Nutrient Timing

Nutrient timing is a program designed to provide the body with the proper nutrients in the proper amounts at the appropriate time before, during, and after an exercise workout or sports event.

Virtually all athletes and trainers are aware that individuals who engage in vigorous exercise require an effective nutrition program so they can perform at maximum efficiency. They also recognize that timing is an important factor in maintaining a proper nutrition schedule. For example, marathon runners have traditionally eaten a dinner heavy in carbohydrates on the night before a race, a process known as carboloading, on the assumption that a huge store of carbohydrates will give runners a store of energy to get them through the event.

Nutrition researchers have studied nutrition timing. John Ivy, a noted scholar at the University of Texas, University of Maryland, and Washington University School of Medicine, published more than 170 research reports and four books on sports nutrition, including the popular Nutrient Timing: The Future of Sports Nutrition. Ivy's conclusions apply directly to anyone who engages in vigorous exercise or sports events. His books address the biochemical pathways that are activated in the body before, during, and after exercise, three periods he classified as the energy phase, anabolic phase, and growth phase:

A nutrition program designed to support each of the three phases of cellular functioning focuses on the types of nutrients needed to maximize the efficiency of energy use and energy generation throughout the phases. Each program is determined by the type of exercise or sport in which the participant is engaged and the physical characteristics of that athlete's cellular biochemistry. Nevertheless, some general recommendations can be made about a nutrition timing program that may benefit any athlete.

The nutrient timing program outlined here is intended specifically for individuals who engage regularly in exercises of some intensity, usually with the goal of improving their overall physical strength or conditioning. The program has no specific application for individuals who are not involved in such activities.

First, although unrelated to the three-phase theory of conditioning, adequate hydration is essential at all stages of any physical activity. The physical consequences of dehydration are well known, ranging from increased strain on the heart at body water loss of only 0.5%; reduced muscular endurance at body water loss of 3%; and cramping, heat exhaustion, and reduced mental capacity at body water loss of 5%. To reduce the possibility of dehydration, Ivy recommended that athletes drink 14–20 oz. of water or sports drink 30 minutes before exercise or an event.

Hydration continues to be the primary concern during the energy phase of exercise. During this period, the body is losing water through perspiration and using up glucose to produce energy. Again, the specific nutritional recommendation for this depends at least in part on the type of exercise or the sport involved, but, in general, rehydration is accomplished with 200–300 mL of a drink containing electrolytes (a balanced solution of sodium, potassium, chloride and magnesium) to replace losses through sweat, 4% to 6% carbohydrates, and 2% to 4% protein. Some sports nutritionists disagree about the protein component of this rehydration process, but Ivy believed that small amounts of protein may help the body start to repair damaged muscle tissue produced during an exercise and may prevent postexercise muscle soreness.

Ivy made the following recommendations for nutrient timing:

Research indicates that the body begins to prepare itself for a recovery phase even before an exercise has been completed. Cells begin making changes that replenish the supplies of essential biochemicals depleted in an exercise workout. Molecules used to transport glucose to muscle cells for conversion to glycogen start to relocate in such a way as to make them more efficient in carrying out this process. Also, enzymes needed for the conversion of amino acids to proteins become more abundant and more active, increasing the rate at which new protein is being produced in cells. The anabolic reactions needed to restore the body to its pre-exercise state do not actually begin to function efficiently, however, until the essential raw materials, nutrients ingested from food sources, start the process. Only a short period exists during which the body can receive exactly the right nutrients, probably not more than 30 to 45 minutes. An athlete who waits 2 hours after exercise to consume a nutritious meal has likely waited too long. The body has probably already switched to its anabolic phase, although at a much less efficient pace than would have been possible with effective nutrition timing. For the first post-exercise meal, Ivy recommended consuming 1.0–1.5 g of carbohydrate and 0.3–0.4 g of protein per kilogram of body weight, depending on the type and intensity of the workout.

Ivy's recommendations for the postexercise growth phase did not differ significantly from those made by many other nutrition experts. Athletes are advised to eat at regular intervals (every few hours), consuming meals rich in carbohydrates, proteins, and other essential nutrients. A nutritious diet of this type supplies the basic raw materials the body needs to complete an exercise or sports event and to support the period of sustained growth that follows.

See also Marathon and half marathon ; Ultramarathons .