This. There’s more to “fasted” than not eating on the bike. Or even necessarily skipping breakfast before a workout, depending on the night before.
I don’t tend to specifically target zone 2 rides - I use 4 hour (approx) social spins with my club/ pals. I normally “fuel”, but not really focused like if I’m racing or doing an event. Normally just when I’m hungry. I have been taking bottle mix, but only getting through 1. Coffee stop get’s me the last half hour/ 40 minutes home!
A typical 2–3 hour endurance ride translates to about 1,600–2,000 kCal, typically first thing in the morning. That is the better part of a day’s worth calories. When I don’t fuel, I fall into a hole after the workout and feel famished. After I eat, I’d be useless for 2–3 hours. Thing is, when I return my wife leaves for the gym and I have to take care of two kids. Fueling my ride not only makes me feel better during the ride, but I don’t fall into auch a big hole. I don’t feel famished, and because my stomach is relatively full, I desire a normal amount of food rather than wanting to stuff my face. And I think I recover more quickly, too.
The issue is not I’ve had no problems with energy levels while riding fasted on water only for upto 3.5hrs. The issue is when I get home and want to eat everything and then have no energy the rest of the day and just want to have a nice lie down. The 2000 calorie deficit has to be made up and I’ve found it easier to start making it up on the bike with sugar water and some snack bars than sit in all afternoon eating cake. If the deficit is not made up fast enough I find that my legs are fatigued the next day.
See this makes sense…and I wish you lead with this. I do most of my workouts in the afternoon and evening when I’ve already had a chance to get some food in.
If you are well trained endurance wise , and near your max fatox you could be oxidising fat at approx 1.1g per minute, which translates to 198g of fatox over 3 hours, which translates to 1782 kCal
You misread my post: even at 170 W average power, you are expending more energy than you can take in. So you don’t need pro-level power here.
The general recommendation does not change, you are supposed to fuel Z2 rides as well. I do eat breakfast before my big weekend endurance ride (either muesli or oatmeal).
Tim Podligar was on the The Science of Getting Faster podcast (at least twice), and he’s one of the experts. Apart from being an active researcher, he’s coaching world tour pro teams on nutrition. You could also look at @Dr_Alex_Harrison’s app, which calculates your nutritional needs. He coaches athletes up to the pro level. When I plug in an endurance ride using my data, the recommendation is 60–70 g/h. Alex also has a nice youtube channel. His videos tend to be long, but he goes in-depth. Lastly, have a look or listen to what the pros are saying, e. g. on the various podcasts or on their Youtube channels. Alex Dowsett and Phil Gaimon address nutrition in quite a few of their videos (including nutrition for endurance rides).
Regarding asking for evidence, I would recommend you have a look at your own post from earlier on:
You make three claims here:
What evidence do you have for this?
There’s a a difference between trying to become fat adapted through diet etc and becoming fat adapted through the nature of your training.
Just because someone who does ultra distance events doesn’t activity try to become fat adapted doesn’t mean they aren’t.
The last bit is mostly, although a lot of ultra distance is spent in Z2, it’s not the entire time.
P.S. I do ultra distance events and have done the past 12 years.
What evidence do you have that improved fatox reduces glycolic ability?
You still misunderstand: the issue isn’t whether the energy during a ride comes from glycogen or fat, or that I run out. I don’t run out, I have done long, under fueled rides for many years. I have the energy on board, and if memory serves 40–60 % come from fat.
The issue is replenishment: my body provides, say, 2,000 kCal for the ride. That means I will have to take in about 2,000 kCal + 2,000 kCal = 4,000 kCal on the day to balance my caloric intake with the calories my body expends. What we are talking about is when and how you ingest these extra calories.
What is more, my stomach is full after the ride, which means I won’t be famished and I tend to eat a more regular meal. After exercise, my sympathetic nervous system gives the keys to the castle to my parasympathetic nervous system. If I need a smaller meal afterwards, and part of the digestion has already taken place, and what I have taken in are simple carbs that are digested more quickly at less energy expense, I don’t fall into as deep a hole where all I can do is rest. When I fuel properly, I am paying part of that caloric debt during my ride, and my body can immediately begin digesting simple carbs, which are easy to digest.
