The foods you eat can either enhance your mental alertness or dull your mind and slow down your reactions. One of the most important rules to follow to increase stamina and reduce fatigue is that your body needs its "fuel" in moderate doses throughout the day to maintain an optimal energy level. By eating four to five times a day, you avoid running low on energy. Eating less, but more frequently, makes good sense for another reason. The larger the meal, the more time it takes to digest. Digestion requires increased blood and oxygen flow to the stomach and intestines. This represents energy not available for the brain and muscles. Dehydration also can cause fatigue. When your body loses fluid, you tend to get tired.