Guide to Nutrient Timing: In-depth

When you eat is just as important as what and how much you eat for peak performance. Proper fueling helps you push through high-intensity activities, training, and extended operations.

By timing certain nutrients (carbohydrates, protein, and water) to match activity phase (before, during, and after exercise), Service Members can fuel and hydrate to perform at their best. Strategic nutrient timing also can help maintain energy, decrease injury risk, and maximize recovery.

The fluid and fuel strategies for each phase depend on the length and intensity of the Warfighter’s activity. Environmental conditions, such as heat, cold, humidity, and altitude also play a role in nutrient strategies. Everyday foods from home, dining facilities on base, grocery stores, and convenience stores can meet the nutritional needs of most Service Members. (Gels, bars, chews, and other portable “sports foods” also work well for the various phases of nutrient timing. They’re just often more expensive.)

Fueling with carbs 

Carbohydrates are the best fuel for exercise—for both mind and body. Warfighters should aim to get enough carbs:

• before exercise to maximize their total supply of carbs;
• during exercise to have enough fuel to match the demands of exercise; and
• after exercise to replenish the fuel used.

The tables below show general recommendations for each phase of nutrient timing that can be customized. Warfighters should choose what to eat based on activity type, intensity, and environmental conditions, as well as their personal preference and experience.

Fluid balance

Getting enough fluids and balancing electrolytes are also essential for peak performance. Military guidelines recommend 3–4.5 quarts (96–144 fl oz) of fluid per day for men and 2–3 quarts (64–96 fl oz) for women.

Service Members need to replace fluids to cover daily water loss as well as sweat losses—especially when they’re active for a long time or at high intensity. Fluid loss of more than 2% body weight can decrease attention, mood, and athletic performance and increase risk for heat-related injuries. Drinking water with meals and snacks, and paying attention to fluid intake during and after exercise can help maintain hydration.

To monitor fluid loss, Service Members can weigh themselves before and after exercise—and rehydrate accordingly. Another way to monitor hydration is by checking urine color. (Generally, the lighter the urine color, the better.)

Service Members should aim to tailor their hydration to sweat rate, type and length of activity, environment (heat, humidity, cold, altitude), equipment and clothing, and opportunity and availability to drink. For optimal fluid balance, Warfighters likely need to increase intake with heat or humidity, heavy clothes or equipment, increased intensity, or exerising longer than an hour. By the time someone feels thirsty, they might already be dehydrated, so encourage a drinking schedule. Service Members might find that flavored and/or sweetened drinks help them drink more fluids. Rehydration is an important focus of the recovery phase, so encourage drinking immediately after a training, mission, or event.

Electrolytes

Electrolytes (nutrients such as sodium, potassium, calcium, and magnesium) are important for muscle function. Loss of electrolytes through urine and sweat can make dehydration worse than just fluid loss alone. Individual sweat rates for men and women can vary between 0.3 and 3.5 liters (about 0.3–3.7 quarts) per hour, so the amount of electrolytes lost through sweat also varies. Electrolyte loss can be significant depending on training status, sweat rate, how much you eat, genetics, and prior heat exposure.

For optimal performance and recovery, a Service Member should consume foods and fluids that contain electrolytes before, during, and after exercise. Warfighters shouldn’t restrict salt in the recovery phase; it helps retain fluids.

Service Members can get enough sodium by eating salty snacks or meals, adding salt to foods, and drinking beverages that contain sodium. Electrolytes can be found in everyday foods including bananas and oranges (high in potassium), chocolate milk (high in calcium), nuts/seeds and whole grains (high in magnesium) as well as sports drinks, sports foods, or a combination. Replenishing electrolytes is crucial for complete hydration.

Caffeine for performance

Caffeine can improve performance during an endurance event ( > 60 minutes) by reducing the perception of fatigue and allowing you to exercise longer at optimal intensity. In general, consuming up to 200 mg of caffeine (amount in 16-oz coffee) approximately 30–60 minutes before an endurance event can improve performance. When using caffeine to boost performance, use it strategically, according to individual caffeine tolerance. Caffeine content varies, and not all product labels include caffeine content.

For extended or sustained operations, re-dose every 3–4 hours as needed. Caffeine intake should not exceed 600 mg in 24 hours (or 800 mg for sustained operations). For more information, read “Caffeine and Performance” from Operation Supplement Safety (OPSS).

For more information on performance nutrition, read HPRC’s “Warfighter Nutrition Guide.”

Fueling for high-intensity activities (45–75 min)

High-intensity workouts lasting about an hour require only a small amount of additional fuel and fluid for peak performance.

Fueling for longer endurance activities (> 60 minutes)

Extended endurance activities—such as a Ruckmarch, extended field operations, a marathon, and playing soccer or other “stop and start” sports—require more fuel and hydration to sustain performance before, during, and after each event.