Debunking the Fat Burning Zone

Breaking down the barriers and setting the facts straight for optimizing fat loss

By: Chris Policastro, MS, CSCS

How many times do you walk into the gym, only to see rows of people trudging away on cardio machines for hours at a time, falsely thinking that they are blasting calories and burning fat? This is common practice, especially as warmer weather approaches. 

Are those seemingly endless overtures on the treadmill conducted at low intensities worth the investment?

Whether it’s the treadmill, elliptical or stationary bike, these machines typically have a “fat burning zone” setting. This zone, which still offers an adequate workout, can be quite misleading. If it were that easy to exercise at low intensity and see fat loss, wouldn’t we all be a lot leaner? Nothing is more discouraging than putting in hours in the gym week after week only to lose little or no fat. The average gym goer doesn’t know much about intensity levels and its impact on metabolism. These individuals read the labels on cardio equipment and see “fat burning zone” and think “Hey that’s what I’m after; this must be the best thing for me to do.”


This low intensity zone (50-80% of max heart rate) is often known as LISS “low intensity steady-state” cardio and it burns a greater percentage of fat calories than carbohydrates. This means that fat is oxidized as the primary energy source. However, the key here is ratio. At a low intensity, you burn approximately 50-60% of your calories from fat, and 40-50% from carbs. But, it’s the total number of calories burned (energy expenditure) that determines results.

LISS must be progressive and there is only so much duration you can add. Unless you have all the time in the world to jog on the treadmill, LISS cardio will not burn the number of total calories needed for fat loss. Although it does sound better to do LISS for the fact that it uses fat stores directly as the main source of energy, your body only burns those fat calories at that precise moment. When you’re looking for a shredded physique and muscle mass retention, HIIT (high intensity interval training) is the way to go.


Contrary to LISS, HIIT requires short spurts of high intensity (80-90% of max heart rate) and low intensity (think peaks and valleys). HIIT burns more total calories (60-65% from carbs and 35-40% from fat) for an equal amount of duration and will maximize fat loss due to the body using calories to repair damaged tissue post exercise. This after burn, also known as EPOC (excess post-exercise oxygen consumption), represents the additional calories your body will burn after the exercise session has been completed in order to return your body to its resting state.

If you want to see changes in your body, you have to increase your metabolism. One of the main reasons why HIIT is so beneficial for fat loss is because it increases your resting metabolism (your fat burning furnace). This 24-hour energy expenditure will burn more calories post exercise than LISS and will allow you to maintain your muscle mass because HIIT elicits a growth hormone response.


Let’s use an example to illustrate how this all works:

Let’s say you perform 30 minutes of LISS exercise and burn approximately 200 calories. Based on ratios about 120 of those, or 60 percent, come from fat. However, exercising for the same amount of time at a high intensity will burn approximately 400 calories. About 140 of those, or 35 percent, come from fat.  This shows that the high intensity workout burned a total of 200 calories more and an additional 20 calories came from fat.

While steady state cardio does have its benefits – especially for those who are very deconditioned, have medical or orthopedic issues, or are sport specific training – people should focus their time in the gym with HIIT to optimize fat loss. Your cardio program should not look like that of a marathon runner or you will definitely start to compromise your strength and muscle gains.

Keep in mind that you lose weight and body fat when you expend more calories than you consume, not because you burn fat at a certain ratio. So how do you optimize your time in the gym? There are hundreds of heart-pumping exercises out there for more efficient ways to burn fat. Crank up the intensity with these sample workouts!


Four Week HIIT Training Program:

Choose any mode of exercise: hill sprints, bike sprints, treadmill climbs, the rower, etc.

Week 1: work to rest ratio of 1:4. Complete 8 rounds.  (15 sec work, 1 min rest)

Week 2: work to rest ratio of 1:3. Complete 8 rounds. (30 sec work, 1:30 min rest)

Week 3: work to rest ratio of 1:2. Complete 8 rounds.  (30 sec work, 1 min rest)

Week 4: work to rest ratio of 1:1. Complete 8 rounds.  (30 sec work, 30 sec rest)

You may vary the amount of rounds; however, you should limit total time to 20-30 minutes to spare metabolic damage and strain on the CNS. Alternatively, you can remain at a certain phase for more than one week to suit your current level of fitness. However, if you feel like can do a ton of rounds, you probably aren’t keeping the intensity high enough.

This type of training will speed up your progress by maximizing fat loss and maintaining muscle mass. Try to do these HIIT workouts on non strength days and allow for proper recovery.


Another form of HIIT can be done with strongman exercises. This type of training really is the epitome of functional strength and will improve overall strength and conditioning. It can be used to train the anaerobic endurance system. Here is a sample routine:               Circuit: 3 rounds, 2-3 min rest between rounds

A1 Deadlift- 6-8 reps

A2 Tire Flips- 6-8 flips

A3 Sledgehammer strikes- 20 strikes

Circuit: 3 rounds, 2-3 min rest between rounds

B1 Squat- 6-8 reps

B2 Farmer’s Walk- 40 yards
B3 Clean & Press- 6-8 reps

Each exercise should take no longer than approximately 20-30 seconds to complete. Use appropriate loads that will not compromise form.




How does diet influence fat metabolism, and how should you eat around a HIIT cardio session?

In order to lose body fat, fatty acids must be mobilized or released (from resistance training or HIIT) from fat stores and sent to mitochondria, which are cellular organelles that convert nutrients into energy. You want to first create an energy deficit through limiting carbohydrate intake prior to the session. This will encourage your body to place a greater reliance on fat oxidation as opposed to burning sugar. The consequent stress on energy production will then stimulate an increase in mitochondria, which will allow for a greater rate of fat oxidation. As the saying goes, “Use it or lose it.” If you don’t give your body a reason to change through an appropriate level of stress, the mitochondria in your cells won’t change.

After an intense workout, the body’s immediate energy stores have been depleted. Without adequate nutrients to fuel the repair process, our muscle tissue is predisposed towards breakdown (catabolism). To counteract this, we must consume protein to help repair our damaged muscle fibers. Consider having either a protein supplement or protein-rich meal within 30-60 minutes of completing your session. This is important because amino acids are the building blocks of protein and will kick start protein synthesis in addition to limiting muscle protein breakdown.  Aim to ingest a daily total of 0.8-1 gram of protein per pound of lean body mass.

You need to periodize your diet just like you would your training to ultimately reach your goals.

Final Thought

For fat loss, what matters most is the difference between the number of calories you expend and the number of calories you consume. The total number of calories burned each day needs to be the main focus, not the ratio of fats and carbs. It matters little where the calories come from, as long as it’s not from protein! Focus your exercise program on resistance training and HIIT to keep your metabolism elevated and your hard earned muscle. Get comfortable with being uncomfortable!