Breakfast consumption does not rapidly increase liver or muscle glycogen content in well-trained cyclists

A carbohydrate-rich breakfast is commonly consumed by cyclists to compensate for an overnight decline in liver glycogen content and, as such, to maximize liver glycogen stores in the hours prior to exercise. However, the extent to which liver glycogen content increases in response to the intake of a carbohydrate-rich breakfast in well-trained cyclists remains unexplored. Twelve well-trained male cyclists (age: 25±5 y; V̇O 2 peak: 67±5 mL•min −1 •kg −1 ; W max : 5.8±0.7 W•kg −1 ) participated in this trial. Carbon-13 Magnetic Resonance Spectroscopy ( 13 C-MRS) at 7T and Magnetic Resonance Imaging (MRI) at 3T were applied to assess muscle and liver glycogen concentrations and volume, respectively, before and 3 hours after ingesting a carbohydrate-rich breakfast providing 3 g carbohydrates per kg body mass. Following breakfast ingestion, muscle glycogen concentrations, muscle volumes, and total muscle glycogen content did not change ( P>0.05). Liver glycogen concentrations increased by ~10% (from 164±30 to 180±33 mmol/L; P=0.036) whereas liver volumes decreased by ~6% (from 1.96±0.28 to 1.84±0.27 L; P<0.001) in the 3 hours following breakfast ingestion. Consequently, no net change in overall liver glycogen content was observed following breakfast ingestion (from 53±15 to 54±13 g; P =0.516). Ingesting a carbohydrate-rich breakfast (providing 3 g carbohydrates per kg body mass) does not elevate liver or muscle glycogen content during the subsequent 3-hour post-prandial period.