I’m sure you’ve heard all about Intermittent Fasting and all its touted benefits by weight loss “gurus” and experts” such as:
- Faster weight loss
- More energy
- Less hunger
- And more
However, are all of these claims really even true? Is there actually any scientific evidence that proves these claims?
Well, let’s not waste any time here.
What is Intermittent Fasting Anyway?
Well before we figure out if it works, we have to know a little bit about it. There are many versions of fasting out there, but the “intermittent” part of fasting, meaning occurring at regular intervals, is the most common form of fasting in the fitness realm, so that’s where we will focus our attention. This includes eating all of your meals within a 4-8 hour “feeding window” and fasting for the remainder of the day (Chaix et al. 2014).
The theory for this type of diet is that, with calories equated (equal to another group), it is more effective at fat loss and muscle mass maintenance/growth when compared to a standard calorie-restricted diet. However, the answer is not so black-and-white.
There’s no point to a diet if you can’t stick to it. In the scientific literature, we call this “adherence” or “compliance”.
In a 2016 study, subjects that were part of a fasting group ate less total calories than the traditional diet group over an 8 week time period. A questionnaire was given to participants of the fasting group after the conclusion of the study. The majority of participants claimed that the only difficulties that they had with adherence was during the weekend due to differences in one’s schedule and the social opportunities that presented themselves (Tinsley et al. 2016).
In a study concerning obese subjects, individuals became used to the fasting protocol in as little as 2 weeks (Johnstone, 2015). This used a fasting every other day approach, which is even more difficult to follow for most people. This was measured every fasting day by asking the subjects about their changes in perceived hunger, satisfaction with the diet, and satiety (feeling of fullness). The conclusion was reached after a majority of the subjects reported very little hunger on the fasting days. The data also illustrates that the subjects became increasingly satisfied with their diets after 4 full weeks. The only parameter to not increase significantly was the feeling of fullness; however, for obese subjects undergoing a caloric deficit, this is common.
Now, even though the focus here is primarily on athletic populations, the fact that significant amounts of adherence are seen in the obese is a great indicator for athletes to have success with this type of diet. This is because athletes are stereo-typically more determined than most populations, especially the obese, as it pertains to achieving their physical fitness goals. If obese subjects are able to adhere to a diet in as short of a time as 2 weeks, than the possibilities of success with this same type of diet for athletes looks positive.
Effects on Testosterone and Other Anabolic Growth Factors
One primary concern about beginning a fasting plan (particularly for men) is the effect fasting has on ones’ anabolic hormonal levels. Moro et al. (again, “et al.” means that others were included in the research besides Moro himself) discovered that after 8 weeks of fasting, the growth factors of insulin, IGF-1 (Insulin-Like Growth Factor 1), and testosterone decreased. However, no negative changes in body composition or muscular strength were detected when compared to the traditional calorie restriction group, which is a good sign. And this trend is seen across the board among various studies as well.
But Do You ACTUALLY Burn More Fat When Fasting?
A 2011 article in the Strength and Conditioning Journal describes the examination of stored body fat burning only during an exercise session itself as extremely shortsighted (Schoenfeld, 2011). The body is ever-changing and it continually adjusts its energy utilization due to a host of factors such as hormonal secretions, enzyme activity, etc. Ultimately, if one burns more carbohydrate during training, than fat will be utilized more greatly during the post-exercise period, and vice versa.
So unfortunately, the answer is no. There is simply not enough evidence out there to make a decisive answer to this question. However, the research shows that many people can better stick to this diet as compared to a traditional calorie-restricted diet. Therefore, it’s up to the person, if you can better stick to this diet compared to any other, then yes, this diet will help you burn more fat FOR YOU, but probably not for somebody else. Give it a shot, if you don’t like it, that’s okay, there’s definitely another diet out there for you. But as for the physiology behind it, no, there is nothing magical about it.
- Chaix, A. Zarrinpar, P. Miu, S. Panda (2014). Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges. Cell Metabolism, 20, pp. 991-1005
- Johnstone, A. (2014). Fasting for weight loss: An effective strategy or latest dieting trend? International Journal of Obesity, 39(5), 727-733. doi:10.1038/ijo.2014.214
- Schoenfeld, B. (2011). Does Cardio After an Overnight Fast Maximize Fat Loss? Strength and Conditioning Journal, 33(1), 23-25. doi:10.1519/ssc.0b013e31820396ec
- Tinsley, G. M., Forsse, J. S., Butler, N. K., Paoli, A., Bane, A. A., Bounty, P. M., . . . Grandjean, P. W. (2016). Time-restricted feeding in young men performing resistance training: A randomized controlled trial. European Journal of Sport Science, 17(2), 200-207. doi:10.1080/17461391.2016.1223173