Saturday, April 12, 2008

High Carb diet makes it harder to burn fat?

What do you make of this? (my understanding of this science is still developing, but Lyle McDonald's Stubborn Fat Loss Solution is helping a lot)

The study indicates that a short term high carb diet leads to a decrease in the amount of fat that is burned and an increase in the amount of fat that is stored in muscle and liver. That is not good.

UPDATE - thinking about it, I suppose this does make sense since (from Lyle) insulin impairs fat mobilisation and carbs drive insulin. So if the fat is not getting out of the fat cells you can't burn it.

Reduced oxidation of dietary fat after a short term high-carbohydrate diet.

BACKGROUND: Short-term high-carbohydrate (HC) diets induce metabolic alterations, including hypertriacylglycerolemia, in both the fasting and postprandial states. The underlying tissue-specific alterations in fatty acid metabolism are not well understood.
OBJECTIVE: We investigated alterations in exogenous and endogenous fatty acid metabolism by using stable isotope tracers to label meal triacylglycerol and plasma fatty acids.
DESIGN: Eight healthy subjects consumed isocaloric diets containing a high percentage of energy from carbohydrates or a higher percentage of energy from fat for 3 d in a randomized crossover dietary intervention study. A test meal containing [U-13C] palmitate was combined with intravenous infusion of [2H2] palmitate to label plasma fatty acids and VLDL triacylglycerol. Blood and breath samples were taken before the meal and for 6 h postprandially. Blood samples were drawn from the femoral artery and from veins draining subcutaneous adipose tissue and forearm muscle for monitoring of tissue-specific metabolic substrate partitioning.
RESULTS: Systemic triacylglycerol concentrations were increased in both fasting (P = 0.02) and postprandial (P = 0.02) periods, and a greater amount of infused labeled fatty acid appeared in VLDL triacylglycerol after the HC diet than after the higher-fat diet (P = 0.05). Significantly less 13CO2 was exhaled after the HC diet (P = 0.04) and significantly less production of 13CO2 was seen across forearm muscle (P = 0.04). Systemic 3-hydroxybutyrate was significantly lower, postprandially, after the HC diet (P = 0.02).
CONCLUSION: Metabolic alterations suggestive of repartitioning of fatty acids away from oxidation toward esterification in both liver and muscle occur in response to short-term adaptation to a HC diet.

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