Tools for Practice


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


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


BOTTOM LINE
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
“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 


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Author(s):

  • Adrienne J Lindblad BSP ACPR PharmD
  • Jessica Kirkwood MD CCFP
  • Natalie Holden BSc BScPharm

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.