Morning to evening changes of intramyocellular lipid content in dependence on nutrition and physical activity during...

Intramyocellular lipids (IMCL) were shown to be metabolically highly active. In order to get insight into short-term regulation of IMCL and to reveal related problems with standardization in metabolic studies using the common signal ratio IMCL/Cr3, relative concentration changes from morning to evening in the same day were examined under four different nutritional and exercise conditions.

Twelve healthy male volunteers participated in an interventional program, comprising single days of fasting (F), low-caloric/low-fat diet (LC), or high-caloric/high-fat diet (HC), combined with low physical activity. A forth day course consisted of unchanged nutrition and extensive exercise (EX). (1)H-MRS of tibialis anterior (TA) and soleus muscle (SOL) was performed on a 3 T whole-body imager in the early morning and 12 h later after the intervention applying a single voxel STEAM technique.

Interventions resulted in a clear reduction of IMCL/ Cr3 after F (IMCL/Cr3(TA): -28.1 ± 4.9%, IMCL/Cr3(SOL): -21.0 ± 3.7%) and EX (IMCL/Cr3(TA): -33.9 ± 4.9%, IMCL/Cr3(SOL): -18.3 ± 3.9%). LC led to slightly decreased IMCL/Cr3 ratio in the evening (IMCL/Cr3(TA): -8.7 ± 4.4%, IMCL/Cr3(SOL): -7.3 ± 2.7%), whereas negligible changes were detectable after HC (IMCL/Cr3(TA): + 0.6 ± 2.3%, IMCL/Cr3L(SOL): -0.2 ± 1.3%).

Only high-caloric/high-fat diet combined with low physical activity led to nearly unchanged IMCL/Cr3 ratios in the evening when compared to corresponding measurements in the morning. In contrast, low-caloric/low-fat diet and especially fasting led to increasingly depleted IMCL stores in the evening. This depletion seems to be further emphasized by increased physical activity. An interesting aspect is the marked reduction of IMCL/Cr3 after 12 h of fasting, since a dramatic increase in IMCL has been reported after starvation over several days. Results of this study imply that highly standardized conditions regarding diet and physical activity are necessary for a proper assessment of IMCL data in metabolic studies.