It’s important to realize that as a dedicated athlete who trains hard, what applies to the general population doesn’t necessarily apply to you. Misatakes are made when people, including researchers and physicians, extrapolate studies done on general populations to athletes. Sometimes it’s just plain wrong. An example of this can be seen in my article in the Education/Articles section of this site Athletes and the Cardiovascular System.
Another example that I haven’t as yet covered in an article, but soon will in detail, is the presence of fat in muscle cells. If you’re an athlete who takes your training seriously, you will have a significant amount of fat globules in your muscle cells. In the general population these fat globules, called intramuscular triacylglycerols (IMTG) are a result of a couch potato lifestyle and bad eating habits and contributes to insulin resistance, metabolic syndrome and diabetes. In other words IMTG are considered bad for your health.
However, in the case of athletes, and somewhat more so in endurance athletes, the presence of IMTG is present along with increased insulin sensitivity and are not indicative of a pathological condition. In fact increased IMTG levels are a positive factor for both health and athletic performance.
In those that follow my phase shift diets, fat is the primary fuel for generating energy, including energy needed for skeletal muscle contraction. In athletes, especially those that are fat adapted, IMTG are in direct contact with mitochondria and are a dynamic source of energy that is readily available and used first after ATP and phosphocreatine to provide needed energy. IMTG are used before stored glycogen and extracellular sources of fatty acids and glucose.
Along with following my phase shift diet, some targeted nutritional supplements also increase IMTG levels and the use of fat as a primary fuel. For example, I often recommend GHboost (see info on GHboost in the store) for various reasons. Among these are it’s effects on IMTG levels and use. A recent study found that growth hormone (GH) not only stimulates fat breakdown and the use of fat as a fuel, but it also increases the amount of fat in muscle cells.
Along with the known effects of GH on increasing lipolysis and fat oxidation, the increase in insulin sensitivity coupled with the presence of IMTG forms a powerful combination for the use of fat as a primary fuel for muscle contraction, including it’s use at higher intensities of exercise than is found in carb adapted power and endurance athletes.
Moro C, Bajpeyi S, Smith SR. Determinants of intramyocellular triglyceride turnover: implications for insulin sensitivity. Am J Physiol Endocrinol Metab. 2008 Feb;294(2):E203-13.
Krag MB, Gormsen LC, Guo Z, Christiansen JS, Jensen MD, Nielsen S, Jørgensen JO. Growth hormone-induced insulin resistance is associated with increased intramyocellular triglyceride content but unaltered VLDL-triglyceride kinetics. Am J Physiol Endocrinol Metab. 2007 Mar;292(3):E920-7.
Diabetes. 2011 Aug 26. [Epub ahead of print]
Skeletal-Muscle Triglycerides, Diacylglycerols, and Ceramides in Insulin Resistance: Another Paradox in Endurance-Trained Athletes?
Amati F, Dubé JJ, Carnero EA, Edreira MM, Chomentowski P, Coen PM, Switzer GE, Bickel PE, Stefanovic-Racic M, Toledo FG, Goodpaster BH.
OBJECTIVE Chronic exercise and obesity both increase intramuscular triglycerides (IMTGs) despite having opposing effects on insulin sensitivity. We hypothesized that chronically exercise-trained muscle would be characterized by lower skeletal-muscle diacylglycerols (DAGs) and ceramides despite higher IMTGs and would account for its higher insulin sensitivity. We also hypothesized that the expression of key skeletal-muscle proteins involved in lipid-droplet hydrolysis, DAG formation, and fatty-acid partitioning and oxidation would be associated with the lipotoxic phenotype.RESEARCH DESIGN AND METHODSA total of 14 normal-weight, endurance-trained athletes (NWA group) and 7 normal-weight sedentary (NWS group) and 21 obese sedentary (OBS group) volunteers were studied. Insulin sensitivity was assessed by glucose clamps. Intramyocellular triglycerides (IMTGs), DAGs, ceramides, and protein expression were measured in muscle biopsies.RESULTS DAG content in the NWA group was approximately twofold higher than in the OBS group and ~50% higher than in the NWS group, corresponding to higher insulin sensitivity. While certain DAG moieties clearly were associated with better insulin sensitivity, other species were not. Ceramide content was higher in insulin-resistant obese muscle. The expression of OXPAT/perilipin-5, adipose triglyceride lipase, and stearoyl-CoA desaturase protein was higher in the NWA group, corresponding to a higher mitochondrial content, proportion of type 1 myocytes, IMTGs, DAGs, and insulin sensitivity.CONCLUSIONSTotal myocellular DAGs were markedly higher in highly trained athletes, corresponding with higher insulin sensitivity, and suggest a more complex role for DAGs in insulin action. Our data also provide additional evidence in humans linking ceramides to insulin resistance. Finally, this study provides novel evidence supporting a role for specific skeletal-muscle proteins involved in intramyocellular lipids, mitochondrial oxidative capacity, and insulin resistance.