Compare that to an underfueled ride: I used to feel famished, and after I had eaten copious amounts, I’d be really sleepy — my parasympathetic nervous system has to work harder because the foods I have eaten are more complex, I have eaten more than I usually do in a shorter amount of time. The worst thing you can do is eat something fatty, fat takes quite a bit of energy to be digested properly.
In addition, there is another big issue that fueling properly during my rides has largely solved: when I relied on eating “natural foods” after workouts, I had a lot of trouble adapting to variations in training load. I’d get used to consuming very large portions during breakfast, and this hunger wouldn’t go away when I couldn’t train for a week or had a rest week. It was worst when taking time off the bike: I’d feel like I was on a diet even though I was in a calorie surplus 
If you want to become a fat-adapted endurance athlete, you have to change your training and your nutrition. It is not one or the other. Note that fat-adapted ≠ improving your fat oxidation.
You might need to increase your fat oxidation to keep pace with your increased glycolytic capabilities, which are necessary to fuel muscles when you increase your lactate threshold.
If you offer your body carbs, it will prefer carbs over fat. So if you are an ultra endurance athlete who takes in gels, stroopwafels and beta fuel, then their dominant energy source will be carbs. And they will not be fat-adapted. Are they relying more fat than someone who is not an ultra endurance athlete? Perhaps, I don’t know. But that’s different from being fat-adapted.
We have to be careful here: my comment was in the context of fat adapted endurance athletes. You are asking me to provide evidence to a claim that I did not make.
Some research articles supporting fasted Zone 2 workouts below
I used fasted Zone 2 to good affect in my training. I was that rider that had to carry a kitchen on long rides, my back pockets were literally overflowing with fuel. This hindered me on hard group rides and races. I decided to do some Fasted Zone 2 Rides twice a week between 90 minutes - 2 hours. Anything more I fuel every hour and before the workout. Now days I can do a 4 hour group ride with 1/8th of what fuel I used to carry and my general performance has improved. Note for my long group rides I fuel before and during the ride. So it’s not fasting every Zone 2 ride. It twice a week, in a controlled environment (my trainer), eating mostly protein the night before and big breakfast after the workout.
Here are the research articles:
Methods: Fifty-five trained athletes (Functional Threshold Power [FTP]: 258 ± 52W) completed a home-based cycling training program consisting of evening high-intensity training (6 × 5 min at 105% FTP), followed by low-intensity training (1 hr at 75% FTP) the next morning, three times weekly for three consecutive weeks. Participant’s daily carbohydrate (CHO) intake (6 g·kg-1·d-1) was matched but timed differently to manipulate CHO availability around exercise: no CHO consumption post- HIT until post-LIT sessions [Sleep Low (SL), n = 28] or CHO consumption evenly distributed throughout the day [Control (CON), n = 27]. Sessions were monitored remotely via power data uploaded to an online training platform, with performance tests conducted pre-, post-intervention.
Results: LIT exercise intensity reduced by 3% across week 1, 3 and 2% in week 2 (P < 0.01) with elevated RPE in SL vs. CON (P < 0.01). SL enhanced FTP by +5.5% vs. +1.2% in CON (P < 0.01). Comparable increases in 5-min peak power output (PPO) were observed between groups (P < 0.01) with +2.3% and +2.7% in SL and CON, respectively (P = 0.77). SL 1-min PPO was unchanged (+0.8%) whilst CON improved by +3.9% (P = 0.0144).
Conclusion: Despite reduced relative training intensity, our data demonstrate short-term “sleep low-train low” intervention improves FTP compared with typically “normal” CHO availability during exercise. Importantly, training was completed unsupervised at home (during the COVID-19 pandemic), thus demonstrating the feasibility of completing a “sleep low-train low” protocol under non-laboratory conditions.
Purpose: We investigated the effect of a chronic dietary periodization strategy on endurance performance in trained athletes.
Methods: Twenty-one triathletes (V˙O2max: 58.7 ± 5.7 mL·min(-1)·kg(-1)) were divided into two groups: a “sleep-low” (SL) (n = 11) and a control (CON) group (n = 10) consumed the same daily carbohydrate (CHO) intake (6 g·kg(-1)·d(-1)) but with different timing over the day to manipulate CHO availability before and after training sessions. The SL strategy consisted of a 3-wk training-diet intervention comprising three blocks of diet-exercise manipulations: 1) “train-high” interval training sessions in the evening with high-CHO availability, 2) overnight CHO restriction (“sleeping-low”), and 3) “train-low” sessions with low endogenous and exogenous CHO availability. The CON group followed the same training program but with high CHO availability throughout training sessions (no CHO restriction overnight, training sessions with exogenous CHO provision).
