http://www.nutritionandmetabolism.com/content/5/1/2

Does prior acute exercise affect postexercise substrate oxidation in response to a high carbohydrate meal?

Wiley Long III, Katherine Wells, Virginia Englert, Stacy Schmidt, Matthew S Hickey and Christopher L Melby

Nutrition & Metabolism 2008, 5:2doi:10.1186/1743-7075-5-2


Published: 27 January 2008 Abstract (provisional)

Background

Consumption of a mixed meal increases postprandial carbohydrate utilization and decreases fat oxidation. On the other hand, acute endurance exercise increases fat oxidation and decreases carbohydrate utilization during the post-exercise recovery period. It is possible that the resulting post-exercise increase in circulating nonesterified fatty acids could attenuate the ability of ingested carbohydrate to inhibit lipid oxidation. The purpose of this study was to determine whether prior exercise attenuates the usual meal-induced decline in lipid oxidation.

Methods

Six healthy, physically active young subjects (x age = 26.3 years, 4 males, 2 females) completed three treatments in random order after a ~10 h fast: (a) Exercise/ Carbohydrate (Ex/CHO): subjects completed a bout of exercise at 70% VO2peak (targeted net energy cost of 400 kcals), followed by consumption of a carbohydrate-rich meal; (b) Exercise/Placebo (Ex/Placebo): subjects completed an identical bout of exercise followed by consumption of a placebo; and (c) No Exercise/Carbohydrate (NoEx/CHO): subjects sat quietly rather than exercising and then consumed the carbohydrate-rich meal. Blood samples were obtained before and during the postprandial period to determine plasma glucose, insulin, and non-esterified fatty acids (NEFA). Respiratory gas exchange measures were used to estimate rates of fat and carbohydrate oxidation.

Results

Plasma NEFA were approximately two-fold higher immediately following the two exercise conditions compared to the no-exercise condition, while meal consumption significantly increased insulin and glucose in both Ex/CHO and NoEx/CHO. NEFA concentrations fell rapidly during the 2-h postprandial period, but remained higher compared to the NoEx/CHO treatment. Carbohydrate oxidation increased rapidly and fat oxidation decreased in response to the meal, with no differences in the rates of carbohydrate and fat oxidation during recovery between the Ex/CHO and NoEx/CHO conditions.

Conclusion

The plasma NEFA concentration is increased during the post exercise period, which is associated with elevated fat oxidation when no meal is consumed. However, when a mixed meal is consumed immediately following exercise, the initially elevated plasma NEFA concentration decreases rapidly, and postexercise fat oxidation during this 2-h postexercise, postprandial period is no higher than that of the 2-h postprandial period without prior exercise.

In English?

After exercise, the body continues to burn fat at a high rate. If you eat some carbs after the exercise, your body rapidly stops burning fat and goes into the glucose using mode.

LOL, thanks, Mike! I kind of got that from your title, but the science speak really got me.

Not surprising since carbs cause an insulin release. I doubt a low-carb protein shake has the same effects even if insulin is needed to build muscle.

I think that is correct,in the past i would grab a foot long sandwich from subway next door and feel sluggish but now I dont, i am still energized so i know something is working
I also notice i am getting more toned and defined,i lost 11 lbs but i can tell i am losing inches as well, so i think the fat is getting burned off

mike_d,

There is some new research that has come out that seems to show that insulin is not needed for muscle growth or in this case muscle growth in a low-glycogen invironment. Check out Art DeVany's post on the subject at:

http://www.arthurdevany.com/?p=810

I think he's saying what Taubes says, that fat cells stop releasing fatty acids when there's carbs ingested. The body prefers carbs for energy because it's immediate. Without carbs the fat cells continue to release fatty acids to be burned for energy. The conclusion is don't eat carbs after a workout and you'll continue to burn fat.

I always though Anthony Colpo's recommendation to consume simple carbs in the half hour after a WO to 'replenish glycogen reserves' sounded like nonsense. He argues that as long as you don't wait longer than half an hour, the carbs would go directly into glycogen replenishment and not interfere with fatburning. Seems like another intellectual crash and burn for my countryman.

Stuart

That sounds conceivable if glycogen stores are depleted like they would be generally on a LC plan, but not on a "normal diet." It takes the equivalent of ~40 slices of bread to refill liver and muscle glycogen so I would suspect a slice of apple or some berries, if desired post workout wouldn't matter much. Possibly the best post WO carb would be maltodextrin a complex starch and the digestion-resistant type is a soluble fiber.

So, am I correct in concluding that it's silly to drink an LC whey protein drink after a workout if I already have a nice roll of fat I want melted away? Actually, I guess the argument is that the whey protein goes directly to muscle development so I imagine it would have little impact on the body's fat burning.

Who is SuperMike, I have had friends call me that

mike_d

Here is Super Mike:

http://www.arthurdevany.com/?p=766

Just out of curiosity.. How long would you then have to wait to eat carbs after exercise?

I may be weird, but I never eat carbs after exercise. I just don't get the whole "you must replenish your glycogen stores" thing. I never replenish my glycogen stores, and I do just fine.