Intermittent Fasting and High Intensity Interval Training

Intermittent Fasting and High Intensity Interval Training

Intermittent Fasting 101

Intermittent fasting (IF) is an eating strategy in which you fast for part of the day and consume all of your meals within a specified time period.  There are myriad ways to accomplish this.  The most common example is to eat all of your meals within an 8 hour window (12noon – 8PM), while fasting for 16 hours.

Many studies have shown that this is a very effective strategy for weight loss, along with enhancing health in a number of other ways, such as:

  • Normalizing your blood pressure
  • Normalizing LDL and total cholesterol levels
  • Reducing oxidative stress
  • Improving insulin sensitivity
  • Improving metabolic efficiency and body composition
  • Improving pancreatic function

Here is one example of a recent study showing favorable results Intermittent Fasting – Mini Fasting for Fat Loss.

For those who would like to learn more intermittent fasting and need some help getting started, please check out this awesome intermittent fasting calculator from my friends at FitnessVolt Intermittent Fasting Calculator

Exercising in a Fasted State

The combination of fasting and exercise maximizes the impact of cellular factors that force the breakdown of fat and glycogen for energy.  A study published in The Journal of Physiology Training in the fasted state improves glucose tolerance during fat-rich diet, showed good results for fasted exercise.  The researchers took 28 healthy men (ages 18-25 yrs) and divided them into 3 groups.

  • Group 1 exercised before eating a high carbohydrate breakfast, drinking only water during their workout.
  • Group 2 did the same as Group 1, but drank sugary drinks while working out.
  • Group 3 ate the same diet but did not exercise.

The exercise protocol consisted of running and cycling at a strenuous intensity 4 times a week.

Results:   Groups 2 and 3 gained weight (3-6 pounds) and developed insulin resistance (pre-cursor to Type II diabetes). Group 1, however, did not gain any weight and showed no signs of insulin resistance, thus concluding that fasting before working out was effective.

Keep in mind, however, that fasting or exercising in a fasted state, would be unwise if you continue to eat a diet full of processed foods. Addressing your diet is a critical step prior to venturing into any kind of fasting protocol. And it’s also important to note that when fasting, the foods to restrict should be mostly sugary and junky carbohydrates, NOT vegetables and fruits.

High-Intensity Interval Training

High Intensity Interval Training (HIIT) workouts involve repeated bouts of high-intensity effort followed by varied recovery times, ranging from five seconds to eight minutes long. These workouts are intense but over with quickly.  They can involve cycling, walking, swimming, running, bodyweight exercises, plyometrics and even weighted exercises.

HIIT workouts ramp up the heart rate fast and create a good lactic acid burn.  These workouts allow you to burn a lot of calories in a short amount of time, and studies show that HIIT workouts produce strong health benefits.

For additional information on some recent HIIT studies, read this High Intensity Interval Training (HIIT) – Latest Studies.

Combining Intermittent Fasting and HIIT

So, is it wise to combine IF and HIIT?  Conventional wisdom suggests that one must eat carbs to have enough energy to get through a workout.  However, in this case, that doesn’t really apply.  As mentioned above, HIIT workouts tend to be very short – ranging from 4 minutes – 20 minutes.  The vast majority of people have more than enough stored glycogen to do a short and intense workout without eating beforehand.

Some studies show that doing a HIIT workout in a fasted state will help to release more fat cells AND burn those fat cells more efficiently.  And this is the holy grail for fat loss. ​

3 thoughts on “Intermittent Fasting and High Intensity Interval Training”

  1. Then I read this: Research dating back to 1997 shows that moderate to high intensity exercise breaks down significantly more fat than the body can use for fuel, and so it’s simply reabsorbed.

    A more recent 2013 study testing subjects specifically performing HIIT demonstrates that there is “no significant differences between a fasted and fed state existed for any measurement.”

    Reply
  2. Fasting AFTER a workout may be more significant for fat loss since the body will need to replace the depleted liver and muscle glycogen from somewhere. If there is no new energy source on board (i.e. recent feeding), then it will have to go after fat stores.

    Reply

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