Zone 2 fueling, fat loss & aerobic conditioning

I’m looking to trim down body fat and build a better aerobic base by concentrating on longer zone 2 rides.

If I eat a carb heavy meal before the ride, will this stop all the zone 2 fat burning benefits as I’ve just flooded my my body with glycogen?

Your stated goal is to lose body fat, not to make your body more efficient at burning fat. There’s a big difference.

The reason why the latter is desirable for ultra-endurance athletes is because it can be difficult to fuel a 5,000+ kJ race. Being more efficient at burning fat means lower chance of bonking if underfueled.

For weight loss, going into the ride fasted won’t make a noticeable difference. You’re aiming for a caloric deficit. On my Z2 rides, 3,000+ kJs, I aim to fuel 50% of what I burn. Breakfast is included in the 50%. Then I eat a normalish 2,000 kCals for the rest of the day, which gives me a 1,500+ kCal deficit for the day. Going into a long ride fasted and/or underfueled makes the experience much less enjoyable, may result in fewer miles at a slower pace, and increases the chances of overeating later in the day.


I agree on the big pre-ride breakfast. If you dont, at best youre hungry and grumpy, or worse, you bonk. I have 2 young kids so kinda have to sneak out of the house first thing so Ive been doing overnight oats before longer rides and a gel and/or clif bar throughout. Super easy to make the night before and can eat it as im getting everything together.

In short, the answer to your question is no. You will still be burning sugar to some extent, just a larger % coming from fat. Even for diabetics, going for a walk around the neighborhood (z1, may touch z2 for a bit) has still been showed to lower blood glucose


Fuel your rides. Every ride. Z2, threshold, sweet spot, it doesn’t matter.

I used to not fuel my Z2 rides, thinking I’d lose weight more quickly. But in the end, I would more than make up for that by feeling ravenous and have a big breakfast (I train in the morning before breakfast).

Fueling every ride, including endurance rides, has led to several improvements for me:

  • My breakfasts stay consistent, no matter how much I train. That’s big. When your calorie deficit is just a few hundred kCal instead of 1.000 kCal, it is much easier to keep your meals consistent no matter whether and how much you train. My weight when ending a training season yo-yos much less than it used to before.
  • I practice fueling, which is a valuable skill. I internalized how much I need on an intuitive level how much I need, and my fueling when riding outdoors is much, much better now. Even when I don’t keep track of how much I eat, I would fuel quite well. In the past I sometimes felt I would overeat outdoors, but from crunching the numbers I know it is virtually impossible to “overfuel”.
  • Fat burning is not a useful skill for most cyclists. Yes, if you love ultra endurance stuff, then maybe, but for the vast majority of us, you don’t want to burn fat, you want to expend calories.

This should not be ignored - you need to look at your whole day, not just calories in/out while on the bike.


expend calories: what do you think you are doing when burning fat?..I also argue that you ALWAYS want to run a more efficient machine, in terms of fat burning ability. Drinking sugar is easy and should be done strategically. All serious cyclists know this.

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The underlying mental image is that if you want to lose fat and your body burns carbs, your fat loss will be lower. Eating carbs would turn down the fat spigot, which, in turn, would reduce fat loss. That’s a common misconception.

If your primary goal is weight loss, you need to establish a permanent calorie deficit. Whether you take in the calories as fat, protein or sugar does not matter on this side of the equation. As far as I remember, you can train to predominantly burn fat up until 2/3 of FTP. Hence, anything above low tempo needs glycogen (coming from carbs) fuel as the main source of calories. To maximize weight loss, you should establish a permanent calorie deficit, and that is easier if you up your FTP and expend as many calories as possible. So doing a well-rounded training plan that includes sweet spot is better than just doing butter burner rides.

