P. Schrauwen et al., Increase in fat oxidation on a high-fat diet is accompanied by an increasein triglyceride-derived fatty acid oxidation, DIABETES, 49(4), 2000, pp. 640-646
The aim of this study is to investigate the mechanism behind the slow incre
ase in fat oxidation on a high-fat diet. Therefore, we determined 24-h subs
trate oxidation using respiration chambers and the rate of appearance and o
xidation of plasma-derived fatty acids in seven healthy nonobese men (age 2
3 +/- 2 years, height 1.85 +/- 0.03 m, weight 70.4 +/- 2.3 kg, % body fat 1
3 +/- 1). Before testing, they consumed a low-fat diet (30% fat, 55% carboh
ydrate) at home for 3 days. Measurements were performed after 1 day consump
tion of either a low-fat diet (LF), a high-fat diet (HF1, 60% fat, 25% carb
ohydrate), or a high-fat diet preceded by a glycogen-lowering exercise test
(HF1+EX), and after 7 days on a high-fat diet (HF7). After an overnight fa
st., an infusion of [U-C-13]palmitate (0.00806 mu mol . min(-1) . kg(-1)) w
as started and continued for 2 h at rest followed by 1 h of exercise at 50%
of maximal power output (W-max). Whole-body fat oxidation was measured usi
ng indirect calorimetry and plasma-derived fatty acid oxidation was evaluat
ed by measuring breath (CO2)-C-13 enrichment and corrected with the acetate
recovery factor. Twenty-four-hour fat oxidation gradually increased on the
high-fat diet. Both at rest and during exercise, there was no change in ra
te of appearance of fatty acids and plasma-derived fatty acid oxidation. Tr
iglyceride-derived fatty acid oxidation tended to be higher after 7 days of
high-fat diet at rest (P < 0.07). This difference was significant during e
xercise (P < 0.05). In conclusion, the results from this study suggest that
triglyceride-derived fatty acid oxidation VLDL or intramuscular triglyceri
des) plays a role in the increase in fat oxidation on a high-fat diet, but
plasma-derived fatty acids remain the major source for fat oxidation.