I’m having a hard time believing that carbs are a key ingredient to long term performance.
I think if you’re actually hitting your bottleneck, which is going to be quality recovery, carbs aren’t moving that needle.
What am I missing here? If my body can handle only so much training, why wouldn’t I focus on maximizing my fatmax power first? If you’re at your maximum absorbable load, wouldn’t it make far more sense to do it all on fat and also reap the benefits of the weight loss?
Fatmax describes the physiological point where your metabolism has the highest capacity of oxidising fat. Beyond that point, fat oxidisation becomes less efficient.
The way this is named leads to the common misconception that we do not burn many carbohydrates in this physiological state. This is not true, in fact we oxidise enormous amounts of carbohydrates at the fatmax point. Someone else can probably pull up a nice chart where you can see the oxidation profiles of the two different fuel types at increasing intensity. Your body needs sugars to maintain the intensity at which it can most efficiently burn fat. You might do that with your muscle glycogen first, but that will be depleted eventually and your fat oxidation becomes less efficient as a result. If you want to burn the most fat you will have to fuel the fire with carbs.
I am not a sport scientist so take this with a grain of salt. My understanding is based on my memory of discussions from various sport science podcasts.
The more carbs you consume, the less fat you burn. This has been scientifically proven. If you consume 120 g of carbs per hour during a leisurely 1-hour ride, you’ll burn virtually no fat.
I also recall a study that showed muscle glycogen is always used up first. The assumption is that the more carbs you consume, the better your recovery will be, meaning your glycogen stores are replenished more quickly. During very long rides, this can also lead to an increase in your TTE (since your stores are being replenished while you’re still riding). However, there is currently no evidence that consuming carbs allows you to generate more power in any way.
My personal opinion is also that a general recommendation of 120g/h of carbs is wrong. First, everyone has their own optimal metabolism. Second, I consider recommendations like “train your gut” to be highly questionable from a health perspective. Most of us here are ambitious amateur athletes, but none of us are riding the Tour de France. If you ride three times a week, you don’t need to worry about it at all. Even if you do short rides six times a week, I don’t think you need any special nutrition strategy. Most of our diets are set up so that we consume plenty of carbs even when not on the bike.
You should definitely replenish your calories during long rides. Riding long distances on an empty stomach is, of course, just as misguided.
For races, liquid carbs might make sense because you don’t want to take a break to snack, and it’s hard to chew when you’re pushing yourself to the limit.
But for training rides, I prefer to eat real food.
That’s the conclusion I’ve drawn from many discussions. I’m aware that this doesn’t align with current recommendations. But when some podcasts are “sponsored by Maurten” or similar, how much can you really trust those recommendations?
A graph from the insyncd website
Is the maximum absorbable training load affected by fuelling? Yes.
Whilst the body does not run on fat alone as fuel, it does make sense to train the aerobic system to become better at using fat for fuel.
It does not (to me at least) make sense to continuously train with deliberately depleted glycogen stores and no carbohydrate intake.
One of the benefits some cite for fuelling the ride (with carbs) is that they are not hungry at the end of the ride and don’t, therefore, end up going through the cupboards and fridge like a plague of locusts. That helps with overall diet management. Back in the day there was phrase “get fit on the bike, lose weight in the kitchen.”
It is only an example: the one shown on the insyncd website at the link in the post.
It is not (or at least it is very unlikely) to be yours!
I included it to show that 1) Fatmax <> only fat being used for fuel and 2) It can be at (or below) the lower end of the fatmax zone where the ratio of Fat:carb is highest.
Sentiero is the right free tool to start analyzing your Carb needs.
To an extent it really depends what you mean by ‘performance’? Is this competition performance, general training performance, life performance? And for the weight loss, it would either come from an increase in energy expenditure (either intensity, duration or both) and/or a decrease in intake. There’s nothing specifically magical about FatMax.