Now you could object, we are only talking about whether or not to fuel endurance rides. But even here, it isn’t advantageous:

  • You want your calorie deficit to be consistent. E. g. I did a 1,100 kCal endurance ride this morning, pretty mellow (IF = 0.61 or so, I think). If I hadn’t consumed any carbs, then naïvely you would think that my calorie deficit for the day is 1,100 kCal. But in reality it is not, because my body would have craved food afterwards. I know, because I have been there. The calorie deficit is too large. You don’t want to exceed 500 kCal per day, which is pretty much my caloric deficit for the ride after taking in about 100 g/h in carbs.
  • Unless your FTP is really, really small, your intake during training will not exceed your energy expenditure.
  • Not fueling increases RPE, which, in turn, has a negative effect on consistency. And consistency is king.
  • When fueling correctly, it is much easier to maintain a steady diet off the bike. This is the biggest contributor to your weight yo-yoing. In the past when I did not fuel properly, I’d quickly gain weight in the off-season, because it’d take a while for my body to adapt to a lower calorie intake.

Some good advice above.

I would just add, think about the type (and volume) of carbohydrate your eating. No need to eat a big bag of processed sugar ahead of a Z2 ride, better off having a mixed meal with a bit of fat and protein included too (e.g., muesli/porridge with peanut butter etc).


This is the kind of advice that creates confusion on the topic. The two things are not related. Fuel source and fat loss. The simple answer to his question is, no, eating carbs before a ride will not affect fat loss. energy expenditure and storage is always in flux, so regardless of where you get your fuel (fat or glycogen), it will be either used or stored based on a calorie deficit or surplus. The ability to ride your bike without glycogen onboard is a misdirecting point.


Consensus above is that what’s important for weight loss is maintaining a steady overall calorie deficit, which I agree with. My N=1 experience has been that fasted or semi-fasted riding can be a useful tool for this though.

Just looking at the calorie deficit side of things (i.e. not getting into whether fasted riding enhances fat burning ability or whether enhanced fat burning is an adaptation you should be pursuing anyway) I find it pretty easy to head out for an early Z2 ride without eating, then have breakfast when I get home (if I’m riding >2 hours I’ll start fuelling at some point 1-2 hours into the ride). I’m not usually hungry when I first wake up, quality of Z2 work doesn’t seem to be impacted by not having eaten for ~10-12 hours (other than a pre-ride espresso), and a good breakfast afterwards means I’m not overeating during the rest of the day and my post-ride recovery is good.

On the other hand if I eat a good breakfast before heading out on a Z2 morning ride, I then need what effectively becomes a second breakfast when I get home. As I’m normally hungry by then, and if I don’t have a fairly substantial post-ride snack/meal then I end up overeating later. Plus it’s probably needed for post-ride recovery. So for me at least I find it easier to maintain calorie balance or deficit by only fuelling during or after early Z2 rides than by fuelling before and after. Higher intensity rides are a different story of course, they need fuelling.


This is a good topic. I am also trying to lose a little body fat and get under 10%.

For me, I can totally feel the lack of food on my early morning Z2 rides. I have to eat sugar before and during these rides or I start to get that low blood sugar feeling about 30 minutes in. I don’t if my body is just bad at burning fat, if my metabolism is too high, or what. These are true Z2 rides (1.5 hours) with my heart rate averaging around 110. Is it normal to need sugar like this on easy rides?

A question about calorie deficit: I am aiming for a deficit of around 500 calories a day when I include my morning workouts. It seems to be working but I have also kinda have stalled in my weight loss. Do I need to increase this deficit? Eat the same but do longer rides?


More volume of training would reduce that need. But I’d posit that it isn’t desirable to reduce that need for sugar, and you should just fuel yourself well for z2 rides.

FYI: When weight loss slows down on an equivalent kcal level diet, it usually happens over the course of many weeks, often imperceptibly so, and usually a slow-down from 1% body mass lost to complete flatline takes 8-20 weeks in most folks. The time taken to cut the rate of loss in half might be closer to 4-8 weeks for most people, and it really is a slow and steady change that you would never “sense” unless you were staring at a graph of well organized and religiously-collected weigh-in data If ever for a week or two it seems like all of a sudden weight loss just stopped, there is ALWAYS another underlying reason for it, and unless there was a big shift in exercise intensity/volume, or activity level, or kcal consumption, that underlying reason is something other than calorie balance.

Probably going to result in hypoglycemia and increased hunger, leading to increased kcal consumption.

I’d bet you’re not stalled, unless you’ve increased your kcal intake.


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!

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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