Why High Intensity Workouts Are Best for Weight Loss

May 5, 2015 Updated: May 5, 2015

When it comes to shedding unwanted pounds and reworking your fat-to-muscle ratio, high intensity interval training (HIIT) combined with intermittent fasting is the most effective strategy I know of.

Both of these strategies effectively boost your body’s fat burning capabilities; together they virtually force your body to shed fat. HIIT workouts have been shown to burn more calories than traditional workouts, and burns more body fat in less time.

According to the American College of Sports Medicine, HIIT workouts tend to burn anywhere from 6-15 percent more calories compared to other workouts, thanks to the calories you burn after you exercise. 

Improvements in Glucose Tolerance Restricted to HIIT

The superior effectiveness of HIIT has been confirmed by an ever-rising number of studies. In one of the latest studies looking at high intensity exercise for weight loss, 300 obese individuals were divided into three groups that exercised five times a week, doing either:

  • Low amounts (just over 30 minutes per session) of low-intensity exercise 
  • High amounts (just under one hour/session) of low-intensity exercise 
  • High amounts (40 minutes/session) of high-intensity exercise 

A control group was included, in which no one exercised. (It’s worth noting that the high intensity group was doing quite a bit more than I and other HIIT experts recommend. Recovery becomes more important when you do HIIT, and I strongly believe 40 minutes five times a week is highly counterproductive for most.)

At the end of six months, all three groups of exercisers saw similar reductions in weight and waist circumference. On the whole, those who exercised had lost five to six percent of their body weight at the end of the study, equating to a four to five centimeter reduction in waist circumference.

However, those who exercised at high intensity experienced a nine percent improvement in glucose tolerance. Neither of the two low intensity exercise groups saw any significant improvement in glucose tolerance. In fact, they remained on par with the control group, which did not exercise at all.

This is a noteworthy difference, as normalizing your glucose and insulin levels by optimizing insulin receptor sensitivity is one of the most important benefits of exercise, considering the fact that insulin resistance is a factor in most chronic disease, including diabetes and heart disease. 

Intense Exercise Also Produces Genetic Changes That Promote Fat Loss

High intensity exercise appears to produce its benefits via a number of different mechanisms. It’s quite likely we’ve not even identified all of them as of yet. 

For example, a study published in the journal Cell Metabolism5 in 2012, showed that when healthy but inactive people exercise intensely but briefly, it produces an immediate change in their DNA—some of which specifically promotes fat burning. 

As it turns out, intense exercise causes structural and chemical alterations to the DNA molecules within your muscles, and this contraction-induced gene activation leads to the genetic reprogramming of muscle for strength. 

But other genes affected by intense exercise are genes involved in fat metabolism. Specifically, this study suggests that when you do high intensity exercises, your body nearly immediately experiences genetic activation that increases the production of fat-busting proteins.

High intensity interval training (HIIT) has been shown to burn more calories than traditional workouts, and burns more body fat in less time (Shutterstock)

Identical Twins Reveal How Exercise Affects Health

While it’s virtually undeniable that exercise will alter your body composition and improve your health, a study involving twins—one of whom exercises and one of whom does not—makes for a fascinating case study of the health effects of exercise

The Finnish study, published in Medicine & Science in Sports & Exercise, included 10 sets of identical twins in their early to mid-30s. All of the twins began providing health and medical data starting at the age of 16, and every five years thereafter. As reported by the New York Times:

“The researchers were looking for young adult identical twins… whose exercise habits had substantially diverged after they had left their childhood homes… [E]ventually the researchers homed in on 10 pairs of male identical twins, one of whom regularly exercised, while the other did not, usually because of work or family pressures… 

The dissimilarities in their exercise routines had mostly begun within the past three years, according to their questionnaires… It turned out that these genetically identical twins looked surprisingly different beneath the skin and skull. 

The sedentary twins had lower endurance capacities, higher body fat percentages, and signs of insulin resistance, signaling the onset of metabolic problems. (Interestingly, the twins tended to have very similar diets, whatever their workout routines, so food choices were unlikely to have contributed to health differences.)

The twins’ brains also were unalike. The active twins had significantly more grey matter than the sedentary twins, especially in areas of the brain involved in motor control and coordination.” 

This study underscores just how quickly your body and brain can change, for better or worse, depending on whether or not you exercise. It also highlights the fact that you can indeed overcome any genetic predispositions you might have.