Obesity

Effect of a ketogenic diet, time-restricted eating, or alternate-day fasting on weight loss in adults with obesity: a randomized clinical trial

A 3-month randomized clinical trial (RCT) assessed the effectiveness of four dietary interventions compared to a calorie-restricted Mediterranean diet  in promoting weight loss in adults with obesity. The study enrolled 160 adults aged 18–65 with a BMI of 30–45 kg/m², excluding individuals with diabetes or other major comorbidities.

Participants were randomly assigned to one of five diet groups, each designed to create a daily energy deficit of 600 kcal:

• Mediterranean diet (MedDiet) – control group following a traditional meal plan and schedule.
• Ketogenic diet (KD) – very low in carbohydrates and high in fat, without time restrictions.
• Early time-restricted eating (eTRE) – meals consumed within an 8-hour window from 8 a.m. to 4 p.m.
• Late time-restricted eating (lTRE) – meals consumed within an 8-hour window from 2 p.m. to 10 p.m.
• Modified alternate-day fasting (mADF) – alternated between 3 low-calorie days (25–30% of energy needs) and 4 normal-calorie days each week.

Key Findings

• Weight loss: After 3 months, the following dietary strategies led to significantly greater weight loss than that observed in the Mediterranean diet group:
  • • Ketogenic diet (KD): −3.8 kg (8.3 lbs) greater weight loss
    • Modified alternate-day fasting (mADF): −3.14 kg (6.9 lbs) greater weight loss
    • Late time-restricted eating (lTRE): −2.27 kg (5.0 lbs) greater weight loss
    • Early time-restricted eating (eTRE): −1.22 kg (2.7 lbs) greater weight loss
• Body fat mass: All groups showed reductions in fat mass. Compared to MedDiet, significantly greater fat mass reduction was observed in eTRE and mADF.
• Lean mass: No significant differences between groups.
• Cardiometabolic markers (including glucose, lipids, and blood pressure): No significant differences across groups after 3 months.
• Ketosis:
  • • Highest ketone levels observed in KD and mADF.
    • eTRE and lTRE showed moderate increases in ketones, while MedDiet showed the lowest.

This RCT found that in adults with obesity, a ketogenic diet, time-restricted-eating, or alternate-day fasting resulted in greater short-term weight loss compared to a MedDiet with equivalent calorie restriction. These findings suggest that ketogenic and intermittent fasting strategies may offer effective alternatives for weight management, although long-term adherence and outcomes remain to be evaluated.