By Arnie Baker, MD
Consider for a moment a typical American workday: You work three hours in the morning, have a 15-minute coffee break, take 30 to 60 minutes for lunch, and work for four hours in the afternoon, with another 15-minute break. You consume 500 calories for breakfast and 1,000 calories during lunch and work breaks. You drink many glasses of water, coffee, or other fluids.
Doesn’t it make sense that when you are exercising, you need even more calories and water? Of course! —Yet so many of us train or race until we drop without drinking enough and fueling our bodies.
The priorities for nutrition during endurance cycling, running, triathlons, or walking are water, calories, and sodium.
- For events under an hour, no special nutrition may be needed.
- For most events over an hour, concern yourself mainly with fluids and calories.
- For long-distance events over most of a day or longer, also consider sodium.
Fluid is lost primarily in the urine and through sweating. The kidneys have a tremendous ability to dilute or concentrate urine. They can rid the body of large excesses of fluids when the need arises. They can also concentrate urine if a person becomes dehydrated.
Sweat rate depends upon work rate and climate (heat and humidity). During hard work in hot desert-like conditions, it is possible to lose more than a couple of quarts (liters) per hour. Sweat rates have been measured up to 3.5 quarts per hour and 17 quarts per day.
For events longer than one hour, or one-half hour in the heat, water replacement is important. Although carbohydrate or electrolytes may not be necessary for energy or balancing mineral losses, they aid hydration by increasing the rate of water uptake by the gastrointestinal tract. They also increase palatability: Fluids that taste better encourage drinking. Chilled fluids also help encourage drinking and are absorbed more quickly.
Aim for 8 ounces of fluids every 15 minutes in the heat. That is about one quart (liter) every hour. Although you may lose more, it is doubtful that drinking more will be helpful because your body probably cannot process more than that. (With nutritional training, athletes learn to tolerate up to 12 ounces every 15 minutes.)
During road racing events, most cyclists and walkers must carry waterbottles or hydration systems (for example, CamelBak)—the time distance between aid stations is too great to rely on them for hydration. In addition, walking events often run out of fluids at aid stations. (Runners do not exercise as long, and for them the time distance between aid stations may be short enough so that waterbottles are not required.)
During 40-K cycling time trials, many racers do not bring waterbottles, even in desert events. During races at maximum effort—although dehydration worsens performance slightly—the disruption of rhythm, the time cost of drinking and the aerodynamic cost of water bottles usually justify not drinking.
It is typical to use 2,500 to 3,000 calories during a cycling century (one-hundred miles); twice as much in a double century or an ACE event (one-day altitude climbing, endurance events over 100 miles with more than 10,000 feet of climbing).
Runners and walkers use about 80 calories per mile.
Energy loss depends upon work rate. Work rates may be up to 1,200 calories per hour.
In ultra-distance events, work rates are reduced, but duration—the number of hours of work—is increased. It is possible for a 200+-pound rider cycling 24 hours in a day to burn 15,000 calories. The typical daily energy requirement of a 150-pound racer cycling 22 hours per day is 10,000 calories. Most multi-day ultra-distance riders become calorically deficient, consuming about 85% of their daily energy expenditure.
For more information about estimating caloric expenditure for basal metabolism and exercise, see page 35.
Some of this energy comes from the body’s stores of carbohydrate (glycogen) and fat. Some energy needs can be met by consuming calories while exercising. Depending upon your size, your body can use up to 300 ingested carbohydrate calories per hour (about 1 gram per kilogram per hour). As a rule, try to consume this many calories for every hour you exercise. Multiple studies confirm that athletes perform better when they fuel while exercising. Calories can come from solids, gels, or solutions.
Do you need protein or fat during exercise? Studies have not shown this to be true. (Consume your requirements during the course of the day, not necessarily during exercise.)
The harder you work, the less you are able to tolerate solid food. Cyclists are able to eat solid food while exercising. Most runners cannot.
Although studies show that gels are generally less palatable than carbohydrate solutions, some athletes prefer gels.
Carbohydrate solutions are a convenient way to get calories. Typical sports drinks and diluted fruit juice have 100–125 calories per 16-ounce (500 milliliter) bottle.
More than 400 calories per bottle can be obtained and tolerated with a few specialty sports drinks that contain glucose polymers or maltodextrins. Examples of these products include Extran and Carbo Gain.
Energy bars and gels do work, but after many hours become tiresome for most athletes. If not racing, cyclists do well to stop periodically and eat “real food” —especially early on in a long ride. Leftover breakfast items such as French toast or pancakes, fig bars, bananas, and Pop-Tarts (perfectly packaged for jersey pockets) are favorites for short stops.
Walkers may take short breaks for bananas or other solids.
Runners do not tend to exercise as long and rely more on carbohydrate gels.
Train to Eat
Although it may not be necessary to consume calories during shorter training sessions, it is crucial in long-distance events. You must practice eating, even in shorter training sessions, to allow your gastrointestinal tract to adapt to the process of eating while exercising.
Sodium is the electrolyte priority for the aerobic endurance athlete.
A low concentration of sodium in the blood is associated with weakness, fatigue, seizures, and occasionally death.
The body loses about one gram of sodium per quart (liter) of sweat. After a gallon (4 quarts, 4 liters) of such loss, the average total daily intake of sodium may be inadequate to meet demands, and the blood sodium may drop.
In temperate weather conditions, this may take 4 or 5 hours.
In high heat conditions, sodium depletion can occur in just a couple of hours.
For aerobic-endurance athletes, it is reasonable to plan on an intake of up to a maximum of one gram (1,000 milligrams) of sodium per liter of fluid loss. This is about one-half teaspoon of salt.
Salt in beverages is often unpalatable.
Salty-snacks, including low-fat pretzels, saltines, and pickles are often a good choice for athletes at rest stops.
Carry salt and sprinkle it on oranges or cantaloupe slices.
Weigh-In/Diet Diary/Lab Chemistry
For all-day or multi-day events, repeated, accurate weight measurement can help determine hydration status. Scales accurate to 0.1 pound or kilogram are best.
Some weight loss will reflect glycogen depletion. Read more about acute weight changes in the free supplement to this book available at: https://www.roadbikerider.com/nutritionforsportssupplement.htm.
For multi-day events—for example, the Race Across America—a support crew member charged with recording solids and liquids ingested and eliminated can help evaluate caloric, fluid, and mineral balance.
Spot checks of urine electrolytes and specific gravity, or blood biochemistries are occasionally used by sophisticated crews in multi-day events.
Keep Event Supplies Handy
In events over several hours or longer, most athletes do not eat or drink enough. Athlete nutritional intake is heavily dependent upon what the organizer provides at aid stations. Carb, fluid and sodium replacement is often inadequate to keep up with demands. Plan on personal support unless your event is well-provisioned.
- Aim for at least 8 ounces (250 milliliters) of fluids, every 15 to 30 minutes, depending upon the heat.
- Have carbohydrate-in-water solutions (for example, maltodextrins or sports drinks), rather than plain water.
- Cyclists: Carry two waterbottles. Or use a hydration system (for example, CamelBak). Walkers: Carry a waterbottle.
- For events longer than one hour, consume at least 300 calories per hour of exercise
- For multi-hour events in conditions of heat and humidity, consume salty foods, and sodium-rich solutions and gels.