Tools for Practice Outils pour la pratique


#247 Fact or Fad: Intermittent fasting for sustained weight loss


CLINICAL QUESTION
QUESTION CLINIQUE
 Does intermittent fasting result in greater sustained (>6 month) weight loss than continuous dieting in adults?

BOTTOM LINE
RÉSULTAT FINAL
 Although inconsistently defined, intermittent fasting (example 500 kcal/day for 2 days/week) and continuous dieting (~25% reduction in caloric intake daily) result in similar weight loss, usually ~5-9kg at 6 months-1 year. Discontinuation rates with both diets is up to ~60%.


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EVIDENCE
DONNÉES PROBANTES
 “Fasting” generally refers to reducing caloric intake by ~75% of caloric needs/day; “continuous dieting” generally refers to reducing caloric intake by ~25%/day.  Systematic review of 9 randomized, controlled trials (RCTs) at least 6 months in duration, 981 patients.1 Example regimen: fasting 2 days/week interspersed with 5 days/week regular intake. After 6 months-2 years: 
  • No difference in mean weight loss. 
  • Mean weight loss range in both groups: 2.1-26.6 kg. 
6 RCTs published since above review, 24 to 332 patients, randomized to intermittent fasting (alternate day fasting, 2 days fasting with 5 non-fasting days/week, or weekly fasting) versus continuous dieting and/or no intervention control: 
  • 5/6 RCTs: mean weight loss ranged ~5-9 kg in both arms, not statistically different.2-6 
    • Best quality RCT, 100 patients, randomized to alternate-day fasting, continuous dieting, or no intervention control for 6 months.2 After additional 6-month follow-up: 
      • Weight loss between fasting and continuous dieting: no difference. 
        • Both diets lost ~6% more than no intervention. 
    • 1 RCT, 51 men, both groups decreased calories by 33%. Intermittent fasting (alternating 2-week blocks of fasting with regular diet) or continuous diet for 16 weeks.7 After 6-month follow-up: 
      • Statistically significant difference in weight loss: 11 kg versus 3 kg (continuous). 
      • Only patients who completed the study were included in the analysis. 
Context: 
  • Discontinuation rates 30-60%.1,3,4 
  • Weight loss for most diets peaks ~ 6 months,1 then slow regain.3,6,7 
  • No weight loss diet appears superior to another across populations, however individual results vary widely.8 
  • Mediterranean diet is the only diet that reduces cardiovascular disease.9 

Joseph Westgeest March 9, 2026

like any diet, rates of discontinuation are enormous, and that his only over the study period, not lifetime. Sustained lifestyle change best.

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Author(s)
Auteur(s)
  • Natalie Holden BSc BScPharm
  • Jessica Kirkwood MD CCFP
  • Adrienne J Lindblad BSP ACPR PharmD

1. Headland M, Clifton P, Carter S, et al. Nutrients. 2016; 8(324):1-12.

2. Trepanowski JF, Kroeger CM, Barnosky A, et al. JAMA Intern Med. 2017; 177(7):930-8.

3. Headland M, Clifton P, Keogh J. Int J Obes. 2018 Nov 23 (epub ahead of print).

4. Carter S, Clifton PM, Keough JB. JAMA Netw Open. 2018; 1(3):1-12.

5. Conley M, Le Fevre L, Haywood C, et al. Nutr Diet. 2018; 75:65.

6. Sundfǿr TM, Svendsen M, Tonstad S. Nutr Metab Cardiovasc Dis. 2018; 28:698-706.

7. Byrne NM, Sainsbury A, King NA, et al. Int J Obes. 2018; 42:129-138.

8. Ting R, Dugre N, Allan GM, et al. Can Fam Physician. 2018; 74(12):906.

9. Allan GM, Sharma AM, Lindblad AJ. Tools for Practice #46 online publication. Published April 16, 2015. Available at: https://gomainpro.ca/wp-content/uploads/tools-for-practice/1432830666_updatedtfp46dietforweightloss.pdf Accessed Sept 17, 2019.

Authors do not have any conflicts of interest to declare.

Les auteurs n’ont aucun conflit d’intérêts à déclarer.