Glycemic Index and Intramuscular Lipids

The storage of glucose as glycogen in muscle is dependent upon the dose and form of carbohydrate, and also the timing of ingestion. Low-glycemic index diets can reduce many risk factors linked to heart disease, diabetes, triglyceride levels and LDL cholesterol.^1,2,3 A combination of carbohydrate (CHO) and protein (PRO) after exercise may enhance the anabolic effect, compared to protein alone.

It has been reported that ingesting CHO and CHO/PRO immediately following exercise promotes a greater increase in insulin concentration compared to consuming PRO only, or compared to control groups. Additionally, subjects ingesting a CHO/PRO supplement following exercise had a greater increase in growth hormone than control subjects and those ingesting PRO alone.⁴ Researchers suggest that this increase in insulin and growth hormone concentration may facilitate a more favorable environment for recovery than CHO alone.

Other research has concluded that ingesting CHO and PRO— 2 hours before exercise and immediately following, during three consecutive days of resistance training— increased blood glucose, insulin, growth hormone, and IGF-1 to a greater degree than a placebo. Consequently, there is considerable evidence to support recommendations that athletes ingest CHO and PRO following exercise to optimize glycogen resynthesis, promote an anabolic hormonal environment, and increase PRO synthesis.⁵ I have spoken to many bodybuilders during their pre-contest prep, and most of them start to eliminate carbohydrates from their post-workout drinks as the contest approaches.

Intramuscular Lipids and Glycemic Diets

Bodybuilders have a difficult decision as to when to spike insulin— that is, if they want to build muscle. Studies that used carbohydrate supplementation during exercise have shown that it inhibits adipose tissue lipolysis and reduces non-essential fatty acid availability. In this month’s American Journal of Physiology— Endocrinology and Metabolism, researchers looked at different glycemic diets (high and low) and their effects on intramuscular lipids.

Unlike adipose tissue stored on your glutes or your stomach, intramuscular lipids (IMCL) are stored between muscle fibers. A high amount of intramuscular lipids are associated with metabolic alterations within muscle, such as changes in the cellular location of fatty acid transporter proteins, decreased mitochondrial enzyme activity, and defects in mitochondrial morphology— which likely contribute to obesity and insulin resistance. These defects are thought to play a role in the reduced skeletal muscle fatty acid oxidation and increased intramuscular lipid accumulation that is apparent with obesity and other insulin-resistant states such as type 2 diabetes. Regardless, high intramuscular lipids are associated with a host of health-related issues.  

High-Glycemic Diets Increase Intramuscular Lipids

Researchers assigned young men to a high- or low-glycemic diet after exercise, and examined the effects on intramuscular lipid storage. Carbohydrates were provided at 8 g/kg body mass, and protein and fat content constituted 11 percent and 17 percent of energy, respectively. Researchers found that consuming a high-glycemic diet after exercise resulted in a trend toward higher-starting intramyocellular lipids (IMCL) in the high-GI trial.

Despite these observations, an increased storage of IMCL in the high-GI trial would seem likely, as previous research has shown that consuming a high-GI meal following 90 minutes of exercise reduces fatty acid availability, compared to consuming a low-GI meal.⁶ The observation of a trend toward a higher pre-exercise IMCL content following a high-GI diet warrants further investigation, using an appropriate study design.

It is possible that the higher insulin levels characterizing the high-GI diet could also affect other sources of lipids (such as liver lipid release), although this also requires further study.

Taken together, these observations suggest that high-GI diets produce sustained effects on nonesterified fatty acid (NEFA) availability and intramuscular lipid oxidation during exercise, although the mechanism by which this happens remains to be studied. So if you are looking to burn more fat, switching to a low-glycemic diet may reduce the accumulation of intramuscular lipids and enhance fat oxidation.⁷

The study provides unique insight into the relationship between carbohydrate quality and lipid deposits during exercise. The data show that the amount of liver glycogen used during exercise is related to both the pre-exercise glycogen content and inversely related to the level of circulating fatty acids during exercise— the higher the starting level of glycogen and the lower the level of circulating fatty acids, the greater glycogen use during exercise.

References:

1. Pereira, MA, Swain, J, Goldfine, AB, Rifai, N, & Ludwig, DS. (2004). Effects of a low-glycemic load diet on resting energy expenditure and heart disease risk factors during weight loss. Journal of the American Medical Association, 24, 2482-2490.

2. Sloth, B, Krog-Mikkelsen, I, Flint, A, Tetens, I, Bjorck, I, Vinoy, S, Elmstahl, H, Astrup, A, Lang, V, & Raben, A. (2004). No difference in body weight decrease between a low-glycemic-index and a high-glycemic-index diet but reduced LDL cholesterol after 10-wk ad libitum intake of the low-glycemic-index diet. American Journal of Clinical Nurition, 80, 337-347.

3. Jimenez-Cruz, A, Bacardi-Gascon, M, Turnbull, WH, Rosales-Garay, P, & Severino-Lugo, I. (2003). A flexible, low-glycemic index mexican-style diet in overweight and obese subjects with type 2 diabetes improves metabolic parameters during a 6-week treatment period. Diabetes Care, 26, 1967-1970.

4. Chandler RM, Byrne HK, Patterson JG, Ivy JL. Dietary supplements affect the anabolic hormones after weight-training exercise. J Appl Physiol, 1994;76:839-845.

5. Conley MS, Stone MH. Carbohydrate ingestion/supplementation or resistance exercise and training. Sports Med, 1996;21:7-17.

6. Trenell MI, Stevenson E, Stockmann K, Brand-Miller J. Effect of high and low glycemic index recovery diets on intramuscular lipid oxidation during aerobic exercise. Br J Nutr, 99: 326-332, 2008.

7. Stevenson EJ, Thelwall PE, Thomas K, Smith F, Brand-Miller J, Trenell MI. Dietary glycemic index influences lipid oxidation but not muscle or liver glycogen oxidation during exercise. Am J Physiol Endocrinol Metab, 2009.

Sidebar:

Fat Oxidation During Exercise and Satiety During Recovery Are Increased Following A Low-Glycemic Index Breakfast

Consuming low-glycemic index carbohydrates before exercise results in increased fat oxidation during exercise in trained men and women. It is not known if this phenomenon occurs during low-intensity exercise and in untrained participants. Researchers examined the effect of eating breakfasts containing high-GI (HGI) or low-GI (LGI) foods on substrate utilization during rest and walking exercise in sedentary adults. The metabolic and appetite response to a standard lunch consumed after exercise was also investigated.

On each occasion, participants were provided with a HGI or LGI breakfast 3 hours before walking for 60 minutes. After exercise, participants were provided with lunch and remained in the laboratory for an additional 2 hours. Plasma glucose and serum insulin responses were higher following the HGI breakfast, compared to after the LGI breakfast. During the 3-hour postprandial (occurring after a meal) period, fat oxidation was suppressed following both breakfasts, but remained higher in the LGI trial. During exercise, total fat oxidation was also greater in the LGI trial. There were no differences in the metabolic responses to lunch. Participants reported feeling fuller following lunch in the LGI trial.

Consuming a LGI breakfast increases fat oxidation during subsequent exercise and improves satiety during recovery in sedentary adults.

Reference:

Stevenson EJ, Astbury NM, Simpson EJ, Taylor MA, Macdonald IA. Fat oxidation during exercise and satiety during recovery are increased following a low-glycemic index breakfast in sedentary women. J Nutr, 2009 May;139(5):890-7.

Credits: The information above is a word by word excerpt from MUSCULAR DEVELOPMENT.