Exercising in the Fat Zone: Truth or Myth?

by:  CarolAnn, M.S., CPT, CN

Many clients ask at what intensity they should exercise in order to achieve maximum weight loss results. Moreover, the question becomes more about if they should be in a fat-burning zone to achieve greater results. Much literature is publicized on the issue of exercising at a lower intensity to burn more fat while other information encourages those to exercise at a higher intensity to burn more calories. While both ends of the spectrum are true, here are the facts to help one better understand if exercising in the fat zone is truly more effective for losing weight.

Exercise Intensity Before addressing the fat zone, understanding proper exercise intensity is important. In simple terms, according to the American College of Sports Medicine, in order to improve cardiovascular respiratory function (CRF), one should exercise within a target heart rate zone of 70%-85% of his/her age-predicted maximum heart rate (HR) for 20-60 minutes 3-5 days per week. Maximum heart rate is defined as the maximum amount of times one’s heart can beat in one minute. To improve CRF, one should exercise within the proper target heart rate zone. To calculate your target heart rate zone, here is the formula:

220 – AGE = HR

HR X .70 = Low End of the Target Heart Rate Zone

HR X .85 = High End of the Target Heart Rate Zone


Example for a 35 yr old male:

220-35 = 185

185 X .70 = 130 beats per minute

185 X .85 = 157 beats per minute

To improve CRF, the above individual should exercise at an intensity level that will increase the heart rate between 130 and 157 beats per minute. Although there are other methods that take into consideration gender and resting heart rate, the preceding formula is the simplest calculation.

Oxygen Consumption and Carbon Dioxide Production During Exercise In order to determine if one is in the fat-burning zone or carbohydrate-burning zone, oxygen consumption and carbon dioxide are calculated. This is done by breathing through a special device while exercising. Oxygen consumption (VO) is measured by simply multiplying the volume of air breathed by the percentage of oxygen extracted. In addition, carbon dioxide (CO) is produced as the waste product that is exhaled and measured. The ratio of CO production (VCO) and VO at the cell is called the respiratory exchange ratio (R) which is an important measure in determining what type of fuel is being utilized during exercise.  Now that you know "R" Value, let's move on to the next level of understanding.

Fuel Utilization During Exercise The main nutrients from foods that are energy yielding are proteins, carbohydrates, and fats (buzz word-"macronutrients"). However, because protein contributes less than 5% to total energy production during exercise, the focus will be on carbohydrate and fat as the primary fuels for exercise. Carbohydrate is utilized in the form of muscle glycogen and blood glucose, derived from liver glycogen.  Fat is utilized in the form of free fatty acids from adipose tissue and intramuscular fat. The respiratory exchange ratio (R) can provide good information about metabolism of carbohydrates and fats during exercise by understanding the following observation. When R = 1.0, 100% of the energy utilized during exercise is derived from carbohydrates and 0% is from fat. When R = .70, 100% of the energy utilized during exercise is derived from fat and 0% is from carbohydrates. When R = .85, 50% of the energy is from carbohydrates and 50% is from fats. When calculating the R value, one must be in a steady state of exercise. In other words, the heart rate is stabilized. What is important to understand, is that when at rest, one is at a higher level of fat-burning. In other words, at rest, a typical R value is .8.

The Effect of Exercise Intensity Now that we have a basic understanding of proper exercise intensity and the R value, we can now determine at what point during exercise we are in the fat zone and carbohydrate zone. According to research, R increases at about 50% to 60% of HR which indicates that carbohydrates are becoming a more important fuel source. Before you take hold of that information and maintain a lower heart rate for the sake of remaining in a fat-burning state during exercise, it is important to understand that the muscles obtain about 6% more energy from each liter of oxygen when carbohydrates are used. In other words, more calories are burned when the R value is higher. In addition, research has shown that during prolonged exercise of around 90 minutes within an intensity level of 70%-80% of HR, R decreases over time, indicating a greater reliance on fat as fuel. Put into applicable terms, one burns more calories at a higher intensity in a shorter amount of time. In order to burn the same amount of calories at a lower intensity, one must exercise longer.

Real Life Application Because in real life, we are typically not hooked up to a special device to measure fuel utilization, there is no need to obsess over if you are burning more fat or carbohydrates. Remember, even at a resting state, you are burning more fat; therefore, more emphasis should be placed on burning more calories as opposed to the percentage of fat and carbohydrate utilization. The bottom line is, the more calories you burn, the more weight you are going to lose. Weight loss is about creating a caloric deficit on a daily basis through proper nutrition and exercise. Over time, as long as you can create a caloric deficit of about 500-1000 calories a day, you will lose about 1-2 pounds per week. One should not obsess about the fat-burning zone, because during exercise, you are never in a 100% state of fat-burning anyway. It is a combination of the two energy pathways that enables one to exercise. Exercise at an intensity level in which you are breathing heavy and can say short sentences. Aim for exercising at that intensity level for at least 30 minutes. Any extra time is bonus. In short, focus on moving more and eating less and the weight loss results will come.

To learn more about the Chiseled Faith program and start your health and fitness journey, visit www.ChiseledFaith.com

Live Happily Ever Fit,  

Carol Ann


About CarolAnn: CarolAnn, M.S., the creator of Chiseled Faith®, is a 25-year industry veteran holding positions such as program director, studio owner, educator, presenter, and author.  She has developed programs for organizations such as FiTOUR, Hydracize, MedFit Network, and PT Global.  Along with producing and starring in several fitness videos, she is a health and fitness expert contributor for publications such as Livestrong, PFP, and New Tampa Style Magazine.  She is currently on the Health Advisory Board for MedFit Network.  She has been selected to be a 2019-2021 National Fitness Hall of Fame Fitness Superstar.




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