Zone 2 fueling, fat loss & aerobic conditioning

Except when it requires restricting carbs to do so, which negatively impacts carb burning efficiency, capacity, and physical performance.

But I think you agree, based on:

… so that was just clarifying for OP.


Thank you for the detailed answer!

1 Like

Others have added much more detailed and scientific answers. But as I have started to fuel z2 rides while losing weight this might be the important take away in the thread. By fueling all of my workouts I have cut down on overeating a ton. I make sure to take at least 25g of carb, if not 50g, during 60 minute z2 rides. I used to binge at night quite often when I didn’t fuel workouts, including z2. I can count on one hand the number of times I have binged over the last few months at night.


Thanks to you all for taking the time to respond to this, feel like I opened a can of worms with alot of helpful information to take in :rofl:


Welcome to the field of nutrition, where every question is a can of worms because everyone eats.


Some great info here.

Keep it simple.

Fuel all your training.

Before, during and after.

Run a deficit over a day, week, month.

Run the deficit off the bike.

This is a huge amount of time, much more than your training.

Do not get greedy, run a very small deficit, do it consistently, results will come.

If you get greedy and run a heavy deficit, you’ll more than likely falter.

Patience, patience, patience. Think months, not days. You’ll get there. You’ll have good days and bad days. Don’t fret, just aim at more good than bad.


You can’t really burn fat until your liver glycogen stores are empty which contains around 100g or around 500 kcal

That feeling is just temporary, it takes around a week for your body to get used to low carb and a further 3 to be completely back to your old level but once you are 1.5-2h sweetspot sessions shouldn’t be a problem to do fasted

Can we make the problem go away if we fuel with canned worms?



This is simply not true. Especially when riding at zone 2, most of the energy you use will come from fat.


This was my thinking. I’ve been listening to alot of Peter Attia’s podcast and his advice is that zone 2 primarily burns fat as a fuel due to the demand placed on the type 1 muscle fibres, as opposed to type 2 that are engaged at higher intensities. Zone 2 also increases mitochondria density which improves fat burning off the bike.
This is what led me to my initial (clearly flippant) question of whether carbs before a ride would negate the fat burning benefits of a zone ride?
Alternatively, I should just stop overthinking and do some riding lol …

1 Like

That’s not correct. Your body metabolizes fat as well. You should think of spigots, one for fat metabolism, one for glycogen and then you have your short-term energy stores for anaerobic efforts. So you don’t have to run your glycogen stores dry before your body uses its fat reserves.

It also forgets that your body will use fat reserves to make up for calorie deficits during the day. Or, if you drink lots of soda, it can convert carbs into fat, too, if you take in more calories than you need.


Not a nutritionist, but is it not a case of CHO in the system has higher oxidative priority than fat?

So, rather than the direct conversion of CHO to fat (de novo lipogenesis), CHO displaces fat as the dominant fuel source, leading to the fat that would have been oxidised now being stored (as body fat).

Happy to be corrected.

What should I fuel zone 2 rides with, on the bike?

I have a couple of longer ones (2 and 4 or 5 hours) planned this weekend. My original thought was to use Skratch Superfuel (almost fully carbs), just at a slower pace than my 100g/hour race pace.

But if the body is primarily burning fat during lower intensity sessions, is there a more appropriate nutrient mix for fueling on the ride?

It sounds like you’ve had a good experience with fasting and it hasn’t effected your performance. That’s awesome. I can tell you my personal experience, and that of everyone I personally know who has tried it, is that fasting and/or keto results in more fatigue, higher RPE, and power loss on the bike. I know some people who have stuck with it because they lose weight, but every one of them says it has hindered their performance on the bike (except one, who says it hasn’t, but his friends all talk about how it has).


I can second that experience. Trained last year for Leadville with a ton of Z2 fasted rides. Lost a ton of weight and took pride in training my body to use fat. After changing my approach this year, the juice is not worth the squeeze IMHO. I was grumpy, recovery was more challenging and RPE higher.

