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Whether you want to slim down, get big and buff, compete at a higher level, or just feel better, you have to properly fuel your body. But ideas about just what “properly” means have been shifting.

Crash dieting, restrictive eating, and processed and prefab foods are out. So are low-fat diets, no-holds-barred protein pushing and conventional carbo-loading. All of which means it’s time for a fitness-fueling update.

We’ve collected some of the best advice from fitness and nutrition experts to help make sense of the latest science and emerging wisdom. You don’t need to be a bodybuilder or marathoner to benefit from these guidelines. Any active person — regardless of his or her goals — can eat better, and live better, by following these principles of nutrition timing and food quality.

Nutrient Timing

We could go on and on about nutrient timing, but all you really need to know is this: You must have gas in the tank to make the vehicle go. And after driving, you need to refill that tank. In other words, you should eat before and after your workout, regardless of your fitness goals.

“It used to be that if you wanted to lose weight, you’d skip meals around exercise,” says Susan Kleiner, PhD, RD, coauthor of Power Eating (Human Kinetics, 2007). “Now we know that everyone needs to eat around the time of their workout, whether their goal is health, performance or weight loss. When you eat around exercise, you increase the rate of calorie burning. And the calories know where to go, so the food goes to good use.”

Exactly what and how much you should eat depends on your body size (larger people need more calories), activity type and intensity (more-active people need more calories; endurance athletes need slightly more carbohydrates than weightlifters, but both need adequate protein).

Fueling for fitness also involves processes that occur between workouts, but basically you can sort nutrient timing into a few essential phases (before, during and after exercise), each of which has different nutritional requirements. Here’s what you need to know about each phase.

1. Preworkout Phase

What to consume: A small, high-carbohydrate meal an hour or two before training.

In general, exercising bodies rely on carbohydrate-based fuels during a workout. The phosphate, or ATP-CP, energy system can provide energy for 15 to 30 seconds; after that, stored muscle glycogen takes over. The longer and more intense the activity, the more important it is to deposit sufficient amounts of carbohydrates into your “glycogen bank account” prior to making a “workout withdrawal.”

Provided that you’ll be replacing glycogen immediately after exercise (see No. 3), a small, high-carbohydrate meal an hour or two before training is probably enough to fill your glycogen bank for most occasions. Forget pasty, starchy and flour-based carbs, though. Slower-digesting, higher-fiber carbohydrates such as whole grains or fruit are best, since they provide sustained energy. (See “The Problem With Processed,” below.)

The same goes for pre-event carb-loading in general: “In the week before, you’ll want to increase your carb intake to fill the tank to threshold levels,” says Kleiner. But here, too, stick with whole-food-based carbs whenever possible.

2. Energy Phase (During the Workout)

What to consume: If your workout lasts under an hour, water will do; over an hour, add small amounts of easily digested carbohydrates.

For energy during your workout, the body uses carbohydrates (in the form of glucose, which turns to glycogen in the muscles) and fats (in the form of free fatty acids stored within the muscle). Some athletes take this to mean they should guzzle sugary sports drinks to prevent glycogen depletion even during light workouts. But experts simply recommend staying hydrated with water and, if your training lasts longer than an hour or so, also consuming small amounts of easily digested carbohydrates. (Most people have glycogen stores in their bodies that can last from an hour to an hour and a half.)

Although the body can use protein in the form of amino acids for fuel, especially during long endurance exercise (such as running a marathon), it generally prefers carbohydrates for this purpose. One study that simulated a duathlon consisting of five hours of bicycling and one hour of running found that protein wasn’t used any more than if athletes were resting, provided that the subjects were consuming enough carbs at regular intervals. Protein is important later, but you don’t really need it during your workout.

If you’re working or training for long periods in the heat, make sure to get some sodium — about 160 to 200 milligrams per 8 ounces of fluid — along with your water. Fluid intake that exceeds fluid loss through sweating and urination can dangerously dilute blood sodium levels — a potentially fatal condition known as hyponatremia. Women are particularly at risk because of their relatively smaller body sizes.

3. Anabolic Phase (Postworkout)

What to consume: A mix of easily digested carbs and protein — as soon as possible! And then repeat two hours later.

Replacing glycogen by taking in some easily digested simple carbohydrates, as well as some protein, immediately after exercise helps replenish your muscles’ energy source and facilitates long-term recovery.

Simple carbohydrates also help stimulate the release of insulin, which helps transport the protein to muscle cells and slow protein degradation. Experts recommend about half a gram of carbohydrates per pound of body weight immediately after exercise, and the same amount two hours later. One easy source is a whole-food-ingredient fruit smoothie.

Be sure to add a protein source (protein powder, tofu, nuts, etc.) to the blender or include some protein with whatever you’re eating. Though it’s rarely burned as a fuel source during training, protein is very important immediately after training. Vigorous exercise stimulates whole-body and skeletal muscle-protein turnover — this includes protein synthesis (the manufacture of new proteins and protein repair) and protein degradation (the breakdown of old proteins). Protein synthesis is most active during the first two to four hours after exercise and lasts for at least 24 to 48 hours.

The muscle-building processes that occur after training apply to exercisers of all ages and both sexes, notes Wayne Westcott, PhD, coauthor of Strength Training Past 50 (Human Kinetics, 2007). His recent research showed that recreational female exercisers (ages 20 to 80) who drank a protein-carbohydrate mix immediately after strength-training sessions gained nearly 2 more pounds of lean mass and lost about 4 more pounds of fat after six months than women who didn’t. “All the women were afraid they were going to gain fat [from the extra calories],” says Westcott. “They didn’t expect this result at all!”