I’m tall and thin, 198cm and 65kg. Not much in terms of stored energy. High liquid carbs for rides 2+ hours completely changed what I’m capable of. Hugely expanded how long and how hard I can go. Fitness and output jumped up as a result. Previously was eating solid foods and always hit the gut wall very early and very hard. Up to 3 hours I do 60g/hr, 90+ for longer rides. Also feel so much better after a ride. And for the next ride. Using sugar+sodium citrate+real lemon poweder. A+.
That’s the million dollar question - what is performance anyway?
The missing piece is that “maximum absorbable load” is not a fixed ceiling that exists independently of fueling. Fueling is one of the things that determines where that ceiling sits.
If you deliberately reduce carbohydrate availability, the same external workload can become more expensive internally. RPE rises, glycogen restoration slows, quality can fall, and the next session may cost more to complete. So if you are already near the limit of what you can recover from, doing everything low carb does not necessarily make that load more productive. It may simply lower the amount of training you can actually absorb.
I also would not make FatMax power the end goal. High fat oxidation is very useful in an endurance cyclist, but the really useful phenotype is metabolic flexibility. You want to oxidize a lot of fat while the pace is economical, preserve carbohydrate where you can, and then be extremely good at using carbohydrate when the pace goes up. Fat simply cannot provide ATP quickly enough for the harder parts of cycling, and carbohydrate gives you more usable energy for a given amount of oxygen.
There is also a distinction between burning fat during a ride and developing the adaptations that make you a better endurance athlete. Yes, eating carbohydrate suppresses fat oxidation during that particular session. But that does not mean the aerobic adaptations from the training disappear. Conversely, training with low glycogen can amplify some of the signaling associated with oxidative adaptation, but more signaling is not automatically more performance. Chronic low carbohydrate availability can reduce training quality, high intensity capacity, and recovery.
That is why I think the useful version of the current carbohydrate paradigm gets lost in the debate. It is not really “eat 120 grams an hour whenever you get on a bike.” It is fuel the work required. A short easy ride may need very little carbohydrate. A long endurance day may need enough to stop the second half becoming a survival exercise. Threshold, VO2, and race specific work usually benefit from high carbohydrate availability. Very high intakes make sense when the duration and intensity justify them and the gut has been trained for it.
I would also separate weight loss from this question. Burning more fat during the ride does not automatically mean losing more body fat over time. If the goal is to get lighter, the energy deficit can be created across the day or week without deliberately compromising the sessions that are supposed to drive adaptation.
So if by “high carb paradigm” we mean 120 grams an hour on every training ride, I agree that makes little sense. But if we mean matching carbohydrate availability to the purpose of the session, that is a very different proposition.
The interesting question is probably not “carbs or fat?” It is which sessions actually benefit from low carbohydrate availability, and which sessions are you simply making worse by withholding it?
I would even go farther, “maximum absorbable load” across what time horizon?
What may be absorbed in 42 days, vs what is the most training you could do in 90? In 180? In the year?
I suspect that at longer time horizons, diets that rely less on carbohydrates and more on fat, will produce better results in certain dimensions.
Two scientists that have done extensive work in this area are Tim Noakes and Philip Prins
You can see some of their publications here (they are joint authors on some).
This paper by Noakes and Louise Burke may be a decent place to start
"Does a low-carbohydrate diet impede endurance sports performance? Debate Consensus"
https://pubmed.ncbi.nlm.nih.gov/42070893/
Along with one of Burke’s other papers
Ketogenic low-CHO, high-fat diet: the future of elite endurance sport?
High-volume carbohydrate intake (such as 120 grams per hour) during high-intensity endurance exercise drives acute metabolic shifts—specifically hyperinsulinemia and cellular potassium influx—that alter cardiac repolarization. When paired with high sodium intake, intense sympathetic activation, and long-term volume overload, these recurring fluid and electrolyte shifts promote structural and electrical cardiac remodeling over years of training (Lobo et al., 2023; Rajanayagam & Alsabri, 2021).
