A Twitter post yesterday highlighted the single most important question in athlete nutrition: How much should I eat? While the answer to the question is dependent on several unique metabolic factors and goals (weight gain, maintenance, loss), unfortunately, the question itself is too often left unasked by athletes and therefore, unanswered. A Twitter post yesterday said: As an RD, “I spend 90% of my time telling people to eat more and 10% telling people to eat more, just in a firmer voice”. Unfortunately, this post rings true as many athletes do not eat enough to fuel their performance.
So what factors go into determining how much you should eat as an athlete? There are 3 primary factors that weigh into energy intake requirements: BMR (basal metabolic rate), Activity level (exercise expenditure + moving around throughout the day), the TEF (thermic effect of food). However, climate, pregnancy, lactation and menstrual cycle phase may also play a role, albeit minor related to the 3 main factors reviewed below.
BMR (basal metabolic rate): Your BMR is the single largest contributor to energy intake requirements and reflects the minimum energy intake required to support vital functions. BMR typically represents 65%-75% of total energy intake requirements. Lean mass is the biggest driver of BMR but genetics may play a role. A metabolic test can be used to measure BMR but typically, a standard formula using age, height and weight (i.e. the Mifflin-Joeur equation) is used to create a valid estimate.
Activity Level: Activity levels typically represent a much smaller portion of energy intake requirements (~15-20%). However, this rule of thumb and the usual activity “multiplier” calculation which adds to BMR may not accurately reflect the activity levels of individual athletes. So while using a device, such as a Garmin, does not provide perfectly scientific estimates of energy burned during exercise, it’s provides a much clearer basis to inform energy intake requirements as it is reflective of the varying nature of energy expenditure from different types of activities, levels of intensity and varying volumes.
TEF (thermic effect of food also known as dietary induced thermogenesis or DIT): TEF is reflective of the increase in energy burned to support digestion. The type of macronutrient consumed influences how much energy is burned in digestion. For example, carbohydrates digest relatively quickly compared to protein so carbohydrates have a lower thermic effect (i.e. energy cost to digest). On average, most energy intake requirement models assume the TEF is ~7-10% of energy intake. However, it could be higher or lower depending on macronutrient composition.
Do you know if you are eating enough to fuel your performance? Schedule a complimentary 15′ call to learn more and to see if sports nutrition coaching is right for you.
Sources:
McArdle, W. D., Katch, F. I., & Katch, V. L. (2015). Exercise physiology: nutrition, energy, and human performance. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins
Lee, R. D., & Nieman, D. C. (2013). Nutritional assessment (6th ed.). New York, United States: McGraw Hill
Mifflin M.D., St. Jeor S.T., Hill L.A, Scott BJ, Daugherty SA, Koh YO. 1990. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 51:241–247.
Fuller, D., Colwell, E., Low, J., Orychock, K., Tobin, M. A., Simango, B., Buote, R., Van Heerden, D., Luan, H., Cullen, K., Slade, L., & Taylor, N. G. (2020). Reliability and validity of commercially available wearable devices for measuring steps, energy expenditure, and heart rate: Systematic Review. JMIR MHealth and UHealth, 8(9). https://doi.org/10.2196/18694
