By Michael Ormsbee, Ph.D., Florida State University

Edited by Kate Findley, The Great Courses Daily

As much as carbohydrates get a bad reputation, they don’t have to be scary or off-limits. In fact, glucose is the preferred fuel source for your brain and your nervous system (as opposed to protein or fat). Dr. Ormsbee explains how many carbohydrates we should consume for optimal performance.

Purpose of Carbohydrates

How active you are, what size you are, and what your specific goals are will dictate how many carbohydrates you need. Of the three macronutrients—carbohydrates, fats, and proteins—carbohydrates are traditionally thought of as the most important fuel for exercise, particularly during high-intensity exercise like running fast, cycling fast, and lifting heavy weights.

Many types of carbohydrates exist and can be found in foods such as fruit, pasta, whole grains, corn, peas, and breads. However, they do not all have the same impact on our bodies. For example, fruit is not the same type of carbohydrate as pasta, nor do candy bars affect us the same way as a bowl of oatmeal or a serving of green beans.

In the context of body composition, we typically think about carbohydrates that we eat as something that either makes us fat or doesn’t. However, we also have to remember that carbohydrates provide us with fuel to ultimately produce energy, especially when we try to exercise at high intensity. 

How Many Carbohydrates Do We Need?

Through a process called glycogenolysis, or the breaking apart of glycogen, glucose fuels active muscles during exercise. About 100 grams of glycogen are stored in your liver with another 300–900 grams stored in your skeletal muscles and just a minor amount circulating in your blood. If you weigh 150 pounds, you will store somewhere around 500–1000 grams of glycogen or roughly 2000 to 4000 calories of fuel as carbohydrate.

The body needs glucose for some actions, and it is estimated that we actually make about 50 grams of glucose per day in a process called gluconeogenesis. This amount is quite low, and for people who are physically active and like to exercise, the amount of carbohydrate needed will likely be more. 

The current Acceptable Macronutrient Distribution Range from the Institute of Medicine for carbohydrates is between about half and two-thirds of your total caloric intake, with no less than 130 grams of carbohydrate per day to meet our basic physiological needs. Because one gram of carbohydrate yields four calories, you will need roughly 500 calories per day from carbohydrates just to meet minimal needs.

However, more and more research is beginning to accumulate showing that we may be able to consume far less than 130 grams per day, so long as the dietary fat and protein are also increased in the diet. Fortunately, when you eat very little carbohydrates, you can still function from the production of ketones, which are simply a byproduct of excessive fat breakdown as a result of a low-carbohydrate diet. This excess fat breakdown is called ketosis.

Ketosis for Weight Loss

Recently, ketone use for energy has been the topic of much research and debate, and in 2015, some experts voiced support for nutritional ketosis for weight loss and health. Nutritional ketosis is induced when a person is put on a very low-carbohydrate diet to encourage the breakdown of excess fat.

Other experts recommend the traditional model of a higher carbohydrate, low-fat diet for weight management and health. In any case, the research is quite clear that some glucose is required for life, and even more is likely needed if you decide to become extremely active.

However, most scientists agree that the United States is an “over-carbed” nation. They recommend that steps should be taken to identify what carbohydrates are best to eat at what times during the day to provide the best health and performance benefits and to minimize negative changes to body composition.

This article was edited by Kate Findley, Writer for The Great Courses Daily.

Dr. Michael Ormsbee is an Associate Professor in the Department of Nutrition, Food, and Exercise Sciences and Interim Director of the Institute of Sports Sciences and Medicine in the College of Human Sciences at Florida State University. He received his M.S. in Exercise Physiology from South Dakota State University and his Ph.D. in Bioenergetics from East Carolina University.