Intermittent Fasting & Weight Loss

Question 1: Is intermittent fasting superior to continuous energy restriction (i.e. cutting down on kcals daily) for weight loss?

We should all expect that intermittent fasting (IF), if followed as prescribed, will lead to weight loss. This is NO different than any other diet out there. Calorie restriction leads to weight loss, and that holds true no matter what formatting of diet is followed: keto, standard daily calorie restriction, intermittent fasting, etc. The true question that we should be asking is whether intermittent fasting is superior to continuous energy restriction (CER) for weight loss. If you want the one-word answer based on literature to date, the answer is NO. It’s not. Sorry to say that we have not found some magic voodoo to help you lose weight more efficiently than focusing on calorie restriction, exercise, and choosing healthy, calorie-dense foods. But please, read on . . .

Numerous studies have demonstrated that there is no significant difference in weight loss between intermittent fasting and continuous energy restriction. I examined > 20 studies and the results were largely the same across the board. Of course, there are always exceptions, though those were few and far between. To date, there is no significant evidence to suggest that intermittent fasting is somehow superior to the more standard diet we have come to know and love (or hate). In a meta-analysis of 11 different studies, 9 demonstrated no significant difference in weight loss between IF and CER. Importantly, studies that were isocaloric, meaning that the calories consumed over the course of the week were matched between the IF and CER groups demonstrated no significant difference in weight loss at the end of the study (with duration > 8 weeks and up to 6 months).

I did find a couple of studies where weight loss in the IF group was greater than that of the CER group (and by greater, I mean < 5 lb. greater). However, these studies highlight some other important points. In one non-isocaloric study, individuals in the IF group lost on average 1.8kg (~4 lb.) more than the CER group over 6 months. However, on follow-up 6 months after the intervention ended, the CER group was able to maintain their weight loss whereas the IF group gained back a considerable amount. After 12 months, weight loss in the CER group surpassed that of the IF group. All of that to say that CER may be more sustainable than IF. To me, that makes sense. CER teaches better lifestyle habits. I can imagine very few people who have the mindset to do IF for life.

A few studies have also demonstrated that dropout rate is greater for IF as compared to CER. Reasons that individuals gave for dropping out of the IF group included: feeling faint, low blood sugar, constipation, or simply not being able to tolerate the diet. Again, this doesn’t seem surprising. Everything in moderation, even moderation. It would be much easier for me to cut down on calories by a small degree every day, rather than the extreme of eating very little or nothing at all a few days per week. But to each their own. We are all different.

One question you may have is whether individuals in the IF groups over-consumed food on their feeding (or non-restricted) days. Interestingly, that answer is no, and actually the opposite occurred. A few select studies found that individuals continued to restrict calories on their feeding days by as much as 25%. In one of these studies, weight loss in IF was superior to CER; however, due to this continued restriction on feeding days, the isocaloric aim was not met. Instead, the group that ate less (the IF group) lost a greater amount of weight. Are we sensing a commonsense theme yet?

A study on alternate day fasting similarly found that individuals ate more than prescribed on restricted days, and less than prescribed on their feeding days. With studies, we always examine prescribed vs. real-world circumstances. The prescribed intervention is the ideal; here meaning that the diet is followed 100% of the time. The real-world circumstance is how individuals actually apply an intervention. In this study, ADF became much more akin to CER due to restriction of kcals on feeding days and increased consumption on fasting days. How different these two interventions were at the end of the study is difficult to say, thanks to a little thing called human nature.

So why has IF gained so much popularity? Your guess is as good as mine. We are all different, and for some it may be easier to have strict black-and-white guidelines (for example, on Tuesday I eat, on Wednesday I fast or alternatively I can eat between 9 and 5). At the end of the day, it’s just another form of calorie restriction. And I’ve always been more of a shades-of-gray kind of gal.

So moral of the story? Figure out what works for you and stick to it. We need to stop thinking of “diet” as a temporary intervention to lose weight. Diet is how you eat on a daily basis; it’s a lifestyle. And when you figure out what works for you, that’s when you will be most successful.

More to come on IF in the next month > > > does it improve your blood pressure, lipid profile, insulin sensitivity? Though weight loss is similar to CER, could it be superior in other ways?

#weightloss #intermittentfasting #calorierestriction #embracemovement #faddiets #eathealthy #exercise #committofit #alternatedayfasting #timedrestrictedfeeding

Resources:

Antoni, R., Johnston, K. L., Steele, C., Carter, D., Robertson, M. D., & Capehorn, M. S. (2019). Efficacy of an intermittent energy restriction diet in a primary care setting. European Journal of Nutrition, 59(6), 2805-2812. doi:10.1007/s00394-019-02098-y

Cioffi, I., Evangelista, A., Ponzo, V., Ciccone, G., Soldati, L., Santarpia, L., . . . Bo, S. (2018). Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: A systematic review and meta-analysis of randomized controlled trials. Journal of Translational Medicine, 16(1). doi:10.1186/s12967-018-1748-4

Harris, L., Hamilton, S., Azevedo, L. B., Olajide, J., Brún, C. D., Waller, G., . . . Ells, L. (2018). Intermittent fasting interventions for treatment of overweight and obesity in adults. JBI Database of Systematic Reviews and Implementation Reports, 16(2), 507-547. doi:10.11124/jbisrir-2016-003248

Hutchison, A. T., Liu, B., Wood, R. E., Vincent, A. D., Thompson, C. H., O’Callaghan, N. J., . . . Heilbronn, L. K. (2018). Effects of Intermittent Versus Continuous Energy Intakes on Insulin Sensitivity and Metabolic Risk in Women with Overweight. Obesity, 27(1), 50-58. doi:10.1002/oby.22345

Mattson, M. P., Longo, V. D., & Harvie, M. (2017). Impact of intermittent fasting on health and disease processes. Ageing Research Reviews, 39, 46-58. doi:10.1016/j.arr.2016.10.005

Rynders, C. A., Thomas, E. A., Zaman, A., Pan, Z., Catenacci, V. A., & Melanson, E. L. (2019). Effectiveness of Intermittent Fasting and Time-Restricted Feeding Compared to Continuous Energy Restriction for Weight Loss. Nutrients, 11(10), 2442. doi:10.3390/nu11102442

Stockman, M., Thomas, D., Burke, J., & Apovian, C. M. (2018). Intermittent Fasting: Is the Wait Worth the Weight? Current Obesity Reports, 7(2), 172-185. doi:10.1007/s13679-018-0308-9