When it comes to low or moderate intensity exercise, fat is the muscle’s primary fuel source. For high intensity exercise, carbohydrates are the primary fuel and are stored in the body in very small quantities. One of the major causes of fatigue during strenuous and prolonged exercise is carbohydrate depletion.   This is because most athletes are sugar burners.  We can adapt our systems to be more efficient and utilize the largest fuel reserve we have in the body, fat.

Fat supplies are nearly unlimited. Even in the thinnest of athletes there are over 18,000 kcal of fat for fuel.  In contrast, we have only 1,500 to 2,000 kcal of glycogen (bodies form of storage for sugar) stored in the body.  By decreasing reliance on carbohydrates for fuel and increasing reliance on using fats for fuel, those who perform low to moderate intensity exercises should be able to perform longer and delay fatigue.

For the average person following a LCHF lifestyle, carbohydrate intake is greatly reduced below the levels that are normally consumed in the standard American diet on a daily basis. This does not affect an individual’s ability to perform basic daily functions or follow a normal workout routine because there is not a huge demand being placed on the body’s glycogen stores. However, endurance athletes following a low carb lifestyle may want to ingest carbohydrates after an event in order to replenish their glycogen stores. Not replenishing the stores could lead to fatigue and muscle weakness.  This is still controversial and the “window” for carb replenishment is from 30 minutes to 8 hours after vigorous exercise depending on the study that is referenced.  Replacing carbs does not mean using sports drinks, chews, beans or bars.  It means using real foods such as low glycemic fruits and non-starchy vegetables to help to replenish the glycogen stores. 

Relevant Studies

The University of Buffalo conducted a study on a group of male and female runners which examined the effect fat consumption had on exercise performance. The results suggested that endurance can be prolonged by increasing fat intake. However, a similar study conducted by the University of Connecticut showed that by consuming more fats than carbohydrates, endurance was reduced in high intensity exercises. 

Can I Perform Intense Exercises While Following a LCHF Diet?

One of the ways to be able to follow a low carb lifestyle and lead an active lifestyle that includes lifting weights and performing exercises that lean more toward the high intensity level, is to have one night per week where carbohydrates are consumed in order to supply your body with enough glycogen to perform more intense levels of exercise throughout the following week.

These carbohydrates are not the empty ones that are found in foods such as cupcakes, candy and junk food. These types of carbs should come from clean sources such as brown rice, legumes (beans) and sweet potatoes. Never fuel your body with refined sugars or flours.

Choose which day of the week you want to designate as your ‘carb night’, and consume as many ‘clean’ carbs as you like between 7pm and 9pm. The key here is to not overdo your carbohydrate intake, so do not force yourself to eat them. This will not derail your LCHF lifestyle. It will simply help to replenish glycogen stores for upcoming workouts to prevent the muscle fatigue and weakness.

What Exercises are Beneficial for a LCHF Lifestyle?

Any low to moderate intensity exercise is ideal. This can include aerobics, swimming and biking. As always, if you experience dizziness or extreme fatigue while exercising, stop immediately. This can be a sign of an overly depleted glycogen store. Starting off slowly on a LCHF diet and gradually increasing your exercise intensity should help to accommodate the body to using more fat for energy and avoid the possible side effects.  High intensity exercise, including high intensity interval training (HIIT), can be done while following a LCHF lifestyle but should bestarted after you have adapted to the changes while performing lower intensity efforts.