Exercise fatty adds

The hydrolysis of TGs to FFAs and glycerol is catalyzed by a lipase in adipocytes called hormone-sensitive lipase. This enzyme catalyzes the hydrolysis of fat deposits in adipose tissue or wherever adipocytes arc found. The rate of liberation of fatty adds and of the byproduct glycerol from the adipose tissue may be greater than the rate at which they can be oxidized by other tissues. Under these conditions, the concentrations of FFAs and glycerol increase in the plasma. The data in Table 4.9 are from a study of human subjects who exercised on a stationaiy bicycle. Blood samples withdrawn during rest and at the indicated times during exercise show that FFA concentrations increased from 0 43 mM at rest to nearly 2.0 mM after 3 hours of work. 

Data presented in previous sections revealed that the concentration of FFAs in plasma may reach 2.0 mM during exercise. How is this possible when the highest attainable concentration in water is only about 0,1 mM This problem was resolved by nature by use of albumin as a vehicle for the transport of FFAs within the circulation. Albumin constitutes about 60% of the protein of blood plasma. It is a major carrier of FFAs, other metabolites, hormones, and drugs- Serum albumin has the capadty to carry several fatty adds. Figure 4.45 shows results from an experiment usingpurificdalbumin.Thenumberoffattyacid molecules bound per protein molecule is plotted versus the concentration of unbound fatty acids in solution. The study, conducted with lauric acid (12 carbons) and myristic add (14 carbons), demonstrates that one protein molecule is able to bind at least 8 or 9 molecules of fatty acid. Albumin has a molecular weight of 69 kDa and occurs in human plasma at a concentration of about 0.6 mM (40 mg/ml) (Halliwell, 1988). 

The material presented in the preceding sections concerns mainly carbohydrate metabolism during exercise. Before considering fatty add metabolism in exercise, a special carbohydrate should be covered — fructose. 

The Food and Drug Administration requires that processed foods list the content of trans fatty adds. A diet low in saturated and trans fatty adds is recommended, along with more fish, whole grains, fruits, and vegetables. The recommendation is also for daily exercise, which is tremendously benefidak regardless of diet. 

In addition to the use of fatty acids liberated from adipocytes, or obtained from the plasma as albumin-bound long-chained fatty adds or in very low-density lipoproteins (VLDLs), research indicates that the intramuscular triglyceride (IMTG) pool can serve as a dynamic fuel source during physical activity. Because no blood transport is required, intramuscular fatty acids can be readily used for energy in exercising muscle. A detailed discussion on IMTG can be found in Section 2.4.1. 

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