Zone 2 fueling, fat loss & aerobic conditioning

There is so much in that study. Some of my takeaways:

  • the study suggests that feeding CHO does not spare muscle glycogen whereas in the end mentioning other studies that contradict that point. So still some confusion on that aspect :man_shrugging:
  • Feeding CHO does not flip a switch putting you into a stop using fat mode. In fact the picture above shows still big amount of energy used from fat even when fed CHO.
  • So even if higher fat oxidation rate when restricting CHO…if taking CHO you’d be able to go longer and so overcompensate overall fat utilized.
  • On the other hand…(and that supports the point you made):
  • But (for the bigger difference) note “from 80 min of exercise to fatigue”… that’s long into a hard exercise (I can’t imagine 70% VO2max for 3-4 hours (citing:“slightly below subjects’ blood lactate threshold”) :exploding_head::exploding_head:) … so it becomes a balancing act if you go down that path and need to keep upcoming training in mind…

What I ask myself:

  • But I don’t even know if one can conclude that let’s say having 10-20% higher fat utilization during some part of a workout effectively results in a permanent change of how your body uses fat for energy (or how many of these sessions would be needed for some permanent effective change)?
  • If so…what would be needed to permanently keep that changed physiology? Or would then taking more CHO again reverse that change?
  • Is it even sure that having let’s say 20% higher fat utilization during some part of a workout effectively trains the body to use fat better than a CHO fed workout with still good (but just not as high) fat use?

Any input welcome!

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I didn’t read the study, just making some causal observations. In studies when you see VO2max it often means the subjects were hooked up to a gas exchange cart, and they were measuring actual % of maximum oxygen consumption (and not power). Also, blood lactate threshold is often the first threshold, LT1, the aerobic threshold, possibly something in the 70-80% FTP range.

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I’m not an expert, and you should look towards others for a more qualified opinion, but in my understanding fat metabolism remains a very, very significant energy source for aerobic activities.

Here is my understanding of the situation: a combination of fat and weight loss is always coupled to a net energy deficit. But it doesn’t matter much where the energy comes from, provided you stay within reasonable ratios for your macros. So drinking lots of soda will make you fat even though soda does not contain a lot of fat, it is mostly carbs. Conversely, just because you take in a lot of carbs, it does not mean that your body can’t use its fat stores to make up a net energy imbalance, if not during exercise, then for the rest of the day. E. g. it will use lipolysis to replenish your glycogen stores after exercise.

Also, I am not convinced that the lipolysis spigot is turned down significantly or turned off if you demand more power from your body. In my understanding it is that the other spigots are turned up, and thus, the ratio will tip in favor of glycolysis even if in absolute term your fat metabolism hasn’t changed much.

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Is there a study that shows this causes chronic increase in fat ox, without concomitant loss in exogenous carb ox? Asking because if yes, I’d like to read it.

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Is the difference significant, though. Seems like it is in the single-percentage range at equal times. “At worst” 40 % of the energy came from lipolysis, which is still a substantial share.

How do you get to a 50 % difference?
If I look at the two figures in this post, if you look at equal times, then we are talking about an absolute difference of a few percentage points, perhaps peaking at 10 %age points. That’s a relative difference of at most 25 % = 10 % / 40 %, but I see nothing that would indicate 50 %.

Or are you referring to other data in the paper?

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: https://etheses.bham.ac.uk/id/eprint/1091/1/Pfeiffer10PhD.pdf
image
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.

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

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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.

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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.

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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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