What to Eat for Peak Athletic Performance: A Sports Dietitian Explains
An athlete walks into the gym and crushes personal bests just 48 hours after making a small but critical change to his diet: shifting from a high-protein, low-carb focus to a more balanced approach with adequate carbohydrates. This real-life example highlights a common issue in athletic nutrition—overemphasizing protein while neglecting the energy powerhouse that fuels performance: carbs.
For athletes, nutrition isn't just about eating healthy; it's about eating strategically to meet the demands of their sport, training schedule, and competition goals. Yet, misconceptions abound, from trendy high-protein diets to underestimating the impact of proper race-day fueling.
I spoke to Carrie Mullin Innes, a dietitian who focuses on sports performance, to explore the vital role of carbohydrates, the reality of protein needs, and how training and competition nutrition differ. Carrie has even worked with athletes on the Canadian Olympic team, so she is a true expert in fueling peak performance.
The Role of Carbohydrates in Athletic Performance
In nutrition for athletes, carbohydrates are often the unsung hero. Protein tends to steal the spotlight in popular fitness culture, but carbohydrates are the primary energy source for most physical activities, especially those involving high intensity or endurance.
Carrie explains that athletes often underestimate how much their carbohydrate needs increase with activity. "When movement is more intense, you need more carbs," she said, pointing out that energy demands scale with both the duration and intensity of training. She also shared that athletes sometimes hyper-focus on protein because it's trendy, forgetting the vital role carbohydrates play in their performance. "Sometimes they focus so much on protein...that they forget they also need carbohydrates," she noted.
This imbalance can lead to suboptimal performance, fatigue, or even hypoglycemia during training or competition. Carrie highlighted the importance of recognizing when you're running low on energy: "Are you noticing your performance slowing down? Are you feeling shaky or experiencing low blood sugar? These are signs that you're not fueling properly."
Protein: Overhyped, or Also Essential?
So what about protein? Is it not important?
According to Carrie, protein is absolutely important for muscle repair and growth. But athletes can overestimate how much they actually need. "Protein needs really vary," she explained. "It depends on the sport, your body weight, your goals, your calorie intake, and even your training age."
Carrie pointed out that as athletes mature in their sport and become more efficient, all of their nutrition requirements tend to decrease. "The more mature you become in your sport, the more accustomed your body is to it, and your protein needs, your calorie needs, and everything aren't as high—you become much more efficient," she said.
For example, older athletes like Tom Brady need fewer calories and protein than less experienced athletes attempting to perform at a similar level. "He can do what he does in his sleep," Carrie noted, "but if I were to try to make you train like Tom Brady, it would be very demanding. Your carb needs, your protein needs, and everything else would reflect that huge demand on your body."
Competition vs. Training Nutrition
Athletes often overlook how their nutritional needs shift between training and competition. Carrie highlighted key differences, explaining that competition nutrition focuses on immediate performance, while training nutrition supports ongoing demands and recovery.
"On competition day, the focus is on hydration and carbohydrates because those are the two things that affect your performance," she said. Protein, while important for recovery, takes a backseat during competition. "We're not going to worry about protein intake today because you always do a good job with that," she sometimes tells clients.
Another key adjustment for competition days can be reducing fat intake. "Fat is filling, and when people have race after race or event after event, you don't want them eating high-fat foods because they're going to feel that food sitting in their stomach," Carrie explained. The goal is to feel "light and primed," not sluggish or heavy.
Competition nutrition requires planning around the specifics of the event. "You have to find out, is it a one-day competition or a two-day? How many events might you have in a day? When would you be eating?" Carrie said. For some athletes, competition days may actually require fewer calories if their activity level is lower than during intense training days. "It just really depends," she emphasized.
In contrast, training nutrition is more about meeting the demands of an athlete's daily workload. This includes ensuring adequate carbohydrates, protein, and fats to fuel workouts, support recovery, and maintain energy throughout the day. Carrie noted that this requires careful consideration of an athlete's schedule, including the timing, intensity, and duration of their workouts.
Fueling Your Personal Peak Performance
There is no single "best" diet for athletes. Carrie emphasized that personalizing an athlete's nutrition plan is critical, as it depends on a variety of factors, including their sport, training schedule, goals, and even individual preferences or dietary restrictions.
Carrie's approach starts with gathering detailed information about an athlete's routine. "You have to find out how often they're working out, what a session looks like, how much rest versus movement time they have, and where it fits into their day," she said.
Personalization also ensures that athletes can sustain their nutrition plan long-term. Carrie avoids rigid meal plans, instead focusing on practical strategies that fit into an athlete's everyday life. "It's about teaching them how to eat, not just following an exact plan," she said. This flexibility is especially important for athletes who may face frequent travel, dietary restrictions, or fluctuating schedules.
Ultimately, personalized nutrition not only supports an athlete's physical performance but also helps them build the tools and knowledge to adapt their diet as needed. By considering the unique demands of each individual, Carrie ensures that her clients get the most out of their nutrition—both on and off the field.
Carrie Mullin Innes, MSc, RD, IOC Dip Sports Nutr, is the founder and principal dietitian at Score Nutrition. Score Nutrition's mission is to empower athletes of all ages and competitive levels to achieve their next milestone.