Ingestion of carbohydrate or carbohydrate plus protein does not enhance performance during endurance exercise: a randomized crossover placebo-controlled clinical trial

Appl Physiol Nutr Metab. 2018 Sep;43(9):937-944. doi: 10.1139/apnm-2017-0835. Epub 2018 Mar 15.


A beverage containing protein (PRO) and carbohydrate (CHO) may have an ergogenic effect on endurance performance. However, evidence regarding its efficacy on similar conditions to athletes' race day is still lacking. The objective of this study was to compare the effects of 3 different nutritional supplementation strategies on performance and muscle recovery in a duathlon protocol. Thirteen male athletes (29.7 ± 7.7 years) participated in 3 simulated Olympic-distance duathlon trials (SDTs) under 3 different, randomly assigned supplementation regimens: CHO drink (75 g CHO), isocaloric CHO plus PRO drink (60.5 g CHO and 14.5 g PRO), and placebo drink (PLA). Supplements were offered during the cycling bout. Blood samples were collected before, immediately after, and 24 h after each SDT for creatine kinase (CK) analysis. Isometric peak torque (PT) was measured before and 24 h after each SDT. The primary outcome measure was the time to complete the 5-km running section (t5km) at a self-selected pace. There was no difference in t5km between CHO (1270.3 ± 130.5 s), CHO+PRO (1267.2 ± 138.9 s), and PLA (1275.4 ± 120 s); p = 0.87, effect size (ES) ≤ 0.1. Pre-post changes for PT and CK were not significant for any of the 3 conditions (PT: p = 0.24, ES ≤ 0.4; CK: p = 0.32, ES = 0.3-1.04). For endurance sports lasting up to 2 h, with a pre-exercise meal containing CHO at 1.5 g·kg-1, supplementation with CHO or CHO+PRO does not offer additional benefits for performance and muscle recovery when compared with PLA.

Keywords: course; cycling; cyclisme; dietary supplements; performance sportive; running; sciences de la nutrition sportive; sports nutrition science; sports performance; suppléments nutritifs.

Publication types

  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Athletes
  • Athletic Performance / physiology*
  • Beverages
  • Bicycling / physiology
  • Creatine Kinase / blood
  • Cross-Over Studies
  • Dietary Carbohydrates / administration & dosage*
  • Dietary Proteins / administration & dosage*
  • Double-Blind Method
  • Humans
  • Male
  • Physical Endurance*
  • Running / physiology
  • Sports Nutritional Physiological Phenomena*
  • Torque
  • Young Adult


  • Dietary Carbohydrates
  • Dietary Proteins
  • Creatine Kinase