How much of my fat stores am I realistically using on a zone 1-2 ride?

I’m currently in a strength-building phase (squats and deadlifts multiple times a week). I’m also looking to add lean muscle and so I’m actually trying to be in a slight calorie surplus.

Here’s my question…

If I go for a 2-3 hour zone 1-2 ride (and be very strict about not going into any higher zones), my various apps estimate that I burn between 1500 - 2k calories (I train with HR and PM). How much of that can I expect to be fat energy? In other words, if I’m trying to be in a calorie surplus to gain some lean muscle, how much of that 1500 - 2000 calorie deficit should be I be looking to make up in food?


To me, those burned calorie estimates seem way too high. Use some different calculators to double check.

Although it may not answer your question directly, you may obtain a lot of insight from the following podcast by Peter Attia, a very thoughtful physician.

In this podcast, they discuss zone 2 training—physiologic characteristics, fuel sources, lactate, and the transition into zone 3, among many other things.

You will be able to find this episode on Apple Podcasts.

1 Like

Uh, at least 1500-2000 calories?


Thanks @tkent, I listened to that podcast a while back, I’ll go back and listen to it again.

1 Like

I’m not sure if you’re trolling, but I’ll answer anyway. This was the whole point of the question. If I’m burning fat stores, then I’m obviously not burning nutritional intake for that day, and so eating 2000 calories after a zone 1-2 ride would put me way over.

Here’s another way to put it… if I do a 45 minute crit race and burn 2000 calories versus a 3 hour zone 2 ride and burn 2000 calories. Yes, I burned the same amount of calories but I’d argue the calories came from different sources, and so they need to be replenished in a different ways depending on your goals.

Of course I’m open to be corrected, which is why I’m asking the question in the first place.

I had a dietitian tell me to eat back at least half calories burned during any cardio type workout
That is also on top of my normal meals I eat during the day.
She also told me to adjust according to my goals. Now I eat almost all the calories back depending the intensity, a zone 2 ride I might eat back all the calories.
It’s a good habit to fuel the work and the standard 60-90 grams of carbs per hour is a good starting place. You will burn fat and glycogen at any intensity, the higher intensity the more carbs and lower intensity might be mostly fat burned.

My personal opinion - I don’t think it matters.

All of it. I say that as someone fueling workouts and losing 8lbs over 4 months without losing muscle. Pay attention to macros.

For an FTP of 248, if I do 5 minute warmup and cool down at 50% FTP, and the main workout at 71% FTP, then 2 hour workout is roughly 1250 calories and 3 hour workout is roughly 1850 calories. So depending on the specifics that 1500-2000 calories is roughly about right for someone with a slightly higher FTP (say 268W).


A calorie is a calorie. If you have a surplus you gain weight. If you have a deficit you loose weight.
In the end of the day, it’s as simple as that.


I don’t think that’s the way it works. Where you burned your calories from won’t matter as the new calories will either be burned or stored depending on the quality of the food and the number of calories you are consuming vs. burning. You can still build lean muscle while being in a calorie deficit, but it is slower. I think you just need to focus on your diet and eating high-carb, low calorie dense foods instead of high fat foods, your body composition will change.

If you are strictly looking at your weight, then it’s calories in vs. calories out.


A gas exchange test would help but you’ll need access to a lab.

I think you should just add that 1500-2000 cals to your total daily expenditure and then have a deficit off of that total. It’s not like if you only eat an extra 1000 cals that you can tell your body “please put that in my muscles first before that fat I burned.” Your body is still going to try to replenish your fat stores to some degree. So there’s no way for you to know if you are leaving your muscle glycogen stores unreplenished.

Edit: I missed that you were ultimately going for a calorie surplus. In that case I would definitely eat back all of those calories. A 2-3 hour bike ride is already so catabolic and against your goal that you would be doing nothing but hampering your ability to build muscle by having it create a calorie deficit.

A significant amount.

Regardless, you still have to make up for those calories on top of your normal daily expenditure, or you WILL be in a deficit for that day.

right, and from a macros point-of-view the macros focus should be:

  • enough protein to support strength building phase (squats/deadlifts)
  • enough carbs to support cycling endurance training

With 2-3 hour zone2 rides you aren’t going to need as many carbs in the diet as you would from doing higher intensity intervals.

I really think it is more about fueling the work.


This is not how it works. Your body will use both glycogen and fat for fueling - how much of each depends on a few things, among them the exercise intensity, how well trained you are, your diet, and its also individual. Availability also plays a role, how easy it is to access an energy store, but this will also change over the duration of the exercise.

When it come to refuelling, the more important energy stores will likely get refreshed first, and fat stores later, but it again depends on many other factors.

Generally speaking, the easier the ride the more calories burned from fat. But it’s worth remembering that energy cannot be created or destroyed, therefore it’s calories in v calories out.

What some people don’t realise is that our bodies are constantly burning fat and storing fat throughout the day. Literally everybody does it. When you’re in a calorie deficit, your body burns more fat from fat cells than it stores in that time period.

Not sure what you’re asking here. All calorie surplus is made up of food… do you mean macronutrients?

I think what you are saying is that you want to be in a small caloric surplus for what muscle building is concerned, but you want to be in a deficit for what fat is concerned.
It just doesn’t work like that. Your body won’t happily keep on “wasting” energy building muscle if it sees the low fat stores being quickly depleted.

we are all a bit different but we do not burn, fat over glycogen its sliding scale. At low exertion efforts you can train the metabolic system to use more fat, but … as always it will use some glycogen.

The link below is how to burn fat.

Utilizing fat for fuel

At low heart rates, 50-60%, you’re burning almost exclusively fat. BUT, you’re not burning a whole lot of calories per hour. Thus, you have to ride a lot of hours to burn a lot of fat. At higher heart rates a lower percentage of your energy comes from fats BUT you’re burning more calories per hour.


Even at such a low intensity, it’s closer to 50/50, at least initially. Only during prolonged exercise will you see RER values markedly lower than 0.80-0.85 (assuming a normal mixed diet, of course).


Was it the Steve Neal on the Flo cycling podcasts that discussed utilising more fat. Is that what fatmax is about ? Using a higher fat % at higher and higher intensities.