Results: There was a significant improvement in delta efficiency during submaximal cycling for SL versus CON (CON, +1.4% ± 9.3%; SL, +11% ± 15%, P < 0.05). SL also improved supramaximal cycling to exhaustion at 150% of peak aerobic power (CON, +1.63% ± 12.4%; SL, +12.5% ± 19.0%; P = 0.06) and 10-km running performance (CON, -0.10% ± 2.03%; SL, -2.9% ± 2.15%; P < 0.05). Fat mass was decreased in SL (CON, -2.6 ± 7.4; SL, -8.5% ± 7.4% before; P < 0.01), but not lean mass (CON, -0.22 ± 1.0; SL, -0.16% ± 1.7% PRE).
Conclusion: Short-term periodization of dietary CHO availability around selected training sessions promoted significant improvements in submaximal cycling economy, as well as supramaximal cycling capacity and 10-km running time in trained endurance athletes.
Resting phosphorylation of AMPK(Thr172), p38MAPK(Thr180/Tyr182), and p-ACC(Ser79) (D2) was greater in FASTED (P < 0.05). Fat oxidation during 120SS was higher in FASTED (P = 0.01), coinciding with increases in ACC(Ser79) and CPT1 as well as mRNA expression of CD36 and FABP3 (P < 0.05). Methylation on the gene promoter for COX4I1 and FABP3 increased 4 h after 120SS in both trials, whereas methylation of the PPARδ promoter increased only in FASTED. We provide evidence for shifts in DNA methylation that correspond with inverse changes in transcription for metabolically adaptive genes, although delaying postexercise feeding failed to augment markers of mitochondrial biogenesis.
Keywords: HIT; cycling; muscle glycogen; sleep-low; train low.
In conclusion, F (Fasted State) is more effective than CHO (carbohydrates) to increase muscular oxidative capacity and at the same time enhances exercise-induced net IMCL degradation. In addition, F but not CHO prevented drop of blood glucose concentration during fasting exercise
Methods: Fourteen well-trained cyclists were pair-matched and randomly assigned to HIGH- or LOW-glycogen training groups. Subjects performed nine aerobic training (AT; 90 min at 70% VO2max) and nine high-intensity interval training sessions (HIT; 8 × 5-min efforts, 1-min recovery) during a 3-wk period. HIGH trained once daily, alternating between AT on day 1 and HIT the following day, whereas LOW trained twice every second day, first performing AT and then, 1 h later, performing HIT. Pretraining and posttraining measures were a resting muscle biopsy, metabolic measures during steady-state cycling, and a time trial.
Results: Power output during HIT was 297 ± 8 W in LOW compared with 323 ± 9 W in HIGH (P < 0.05); however, time trial performance improved by ∼10% in both groups (P < 0.05). Fat oxidation during steady-state cycling increased after training in LOW (from 26 ± 2 to 34 ± 2 μmol·kg−¹·min−¹, P < 0.01). Plasma free fatty acid oxidation was similar before and after training in both groups, but muscle-derived triacylglycerol oxidation increased after training in LOW (from 16 ± 1 to 23 ± 1 μmol·kg−¹·min−¹, P < 0.05). Training with low muscle glycogen also increased β-hydroxyacyl-CoA-dehydrogenase protein content (P < 0.01).
Conclusions: Training with low muscle glycogen reduced training intensity and, in performance, was no more effective than training with high muscle glycogen. However, fat oxidation was increased after training with low muscle glycogen, which may have been due to the enhanced metabolic adaptations in skeletal muscle.
What’s the difference? My understanding of being fat-adapted was that it simply means you can better use fat as a fuel source, which is the same as improving your fat oxidation. Happy to be corrected.
