Confused by Carbs?

The low-carb diet fad has some truth in it, but it’s not for competitive athletes. Our nutrition expert gives the skinny on carbohydrates and performance.

By Leslie Bonci

Leslie Bonci, MPH, RD, is Director of Sports Nutrition at the University of Pittsburgh Medical Center and serves as a consultant to the Pittsburgh Steelers, Pitt athletics, and several area high schools.

Training & Conditioning, 14.3, April 2004,

Just as athletes are starting to get the message that consuming carbohydrates is an important component of enhanced performance, the anti-carb movement has begun jockeying for position again. From Atkins to advertising, the anti-carb movement has many athletes doubting the standard sports nutrition recommendations.

Athletes need to be able to separate fact from fiction. Yes, low-carb diets can lead to weight loss. Yes, low-carb diets can provide a healthy alternative for many non-athletes. But they’re not right for everyone, and athletes who follow low-carb diets will only compromise their performance.

With a glut of misinformation in the market, your athletes need to know the facts about healthy nutrition. Fact number one is that carbohydrates are a necessary part of any healthy diet. Fact number two is that carbohydrates have always been and will always be the primary energy substrate for most exercise. Fact number three is that athletes who cut carbs will pay the price with decreased speed, strength. and stamina.

Let’s being this discussion with a definition of carbohydrate. A carbohydrate is a macronutrient composed of carbon (carbo-) and water (-hydrate). Carbohydrates are composed of saccharides (sugars) of varying length.

Point No. 1. We eat food, not just carbohydrates. Some foods are primarily carbohydrate, such as carbonated beverages. Others, such as skim milk, are a mix of carbohydrate and protein.

Point No. 2. The categorization of carbohydrates into two types, simple and complex, is much too simplistic for today’s athletes. Using these terms may persuade people to cut foods from their diet unnecessarily, making the incorrect assumption that simple carbohydrates are bad and complex carbohydrates are good.

The facts are more complicated. Some of the foods that people traditionally classify as simple carbohydrates—fruit, non-starchy vegetables, honey, maple syrup, grains (rice, corn, oats), and dairy foods such as milk and yogurt—are often a healthier choice than the foods we think of as complex carbohydrates.

In addition, some complex carbohydrates such as sweetened cereals have fiber removed, and may not be as nutrient-dense as simpler carbohydrates like fruit and non-starchy vegetables (green beans and broccoli, for example) which contain fiber, phytonutrients, vitamins, and minerals.

Point No. 3. Contrary to the titles of today’s top-selling diet books, your athletes need to eat a balanced diet that includes all kinds of carbohydrates.

Low-carb diets are hot right now as the way to lose weight. According to a number of popular plans, most carbs are bad and need to be eliminated. At the same time, new low-carb products are flooding the marketplace and "success stories" abound of people who have lost weight by severely limiting or eliminating carbs.

Why do people lose weight on low-carb diets? For one thing, there are fewer food choices, which makes the diets easier to follow. Many people on low-carb diets also say they are simply not as hungry, which may be because protein makes people feel fuller, and also because low-carb diets typically allow high fat foods, which also contribute to satiety. And decreasing carbohydrate intake results in fluid loss, which shows up on the scale as rapid weight loss.

In addition, it’s harder to cheat on a diet that restricts carbohydrates. Many carbohydrate-containing foods are handheld and ready-to-eat, like bagels or crackers, whereas protein-containing foods tend to require preparation, utensils, and sit-down meals. Carbohydrate-containing foods are more likely to be eaten as snacks and on the go, which can lead to mindlessly consuming much more than is healthy.

If low-carb diets result in weight loss, why shouldn’t athletes jump on the bandwagon and start cutting carbs? Because carbohydrate, not protein or fat, is stored in the muscles and liver as glycogen, which provides fuel for exercising muscles.

The body cannot manufacture its own carbohydrate. If carbohydrate needs are not met, the body will either break down stored fat to provide fatty acids (which can in part be converted to glucose through a process known as ketosis), or break down lean muscle mass to yield glucose. Most athletes would probably rather preserve muscle mass, and stored fat should be a fuel substrate for exercise, not a substitute for adequate carbohydrate intake. It is also important to realize that exercise itself depletes glycogen stores, which need to be replenished with carbohydrate, not protein or fat.

Consuming carbohydrate before exercise can help prevent hunger, delay fatigue, and provide energy during the workout. Eating carbohydrate post-exercise expedites liver and muscle glycogen resynthesis so that athletes can recover more quickly. Amazingly, there are low-carb sport bars, no-carb sports drinks, and many "energy" products with water, caffeine, and artificial sweeteners as the primary ingredients. They may taste sweet, but they are not very healthy for an active body.

