Why Athletes Should Avoid The Keto Diet

If you're an athlete — meaning someone who exercises most days of the week and has a goal based on performance, whether it's running a marathon or competing in your regional CrossFit Games — you may want to think twice before starting the keto diet, which cuts carbohydrates out of your daily intake almost entirely. 

While you may have been tempted to try the keto diet in order to lose weight quickly, it probably won't be as effective as you hope. "Strength and power athletes as well as athletes engaged in high-intensity sports should skip over ketogenic diets," registered dietitian Marie Spano, one of the country's leading sports nutritionists, explains. "There are better ways to lose fat and fuel your activity." Without carbohydrates, you may find it's harder to train hard, which can hinder both fitness and weight loss efforts. 

A 2017 study showed that anaerobic performance — those hard efforts like power or sprint-based sports — were negatively impacted by a ketogenic diet. "Studies have demonstrated that high-intensity aerobic exercise performance may be compromised by low-carb diets — including keto," says the lead researcher Edward Weiss, PhD (via Healthline). 

Nutrition expert Mitch Kanter, Ph.D., explained to mindbodygreen that carbohydrates are the "only macronutrient that can be broken down rapidly enough to provide energy during periods of high-intensity exercise." That means if you need to fuel during a workout, you almost certainly will need carbs to provide your body the boost that it needs by replenishing depleted muscle glycogen stores. 

There is some research suggesting that ultra-endurance athletes — those running, swimming, rowing, or cycling at a relatively low intensity for long periods of time — may do well on a low-carb, high-fat diet like the keto diet, but most of the studies have been done on a small sample of young, elite male athletes. It's important to remember that a keto diet may work for some people, but not necessarily for everyone. If you find that you're continuously experiencing gastrointestinal distress, struggling to eat enough, or aren't seeing the body composition changes you were hoping for, it may not be right for you (via mindbodygreen). 

If you are an athlete who's still interested in trying a keto diet, seek professional help from a registered dietitian who can help you with the process, and if it feels as though it isn't working for you, don't be afraid to go back to eating carbohydrates. It's important to note that even athletes who are on a low-carbohydrate or keto diet will often eat carbs while training strenuously. Ultra-runner Zach Bitter has become well known for his ketogenic approach to fueling, but even he refers to carbohydrates as "rocket fuel" and uses them during certain training runs and in races (via Canadian Running).