It is quite clear that for athletes, consuming protein and carbohydrate after a workout is crucial to recovery for subsequent sessions (replenish glycogen) and performance improvement. The doses of each macronutrient, as well as the inclusion of fat (which according to preliminary evidence, certain types of fat may further increase protein synthesis, and fat for endurance athletes may increase total energy intake and increase performance) is debatable for endurance exercise versus resistance training, of which will be explored in future posts.
But, should similar post-workout recommendations for athletes be adopted by casual exercisers, where the goal is health instead of maximizing performance? More importantly, should people with metabolic problems be chugging gatorade and the like after their workouts to replenish their glycogen?
A recent study by Newsom et al. (1) suggests that one marker of metabolic health, insulin sensitivity, is influenced by carbohydrate content that is consumed after exercise, and not total energy intake, and perhaps carbohydrate consumption should be kept low to maintain insulin sensitivity into the next day.
The study consisted of the following:
- 9 normal weight (BMI </= 25) sedentary men, average age 29+/-1 year with no history of metabolic or cardiovascular disease.
- 3 exercise trials (each 2 days) 7 or more days apart, exercising at a moderate intensity (60-65% VO2peak) for ~90 minutes (~45 minutes of treadmill exercise and ~45 minutes of cycle ergometer exercise) on the first day (roughly 800 kcal expended), and a number of metabolic tests were done on day two (VO2, VCO2, insulin sensitivity, intramuscular triglycerides). The exercise intensities and durations intended to reduce glycogen by ~55%.
- For the 4th trial, subjects were sedentary.
The post exercise meals were the following:
- -adequate carbohydrate and total energy to replace what was expended (BAL)
- -deficient in carbohydrate but total energy replaced what was expended (LOW-CHO)
- -adequate carbohydrate but deficient in total energy that didn’t replace what was expended (LOW-EN)
The meals were consumed a half hour, 3 hours, and 8 hours after exercise was completed (and a snack 11 hours after). The exercise was performed at 9:30am after an overnight fast and completed at 11:00am.
The total macronutrient breakdowns and energy over all meals are as follows (subjects were fasting going into the exercise):
Resting energy expenditure, exercise energy expenditure, and respiratory exchange ratio during exercise were similar among the 3 trials, as intended.
Insulin sensitivity was measured on the day after the exercise, and while elevated in all trials compared to the sedentary group, statistical significance was only achieved in the LOW-CHO compared to the control group. The LOW-EN and BAL groups (the same carbohydrate intakes, but different energy intakes) were similar, suggesting that carbohydrate is the important factor for insulin sensitivity.
In the LOW-CHO group, muscle glycogen was ~25% lower on the day after the exercise compared with CON, and in the BAL and LOW-EN groups, glycogen was similar to CON, suggesting that carbohydrate and not total calories is the important factor for glycogen replenishment.
Intramuscular triglycerides were similar in all groups on the day after exercise.
Palmitate rate of appearance and disappearance and oxidation were elevated in the LOW-EN trial compared to the CON.
Fasted plasma glucose, fatty acid, and insulin were similar the morning after exercise. Plasma triacylglycerol concentrations in the morning after were not effected by exercise in the BAL group, but they were significantly lower in the LOW-CHO trial compared to the other trials. Unexpectedly, triacylglycerol concentration in the LOW-EN group was significantly higher than the BAL group (with less fat and the same amount of carbohydrate).
The important findings for the study include the following:
- an energy deficit after 1 exercise session does not enhance the increase in insulin sensitivity to exercise
- a low carbohydrate consumption results in a lower muscle glycogen the next morning
- a low carbohydrate consumption results in an increased insulin sensitivity the next day
- insulin sensitivity improved even with an energy balance
The results confirm previous studies that suggest that when muscle glycogen is kept low, insulin sensitivity is maintained. A recent study by Holtz et al. found that the the greater the carbohydrate deficit, the greater the insulin action, except they did not find an effect when subjects were in an energy balance. However, as noted by the authors in this study, the carbohydrate intake was only 25% of total energy, compared to Holtz’s 50%. It is possible that there is some threshold of carbohydrate restriction necessary to maintain insulin sensitivity the next day when in an energy balance.
Additionally, this study found that with differing energy or carbohydrate contents, fasting plasma triacylglycerol concentration is affected the next morning (but not by exercise itself), which adds to our limited understanding of how nutrition alters this. As noted previously, the LOW-CHO trial suppressed triacylglycerol concentration, corroborating research showing that high carbohydrate diets elevate plasma triacylglycerol concentration.
Lastly, this may be support for low carbohydrate diets/ketogenic diets in combination with exercise for optimal improvement in metabolic markers of health, but further research is necessary.
Because fat had to be reduced in the LOW-EN trial and increased in the LOW-CHO trial, it may have influence on the results. However, fat is known not to have a great effect compared to carbohydrate on insulin. Also, because of the low subject number, statistical significance of some of the measurements may not be appropriately represented. Finally, hepatic glucose metabolism should be measured in subsequent studies along with the skeletal muscle to represent whole-body insulin sensitivity, and be conducted in other populations.
Studies will also have to elucidate whether any lack or difference in a change in insulin sensitivity is clearly associated with health risks or benefits, and if subsequent exercise sessions abolish any differences. Until then, with much research showing superiority of high fat, low carbohydrate diets for people with metabolic problems/diabetes on metabolic markers, it is my opinion that this research further supports a low carbohydrate diet in concert with exercise for optimizing metabolic health.
1. Newsom SA, Schenk S, Thomas KM, Harber MP, Knuth ND, Goldenberg N, & Horowitz JF (2009). Energy deficit after exercise augments lipid mobilization but does not contribute to the exercise-induced increase in insulin sensitivity. Journal of applied physiology (Bethesda, Md. : 1985) PMID: 20044472