Why High Intensity Workouts Are Best for Weight Loss

High-Intensity Interval Training

Story at-a-glance -

  • High intensity interval training (HIIT) has been shown to burn more calories than traditional workouts, and burns more body fat in less time
  • In one study, HIIT was the only form of exercise that improved glucose tolerance. Low intensity exercisers had glucose tolerance on par with the control group, which did not exercise at all
  • Research comparing identical twins highlight the speed at which you can improve your health regardless of genetic predisposition. Active twins had greater endurance, lower body fat, and significantly greater gray matter in their brain

By Dr. Mercola

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.1

According to the American College of Sports Medicine,2 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.

The HIIT approach I personally use and recommend is the Peak Fitness method, which consists of 30 seconds of maximum effort followed by 90 seconds of recuperation, for a total of eight repetitions.

Super Slow strength training, as discussed in my previous interview with Dr McGuff, may even be more effective than Peak Fitness cardio. I’ll review both methods toward the end of this article.

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 studies3,4 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.

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,6 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:7

“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.

Add Intermittent Fasting to Really Maximize Weight Loss

While high intensity interval training is the best exercise to shed fat, intermittent fasting is by far the most effective way to lose weight overall. There are a number of different intermittent fasting regimens to choose from, and you may want to experiment to see which one fits your personal situation and temperament the best.

The version I recommend for those who are overweight is to simply restrict your daily eating to a specific window of time—ideally a window of eight hours or less. This means no calories at all during your non-eating window. You can have water, tea and coffee, but no milk or sugar added. While this is one of the most aggressive intermittent fasting regimens it also tends to be one of the easiest to comply with, and this, of course, is important for success. 

If daily fasting sounds intimidating, keep in mind that this does not have to be a permanent eating program. Once your insulin resistance improves and you are normal weight, you can start eating more frequently again. By then, you’ll have reestablished your body’s ability to burn fat for fuel, and that is the key to sustained weight management. Additionally, once your body has made this shift to burn fat rather than sugar as its primary fuel, sugar cravings will be a thing of the past, so even though you may eat more frequently, you’re far less likely to indulge in sugary junk.

Be Mindful of the #1 Driver of Obesity

Any discussion about weight loss would be incomplete without touching on food choices, as certain foods will effectively counteract, and possibly nullify, all your valiant efforts in the gym. The research is quite clear on this point: if you want to lose weight, you need to avoid processed fructose and other refined sugars. While excess sugar in general will pack on the pounds, fructose, such as the high-fructose corn syrup found in most processed foods, is by far the worst of the bunch.

Fructose actually breaks down in a manner that is similar to alcohol, and causes mitochondrial and metabolic dysfunction in the same way as ethanol. It also causes more severe metabolic dysfunction because it’s more readily metabolized into fat than any other sugar. Dr. Robert Lustig was one of the first to bring attention to the fact that processed fructose is far worse, from a metabolic standpoint, than other sugars, including refined sugar, but other researchers are now backing up his claims.

For example, a meta-review published in the Mayo Clinic Proceedings8 earlier this year confirms that all calories are in fact not equal. They also confirmed that sugar is the principal driver of both obesity and diabetes. As noted by lead author DiNicolantonio:9

“We need to understand that it isn’t the overconsuming of calories that leads to obesity and leads to diabetes. We need to totally change that around. It’s refined carbs and added sugars that lead to insulin resistance and diabetes, which leads to high insulin levels, which drives obesity.”

In another recent study10,11 female mice fed a diet in which 25 percent of calories came from corn syrup had nearly double the death rate compared to mice fed a diet in which 25 percent of calories came from sucrose (regular table sugar). Corn syrup-fed mice also produced 26.4 percent fewer offspring than those fed table sugar. According to senior author Wayne Potts,12 “this is the most robust study showing there is a difference between high-fructose corn syrup and table sugar at human-relevant doses.”

As a standard recommendation, I strongly advise keeping your total fructose consumption below 25 grams per day. If you have signs of insulin resistance, such as hypertension, obesity or heart disease, I suggest limiting your total fructose consumption to 15 grams or less until your weight and other health conditions have normalized. The easiest way to comply with these recommendations is to swap processed foods for whole, ideally organic foods.

