By Therese Iknoian

Although research continues, here's how the glycemic index pieces seem to fit together. Meanwhile, have some fun reading labels on sports drinks and energy bars to see how various ones fit better into different part of a workout or are truly formulated based on the science. Some of the top energy bars and drinks have both low- and high-index carbs so they give you a quicker boost, but then also sustain that boost.

Before a workout, perhaps up to several hours before, eat carbohydrates lower on the index, about 25-30 grams, or 100 to 120 calories worth. This is especially true before long endurance activities. Low-index foods provide a steadier stream of fuel rather than a quick spurt that may leave you high and dry when the workout progresses.

• In the early stages of an endurance activity, such as a long hike or bike ride, stick mostly to slower-acting foods to continue that steady energy supply.
• In the latter stages of a long workout, switch over to high-index foods to provide the quick spurt or kick you'll need to tough it out.
• During intense, stop-and-go activity such as soccer games or weight lifting, also go for high-index foods. Stop-and-go sports deplete energy quickly, and you'll need the quick pick-me-up a faster-acting carbohydrate can provide.
• After a workout, replenish energy stores as soon as possible with moderate- to high-index foods. This is not the time to applaud yourself for calories used toward weight loss, or to dawdle in the sun. Get fast-acting carbohydrates in you, and get them in fast. An average 150-pound person will need 50 grams of carbs (about 200 calories) in the first two hours after a workout to fill up depleted glycogen stores. That's when the storehouses are thirsty for energy and able to soack it up the best. If you don't eat right away, your workouts days later could be weak.

Two caveats for the above: Any amount of fat -- for example, that slap of cream cheese on the bagel or butter in the oatmeal -- will inhibit the energy spike.

The glycemic index can be a great supplement to workouts. But a good carb won't make up for a bad night's sleep or a poor habit of skipping lunch and breakfast.