Wednesday, March 13, 2019

Does intermittent fasting improve rate of weight loss?

Intermittent fasting has become a popular weight loss strategy in recent years. Many best-selling diet books advocate intermittent fasting as an efficient and natural way to lose weight that is more effective than conventional methods. A randomized controlled trial was recently published that compared an intermittent fasting protocol to a standard weight loss diet where calories where slightly reduced on a daily basis.

The Article
This randomized trial was conducted in Germany and was recently published in The American Journal of Clinical Nutrition (Reference 1). In this investigation, 150 overweight and obese men and women were randomized to one of two weight loss diet groups. The intermittent calorie restriction group (ICR) had a weekly schedule of 5 days without energy restriction and 2 days with an energy restriction that was 75% of usual calories. The goal of the continuous calorie restriction group (CCR) was to reduce calories by 20% each day.

There was a 12 week intervention phase, a 12 week weight maintenance phase, and an additional 26 week follow period for a total of 50 weeks of follow-up. By the end of the 12 week intervention, there was no significant difference in weight loss between the two groups. By the end of the 50 week follow-up, there was still no significant difference between groups in the amount of weight lost.

There were a few other notable findings:
-Physical activity was measured by means of an accelerometer at the start of the study and in Week 12. Levels of physical activity increased by .2% in the continuous calorie restriction group but decreased by 13.4% in the intermittent calorie restriction group.

-By the end of Week 12, fasting glucose had been reduced more in the continuous calorie restriction group than in the intermittent calorie restriction group (-7.6% vs. -2.9%). This difference was statistically significant.

-Five times as many subjects reported uncomfortable side effects in the fasting group compared to the daily calorie restriction group.

Other Research
Several other research publications I have covered in my blog showed negative outcomes with diets using intermittent fasting. These include: an increased LDL cholesterol, glucose dysregulation, increased inflammation, increased hunger and a decreased energy expenditure. If you want to reference these studies, please refer to my review of the Obesity Code (click here).

Conclusions And Recommendations
Despite its recent popularity, intermittent fasting does not appear to be a better weight loss strategy than moderate daily calorie restriction. In fact, it appears to have some real negatives. There is no reason to starve yourself in order to lose weight. I have found that the combination of a blood sugar stabilizing low glycemic load Mediterranean diet, adequate cardiovascular exercise and resistance training is absolutely the way to go if you want to lose weight, feel great and reduce your risk of today’s most deadly diseases.

1) Schubel R, et al. Effects of intermittent and continuous calorie restriction on body weight and metabolism over 50 weeks: A randomized controlled trial. American Journal of Clinical Nutrition 2018; 108:933-45.


Unknown said...

Tom, unfortunately this study does not really study intermittent fasting. The method of IM that most people use is not the 5 and 2 day method but rather using a shorter eating window every day. So usually it's an 18/6 or 16/8 type scenario where you fast for 18 hours and eat within the 6 hours only. This is the true model of Intermittent fasting. Additionally, the recommendations include no sugar, and no snacking, 2 things I know you will approve of! Look at some of the studies using this model before condemning IM. Those other studies use a flawed system of IM.

Dr. Thomas Halton said...

Thanks for commenting on my post Elizabeth,
I have just a few thoughts:

-I am not anti-fasting. I have an open mind when reading the research literature. My recommendations are research based. I am always looking for any possible way to help my clients attain their weight loss goals efficiently and safely. This is a big reason why I read the nutrition literature each and every month.

-Having said this, the study in the above post is now the 4th investigation appearing in what I consider top journals that showed either: 1) No increased weight loss with intermittent fasting compared to conventional methods. 2) Potential harm to various metabolic measurements, or 3) Results that would make weight regain more likely than conventional methods.

-You may have a good point about the fasting strategy. The 4 studies mentioned above use a variety of methods of intermittent fasting. Rest assured, if a well designed study in a reputable journal publishes a paper using the strategy you speak of, I will cover it on this blog, for sure.

-I love the idea of no sugar and no snacking. In my opinion, they are both critical if lasting weight loss is the goal.