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Title: Gluconeogenesis during endurance exercise in cyclists habituated to a long-term low carbohydrate high fat diet

Author
item WEBSTER, CHRISTOPHER - University Of Cape Town
item NOAKES, TIMOTHY - University Of Cape Town
item CHACKO, SHAJI - Children'S Nutrition Research Center (CNRC)
item SWART, JEROEN - University Of Cape Town
item KOHN, TERTIUS - University Of Cape Town
item SMITH, JAMES - University Of Cape Town

Submitted to: Journal of Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2016
Publication Date: 2/26/2016
Citation: Webster, C.C., Noakes, T.D., Chacko, S.K., Swart, J., Kohn, T.A., Smith, J.A. 2016. Gluconeogenesis during endurance exercise in cyclists habituated to a long-term low carbohydrate high fat diet. Journal of Physiology. doi:10.1113/JP271934.

Interpretive Summary: Glucose is a key energy source for the human body and is an important fuel for endurance exercise. It can be derived from ingested carbohydrates, from stored glycogen and from newly synthesized glucose in the liver. The objective of this research was to determine whether athletes that habitually follow a low carbohydrate/high fat diet would have higher rates of new glucose synthesis in the liver during exercise compared to those that follow a mixed macronutrient diet. This study demonstrated that cyclists on low carbohydrate/high fat diet had lower rates of total blood sugar production and blood sugar derived from glycogen stores compared to those on the mixed diet. Both groups had similar rates of new glucose synthesis in the liver. Our findings indicate that the cyclists on a low carbohydrate/high fat diet did not compensate for reduced dietary carbohydrate intake by increasing glucose synthesis in the liver during exercise but rather adapted by altering fat and carbohydrate utilization. This study shows that the carbohydrate content of the diet influences the amount of glucose derived from glycogen stores and adapts the energy source during exercise condition.

Technical Abstract: Endogenous glucose production (EGP) occurs via hepatic glycogenolysis (GLY) and gluconeogenesis (GNG) and plays an important role in maintaining euglycemia. Rates of GLY and GNG increase during exercise in athletes following a mixed macronutrient diet; however these processes have not been investigated in athletes following a low carbohydrate high fat (LCHF) diet. Therefore, we studied 7 well-trained male cyclists that were habituated to either a LCHF (7% carbohydrate, 72% fat, 21% protein) or mixed diet (51% carbohydrate, 33% fat, 16% protein) for longer than 8 months. After an overnight fast, participants performed a 2-hour laboratory ride at 72% of maximal oxygen consumption. Glucose kinetics were measured at rest and during the final 30 min of exercise by infusion of [6,6-2H2]-glucose and the ingestion of 2H2O tracers. Rates of EGP and GLY both at rest and during exercise were significantly lower in the LCHF group than the mixed diet group (Exercise EGP: LCHF, 6.0 +/- 0.9; Mixed, 7.8 +/- 1.1 mg/kg/min, P < 0.01. Exercise GLY: LCHF, 3.2 +/- 0.7; Mixed, 5.3 +/- 0.9 mg/kg/min, P < 0.01). Conversely, no difference was detected in rates of GNG between groups at rest or during exercise (Exercise: LCHF, 2.8 +/- 0.4; Mixed, 2.5 +/- 0.3 mg/kg/min, P = 0.15). We conclude that athletes on a LCHF diet do not compensate for reduced glucose availability via higher rates of glucose synthesis compared to athletes on a mixed diet. Instead, GNG remains relatively stable while glucose oxidation and GLY are influenced by dietary factors.