You bring up really good points re: differing goals and metabolic health. This is a huge challenge for us on the podcast in terms of sharing information to a wide range of individual cases. I really appreciate you bringing these up, because some discussion here might benefit folks following this thread.
In this episode, I did my best to frame my recommendations specifically for performance, defined as maximizing your capacity to do quality work in the workout. With practice and adaptation, fasted sweet-spot training is doable and definitely confers some benefits. When it comes to cycling performance (not just aerobic fitness), however, one’s capacities in training zones above threshold are essential, and these become impaired when training in a low-glycogen (e.g. fasted or low-carb/high-fat LCHF) state.
Chris Froome limits his carbohydrate-restricted (LCHF, not fasted) training to endurance/sub-threshold rides and only with certain frequencies during certain times of the year (see e.g. this interview), because he still needs to train threshold, VO2, and his anaerobic/neuromuscular systems and needs carbohydrate to train those zones effectively.
BUT, not everyone is training for the Tour, and not everyone needs to train those zones effectively! If you’re not racing, for example, you don’t need to develop a high work capacity in supra-threshold zones. You can get very aerobically fit doing sub-threshold work - totally legit! But, not ideal if you’re aiming for performance specifically, which is what I aimed to address in this episode.
Jumbo Visma (among other pro teams) use exogenous ketones as a supplement, but they take these while eating a carb-rich diet that supports training and racing at intensities above threshold. The theory is that the presence of circulating ketone esters and full carbohydrate (glycogen) stores can spare carbohydrate during exercise and blunt catabolic effects. There is some confusion around this, because most people read about ketones in context of Low-Carb/High-Fat (LCHF) or ketogenic diets. On a ketogenic diet, carbohydrate stores become so depleted due to fasting or LCHF that the body produces ketone bodies, and these confer some great benefits in context of depleted glycogen. While these endogenous ketone bodies help, the depleted glycogen state hinders performance and thus doesn’t confer any performance advantage. (There’s good reason you’ll never see pros racing in a low-glycogen state.) The goal of ketone supplementation among pros, on the other hand, seeks the best of both worlds: benefits of ketone esters with the benefit of fully stocked glycogen. The goal is not to reduce the need for carbohydrate intake.
For example, from Dearlove et al. 2019:
This not to say that LCHF or fasting don’t offer benefits. On the podcast, we walk a fine line, because we have a very broad audience. Eating disorders are extremely common in sport and fitness, and have the highest mortality of any other mental illness. Fasting is a common way to restrict calories or eating in context of an eating disorder, and it’s very hard to discuss any kind of diet with sufficient nuance to avoid misunderstandings. I recently spoke with a sport psychologist who lamented a significant spike in eating disorders this summer due to athletes incorporating fasting to their training regimes to avoid putting on “covid weight.” It’s a real concern with potentially fatal consequences. On the other hand, many people struggle with metabolic disorders that could be well served with some (medically informed and guided) fasted training or with incorporating LCHF. Some of those folks might get more out of not worrying about VO2 power output and focusing instead on interventions specific to metabolic health. Again, even those cases are highly individual.
As regards calorie balance, this episode addressed fueling the workout specifically. Taking in the same amount of calories before/during training as you’ll burn during training doesn’t mean you can’t create a caloric deficit on the day; performance-wise (again in terms of capacity to do effective interval training on the bike), if someone needs to create a caloric deficit, it’s best to fuel the workout, then create a deficit by reducing portion size in another meal (or meals) during the day. If someone does not need to create a deficit, but doesn’t want a surplus, one would adjust intake off the bike to roughly match caloric needs of basal metabolic rate and lifestyle (so total intake = total output on the day). Similarly, people can adjust total carbohydrate intake up or down depending on where they are in their season, or perhaps based on metabolic parameters (e.g. blood glucose) if, for example, they’re addressing metabolic health concerns.
All of this is why we try to offer principal-based guidance, which can be flexibly applied. Most people feel better and can do more work (put out more power) longer, when they fuel their training with carbohydrate. Over time, consistent training and fitness gains will induce many of the same adaptations conferred by low-glycogen states. In my experience (12 years racing at the World Tour level and working with global experts in exercise physiology, performance, and nutrition), the most effective training is consistent training, and consistent training comes down to good habits. It’s easier to be consistent when you approach every workout with the same habits: fueling habits, hydration habits, even music choice, time of day, or pre/post-ride routine. Most people (barring certain medical conditions) will be able to train more effectively, feel better, and thus be more motivated to train consistently, when they give their bodies the fuel they need to crush intervals, and in most cases that’s carbohydrate.
The key really is to experiment and figure out what works best for you, and it sounds like you’ve found a groove that serves you and your goals really well in light of your schedule and the demands of your life. That’s exactly what we hope for all of our athletes, and we do our best to help empower people with tools and information to apply with their best judgment to their own circumstances.
I’ll do my best in the future to try to frame our discussions more clearly, because this is nuanced stuff and can be easily misconstrued. If nothing else, I hope this offers some interesting food for thought to the thread.