This study showed that the 4-week CAJ supplementation increased fat contribution and decreased CHO contribution to total energy expenditure during high-intensity exercise in both the trained and untrained subjects, with a greater change in the trained subjects.
It should be noted that this study assessed whole-body substrate utilization. Therefore, the changes in specific sources of energy used cannot be defined. Normally, at high-intensity exercise, oxidation rates of muscle glycogen and plasma glucose increase and those of both plasma free fatty acids and triacylglycerol fat sources (sum of intramuscular plus lipoprotein-derived triacylglycerol) decrease . The reduction in fat oxidation is most likely due to a downregulation of carnitine palmitoyltransferase I, which may be due to a decline in intracellular free carnitine availability or pH. The supplementation with CAJ may enhance fat oxidation via the effect of one of its constituents, vitamin C [6, 7], on carnitine synthesis . Vitamin C acts as a co-factor for two necessary enzymes, ε-N-trimethyl-L-lysine hydroxylase and γ-butyrobetaine hydroxylase, which are required for the biosynthesis of carnitine [20, 21], an important co-factor in fat oxidation in skeletal muscle .
In addition, leucine, another constituent of CAJ, appears to have considerable effects on energy metabolism [10, 11, 22]. It induced a significant increase in fat oxidation in C2C12 muscle cells  and rats  via an improvement in mitochondrial oxidative function. Leucine also affects adipose tissue, reducing fatty acid synthase expression in human adipocytes . A previous study showed that supplementation with leucine increases hepatic and muscle glycogen concentrations immediately after exercise  suggesting greater fat use during exercise .
The current study did not find any changes in blood glucose and lipids, which are also energy sources for active muscle during exercise. The unaltered concentrations of blood glucose after the supplementation of CAJ in this study may be because subjects were healthy. During exercise, blood glucose concentration must be maintained by hepatic glycogenolysis and gluconeogenesis, as they are energy sources for the brain . Increases in glucagon and catecholamine are apparently responsible for such maintenance .
Another component of CAJ, the anacardic acids , are worth considering but were not analyzed in this study. Dietary anacardic acids at 0.1% w/w have been shown to decrease body fat deposition in rat liver, possibly due to an uncoupling action of the anacardic acids on mitochondrial oxidative phosphorylation . If such a mechanism functions in human subjects, it may contribute to the increased fat utilization after the ingestion in CAJ of this study.
The enhanced fat oxidation rate in this study could be beneficial for endurance performance by providing energy for the muscle and sparing intramuscular glycogen for possible use in the later stages of competitive sports, e.g., long distance running and swimming.
The enhanced effect on fat utilization during exercise seems to be important for some populations, particularly Thai people. Janyacharoen et al.  demonstrated that during exercise at all intensities CHO played a more important role as an energy source than fat. This may be a significant reason for the lower endurance capacity of Thais compared to Caucasian athletes, affecting Thai championship status. Therefore, CAJ ingestion has a potential advantage of bringing Thai sport players to success on the scale of world competition. In addition, quantitative measurements of anacardic acids or other antioxidants in the CAJ, e.g., phenolic compounds, will provide more information of other ingredients in the CAJ that may have an effect on lipid metabolism.