Glycogen Depletion Patterns in Trained Rats Adapted to a High-Fat or High-Carbohydrate Diet

Male Sprague-Dawley rats (n = 48, > 200 g) were progressively treadmill trained over 5 wk where they were running 60 min/d, 5 d/wk. One-half of the group consumed a high-fat diet (HF, 78.7 % of energy), while one-half consumed a high-carbohydrate diet (HC, 68.7 % of energy). On the day of the experiment, 6 rats per diet were run at 29 m/min, 8 % grade for 0,10, 20, or 60 min. Immediately post-exercise rats were anesthetized, and soleus (S), red vastus lateralis (RV), and white vastus lateralis (WV) muscles were removed. There were no significant differences between diets for S glycogen pre-, during, or post-exercise. RV glycogen (μmol · g^-1 wet wt) was lower (p < 0.05) at rest for the HF (27.5 ± 3.9, Mean ± SEM) vs the HC (37.6 ± 3.5), but similar to HC at 60 min (11.0 ± 1.9, HF; 8.6 ± 1.3, HC). RV glycogen use rates (nmol · g^-1 · min^-1) were lower for the HF (985 ± 295, 356 ± 61) than the HC (1593 ± 144, 1055 + 272) for 0 - 10 and 11 - 20 min, respectively. Resting WV glycogen was lower for the HF (25.3 ± 1.6) vs the HC (40.7 ± 5.8), while post exercise values were similar (17.014.4, HF; 15.7 ± 2.0, HC). WV glycogen use was negligible from 0 - 10 and 11 - 20 min in the HF compared to the HC (280 ± 169 and 1601 ± 177 nmol · g^-1 · min^-1, respectively). These data indicate that muscle glycogen is spared during the early stages of prolonged exercise in HF adapted rats and that the sparing occurs according to expected muscle recruitment patterns.

Key words

Diet composition - dietary fat - dietary carbohydrate - endurance exercise - glycogen depletion - substrate utilization