Fat Vs Carbohydrate Utilization During Exercise Calculator

The calculator on this page allows you to estimate, based on your exercise intensity level as measured by your heart rate, the relative contributions of fat and carbohydrates to your total energy expenditure during exercise. In other words, this calculator estimates the percentage of the total calories you burn during exercise that are derived from fat versus carbohydrates, based on your exercise heart rate.

Age (in years)
Heart Rate
(in beats/minute)

Important Note About Fat Versus Carbohydrate Utilization During Exercise

When we exercise, the energy that fuels our contracting muscles is derived almost exclusively from fats and/or carbohydrates (although protein does provide a very minor amount of energy at very high levels of energy utilization). The proportion of our total fuel consumption (i.e. calorie burn) that is derived from fat or carbohydrates is dependent on our exercise intensity level. It has been experimentally demonstrated that at lower exercise intensity levels (i.e. below roughly 65% of maximum heart rate for men or roughly 70% of maximum heart rate for women) fat is the dominant source of energy, but with increasing exercise intensity carbohydrates gradually become the dominant source of energy for contracting muscles. Therefore, as you increase your exercise intensity level the fuel for your muscles will become increasingly derived from carbohydrates and less derived from fat.
It is, however, important to understand that you won't necessarily burn more total fat by exercising at a lower intensity level. At a lower exercise intensity level a larger proportion of the calories that you burn will be from fat, but you will burn more total calories at a higher exercise intensity and, therefore, perhaps (depending on a number of variables) a larger total amount of fat. You can read the following article to learn more about this often misunderstood concept: The Fat-burning Zone Myth.

Method

This calculator is based on linear regression equations (shown below) derived by ShapeSense.com from experimental data gathered by MC Venables, J Achten, and AE Jeukendrup for their study titled "Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study." The experimental data gathered by Venables et al. measured carbohydrate and fat oxidation in both men and women at various levels of exercise intensity, where exercise intensity was measured as a percentage of VO2max.
Since the calculator on this page uses heart rate, rather than percentage of VO2max, as a measure of exercise intensity level, a correlation between heart rate and VO2max is used within the calculator to convert the heart rate input from users to a percentage of VO2max. Determination of maximum heart rate is based on the formula defined by H Tanaka, KD Monhan, and DG Seals in their study titled "Age-predicted maximal heart rate revisited." The correlation between percentage of maximum heart rate and percentage of VO2max that is used is a linear regression formula (shown below) derived by ShapeSense.com from experimental data gathered by DP Swain, KS Abernathy, CS Smith, SJ Lee, and SA Bunn for their study titled "Target heart rates for the development of cardiorespiratory fitness."
The experimental data points on which this calculator is based cover an exercise intensity level that ranges from between 41% to 61% of VO2max. The calculator will not provide an estimate of fat versus carbohydrate utilization below 41% of VO2max (or roughly 64% of maximum heart rate according to the Swain et al. correlation) because there is no experimental data available, and the trend does not seem to be easily extrapolated, below this intensity level. However, the calculator will provide an estimate of fat versus carbohydrate utilization up to 97% of VO2max (or roughly 100% of maximum heart rate according to the Swain et al. correlation), since the relationship between exercise intensity and fat versus carbohydrate utilization appears to be linear above 48% of VO2max for men and above 53% of VO2max for women. Therefore, any determination of fat versus carbohydrate utilization above 61% of VO2max (or roughly 77% of maximum heart rate according to the Swain et al. correlation) is based on an extrapolation (i.e. an assumption that the data correlation holds outside the limits of the gathered data points) of the experimental data rather than an interpolation.

Equations

Equation for Determination of Maximum Heart Rate Based on Age

Maximum Heart Rate (beats/minute) = 208 - (0.7 x Age)

Equation for Exercise Intensity Conversion from %MHR to %VO2max

%VO2max = 1.5472 x %MHR - 57.53

where

%MHR = Percentage of maximum heart rate

Fat and Carbohydrate Utilization Equations for Males

For 41% ≤ %VO2max < 48%:

F = -0.0497 x (%VO2max)² + 3.8528 x (%VO2max) - 23.55
CHO = 0.0497 x (%VO2max)² - 3.8528 x (%VO2max) + 123.55

For 48% ≤ %VO2max ≤ 97%:

F = -1.2746 x (%VO2max) + 108.24
CHO = 1.2746 x (%VO2max) - 8.24

where

F = Fat utilization as a percentage of total energy expenditure
CHO = Carbohydrate utilization as a percentage of total energy expenditure
%VO2max = Percentage of maximal oxygen consumption

Fat and Carbohydrate Utilization Equations for Females

For 41% ≤ %VO2max < 53%:

F = -0.0497 x (%VO2max)² + 3.8528 x (%VO2max) - 13.55
CHO = 0.0497 x (%VO2max)² - 3.8528 x (%VO2max) + 113.55

For 53% ≤ %VO2max ≤ 97%:

F = -1.59 x (%VO2max) + 135.11
CHO = 1.59 x (%VO2max) - 35.11

where

F = Fat utilization as a percentage of total energy expenditure
CHO = Carbohydrate utilization as a percentage of total energy expenditure
%VO2max = Percentage of maximal oxygen consumption

Swain DP, Abernathy KS, Smith CS, Lee SJ, Bunn SA. Target heart rates for the development of cardiorespiratory fitness. Med Sci Sports Exerc. January 1994. 26(1): 112–116.

Tanaka, H., Monhan, K.D., Seals, D.G., Age-predicted maximal heart rate revisited. Am Coll Cardiol 2001; 37:153-156.

Venables MC, Achten J, Jeukendrup AE. Determinants of fat oxidation during exercise in healthy men and women: a cross-sectional study. J Appl Physiol. 2005 Jan;98(1):160-7.