This year, my FTP is up (300 vs 270 ish), workouts are easier, weight slightly up (5 pounds but I think I could attack that differently), and I’m not nearly as irritable. Fasted is good for losing weight but not so much for training for me.


Where’s the fun in that!? Welcome to the “thinks about everything twice as much as they actually do it club.” It’s fun here!


Still just carbs needed. Body has plenty of body fat to mobilize for fuel and can do it at sufficient rates to support exercise, alongside good carb fueling.

This is a good option. You’ll still want high carb fueling for a 4-5-hr ride.


This does happen. As do about 100 other annoying cellular and physiological processes. I’m glad you brought this up.

Just wanted to offer a clarification and maybe help folks understand how to think about nutrition here a bit.

Making any decisions about anything nutritionally based on one pathway alone is a virtual guarantee for erroneous nutrition strategy.

Reason: homeostasis. There are opposing physiological processes that reverse whatever process a person is trying to acutely exploit, as soon as they cease that strategy.

The best way to make decisions on nutrition strategy is to look at the applied science first, rather than physiology. What makes someone faster? What makes someone lose weight? What are the very basics, boring, repeated so often they’re hated and totally cliché? Those are probably the things that work. Identifying mechanisms like carb burn rates, pathway upregulation, specific hormone responses, etc, is excellent for passing exercise physiology exams, and terrible for making decisions about someone’s nutrition strategy.

@d_diston I hope you don’t feel like I am singling you out at all, and I’m grateful for your post and openness to learning. Please feel free to ask any and all the hard and oppositional questions and I’m happy to help where I can.


I think there’s a huge variation in what people are talking about when they talk about fasted riding. My personal experience is almost the complete opposite of yours - I and nearly everybody I know who has tried it has found fasted rides to be manageable and beneficial if done right. That includes a lot of the strongest riders/racers I know who regularly do fasted rides. The times when the experience has tipped into being negative have invariably been when people take the view that if fasted riding is good then more fasted riding is better! I.e. pushing the frequency, length and/or intensity of fasted rides. In which case I totally agree that it quickly becomes counterproductive and the negative aspects you mentioned come into play.

FWIW, what works for me (and seems to align well with others positive experiences) is:

  • Doing them first thing when your body is naturally carb-depleted (especially if you’ve had a fairly low carb dinner the evening before). Going carb depleted through the day in order to do a fasted evening ride is a good recipe for grumpiness, fatigue, less productivity at work, etc
  • Keeping it Z2 or below. I also tend to focus more on HR and RPE than watts during these rides, I’m keeping pressure on the pedals but keeping it fairly comfortable. I’ve known people push up into doing Tempo or SS work and while some have been able to suffer through it nobody seems to enjoy it or get benefits from doing it
  • Keeping it to ~2 hours or less, or if riding longer than that then starting to fuel at some point before 2 hours so that the latter part of your ride is fuelled
  • Decent meal/snack afterwards (and maybe starting fuelling near the end) to ensure good recovery and that glycogen levels are replenished for your next workout
  • Limiting them to once or twice a week. More often than that I think has diminishing returns and fitting them in without impacting the quality of the key higher intensity workouts becomes difficult. Maybe more doable if you were in off season and doing mostly Z2 riding
  • Coffee beforehand seems to help lower the RPE and hunger, probably some psychological aspect to this
  • A nutritionist friend suggested adding some BCAA powder to my water to reduce muscle catabolism. Probably psychological as well but does seem to make the rides more enjoyable

I also think the gains from fasted riding are somewhat marginal. Almost certainly not worth doing if you’re riding 3-4 days/week or less, you’d be better off using those rides to incorporate more work and fuelling it. Probably not worth doing if you’re still relatively new to riding and making those big early gains. But if you’ve been training consistently for a few years, are starting to see the gains tail off, and are riding enough days and hours that you have quite a few Z1-2 miles on your plan to play with, then I think incorporating some fasted riding can be beneficial. It certainly doesn’t seem to do any harm.

1 Like