Guess it depends a bit on the definition of fat adapted as above. But certainly you can improve your ability to utilise fat as a fuel source simply by training more. I’m not an expert on this, but I have participated in lab studies and got to pick the brains of people who are. Did a recent study looking at how power and substrate utilisation were affected by different fuelling strategies (including fasted, ketones, sodium bicarbonate, carb drink, and various combos thereof). In the initial benchmarking test the guy running the study said I was “pretty well fat-adapted” and similar or better at using fat as a fuel source than other participants who followed a low carb/keto diet. I eat a lot of carbs and fuel well for all my intensity and longer rides. But I also do a fair bit of volume (~500 hours/year) and have done for over 2 decades, he said that would absolutely explain the ability to burn fat. Basically, if you do enough endurance training your body gets better at using fat pretty much regardless of what you’re eating or how you’re training.
I think it depends a lot on context including looking at your nutrition through the day, what the purpose of the ride is, what phase of training you’re in, whether you’re trying to overall lose, gain or maintain weight, what training you have the next day (or later the same day if you’re a multisport athlete).
E.g. right now I’m a few pounds heavier than normal after an off season break and some disrupted training, and I’m not planning to get too serious about my training again until January.
So I don’t have to overly worry about ensuring I’m fully replenishing glycogen stores for a key workout the next day, plus I’d like to shift that weight before January. So up to about 90 minutes Z2 riding I likely wouldn’t take any calories in during the ride, just have a good meal after. For 2+ hours I’d take some carbs on but probably not too much, maybe 25g/hour for a 2 hour ride, 50g/hour for a 4 hour ride, longer than that and there’d be a food stop anyway! At those low fuelling rates I’d also prefer to use things like bananas, dates, trail mix, cereal bars to fuel. It helps that I have a pretty good idea of my fuel oxidation at different intensities from lab testing - at 200W I’m getting ~80% of my energy from fat, at 250W it’s about 50:50 fat:carbs. 250W is towards top of my Z2, so a disciplined Z2 ride I’d get more than half my calorie needs from fat. Maybe 800cal/hour total burn with 300cals (=75g) of that from carbs.
If I was in a build phase and looking to maintain not lose weight, then for a long Z2 ride I’d aim to fuel at ~75g/hour right from the start of the ride to replace the carbs I’m burning, and I’d switch more towards simple sugars for those calories.
We know for certain? pretty sure that is at super low intensities where you burn fat but what is the benefit. At the end of the day, energy balance is surely the governing equation here.
Personally, this fat burning stuff does not make any sense at all to me.
I would just do the ride, if you feel a bit “meh”, eat a bit more, experiment. Simple solution.
zone 2 is not easy work - far from it. The majority will be still burning carbs and the body does not work as a switch, it is a continuum, isn’t it?
Off the bike modelling I cannot see applying - a whole load of systems are bypassed when you are on the bike.
how does that matter if you are trying to shore up your general fat stores? The question is remarking about not overdoing it also for leaness, this is a pure thermodynamic equation (internal mechanics aside).
Unless you’re in an overall calorie deficit…
Unless there is data to the contrary, I’m inclined to think that is pretty darn marginal in the grand scheme of things. I don’t think you’re going to store as much water as the fat you’re getting rid of 
Zone 2 are easy/endurance rides. You likely have 2000 or so calories stored up in the form of glycogen (a form of glucose) in your muscles, blood and liver. At Zone 2 you are burning approx 50% carbs and 50% fat. At Zone 2 say at 180W, you are burning about 320 calories of carbs per hour (the rest is fat burn). So you have 5-6 hours worth of glucose fuel, ready to power your muscles. I wouldn’t push it to the limit like that. But I DO do my 3-4 hour Saturday IRL rides with just water. Besides not really needing to absorb excess sugar for 2-3 hour Zone 2 rides, you can also improve your fat metabolism efficiency by riding without consuming all those excessive calories.
That said, when I decide to ride with our A group, I do regret not brining a sports nutrient drink. But then I’m in Zone 3/4. At that point sugars really do help.
My experiment this summer was fueling at 100-120g/hour of maltodextrin-fructose on all workouts/rides and I put on 5 pounds despite reducing calories off the bike. I felt the same on the bike, it did not improve my ability to consistently do 1.5-3 hour workouts. It did not improve my recovery. I was already winning in the kitchen and providing myself with adequate carbs off the bike.
So I went back to consuming 40g/hr on my 1.5-3 hour workouts. And upping that to 60-120g/hr on 3-5 hour workouts, depending on how I feel and off-the-bike fueling.