4. Discussion
RET
CHOLINE DEFICIENCY, LEAKAGE
The purpose of the present study was to determine the effects of different amounts of choline intakes on muscle responses to RET. We found that low choline intake (~51% of AI) resulted in diminished strength gains with 12 weeks of RET in 50-to-69-year-old individuals, compared to choline intakes of ~68% or ~118% of AI. We also observed that a high choline intake (greater than AI) did not provide additional positive effects on RET responses.It is well known that RET is important for the health and well-being of humans, especially for older individuals [Choline may affect muscle responses to RET through many potential mechanisms. Since choline is a precursor to a neurotransmitter, ACh, which relays a signal from motor neurons to skeletal muscle to contract and generate force, and of which synthesis is reported to be affected by availability of choline [Choline can also influence methylation reactions. A portion of choline is irreversibly converted to betaine, which is used to convert homocysteine to methionine, which is then used to generate Choline is also a precursor to PC, the predominant type of phospholipid in all cell membranes. Therefore, choline contributes to the stability and integrity of cell membranes, and choline deficiency results in weakened cell membranes and the leakage of intracellular enzymes into the circulation. Da Costa et al. [We did not observe any negative effects of low choline consumption on plasma CK concentrations. This may be explained by the difference in the amount of choline intakes between da Costa et al.’s study (<10% of AI) [We also examined the effect of choline intake on blood lipid profiles, since total blood cholesterol and LDL-C were previously reported to be positively associated with lean mass gains [It should be noted that our study results do not necessarily promote high consumption of choline. While the lower (~51% of AI) choline intake resulted in less strength gains, the higher (~118% of AI) choline consumption did not provide any additional training benefits in the present study. Therefore, more emphasis should be placed upon consuming an adequate amount of choline rather than encouraging a higher-than-necessary amount of choline intake. Choline is mainly found in animal-based foods such as eggs and meats, which generally contain high cholesterol [Our study has some limitations, including the inability to determine the mechanisms through which choline may affect RET responses. Since we consistently observed the effects of dietary choline (especially the negative effects of low choline intake [~50% of AI]) on muscle responses to RET, future studies should be focused on elucidating the mechanism(s) of those effects. Moreover, the well-known tendency to under-report food intake associated with diet logs may have obscured the accuracy of our data [