Question

How is the usage of fat as an energy source regulated, and what would you expect to be the effect of caffeine or theophylline on fatty acid mobilization?

Answer 1

The Fatty acids are most abundant source of endogenous energy substrate. They can be mobilized from peripheral adipose tissue and transported via the blood to active muscle.

During higher intensity exercise, triglyceride within the muscle can also be hydrolyzed to release fatty acids for subsequent direct oxidation.

The process of lipolysis normally provides free fatty acids (FFA) at a rate in excess of that required to supply resting energy requirements.The large increase in FFA turnover after caffeine ingestion was probably due to the combined effects of caffeine on β-adrenergic lipolytic stimulation and on antagonism of the antilipolytic effects of adenosine.

The result of caffeine on lipid mobilization in resting situations can be taken in two ways:

• lipid mobilization is inadequate to drive lipid oxidation.
• large increments in lipid turnover result in small growths in lipid oxidation.

the mechanism of control of fatty acid oxidation in the muscle is the rate of entry into the mitochondria. generally the rate of glycolysis is the predominant regulator of the rate of carbohydrate metabolism in muscle, and that a rapid rate of carbohydrate oxidation caused by mobilization of muscle glycogen during high intensity exercise prevents fatty acid oxidation by preventive transport into the mitochondria

Caffeine ingestion enlarged energy expenditure 13% and doubled the turnover of lipids, of which 24% were oxidized and 76% were recycled