Your body is a machine. And, like all machines, it needs the right fuel to run well—especially if you are active. But what foods should you eat to benefit your workout? And when?

Rule # 1: Pay attention

You might be surprised how many active adults overlook the importance of nutrition basics—and then run short on key nutrients.

Not getting enough vitamins, minerals and other nutrients can compromise your health and your performance.

Yet fueling up for activity is as easy as following the well-established rules of a healthy diet: Eat plenty of fruits and vegetables, consume lean proteins, eat healthy fats, get your whole-grain carbohydrates, and drink plenty of fluids, especially water.

Rule # 2: Fuel up (even if your goal is to lose weight)

Give your body the energy it needs to do the job you want—even if you are trying to lose weight.

Skimping on nutrition can reduce muscle mass, lower bone density and cause fatigue. This puts you at risk of injury and illness, increases recovery time, causes hormonal problems, and, for women, menstrual issues.

Make sure your diet plan supplies enough nutrient-dense calories so you can exercise and stay injury-free and healthy.

Rule # 3: Love carbs (you need them)

Carbohydrates get a bad rap with some people. But research over the past 50 years has shown that carbs help your body during long and high-intensity exercise. In fact, the more active you are, the more carbs you need.

But what about the trend for athletes to eat high-fat, low-carb diets? Evidence suggests these diets don't boost athletic performance and actually hinder it at higher intensities.

During a workout, carbohydrates fuel your brain and muscles.

• Carbs for the average workout—If you are in good shape and want to fuel a daily, light-intensity workout, eat about 3 to 5 grams of carbohydrates for every kilogram of body weight. For someone who weighs 150 pounds (68 kilograms) that's between 200 and 340 grams a day.
• Carbs for longer workouts—If you exercise more than an hour a day, you may need 6 to 10 grams of carbs per kilogram of body weight. For a 150-pound person, that's 408 to 680 grams a day.

Pick healthy carbs like brown rice, quinoa, whole-grain bread and pasta, sweet potatoes, fruits, and vegetables.

Rule # 4: Rebuild with protein

Protein is important because it provides the amino acids your body needs to build and repair muscle.

Most research suggests very active people should eat 1.2 to 2 grams of protein per kilogram of body weight. That means a 150-pound person should eat 82 to 136 grams each day. People who aren't active should eat less protein. Aim for .8 grams per kilogram of body weight each day.

Good sources of protein are poultry (25 grams in 3 ounces) and fish (20 grams in 3 ounces). Those who prefer to avoid meat can try soybeans (20 grams per cup) and legumes like beans, peanuts and chickpeas (about 15 grams per cup). Eggs, Greek yogurt, cheese and tofu are good sources, too.

Rule # 5: Don't ignore fats

Fat is a confusing topic for many people. But it's essential to a healthy diet. Fat provides energy and helps your body absorb vitamins. Some vitamins (like A, D, E and K) actually need fat to properly benefit your body.

Be sure to pick unsaturated fats. Good sources are avocado, olive and canola oils, flaxseed, and nuts.

Rule # 6: Know what you need pre-workout

If you work out less than an hour at a time, eating throughout the day should give you enough energy. However, to avoid GI issues, you may want to avoid eating right before you exercise.

As a general rule, eat 1 to 3 hours before your workout, even if you are going to do sustained, high-intensity activity, like a half marathon.

Rule # 7: Remember the post-workout 15

Your body uses its stored energy sources during a workout. After you exercise, you need to restore those nutrients as soon as possible.

Research suggests that eating foods high in protein after your workout (within 15 minutes), provides essential amino acids that build and repair muscles. This may also increase the energy your body puts into storage to draw from in the future.

You'll want to replenish your carbs and fluids after your workout, too. One strategy is to drink a post-workout smoothie.