Effects of intermittent fasting (time-restricted eating) for 30 days on body weight, visceral fat, and muscle mass in adult workers

Abstract

Obesity among workers is an important occupational health concern because of its association with cardiometabolic risk and productivity loss. Time-restricted eating (TRE) 12:12 is a mild intermittent fasting protocol that limits food intake to a 12-hour eating window and may be feasible for workplace implementation. This study aimed to evaluate the effect of a 30-day TRE 12:12 intervention on body weight and body composition among adult workers. A quasi-experimental one-group pretest–posttest study was conducted among adult workers in Semarang, Indonesia. Participants followed TRE 12:12 for 30 days without prescribed calorie restriction. Body composition was assessed before and after the intervention using bioelectrical impedance analysis. Changes in outcomes were analyzed using paired-samples t-test and Cohen’s d, while adherence and participants’ perceptions were summarized descriptively. After 30 days, body weight decreased by 2.38±1.97 kg, body mass index (BMI) by 0.90±0.70 kg/m², body fat by 1.08±1.23%, visceral fat level by 1.12±0.72, and waist circumference by 5.82±3.37 cm, with all changes statistically significant (p≤0.001). Skeletal muscle mass increased slightly by 0.36±0.55% (p=0.008), which was interpreted as muscle preservation rather than meaningful muscle gain. Overall adherence was high (98.1%), reported side effects were mild, and most participants perceived the intervention as beneficial. This study highlights that TRE 12:12 was associated with short-term improvements in body weight and body composition among adult workers, particularly reductions in visceral fat and waist circumference, while preserving skeletal muscle mass. Further studies with larger samples and longer follow-up are needed to confirm its effectiveness and sustainability in working populations.