How much carbohydrate is enough to fuel optimal performance? The Institute of Medicine’s Dietary Guidelines revisions call for a diet containing 45-65 percent carbohydrate and not less than 130 grams of carbohydrate per day. (By contrast, some of the low-carb diets recommend an initial carbohydrate intake of 20 grams a day—the equivalent of six ounces of orange juice, four gummy candies, or two-thirds of a cereal bar.) Some athletes may do better with a higher percent (65 percent) of calories from carbohydrates, whereas others may prefer a more moderate carbohydrate intake, but no athlete will improve performance when the carbohydrate content of the diet is less than 40 percent of their daily caloric intake.

To help athletes translate the 40 to 65 percent recommendations to information they can use to plan meals, have them imagine their plate divided into thirds. The protein should fit on one third, while the rest of the plate should be covered with carbohydrate-containing grains, fruits, and vegetables.

Better advice for athletes is to discriminate, not eliminate, when it comes to carbohydrates. Portions, timing, and type of carbohydrates chosen are extremely important. Instead of relying on simple and complex categories, experts have turned to a new system for sorting carbs: the glycemic index. The glycemic index helps athletes adjust carbohydrate intake by choosing and timing carbohydrates according to the glycemic response, or effect on blood glucose and insulin levels.

Basically, eating any carbohydrate-containing food results in an increase in blood glucose levels, causing insulin to be secreted from the pancreas. The higher the blood glucose, the more insulin is released. Some scientists believe that the extent and rate with which carbohydrate-containing foods increase blood glucose and the insulin response may affect the risk for obesity, cardiovascular disease, hypertension, and Type II diabetes.

In the glycemic index system, carbohydrate-containing foods are classified according to how quickly and how much they raise blood glucose levels (i.e., their glycemic index). Foods with a lower glycemic index raise blood glucose slowly, whereas foods with a higher glycemic index raise blood glucose more rapidly. The glycemic index of a food is affected by:

Particle size. Larger particles take longer to digest and slow the rise of blood glucose. That’s why regular oatmeal has less of an effect on blood glucose than instant oatmeal, which has a smaller particle size.

Soluble fiber content. Foods like oats, barley, and dried beans take longer to digest and therefore the body’s glycemic response is more gradual.

Fibrous coverings. Foods such as beans and seeds take longer to digest, lowering their glycemic index.

Acidity. Acid-containing foods such as fruit, vinegar, and pickled foods take longer to digest.

Fat content. Foods containing fat take longer to digest.

Sugar type. Fructose takes longer to digest than glucose.

From a sports perspective, foods with a higher glycemic index will produce a greater and more rapid change in insulin, resulting in enhanced glycogen replacement in the muscle. When the goal is rapid repletion, there may be an advantage to consuming higher glycemic index foods. Moderate and low glycemic index foods take longer to enter the bloodstream and may be preferred for endurance exercise to promote sustained carbohydrate availability.

I recommend that my athletes choose carbs based on the duration of their events. Athletes who have early morning practice and no time for preparing breakfast beforehand may benefit from carbs that are processed more quickly, such as sports drinks. Athletes who have long or back-to-back events may feel better with a longer-empty grain such as oatmeal, whole grain waffles, or toast before exercise. (For lists of other high, moderate, and low glycemic index foods, see "Using the Index" below.)

What about choosing low-carb versions of regular foods as a way to keep carbohydrate intake at the recommended 40 to 65 percent? New low-carb foods are everywhere, from health clubs to fast food restaurants. Some of the more popular products include low-carb beer, pasta, candy, chips, muffins, pizza crust, bagels, cereal, sports drinks, and milk (the lactose is replaced by artificial sweetener and extra protein).

However, these foods are not the best choices for athletes. Some low-carb products are actually higher in calories and fat than the regular-carb versions. Others contain sugar alcohols, which can have a laxative effect. Some have an unpleasant taste and texture, and most cost significantly more money! When low-carb foods are added to a low-carb diet, variety goes up, but with it go calories, portions, and weight.

In addition, there is no industry-accepted definition for low-carb. Even more misleading, many products advertise on their labels the number of "net carbs" or "net effective carbs" in the food. The manufacturers have used net carbs as an advertising gimmick to make people believe that they are consuming fewer calories. This figure on the label is determined as follows:

Net carbs) = Total Carbohydrates – Fiber – Sugar Alcohols – Glycerine.

