Despite the common misconception that meat gives us energy, hard-working muscles run primarily on glycogen, a form of carbohydrate stored in our liver and muscle. Carbohydrates, which come almost exclusively from plants, also provide our brain with its primary and preferred fuel — glucose — which helps us stay sharp and focused during intense training sessions, competitions (1), or long days at work or at home (2).
Performance-based diets built around meat and other animal products often provide dietary fat at the expense of carbohydrates (3-6). Unlike carbohydrates, fat can’t produce energy fast enough to meet the demands of intense exercise, so diets that sacrifice carbohydrates typically impair high-intensity performance (1). Low-carbohydrate diets, including the ketogenic (keto) diet, have been shown to cause so much fatigue that they even affect our motivation to begin a training session, let alone finish it (7-9).
Protein can also be used as a fuel source, but it’s highly inefficient, wasting 20-30% of each calorie as heat (10).
All told, carbohydrates are the ideal source of energy for optimized performance, whether it’s doing squats, playing football, or running a marathon.
And as we discuss in Getting and Staying Lean, despite the common misconception that “carbs make you fat”, unrefined carbohydrates — like those found in whole plant foods, including oats, sweet potatoes, and bananas — are consistently associated with decreased body fat, another advantage for most performance and fitness goals.
(1) Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and Athletic Performance. Med Sci Sports Exerc. 2016 Mar;48(3):543-68.
(2) Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002.
(3) Kanter M. High-Quality Carbohydrates and Physical Performance: Expert Panel Report. Nutr Today. 2018;53(1):35-9.
(4) Masson G, Lamarche B. Many non-elite multisport endurance athletes do not meet sports nutrition recommendations for carbohydrates. Appl Physiol Nutr Metab. 2016 Jul;41(7):728-34.
(5) Clark M, Reed DB, Crouse SF, Armstrong RB. Pre- and post-season dietary intake, body composition, and performance indices of NCAA division I female soccer players. Int J Sport Nutr Exerc Metab. 2003 Sep;13(3):303-19.
(6) Jenner SL, Buckley GL, Belski R, Devlin BL, Forsyth AK. Dietary Intakes of Professional and Semi-Professional Team Sport Athletes Do Not Meet Sport Nutrition Recommendations — A Systematic Literature Review. Nutrients. 2019 May;11(5):1160.
(7) Butki BD, Baumstark J, Driver S. Effects of a carbohydrate-restricted diet on affective responses to acute exercise among physically active participants. Percept Mot Skills. 2003 Apr;96(2):607-15.
(8) Keith RE, O’Keeffe KA, Blessing DL, Wilson GD. Alterations in dietary carbohydrate, protein, and fat intake and mood state in trained female cyclists. Med Sci Sports Exerc. 1991 Feb;23(2):212-6.
(9) White AM, Johnston CS, Swan PD, Tjonn SL, Sears B. Blood ketones are directly related to fatigue and perceived effort during exercise in overweight adults adhering to low-carbohydrate diets for weight loss: a pilot study. J Am Diet Assoc. 2007 Oct;107(10):1792-6.
(10) Westerterp KR. Diet induced thermogenesis. Nutr Metab (Lond). 2004;1(1):5.