Spoiler alert: You don’t need to drink bulletproof coffee, you don’t need to shovel carbs down your throat and you don’t need to “convert” to ketogenesis.
The key to maximizing endurance performance, or performance in general, is getting the required adaptations from ALL sessions, you could be shooting yourself in the foot, unwittingly, read on to find out more.
This is a topic that gets hotly debated by many, mostly people on polar opposite ends of the spectrum in terms of high fat and high carb advocates, with both side putting forward their centerpiece argument, be it mitochondrial biogenesis or mTOR pathway activation. Both sides are correct, but it is important to note that both sides are equally as dogmatic and pedantic as they are correct, in technical terms, and nobody wins. Once again, the answer lies in the murky grey area as to how to use carbs & fats in your sporting or fitness endeavors to get the absolute most out of it. In summary, the low carb approach can be looked at almost in the same light as ergogenic aid (a supplement), there are certain sessions where it is beneficial, it has drawbacks if over utilized and it is not magic in isolation, also the results are less likely to benefit increasingly elite athletes.
So why can’t we go low carb for all the time? You can, if your training regime consists solely of easy aerobic work, you don’t train everyday and your not really buzzed about your performance, as your recovery will be impeded, thus your progression will be. If you have no tough sessions, nothing with a hint of intensity, no actual performance goals, and you don’t mind feeling sluggish, then go bananas (or avocados, rather), do all the fasted cardio you can manage, but just consume your carbs after training, don’t hold out on glycogen repletion. If you have an actual race season, some performance goals and you work all elements of your aerobic and anaerobic system (any reps, hill sprints, intervals, weights, threshold work etc.) then you cannot* do those workouts off of no or low carbs. *Technically you can, BUT your rate of perceived exertion will be much higher, your oxygen cost for a given intensity will be much higher and you won’t be able to actually go near the high end of your aerobic capacity, your exercise tolerance will also drop a bit. With increasing intensity, less blood flow gets to your adipose tissue, meaning less fats are metabolized (lipolysis rates go down when intensity rises), when the PH of your muscle drops as a by product of acid formation, transporters involved in getting long chain fatty acids into mitochondria are inhibited, also in part due to a depletion in free carnitine, which acts to buffer excess Acetyl Co-A produced, to allow for maintained intensity (Acetyl Co-A accumulation down regulates how your body makes more fuel available for work). These things all result in you feeling like your parents stuck a limiter after 4th gear in your car. If you want to get the most out of the tough work your doing, if you need to power up a hill or indeed you have a race (which has short bursts of sprints, climbs etc. which often dictate race placings), that isn’t the time for low carb. I hope that makes sense, in essence, if your workout is hard, or intense, only carbohydrates can match the rate of feul burning needed, and won’t be inhibited by the by-products of high intense exercise.
Also bear in mind, for those of you reading this, who are shaking their heads, tutting and repeating over & over that “I am an endurance athlete, I ONLY use fats, because the intensity is LOW”, to you guys/gals, I say, you couldn’t be more incorrect. Fat oxidation is optimized between 45-65% of your VO2max, easy running or jogging would be just about over that range, so unless you plan on strolling race day, or your Sunday long runs are actually strolls, you are using carbs also. Now, it is a sliding scale, and it is still possible to train low carb, I’m just making a point, that carbohydrate metabolism is ALWAYS involved, from low to high end of range. Elite marathon runners will belt around 26.2 miles at 85-90% VO2max, non-elites wont get quite that high, but not from it, you guys are simply slower at running, the intensity may not differ though, triathlon would be similar, there is a case for Iron-man being an exception (which I disagree with, but that’s another blog entirely). So even for longer “slower” events, this still applies.
So when CAN we use the low carb approach, and how do we do it? Great question, let’s take a look. If you are in off season, which is winter for cyclists and most runners, then this is the time to do it, reason being is that you have no races upcoming (no important ones), and the majority of your training is easier in terms of intensity, so recovery has a little more wiggle room at this time of year. Carb fasted sessions take a bit longer to recover from in terms of glycogen depletion and repletion, which in turn can suppress your immune function, and can make subsequent bouts of exercise feel more difficult or be poorly executed. For these reasons, it is silly do it in race season, or in a block of high intensity, where recovery and session performance are PARAMOUNT to adaptations and athlete confidence. So keep it for easy weeks, off season & cross-training. Pick which sessions to try fasted or low carb based off of the following criteria:
1) How long is the session, if its <100 mins, go for it. You have enough body glycogen at low intensity exercise to last approx 100 mins, I wouldn’t push it past that. If your run is longer, take a gel at THIS point and complete the rest of your session.
2) If it’s ONLY easy cardio, go for it. If your questioning this, read the article again.
3) Can it be done first thing in the morning, or after breakfast, if so, do it. It’s okay to train fasted, or to have one meal as a low carb meal (or low GI – you more so don’t want any insulin response for “low carb” training). I don’t think it’s a good idea to opt for low carb protocols for a whole day, as it tends to be restrictive and you cut out many staple foods, risking the overall health composition of your daily diet (remember, I’m a dietitian… health first!!)
If you satisfy all the above criteria, go mad, and enjoy it. Low fat sessions can improve your ability to efficiently oxidize fats, and it can cause elevations in circulating PGC-1a, an enzyme that leads to mitochondrial biogenesis, basically the powerhouse units of your cells get bigger and more in number, meaning you can tack on points to your aerobic capacity.
For more information, or advice regarding how you can optimize your training around your life, goals and needs, get in touch. I specialize in endurance athletes and am confident that if you haven’t already addressed this topic, that nutrition can add dividends to your sporting performance. Get in touch via the website or email me at: firstname.lastname@example.org.
Thanks for reading,