Nancy Clark's Sports Nutrition Guidebook: Summary & Key Insights

Every athlete’s foundation begins with energy balance. Too much emphasis is placed on body weight alone, when what truly matters is energy intake aligning with energy expenditure. Calories are not the enemy—they are fuel. To perform your best, you must eat to meet your training demands, not restrict or fear your food.

Caloric needs vary with sport, intensity, and goals, but all athletes share the same principle: to maintain consistency in training, your muscles, brain, and metabolism must be adequately supplied. Under-fueling leads to fatigue, loss of strength, impaired recovery, and in the long term, hormonal imbalances and injury risk. Over-fueling, in contrast, may cause sluggishness and unwanted weight gain, but it’s often less damaging than chronic deprivation.

I help readers calculate approximate calorie needs based on body weight, activity type, and training volume. From there, we focus on distributing energy among carbohydrates, proteins, and fats. Carbohydrates should make up the bulk of an athlete’s diet, as they are the most effective source of muscle fuel. Proteins support repair and adaptation, while fats sustain endurance and overall health. Balancing these is not a formula to memorize—it’s a dynamic relationship you learn to feel through daily awareness. When you eat right, you can tell: your training feels stronger, recovery sharper, and mood steadier.

Carbohydrates are the powerhouse of athletic performance. Despite decades of diet myths demonizing carbs, they remain the body’s preferred source of energy, particularly for high-intensity or endurance activities. Your muscles store carbs in the form of glycogen, and when those stores run low, fatigue sets in. You can train your muscles, but you can’t train them to perform well without proper fuel.

I encourage athletes to understand carbohydrate timing. Eating carbs consistently throughout the day—before, during, and after workouts—prevents the dreaded energy crash. Before exercise, carbs prime your muscles; during exercise, they maintain your stamina; and after exercise, they rebuild depleted glycogen for tomorrow’s training. Recovery nutrition is not a luxury—it’s an investment in the next session.

The best sources? Whole grains, fruits, vegetables, legumes, and dairy all have their place in an athlete’s diet. Simpler carbohydrates like sports drinks, gels, or fruit juice become useful tools during extended events. What matters most is not avoiding carbs, but matching them to your energy cycle. When you learn to trust carbs again, you rediscover vitality, strength, and focus during exercise.