This means cooking from scratch with fresh ingredients rather than relying on prepackaged fare. Be sure to check your condiments, dressings, and marinades as well, as many are absolutely loaded with fructose. My free nutrition plan offers a step-by-step guide to eating for optimal health.

Your Body Was Built for Brief, High Intensity Workouts

Getting back to exercise, the human body evolved performing very high-intensity activities for brief periods of time, and this kind of activity appears to be part and parcel of our genotype. Today, when recreating this ancestral activity, you have plenty of options. For example, you can perform high intensity exercises on an exercise bike or elliptical machine, or take the high intensity route to strength training. The primary difference between cardio HIIT and high intensity strength training is the degree to which you achieve muscular fatigue. As noted by super-slow strength training aficionado Dr. Doug McGuff:

“In evolutionary terms, high-intensity interval training is like being on the hunt and intermittently sprinting for your life for a short span of time, whereas high-intensity strength training would be like getting in a life-and-death wrestling match with someone almost perfectly matched to your capabilities. It would be a massive struggle with great fatigue.”

In essence, high intensity strength training gives you all the benefits that HIIT provides—including all the cardiovascular fitness benefits—but in addition to that, it also induces a rapid and deep level of muscle fatigue. This triggers the synthesis of more contractile tissue, the benefits of which include increased production of anti-inflammatory myokines that have a number of potent health benefits. Some of the latest research in high intensity exercise has found that these myokines—a class of cell-signaling proteins produced by muscle fibers—have the ability to combat diseases like metabolic syndrome and cancer. In the following video, I discuss and demonstrate some of the most important super-slow weight training principles.


Download Interview Transcript

Core Principles of High Intensity Interval Training

I recommend incorporating both forms of high intensity exercise into your fitness regimen, although either will work very effectively to boost your weight loss efforts. Following is a summary of what a typical peak fitness routine might look like using either an elliptical machine or stationary bike:

  1. Warm up for three minutes
  2. Exercise as hard and fast as you can for 30 seconds. You want to get your heart rate up to your calculated maximum heart rate. The most common formula for this is to subtract your age from 220. You should be gasping for breath and feel like you couldn't possibly go on another few seconds
  3. Recover for 90 seconds, still pedaling, but at slower pace and decreased resistance
  4. Repeat the high intensity exercise and recovery seven more times, for a total of eight repetitions

This routine requires a mere 20 minutes of your time from start to finish, and only four minutes of that is spent in “all out” exercise. I typically cool down for another three to five minutes, and use a functional parameter of my heart rate. I like to get my heart rate down to around 120 before I stop, which gives me enough time to recover. I highly recommend using a heart rate monitor when doing these exercises, as it is very difficult to accurately measure your heart rate without one.

If this is the only type of exercise you are doing, I suggest doing it two to three times a week. If you’re also doing strength training, let the strength training session count toward the total HIIT sessions. Ideally, you do not want to do more than three HIIT sessions per week, as recovery is an important part of the overall equation.



Diet, Exercise, and Intermittent Fasting Can Help You Beat the Bulge

To summarize, if you’re insulin/leptin resistant, have diabetes, high blood pressure, heart disease, or are overweight, I recommend limiting your total sugar/fructose intake to 15 grams per day until your insulin/leptin resistance has resolved. This applies to at least half of all Americans. For all others, I recommend limiting your daily fructose consumption to 25 grams or less to maintain optimal health. Remember that the number one source of hidden fructose is processed foods of all kinds, so one of the easiest ways to achieve your weight loss goals is to swap out processed foods for whole (ideally organic) foods. 

Next, start incorporating some high intensity exercises. If you’re currently sedentary, consider starting out by taking a daily walk. Even this simple strategy can be turned into a high intensity exercise by doing intervals of three minutes of fast walking followed by three minutes of slow strolling. In fact, I recommend walking more every day anyway, to counteract the ill effects of sitting. Ideally, aim for 7,000 to 10,000 steps per day, over and above any additional exercise. If you’re currently doing nothing in terms of fitness, do consider starting out by walking every day, as a bare minimum fitness goal.

As your fitness improves, move into the other HIIT exercises discussed above. Last but not least, consider intermittent fasting. Again, it can be a temporary strategy to “reset” your body to start burning fat rather than sugar as its primary fuel. An added boon is that once that switch occurs, you’ll naturally be less inclined to snack on junk food as your body will no longer be screaming for a sugar fix every few hours.

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