Does Interval Training (HIIT) 'Beat' Belly Fat?

This is how I got here. I first saw a post on Yahoo! News, "Beat Belly Fat With This 45-minute Running Workout," which brought me to another article by the same title. I noticed there had been 6,000 shares of this article in about 7 hours, and I know many would like to 'beat' belly fat, so I kept reading.

The article details a 45-minute running with 19 different 1-5 min intervals workout ranging from 4.0-7.5 mph, and estimated to expend 334 calories (for a 130 pound woman). It looks like a pretty tough workout, and many might enjoy it.

But, would it really 'beat' belly fat?

I was particularly interested in the statement, "Interval training is proven to blast belly fat," because,

(1) not only can we apparently 'beat' belly fat, but we can also 'blast' it, and

(2) I teach my students that in science, nothing is ever truly 'proven'.

There was a link, which brought me to another article within the same site, "The Secret to Losing Belly Fat."

The Research

This blog article cited a research study from the International Journal of Obesity, titled "High-Intensity Intermittent Exercise and Fat Loss". I downloaded the full article and read it...again. I say, 'again', because I had previously read this article, which was from 2011.

It is a review article, where many individual studies are reviewed and summarized for us, specifically on the short-term and long-term adaptations to high-intensity intermittent training (aka. HIIT).

What is HIIT?

Although HIIT can take many forms, it generally involves brief and intermittent bursts (or intervals) of vigorous aerobic exercise, such as sprints, mixed with intervals of rest or low intensity exercise, such as walking.

Effects on Abdominal Fat

Six studies measured changes in abdominal or trunk fat.

The studies ranged from 8-24 weeks. The majority of studies showed a little change in fat, ranging from 6% to 12% loss.

** For example, this study reported a decrease in abdominal fat after 15 weeks of HIIT, but the change was only 0.33 pounds.

Two studies showed much better results, with 44% and 48% loss of initial abdominal fat. Both studies' protocols were nearly identical, with 3 days a week of exercise for 8 weeks. However, only 1 day per week (of the 3 days) was dedicated to about 20-minutes of HIIE. These two studies also looked type 2 diabetic adults (mostly men) classified as highly overweight or obese.

Thus, we are unclear if the results were due to HIIT or the other exercise they did twice as much as HIIT. Also, perhaps such results are specific to type 2 diabetic adults (mostly men).

Visceral vs. Subcutaneous Fat

Also, the large 44% and 48% losses in fat were visceral, not subcutaneous, via MRI. Thus, we do not have how many pounds of fat that were lost.

Visceral is the fat inside the body around the organs (bad for health). Subcutaneous is the fat under the skin, that most of us are aware of, because we can see and touch it.

From a health standpoint, we are really excited in the large reduction in visceral fat from only 3 days per week. Great stuff.

However, the subcutaneous only saw a reduction of about 18% in both studies – and, subcutaneous fat loss is what most people are referring to when 'blasting' or 'beating' belly fat.

Total Weight Loss

Even though blasting belly fat is the topic of interest, the total body weight in these studies was minimal, ranging from 0.1% to 2%. Actually, other studies reviewed here, support the minimal effect of HIIT on total body weight loss.

So, Does Interval Training 'Beat' and 'Blast' Belly Fat?

No.

The majority of current research evidence supports that 8 to 24 weeks has little impact on abdominal or 'belly' fat – commonly, less than 1 pound of fat. By no means, is this minimal effect 'beating' or 'blasting' anything.

This is another classic case of 'click bait', where headlines use hyperbole to make us click on the article. Of course, such titles are misleading.

Hyperbole (noun): Exaggerated statements or claims not meant to be taken literally.

Other Notes

Now, do not think that HIIT is worthless. By no means, it can provide a number of other cardiovascular and health benefits in a limited time commitment. It might even provide greater aerobic fitness benefit than more continuous aerobic training (e.g. running on the treadmill for 45 minutes).

Also, not everyone is ready for high-intensity exercise, or will enjoy how it makes you feel. So, if you want to give it a try, proceed with caution, and see your doctor before jumping into something this intense.

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References

1. Boutcher, S. H. (2011). High-Intensity Intermittent Exercise and Fat Loss. Journal of Obesity, 2011, 868305. http://doi.org/10.1155/2011/868305
2. Trapp, E. G., Chisholm, D. J., Freund, J., & Boutcher, S. H. (2008). The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. International Journal of Obesity, 32(4), 684-691.