Yeah, that makes sense. Before I had kids, I’d often spend an entire day in the saddle. But even then, I don’t think I could have spent much more than 4 hours without eating — at least not without a significant impact on performance.
That makes sense to me, especially with the graphs I posted in mind: in essence you begin further down in time, so you get a little extra stimulus to rely on exogenous carbs and body fat.
If you unintentionally gain weight while training, then you need to fix your off-the-bike diet. The on-the-bike diet isn’t the issue here.
This is a very absolute statement to make when there are so many variables at play. If I ate 150 grams of pure sugar an hour on the bike for a 3 hour low zone 2 ride, thats 1800 calories.
Sure, im sure you’ll say “then just don’t as much throughout the day, problem solved” but it isn’t so simple.
It is about optimization, and its common sense that overfueling in ANY part of the day, whether dinner or piddling around on the bike, will have a negative effect on your diet.
But who the heck would do this? This thread seems like folks are just trading silly comments
no brother, just a little reductio ad absurdum to illustrate that it isn’t so cut and dry.
And, some people do this, I would bet. People are trying to “train their guts” to take as many carbs as possible. While I understand why, there has to be a point where it becomes counterproductive.
Not sure if I’d call your argument strategy reductio ad absurdum, because even at my small stature of 64kg, I can burn more than 1,800 calories in low zone 2. As you said, could even be a reason to train yourself to take in mega calories.
That seems like a contrived example. But even using your exaggerated numbers, you’d likely still expend more calories than that. On my last TR endurance ride (IF = 0.60, i. e. the lower end of Z2), I burnt about 700 kCal/h (191 W average). So after 3 hours, I’d still have a net deficit of 300 kCal. And that’s using your exaggerated numbers. Taking in 150 g carbs per hour for 3 hours is likely very hard, I don’t think I have ever come close to that.
Plugging in more realistic numbers, though, for me are 80–100 g carbs per hour. On the high side that means I have a net deficit of 300–400 kCal/h in low Z2. It’d be lower for others, but almost always do you come away with a net calorie deficit. Overfueling is not an issue, your nutrition off the bike might be.
As I wrote above, overfueling (on the bike) is not a thing most people have to worry about. Doing a workout with the recommended fuel intake (80–120 g/h for the most part) will result in a net calorie deficit compared to not doing a workout (and hence, not taking in the extra calories). You don’t have to skip meals or cut portion sizes.
Likely, the net calorie deficit will be large enough so that you are on the upper end of the daily recommended calorie deficit (AFAIK up to 500 kCal/day), so calorie-wise you could just continue eating as if you weren’t training. However, the issue is almost always the nutrition off the bike, so you’d benefit from improving your off-the-bike nutrition.
then maybe it wasn’t absurd enough. How about 150 grams of carbs on a 30 minute recovery spin?
The point is that somewhere along the way, there comes a time when you can eat too much on the bike. We’re arguing where that point is… i’d love to hear what professional cyclists are instructed to do to stay lean.
Everyone benefits from making good choices with off bike nutrition. It stands to reason that they would also benefit from making good choices with ON bike nutrition. Not sure why everyone thinks that riding a bike is a license to eat as much sugar as possible.
Yes, much better. You were lacking absurdum. I have degree in philosophy- luckily that’s not the only one lol.
Yes, but who is recommending that?!? You are building a very elaborate strawman here.
Professional cyclists have nothing to worry about. Neither have most amateurs.
Just do the math. I’m far from a professional cyclist and even with your inflated numbers, I physically cannot consume the calories I burn in low Z2. Even on the very chill workout (IF = 0.60) I’d have to take in 175 g/h. Oh, and FTP-wise I am at my low-point for the season. If I had done the same workout in September or October, I would need 190 g/h for the same workout.
Now scale up the numbers to a pro whose FTP is likely 15–30 % higher than mine (comparing peak numbers). While I have heard that pros can consume 150 g/h if need be, they’d still be deep in the red calorie-wise.
