wide (muscle). Physical activity levels were besides importantly little astatine nan extremity of weeks 2 and 3 compared to baseline. Diastolic BP and FBG showed statistically important clip effects, but these changes were short-lived. DBP decreased only astatine week 3, and FBG decreased only astatine week 1; neither marker showed a important quality betwixt baseline and post-intervention. No changes were noted for systolic BP.

Low-dose macromolecule proves insufficient for musculus preservation

Taken together, nan findings illustrated that short-term ADF resulted successful important reductions successful assemblage mass, fat mass, and fat-free mass. Increasing macromolecule intake done a low-dose whey macromolecule supplementation did not mitigate musculus loss.

The study notes that fasting-day macromolecule intake remained beneath nan recommended regular levels and that nan differences successful full macromolecule intake betwixt groups were small, while feeding-day macromolecule intake was not monitored. These factors whitethorn explicate why supplementation grounded to sphere muscle.

Further studies whitethorn analyse the efficacy of macromolecule aliases leucine supplementation during some fasting and feeding days, mixed pinch concomitant guidance training, connected nan preservation aliases betterment of musculus during weight loss.

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