The assumption is that fiber, sugar alcohols, and glycerine do not contribute significant amounts of calories and don’t have to be counted, but this is an oversimplification. There are many factors that affect the glycemic response of a particular food, and lower net carbs doesn't necessarily mean a lower glycemic index.

I caution my athletes to look at all of the nutrition information on the label of a food that claims to have a low number of "net carbs." Often, they’ll find that the product contains the same number of calories as regular versions of the same food. Also, although fiber is not a calorie source for the body, sugar alcohols and glycerine are, so the bottom line is that carb-free does not mean calorie free, and low-carb foods still need to be accounted for in the daily caloric intake.

As nutrition sources, low-carb chips and muffins are not equivalent to fruits, dairy foods, and vegetables. Instead of going for low-carb gimmicks, athletes would be wise to meet their carbohydrate needs through fruit, dairy products, and grains, while limiting added sugar in desserts and snacks as well as high fructose corn syrup in soft drinks and sweets. (Ingredient lists can be misleading when it comes to sugar. For a list of sugar pseudonyms, see "Sneaky Sugars" below.)

While it’s essential for athletes to consume a diet high in carbohydrates, it is possible to have too much of a good thing. One reason it’s easy to overdo carbohydrates is that it’s easy to lose sight of what constitutes a portion of many carbohydrate-containing foods. There is a disconnect between true serving size and most student-athletes’ definition of a portion. I always tell my athletes, "Never eat anything bigger than your head," and as silly as that advice sounds, it reminds athletes to think about portion size.

Controlling portion size is easier said than done given the fact that a standard bottle of soda is now 20 ounces and contains two-thirds of a cup of sugar. A snack serving varies from the tiny one-ounce served on airplanes to the five-ounce convenience store bag. To help your student-athletes visualize appropriate serving sizes, give them the following examples:

• A two-ounce bagel is the size of a yo-yo, not a Frisbee.
• A cup of cereal is the size of a rolled up pair of sports socks, not the sports bag.
• A cup of hot cereal, pasta, or rice, is the size of a tennis ball, not a basketball.
• A potato is the size of a computer mouse, not the monitor!

Despite popular diet fads, athletes will still run faster, lift more, and last longer with pasta than poultry. The body needs to be fueled, not fooled. It is the responsibility of the athletic training staff, coaches, and all others involved in the athlete’s care and well-being to encourage and recommend a varied eating plan with carbohydrate-containing foods and beverages as a major player at every meal and snack.

High glycemic index foods are recommended for rapid repletion, while moderate and low glycemic index foods are preferable for endurance exercise. Here are some examples:

High Glycemic Index Foods
Angel food cake
Sports drinks
White Bread
Barley bread
Rye bread
Hard candy
Toaster pastries
English muffins
Soda crackers
Cold cereals
Ice cream
Corn chips
Baked/mashed potatoes

Moderate Glycemic Index Foods
Sponge cake
7-grain bread
100% whole wheat bread
Oat bran bread
Brown/white rice
Basmati rice
Bran cereal
Citrus juices
Sweet potatoes
Oatmeal/oat bran
Low-fat ice cream
Candy bars

Low Glycemic Index Foods
Nine-grain bread
100% Bran cereal
Citrus fruits
Rice bran
Apple juice
Raw peaches
Tomato soup
Tomato juice
Ironman Bar
Dried apricots
Raw pears


Look for these names on ingredient lists—they are "secret code" for added sugar:

Barley malt
Beet juice
Brown rice syrup
Cane syrup
Corn syrup
Corn sweeteners
Crystalline fructose
Evaporated cane juice
High fructose corn syrup
Invert sugar
Malt syrup
Maple syrup
Raw sugar
Turbinado sugar

Athletes who make these substitutions at snacks and meals will get fewer carbs from sugar and more carbs from healthy fruits, grains, and vegetables.
For snacks:

Instead of ------------------Choose
Pretzels -------------Trail mix with wheat chex/dried fruit and some nuts
Frozen yogurt -------Fruit flavored yogurt
Chips ------------------Popcorn

For meals:

Instead of --------------------Choose
White rice ---------------- Brown rice
Lettuce salad ---------- Marinated vegetables
Pasta with marinara --Higher protein or wheat pasta and add vegetables to the sauce
Sub on white bread ----Sub on whole grain
Taco salad ---------------Chicken or steak fajita with vegetables/salsa in a whole wheat tortilla
Corn flakes --------------Cheerios