Fuelling your Workouts on a Keto Diet: To Carb or not to Carb?

What are the effects of a ketogenic diet on physical exercise and conditioning?

The benefits of being in a state of nutritional ketosis are widespread, from improved brain function and clarity to disease control such as epilepsy, type 2 diabetes and even cancer. (Beyond weight loss: a review of the therapeutic uses of very-low-carbohydrate (ketogenic) diets).

However, what are the effects of a ketogenic diet on physical exercise and conditioning? And what about carb fuelling your workouts on a keto diet? In a world where fitness professionals and gyms have long been promoting high-carb diets and glucose consumption prior to exercise to improve performance, is there any merit in a low-carb ketogenic diet, or are you simply setting yourself up to fail?

The good news is that although research on this topic is still at a fairly early stage, there is already a good body of evidence to suggest that ketogenic diets and exercise are not only compatible, in many cases, they are superior to a higher carb alternative for moderate to high intensity and ultra-endurance activities.

So how can this be? Well, when we use glucose to fuel our workouts the glycogen stores in our muscles get used up. This will of course be in proportion to the intensity of the workout. But for an activity such as running, you will have between 2-3 hours of glycogen (stored glucose) stored in your muscles. After this, you will need to consume more carbs or glucose (such as gels and ‘energy drinks’) during a long run or bike ride. Otherwise, you will experience the infamous ‘bonking’ or ‘hitting the wall’ where tiredness and fatigue start to kick in.

If instead you can tap into your fat reserves, then this has the potential for amazing results:

‘One recent study in ultra-endurance athletes found that a ketogenic group burned up to 2.3 times more fat in a 3-hour exercise session with no difference in muscle glycogen utilization and repletion compared to a high carb group’ (Metabolic characteristics of keto-adapted ultra-endurance runners.)

What if you are not fat-adapted (which can take up to 2 -3 weeks after starting a ketogenic diet) and want to experience the benefits of a ketone-fuelled workout? The good news is that you can–by supplementing with exogenous ketones (available here). And this is exactly what athletes all over the world have started to try for themselves.