Drinking soda before exercise has two negative effects: first, it can lead to dehydration; second, it can cause a spike in blood sugar that will eventually result in fatigue. These two factors occur because soda contains caffeine and sugar. Neither caffeine nor sugar assists in athletic performance, despite the claims of some energy drinks or other products. On the whole, it is better to drink water, the most natural source of hydration, prior to exercise.
Caffeine and Exercise
Most soft drinks contain caffeine. Caffeine is a psychoactive drug. Many people forget this fact because caffeine is so common in many usages and cultures. Caffeine is a naturally occurring drug; it is present in the coffee bean and some tea leaves. In moderation, like most substances, caffeine is not largely harmful to the body. However, drinking caffeine at the wrong time can lead to poor nutrition. Specifically, caffeine has a dehydrating affect on the body due to its properties as a diuretic. This means it pushes fluids through the body instead of allowing them proper time to be absorbed. When you drink a soda, instead of hydrating yourself, you may actually be doing the opposite. Since exercise and sweating can also dehydrate you, it is better to drink a hydrating beverage instead of a dehydrating beverage before exercise.
Sugar and Exercise
Sugar is another type of naturally occurring stimulant that is fine for the body in moderation. There are two types of sugars: simple and complex. Complex sugars found in foods like fruit, vegetables, and some grains are better for the body because they are processed over a longer period of time. The type of sugar used in soda is simple sugar, which is often an additive such as corn syrup. These sugars are processed very quickly. When they enter the body, the body kicks into overdrive to process the extra calories. This is the "sugar high" sensation you may feel if you drink soda just before exercise. However, you may note a sudden "crash" once the sugar has been processed. Drinking soda before exercise causes this sudden spike and subsequent drop in blood sugar. The result is a crash, or fatigue, after a short period of time.
There are some soft drinks and soda alternatives that are okay to drink before exercise. Water is typically preferred, but some people find it challenging to drink the recommended daily amount of water alone. Sports drinks generally do not have any caffeine. They do have sugar, though, and many contain far too much. Sports drinks are intended for use following exercise to replenish your body's sugar loss. Before exercise, it is best to drink caffeine free, sugar free alternatives. Pure fruit juice or pure vegetable juice contains complex rather than simple sugars. Look for drinks that do not have additional corn syrup, fructose, or fruit juice from concentrate.