Lobo et al. (2023): Atrial Fibrillation in Endurance Training Athletes: Scoping Review (DOI: 10.31083/j.rcm2406155)
Rajanayagam & Alsabri (2021): Intense Endurance Exercise: A Potential Risk Factor in the Development of Heart Disease (DOI: 10.7759/cureus.12608)
Sorokin et al. (2009): Atrial Fibrillation in Endurance Athletes (DOI: 10.1136/bjsm.2009.057885)
PREVENTION PROTOCOL: COMBINED CARDIAC & ELECTROLYTE PROTECTION
Potassium Offset: Include 150 to 300 mg of potassium per hour in your drink mix. This counteracts the rapid insulin-driven influx of potassium into muscle cells, preserving serum potassium levels and preventing delayed Phase 3 repolarization.
Fluid and Sodium Balance: Consume 500 to 1,000 mg of sodium per hour paired with 500 to 1,000 mL of water (adjusted for sweat rate). Maintaining proper serum osmolarity prevents hypernatremia and reduces stress on the sodium-calcium exchanger (NCX).
Magnesium Co-factor: Add 50 to 100 mg of bioavailable magnesium (such as magnesium citrate or glycinate) per hour. Magnesium acts as a natural regulator for L-type calcium channels and the Na+/K+ ATPase pump, preventing intracellular calcium overload and Delayed Afterdepolarizations (DADs).
Daily Dietary Potassium Target: Consume 3,500 to 4,700 mg of potassium daily from whole food sources (potatoes, sweet potatoes, leafy greens, avocados, bananas, and coconut water).
Stable Dietary Calcium: Maintain a steady daily intake of 1,000 to 1,200 mg of dietary calcium to support baseline excitation-contraction coupling without needing high-dose acute supplements.
Post-Exercise Recovery: Drink an electrolyte solution containing both sodium and potassium immediately after long training sessions prior to eating high-glycemic recovery meals to buffer post-workout insulin spikes.
Reserve High-Carb Fueling: Use the 120g/hr intake protocol exclusively for high-intensity, race-pace workouts and target events. Rely on lower carbohydrate targets (30 to 60g/hr) for low-intensity Zone 2 endurance training.
Monitor Autonomic Balance: Track morning Heart Rate Variability (HRV) and Resting Heart Rate (RHR). Persistent drops in HRV signal elevated sympathetic tone and altered intracellular calcium handling, indicating a need for rest.
Medical Screening: If you experience heart fluttering, ectopic beats, or sudden unexplained heart rate spikes during or after exercise, consult a sports cardiologist for a 24-hour Holter monitor and an echocardiogram to check for early atrial enlargement or fibrotic remodeling.
REFERENCES
PubMed ID: 19047339
Finding: Demonstrates the direct connection between years of heavy endurance training, atrial enlargement, and a 2- to 8-fold increase in atrial fibrillation risk.
PubMed ID: 29633276
Finding: Details how exercise-induced volume overload, high calcium/calmodulin kinase II (CaMKII) activation, and micro-fibrosis create the substrate for athletic arrhythmias.
PubMed ID: 26987309
Finding: Explores how fluid-electrolyte shifts, high vagal tone, and mechanical atrial stretch interact during prolonged endurance exercise.
They’re a key to nailing sessions, which leads to repeatedly nailing them, which = long term performance gains. Is this question a serious one, or just trying to bring up a discussion?
If you’re asking these questions seriously, you need to spend a whole ton of time digging in on the topic of why maximizing fat oxidation doesn’t really lead to the gains in performance that you are hoping for.
I think you’ve done what you think “is hammering key sessions” and have that confused with optimal training.
No not really. I meant doing the workout properly. Anyway, have fun with your journey
Just as training can be periodised, diet can be too.
More on harder / higher intensity training days, less on easier / lower intensity days and less again on rest days. Adjust the mix of food types accordingly.
Some good research done in this area by Samuel Impey (who then went on to co-found Hexis, which is used by a few cycling teams) and Jon Bartlett (who is also now at Hexis).
A curated “science” section on the hexis site
