Is the 5:2 fasting diet effective for weight loss?

In a Nutshell

  • The 5:2 fasting plan is less restrictive than modified alternate day fasting in that there are only 2 “fasting” (very low calorie) days per week
  • There must be at least 1 non-fasting day between the 2 fasting days
  • Can still result in intense hunger and other negative symptoms associated with low calorie intake on fasting days

The 5:2 plan, also known as the Fast Diet, is a variation of modified fasting. On non-fasting days – which is 5 days per week – you eat a normal, healthy diet. On the 2 “fasting” days, your consumption is limited to 500-600 calories and should be made up of high protein, high fiber foods to keep calories low and satisfaction as high as possible.

Lifestyle Impacts

Even with 500-600 calories permitted on fasting days, of which there are only 2 per week, on those days you can still experience:

  • Going to bed hungry, which may impact your ability to get a good night’s sleep.
  • Difficulty socializing, as 500 calories is spent very quickly.
  • Family dining complications, as children should not fast.

While the diet does encourage very low- to no-calorie liquids on fasting days to maintain hydration and combat hunger, many of these drinks have caffeine and intake should be monitored to avoid jitteriness, agitation, high heart rate or heart palpitations, and again – sleep disruption.

Since the schedule is not every other day, as with alternate day fasting and modified alternate day fasting, unless the fasting days are laid out in advance on a calendar that is readily visible, one can either miss getting 2 fasting days in per week or end up cramming them back-to-back in a last minute effort to meet the diet guidelines. That being said, some people find it easier to follow than continuous (or daily) calorie restriction.

Scientific & Expert Support

There is no certainty that modified fasting every other day or on a 5:2 schedule brings any health benefits or positively impacts weight management… With one very specific exception.

  • For weight loss, this diet is no better for overall health or weight loss than its older sibling, alternate day fasting, and is not superior to simply monitoring portion sizes.
  • However, for improving insulin sensitivity (in other words, reducing insulin resistance), studies of varying sizes and quality have been ongoing since the early 2000s and are indicating that it may be effective in this regard.

The only study on modified fasting for of any quality and duration in humans (12 months) demonstrated two major differences when compared to a standard daily calorie restriction group: 1) a higher drop-out rate in the fasting group and 2) an elevated LDL (bad cholesterol) in the 6 months after stopping the fasting diet. There was no difference in weight loss between the two groups and no other health benefits were found with this type of fasting.

Early human studies on alternate day fasting and modified alternate day fasting, mostly conducted between 2005-2013 that suggested positive impacts on weight management, asthma, seasonal allergies, heart arrhythmias, menopausal hot flashes and more, were small, of short duration, and have not had their results replicated.

Safety

You should not consider any form of fasting if you are pregnant, lactating, a person with diabetes, under 18, have a history of eating disorders, or are at risk for an unpredictable reaction due to your prescription medications. A good option for those who cannot fast is a transition to cleaner eating.

You should always consult with your physician, and ideally a registered dietician (RD) or nutritionist, before radically changing your diet or eating habits. Fitness experts are not a reliable dieting resource.

Strenuous exercise should be avoided during “fasting” periods.

STRENGTH OF EVIDENCE: C

Modified alternate day fasting was adopted to create the 5:2 approach. The only quality study of this approach to date had negative findings and failed to demonstrate superiority over mere portion control that leads to daily calorie restriction.

OUR RULING:

The 5:2 fasting plan to date has not been shown improve weight management, so if you are considering it for weight loss, consider an approach with more supporting evidence. 5:2 is showing promise, however, with regard to improving insulin sensitivity/reducing insulin resistance and might be considered for those who struggle with this issue.

OUR SOURCES:

  • Cleveland Clinic. (2020, April 30). Intermittent fasting: 4 different types explained. Cleveland Clinic – Nutrition. Retrieved from: https://health.clevelandclinic.org/intermittent-fasting-4-different-types-explained/
  • Gillinov, M. (2018, August 17). Dr. Mark Gillinov talks about alternate day fasting [Video file]. Fox News 8 Cleveland. Retrieved from: https://www.youtube.com/watch?v=3KH8wCH38eA
  • Harvard University – Harvard Medical School. (2020). Special health report – The diet review. Cambridge, MA: Harvard Health Publishing.
  • Mundi, M. (2020, April 21). What is intermittent fasting?Does it have health benefits? Mayo Clinic. Retrieved from: https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/intermittent-fasting/faq-20441303
  • Patterson, R.E., & Sears, D.D. (2017, August). Metabolic effects of intermittent fasting. Annual Review of Nutrition, 37, 371-393.
  • Trepanowski, J.F., Kroeger, C.M., Barnosky, A., Klempel, M.C., Bhutani, S., Hoddy, K.K., Gabel, K., Freels, S., Rigdon, J., Rood, J., Ravussin, E., & Varady, K.A. (2017, July). Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults: A randomized clinical trial. JAMA Internal Medicine, 177(7), 930-938.
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How we grade evidence?

Learn more about it here.