Understanding the mechanisms behind changes in fat metabolism that can occur as a result of various interventions and knowledge of the different sources of fat that can be used is important. The oxidation rate of lipids changes depending on the intensity of physical exercise and diet. Find outnow that you optimize fat burning through diet and exercise!
Physical exercise and fat oxidation
The rate of fat oxidation may vary according to the intensity of physical exercise. Therefore, it is possible to observe that changes in intensity induce changes in the use of the substrate. With the increase in the duration of exercise, fat oxidation increases progressively. The percentage of energy derived from CHO oxidation increases with increasing intensities, while the relative contribution of fat oxidation to total energy expenditure decreases.
Fat oxidation seems to peak in exercises with moderate intensities (45% to 65% of VO2max) and the intensity with which it occurs may depend on sex, training status, VO2max and diet. In exercises with higher intensities, however, fat oxidation is negatively regulated.
Thus, low to moderate intensity exercises are observed, with increased lipolysis, which increases the availability of fatty acids to muscles. This increased availability is accompanied by an increase in absolute rates of fat oxidation. However, when the intensity is increased, the oxidation of carbohydrates is markedly increased, while a decrease in fat oxidation is observed. In addition to the reduced availability of fatty acids, the reduced activity of CPT-I is indicated as the main factor responsible for the negative regulation of fat oxidation in higher intensity exercises.
Feeding and burning fat
Carbohydrate intake (CHO) before or during exercise can result in a marked reduction in fatty acid oxidation. The magnitude of the effect that CHO intake exerts depends on several factors, including type and quantity. In addition, another important factor is the timing of ingestion. When CHO is ingested before the beginning of exercise, the need for energy is significantly higher than during fasting. Fat oxidation suppression has been shown to be apparent in a wide range of exercise intensities. During low and moderate intensity exercise, CHO intake reduces fat oxidation compared to fasting conditions almost to the same extent as when CHO is ingested before exercise.
The effects of CHO intake on fat oxidation depend on a number of factors, including the timing of CHO intake and exercise intensity. However, in most conditions, cho intake decreases fat oxidation. When CHOs are consumed before exercise, large increases in insulin are observed, which affects the rate of lipolysis, thus decreasing the availability of fatty acids for oxidation. In addition, the effect of CHO intake is less when CHOs are ingested immediately before or 20 to 30 minutes after the start of exercise. However, when ingested during high intensity exercise, they seem to have no effect on fat oxidation.
With regard to fat burning, exercise intensity and duration are important determinants of fat oxidation. Fat oxidation rates increase from low to moderate intensity and then decrease when the intensity becomes high. In addition, carbohydrate intake in the previous hours or early exercise significantly reduces the rate of fat oxidation compared to fasting conditions, while fasting longer than 6 h optimizes fat oxidation.
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– Achten J, Jeukendrup AE. Optimizing fat oxidation through exercise and diet. Nutrition. 2004;20(7-8):716-727. doi:10.1016/j.nut.2004.04.005