Primary, Secondary, and Tertiary Effects of Carbohydrate Ingestion During Exercise.
Ian Rollo, Javier T Gonzalez, Cas J Fuchs, Luc J C van Loon, Clyde Williams
Author Information
Ian Rollo: Gatorade Sports Science Institute, PepsiCo Life Sciences, Global R&D, Leicestershire, UK. Ian.rollo@pepsico.com. ORCID
Javier T Gonzalez: Department for Health, University of Bath, Bath, UK.
Cas J Fuchs: Department of Human Biology, NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, The Netherlands.
Luc J C van Loon: Department of Human Biology, NUTRIM School of Nutrition and Translational Research in Metabolism, Maastricht University Medical Centre+, Maastricht, The Netherlands.
Clyde Williams: School of Sports Exercise and Health Sciences, Loughborough University, Loughborough, UK.
The purpose of this current opinion paper is to describe the journey of ingested carbohydrate from 'mouth to mitochondria' culminating in energy production in skeletal muscles during exercise. This journey is conveniently described as primary, secondary, and tertiary events. The primary stage is detection of ingested carbohydrate by receptors in the oral cavity and on the tongue that activate reward and other centers in the brain leading to insulin secretion. After digestion, the secondary stage is the transport of monosaccharides from the small intestine into the systemic circulation. The passage of these monosaccharides is facilitated by the presence of various transport proteins. The intestinal mucosa has carbohydrate sensors that stimulate the release of two 'incretin' hormones (GIP and GLP-1) whose actions range from the secretion of insulin to appetite regulation. Most of the ingested carbohydrate is taken up by the liver resulting in a transient inhibition of hepatic glucose release in a dose-dependent manner. Nonetheless, the subsequent increased hepatic glucose (and lactate) output can increase exogenous carbohydrate oxidation rates by 40-50%. The recognition and successful distribution of carbohydrate to the brain and skeletal muscles to maintain carbohydrate oxidation as well as prevent hypoglycaemia underpins the mechanisms to improve exercise performance.