To build muscle, however, the rate of muscle-protein synthesis has to exceed the rate of muscle-protein breakdown. Carbohydrates help slow or prevent protein degradation; and amino acids, especially leucine, will stimulate protein synthesis. It doesn’t take much protein to do the job — about 10 grams, including up to 3 grams of leucine (the equivalent of about half a chicken breast or a half cup of tofu).

So, to make the most of your workout, have a moderate serving of protein and carbohydrates immediately afterward and again within two hours. Because of its amino-acid profile, milk can be a good part of your postworkout snack (assuming you don’t have an intolerance and aren’t a vegan), but protein can also come from many sources, both animal and vegetable.

For example, vegan triathlete Brendan Brazier, author of The Thrive Diet (Da Capo, 2007), favors a combination of hemp, brown rice and pea protein. Liz Applegate, PhD, director of sports nutrition at the University of California, Davis, suggests foods such as tofu, tempeh, miso, nut butters and ground hemp seed for her vegan clients.

4. Growth Phase (Between Workouts)

What to consume: Whole, unprocessed foods, emphasizing protein and good fats.

In the old-school world of bodybuilding, bland, high-protein diets were king. In his book Brawn (CS Publishing, 1991), Stuart McRobert suggested that aspiring lifters drink several quarts of milk a day. Former Mr. Universe Dave “The Blond Bomber” Draper describes traveling with cans of tuna and an opener in his carry-on bag. (No word on what his seatmates thought of this dietary regimen.)

Today, experts suggest we eat whole, unprocessed foods from a variety of sources at regular intervals, but they still emphasize the importance of protein. And this advice isn’t just for bodybuilders. A combination of resistance training and postworkout nutrition that includes protein can counteract the loss of muscle mass, known as sarcopenia, which occurs with aging.

Westcott also points to research indicating our bodies process protein less effectively as we age and recommends exercisers over 50 try to get a little more protein than the recommended daily allowance (RDA) — up to twice the RDA of .8 grams per kilogram (or .36 grams per pound) of body weight. For most, this amounts to adding about 10 to 20 extra grams of protein, especially after a workout. But don’t overdo the protein thing, Westcott warns, or you will stress your kidneys, which have to work to neutralize the nitrogen in protein. To combat this effect, bump up your protein intake only moderately and drink more water.

Remember, too, that proteins and carbs are only part of the picture: Don’t ignore your body’s need for antioxidants, phytonutrients and good fats. Exercise creates oxidative stress on the body, which is counteracted by antioxidants such as carotenoids — found primarily in the colorful pigments of fruits and vegetables. Both phytonutrients (from colorful fruits and vegetables) and good fats (in the form of nuts, seeds, fresh oils, avocados, coconut and oily fish such as salmon) help reduce inflammation and promote recovery.

Healthy fats also help mobilize stored body fat (important for those watching their waistlines). And research conducted over the past decade indicates just how important fat is for endurance activities. Multiple studies have shown that athletes eating higher fat diets (in which 40 to more than 60 percent of daily calories came from fat) saw moderate boosts in power and performance over low-fat diets and those that included high carbohydrates without much fat.

Get these basics right, says Applegate, and you won’t need to sweat the details. “People tend to forget the big picture,” she notes. “Don’t obsess over a picky little point. Just get all the meals you need, keep yourself well hydrated and fueled, and you’ll be good to go.”

The Problem With Processed

Nature provides a wealth of nutrients that are rarely available in processed foods. Much of conventional supermarket fare is high in simple sugars, such as high-fructose corn syrup, which contribute to fat gain and systemic inflammation. Fruits, vegetables, lean meats and whole grains, on the other hand, provide vitamins and minerals, antioxidants, good fats, and fiber, as well as phytonutrients crucial to optimal health, vitality and metabolism.

We may need fewer calories now than we did during our hunter-gatherer days, but we still need the same amount of nutrition. And processed, refined foods (from which nutrients are generally removed) don’t offer enough. “Every single calorie you eat must be packed with nutrition,” says Susan Kleiner, PhD, RD, coauthor of Power Eating (Human Kinetics, 2007). “The only way to do that is to eat ‘close to the ground.’” That means foods as close as possible to the way nature made ’em.

Whole foods provide ideal, not merely adequate, nutrition. “Who wants to be adequate?” Kleiner asks. “We want optimal! We want to maximize the function of our bodies!” So aim for the least processed foods you can get your hands on.

Resources to Help Fuel Your Workouts


  • The Thrive Diet: The Whole Food Way to Lose Weight, Reduce Stress, and Stay Healthy for Life by Brendan Brazier (Da Capo, 2007) —Vegan triathlete and founder of Vega sports nutrition on how to ensure high performance on a plant-based diet.
  • Nutrient Timing: The Future of Sports Nutrition by John Ivy, PhD, and Robert Portman, PhD (Basic Health Publications, 2004) — Explains how and when the body uses nutrients, and how to eat to optimize these natural processes.
  • Power Eating by Susan Kleiner, PhD, RD, with Maggie Greenwood-Robinson, PhD (Human Kinetics, 2007) — Combines the most up-to-date scientific and practical advice to address the unique nutritional requirements of the power athlete.
  • Get Stronger, Feel Younger: The Cardio and Diet-Free Plan to Firm Up and Lose Fat by Wayne Westcott, PhD, and Gary Reinl (Rodale, 2007) — Brief high-intensity workouts and strength training combined with good nutrition can transform your body and prevent chronic diseases.

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