Are low carbohydrate diets okay for an endurance athlete?

No. One of the downsides of the popular low-carb eating system is that many endurance athletes are finding themselves without adequate nutrients for the final mile, literally! Endurance athletes need carbohydrates.

In my opinion a low carbohydrate diet would be a poor choice for an endurance athlete. A diet low in carbs would eliminate the consumption of healthy fruits, vegetables and other sources of fiber. In order to optimally perform endurance type exercise, the body relies on its glycogen stores as the main source of fuel. A low carbohydrate diet would mean the body would deplete these stores and have no means of replenishing them, forcing the body to shift its focus to utilizing either muscle or fat as its fuel source. Neither of these options are optimal for different but equally important reasons. The burning of fat (fat oxidation) is a process that occurs too slowly to be efficient for endurance exercise and the breaking down muscle as a source of fuel isn’t beneficial for obvious reasons.

Additionally, adherence to a low carbohydrate diet for an extended period of time could induce ketosis which can be dangerous, unhealthy state for the body. Restricting carbohydrates would mean than your diet would consist mainly of proteins and fats which could lead to increases in cholesterol levels.

Katie Davis
Nutrition & Dietetics
In one word: NO. This is a bad, bad, bad idea. Endurance athletes need to be eating 55-60% of their calories in carbohydrate - think 1/3 to 1/2 of your plate at mealtime. Why? Because when completing endurance activity, the body is using energy FIRST from stored carbohydrate. It uses energy from carb most quickly and efficiently (bonus for good performance). Once the carb runs out, it will then turn to protein and fat stores. However, the body doesn't as efficiently metabolize these to provide energy. Plus, this means precious muscle is being broken down for energy. In addition, keep in mind the brain only runs on energy from carb. That's why athletes feel lethargic or disoriented after a hard workout with poor fueling. Don't skimp on carbs - you'll hurt your performance.
Neal Spruce
Neal Spruce on behalf of dotFIT

No, they are counterproductive in every way for endurance athletes. Not only will you compromise performance but you will also not recover properly leading to less productive workouts that further reduce your performance potential. Carbohydrates (fruit, breads, pasta, rice, potatoes, etc) are the body’s primary and preferred energy source. Once eaten, they rapidly break down to blood sugar (glucose). The brain, nervous system and muscles are fueled mostly by glucose. Therefore, a continuous supply of carbohydrate is necessary to prevent body stores from being depleted. Not getting the right amount of carbohydrate leads to low energy levels, fatigue and significantly impaired performance.  Proper management of the amounts, types and timing of this nutrient is required to fill and refill the body's main “fuel tank”. Key carbohydrate guidelines are listed here: 

  • Carbohydrates should make up approximately 60 percent (55-70 is the range based on length of activity -higher for longer) of your total diet.
  • Starches and grains should be eaten at each major meal throughout the day to provide a lasting energy source. Major meals should be eaten every three to four hours.
  • Carbohydrates such as fruit, energy bars/shakes, and sports drinks are ideal for rapid fueling before activity to “top off” the fuel tank and immediately after exercise to optimize recovery.  The pre- and post-exercise timing is very important!
  • Depending on the sport, growing athletes should consume 3 to 4.5 grams of carbohydrates per pound of body weight every day. 

Using the Sharecare Fitness Application, you can design ideal athletic menus individualized for you including proper CHO and protein requirements, meal timing and complete endurance performance food plans. Simply fill in your personal statistics, set your goal and your program is created. The Sharecare Fitness Application is located under the Coach tab; click here for access:

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    Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.