You are decorating your strawman. The advice is not and has never been “Eat as much an anything you can on the bike, independently of your goals, workout type and where you are in the season.”
I’m sure you can find someone, but that number is miniscule. Burning 400 kCal/h on the bike is something most athletes on TR can easily achieve. Ingesting 150 g carbs per hour for 3 hours is not.
1.5 lbs. gained in a matter of hours is just water weight. Drink more water, eat some asparagus - problem solved. 
I reckon there are 0 forum posters and podcast hosts saying to fuel a < 2hr Z2 training ride with 100g of carbs per hour.
That’s interesting. Are you simply saying upto 25% less of the sugar is absorbed and it sits in your stomach before passing through, or that your absorption rate is 25% lower than someone who’s had a high carb diet for years?
Oh, I fuel longer Z2 workouts. If I’m going longer than 3 hours, I’ll have things to eat during the ride. I always have snacks with me on the bike, regardless of the length. I’m not religious about not fuelling my Z2 rides, if I feel the need I’ll have a snack.
During the lockdowns in the UK I did some long Z2 rides without fuelling to see where my limits were. I carried snacks for when I was hitting those limits. I then experimented with what’s the minimum amount of carbs I need to consume an hour to maintain performance at Z2. I found out that answer on Z2 rides up to 10 hour duration.
I’m off on a 4-5 hour Z2 ride in about an hour. I have no intention of not snacking on this ride.
Because I ride ultra distance I’ll find my limits now and again. For ultras it’s useful to know where they are, and how far you can push it. For instance if the 24hr garage isn’t open at 3am, can you keep going till something is open in the morning, or do you need to stop and sleep as you don’t have enough food supplies for the next leg?
I also think it is genetic , and some of it is exercise induced. In other words at rest your absorption maybe the same as another person. But during prolonged or intense exercise your absorption may dramatically drop whilst theirs doesn’t.
Because ultra distance involves prolonged duration even if at a relatively easy effort, stomach issues are a common complaint later on. Reducing the amount you need to eat to fuel these events goes a long way to coping with the reduced gastric emptying.
“As exercise intensity and duration increases, there is considerable evidence for increases in indices of intestinal injury, permeability and endotoxaemia, together with impairment of gastric emptying, slowing of small intestinal transit and malabsorption. The addition of heat stress and running mode appears to exacerbate these markers of gastrointestinal disturbance. Exercise stress of ≥2 hours at 60% VO2max appears to be the threshold whereby significant gastrointestinal perturbations manifest, irrespective of fitness status.”
You did mention decades of bad high sugar diet though, which is impossible for teenagers to achieve.
Ain’t that the truth! I tried, and failed.
Yeah, some people get extremely caught up in trying to prove a point. Maybe i did too? I think your post very accurately describes my approach.
Nailed it. 
There are no absolutes of always doing this or that. I add sugar with salt and citric acid to bottles depending on a few things. For example:
If I skipped breakfast and doing a workout before lunch, will always add sugar. About 60g per hour for shorter Z2 seems to work. And if going a bit faster/multiple hours will bump it to 80g- 100g in each bottle regardless of having had breakfast or not and might then start adding solid carbs too.
Depending on the temperature, might add 1g to 3g of NaCl to each bottle.
If I did have breakfast then I might just drink plain water for shorter Z2 rides or just add in 20g to 40g of sugar per bottle.
I am able to ride multiple hours without eating on the bike if I needed to, but it is just not enjoyable as RPE starts going up. There is just no need and typically I am eating only 25%-50% of calories consumed during the ride, sometimes balancing on the edge of fueling just enough to keep the RPE from going up unnecessarily.
There is a lot more to fluid retention than sugar intake.
To be fair - I wasn’t suggesting I fueled all Z2 workouts at that level, nor that everyone should. I was merely giving an example of where fueling at that level was helpful for me.
If you have an FTP similar to mine and are doing Z2 workouts to start your day (straight out of bed) then I would recommend trying it, but I did not intend to suggest all of my Z2 rides were fueled like this, or that it would work for everyone