What you eat before exercising affects performance

  • Published
  • By 1st Lt. James E. Brown IV
  • 71st Medical Operations Squadron
VANCE AIR FORCE BASE, Okla. --  Walk into any sports supplement store and the shelves are lined with products meant to enhance human performance.

With a huge selection of pills, powders, packs, and more it can be hard to discern what has supportive scientific research and what will just lighten your wallet.

One area neglected by many is the pre-workout phase of nutrition. What you eat in the hours leading up to and immediately before the workout can have a great impact on your performance.

This is an exciting area of research that is constantly evolving. Years ago the only choice the athlete had was sugar-laden Gatorade beverages. But now there are literally hundreds of choices available.

Nutrition recommendations differ from sport to sport and athlete to athlete. The following are general recommendations about nutrition during this phase of nutrition. Performance versus body composition changes will also dictate what is ingested during training.

First, we'll define what makes up the pre-workout window. The exercise physiologist Lyle McDonald breaks pre-workout nutrition into two distinct phases. Phase I being one to four hours before training. Phase II is zero to 30 minutes before training, including the warm-up.

The primary goal of Phase I is to top off stored carbohydrates within the muscle and liver -- glycogen -- which limits fatigue during high-intensity training.

Phase II focuses on supporting blood glucose levels during the exercise event.

The closer you are to exercising, the smaller your meal should be. Hard to digest foods such as those high in fiber and fat should be limited during this time.

These foods take much longer to assimilate and digest, taking precious blood flow away from the musculature and brain during exercise as the body shunts blood flow to assist in digestion. This can lead to nausea during exercise and you may also see your food again.

Each person is different in how well they can handle pre-exercise macronutrient intake. Some have no problem handling large meals before exercise. Others cannot.

The intensity of the workout also dictates fuel demand, with higher intensity work requiring more fuel than lower intensity work.

If a person is trying to make weight or cut body fat, there is supportive research showing fasted training to be beneficial in activating beta adrenoreceptors and blocking alpha andrenoreceptors which can increase blood flow to those stubborn fat areas of the body. Low carbohydrate diets can also do this.

Another exception may be those who wake up and exercise first thing in the morning. The benefits of getting in additional sleep may be greater than getting a meal in hours before the exercise event.

But in general, eating pre-exercise can significantly increase your exercise performance, improving training quality, intensity, volume and recovery. It can also decrease fatigue, muscle damage and support training adaptation.

Even if you are unable to handle solid food around this timeframe, sports drinks containing carbohydrates and protein can enhance exercise performance and help delay fatigue.

The Phase I meal, one to four hours before training, should represent an athlete's normal meal. As you get closer to training time, the size of the meal should decrease, with both fiber and fat content taken into consideration.

The goal of the Phase II window, zero to 30 minutes before training, is to ensure optimal blood glucose levels and hydration. Liquids are generally a better choice here as they are less likely to sit heavy in the stomach than solid food.

Fast digesting carbohydrates, like dextrose or maltodextrin, are preferred to slower digesting carbs. Fast digesting protein such as whey would be preferred to slower digesting proteins such as casein during this timeframe.

(For more information, contact Lieutenant Brown at 213-7931. He is part of the Human Performance Training Team with the 71st MDOS Aerospace and Operational Physiology Flight.)