Perhaps no one has done more to raise keto’s profile among sports fans than LeBron James. In 2014, the Cavaliers star famously dropped a bunch of weight, thanks to eating nothing but meat, fish, vegetables, and low-sugar fruit for 67 days. But that was during the off season, and the debate over whether ketosis improves athletic performance is far from settled.
What is well-established is that workouts are harder (some would say near impossible) when one starts on keto. While the body is adapting to using ketones (as opposed to glucose) as fuel, exercising can be a joyless struggle. What lies beyond that few-week to few-month period has been the subject of some, though not extensive, scientific research. A few of the bigger takeaways so far include:
- Ketosis may be beneficial for endurance athletes, since it keeps them from depending on glycogen stores, which are typically sufficient for just a few hours of hard exercise. Running on ketones may keep them from ‘hitting the wall’ when glycogen stores are depleted.
- Because they’re not relying on glycogen, keto-adapted athletes burn significantly more fat than carb-reliant athletes during exercise. In a University of Connecticut study, ultra-endurance athletes on a keto diet burned fat up to 2.3 times more fat than those on a high-carb diet.
- For sports that require short-burst, anaerobic exercise (for example, sprints, high jump, soccer), carbs may have the edge. Research from Saint Louis University lends support to this, though the athletes studied had followed either a high-carb or keto diet for just four days (hardly enough time for fat adaption for the keto group).
When it comes to building muscle, evidence for keto over a normal- or high-carb diet (and vice versa) is inconclusive. A series of studies in Brazil, described well in Men’s Health, found no difference in muscle growth or muscle mass between the two groups, given equal protein intake. The takeaway so far may be that neither diet is necessarily better for building muscle, but it certainly is possible on a low-carb, keto diet.
What if you’re not an endurance athlete or a power lifter, but instead, follow a more modest exercise regimen? From my own experience, I was far more easily winded during my first few months on keto — I clearly remember needing to stop and rest to make it up the same sets of stairs at work I’d climbed easily for years. But, over time, I definitely felt more energetic — or, perhaps more precisely, more even in my energy levels, without the big highs and lows. The keto diet also cut through the brain fog that had plagued me pretty much always. The people I know who also do keto report similar things. Niklas (Hälsobar's other half) found that he feels stronger and has more stamina — though those benefits took a year to fully kick in.
What seems to be important — no matter your lifestyle or fitness routines — is to give keto time before drawing conclusions.