Zone 2 fueling, fat loss & aerobic conditioning

i recently asked myself a similar question. I’m at a healthy weight, could shed 3-5kg for optimal climbing maybe, so i’m not focused on dropping - but still curious.

What i found is this PHD thesis:
WATer compared to 108g sugar (glu+fru) per hour via GEL or DRINK
Fueling during an endurance workout will lower your fat oxidation, but not shut it off.
Lots of other interesting datapoints in there, like comparisons of solid with liquid CHO intake, datapoints on gastro-intestinal distress in different athletes, running vs. cycling… recommended read.

I feel like fueling my workouts, including Z2, helps me recover. If i’m ready to do more work tomorrow, i’ll get more work in total. (similar approach in going to the gym: if i work hard enough to suffer from DOMs for 4 days and not want to work out again, how has that helped my goals?)

The trick for dropping weight is probably more in what you eat between your workouts.


You can leave that “probably” out of it. It’s all about what you eat between workouts.


I admit it is a bit hard to tell, but according to my eyeballs the values after 2.5 hours are about 50 % for the placebo group and 58 % for the carb group. To get 40 % vs. 60 % you’d have to evaluate the placebo group at about 2:40ish and the other group at 2:30ish.

I don’t want to quibble over millimeters in a graph. So let’s look at the trends: for the placebo group, you see a decline from about 42 % fat utilization to 55 %, 60 % at the very end. From 2 hours onwards the carb group seems to stabilize and oscillate between 42 % and 53 %, may hitting 50 % at the very end after hour 4. I’d say the difference says within 10 %age points most of the time, which amounts to 20–25 %. There are even phases where the carb group has a higher fat utilization (from 0:45 till 1:20).

However, let me point out one additional thing: the total fat burn in the carb group was certainly higher than in the placebo group, because they rode longer. Now I don’t know why the placebo group “only” had to ride for 3 hours, but if I had to guess it was that it gets really hard to ride that long if you don’t replenish your carbs. From my own experience, when I run out of carbs, I can hold 60, perhaps 65 % of my FTP, i. e. Z2. According to @WindWarrior’s comment, these riders most likely rode in Z3.

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search forum for the PD Gollnick discussions. Within 5 months of what was essentially 4x per week 1 hour threshold training, most of the participants were doing 85% vo2max for an hour. For athletes well trained on hour efforts (time trial specialists), 70% vo2max would be fairly straightforward. But if your threshold was lower, say 75% vo2max, the 70% effort in the carb/fat burning study would be more challenging.

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I don’t know if this point was in that episode, but my understanding is that what you eat and what substrate you use for aerobic metabolism during exercise does not alter the underlying aerobic adaptation in any fundamental way. No exceptions. The mechanisms of aerobic adaptive signaling DGAF.

With the exception of short easy recovery spins, I think fasted rides are useless and never suggest anyone restrict energy intake even at the start of rides. Diet manipulation is method that is used sometimes but has a lot of practical drawbacks that make it rare to pull out of the toolbox, since odds it doesn’t work or fully backfires are fairly high. I think you likely heard me discussing this method on another podcast, but restricting food to increase fat burning doesn’t sound like something I’d advocate.

You may be confusing that with my suggestion to always start endurance rides easier because lipolysis takes time to fully make blood borne FFAs available so you end up dipping into glycogen stores too much early on, which often becomes a positive split ride that feels awful at the end vs a negative split ride that feels great later on.


What is the white veg under the carrots?

onion? ultimate z2 fuel

I have never seem an onion like that, looks more like a white radish or turnip but they normal have a touch of pink.

I can identify everything else.

Egg Plant / Aubergine, Cauliflower, Carrot, **? The white bulb ? snowball Turnip??? **, Basil, Kale. Parsley, Broccoli, Beans, Red Bell Pepper, Coriander, Courgette, More carrots, Garlic, Squash, Tomato, Chilli Pepper, Cucumber, Red Cabbage.

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Could be Garlic?!

No, well it could be giant garlic, but I don’t think so, white turnip is my bet but would love to know for sure.

The garlic is beneath the potatoes, to the right of the squash, above the second lot of carrots and to the left of the broccoli.

Of course :joy: that was what I was referring to. I didn’t spot the other carrots and mystery veg!

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I’m not a nutritionist or doctor. This is just what has worked for me. We’re all slightly different so you will probably need to experiment and tweak your process.

Cycling is a great exercise amongst many that will help burn calories and get you into shape and improve your health. But probably the best approach to losing belly fat is to first start controlling what you eat and how much you eat and for some, the feeding window during a day.

I try my best to eat whole foods, avoid refined grains, sugars, seed oils, processed foods, junk food and drink only water. I eat either protein/fat or protein/carbs and avoid carb/fat combo.

That said, i am generally eating a low carb diet and I do a lot of my Z2 rides fasted, up to about 100km. If my ride will be 100+ then I will start to consume Vitargo at 70 grams per hour starting on the second hour and maybe protein bars depending on how I feel. But this will also depend on how I slept the night before, how fatigued I am that morning and many other factors so I will eat when necessary.

If during the ride I will be in higher zones for periods of time then I will definitely fuel with carbs.

If I were to race, definitely carb fueling is essential.

After long rides regardless of zones, I will always consume some fruits after the ride to replenish glycogen.

I’m 58, 3.4 W/Kg and average around 250km per week during summer outdoors riding. I also walk a lot and do at least 3x weight sessions per week. I’m lucky to have the free time with the kids out of the house.


So cool to have you commenting here and great advice! Maybe you did not see my post somwhere up above your post but you touched some points, thanks!

Kudos for the podcast, keep it up!

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Sure, we’d all like studies like that, which look at the topic holistically. Impact on training volume and training consistency? RPE? Just combining what I know with my own experience, I’d still say we should err on the side of fueling every single workout properly.

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Didn’t know that, perhaps that explains why I’m often feeling rubbish at the start of early morning rides, and feel like it takes me 30-45mins to “wake up”. Could be low on glycogen, so need to wait for lipolysis to power up. Knowing that there is an actual reason for that feeling makes trusting that I’ll feel better later on easier. (Probably also means I should’ve eaten more the day before…)


If you all decide to use the app I’m writing, we’ll have answers sooner than later. Data aggregation & analysis like TR, but for fueling & nutrition.

Anyone know anyone who wants to write some code for an app they’ll actually use? Equity on the table.


I’m interested, if you need beta testers, feel free to send me a DM.

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Also interested. Feel free to DM!


Code yes, but sounds like you’re mostly looking for frontend stuff - definitely happy to be a beta tester as well though! :slight_smile: