Briefly

If on alternate days you cycle and rest, and your ride uses, say, 1200 calories, what's better, to eat 2600 calories daily (and then where does the deficit come from on the riding days?) or to alternate between 3200 and 2000 calories (and what kind of diet supplies you with 3200 without disturbing your digestive system?).

For the impatient, let me illustrate the question with a figure.

Not So Briefly

My cyclocomputer tells me that my ride used 1200 calories. I'm here not trying to determine whether the figure is accurate. I'm trying to better understand the appropriate diet for a workout that uses such a substantial fraction (or, for some, a multiple) of the basic daily caloric needs. The other question (how can we—or how does a cyclocomputer—determine the calories used given distances, altitudes, heart rate samples, and speeds) is a very interesting question, but it is not the subject of the present discussion.

Since going through what was most likely "hitting the wall," I've been cautious to eat more, especially carbs.

During the ride I can get 350 or so calories from three small snacks.

Right after the ride I attempt to use this glycogen replenishment window and consume 170 g (about a third of a pasta package) to get ~550 calories heavy in carbs. With a sauce and fruits this after-the-ride lunch might add up to 800 calories, which is not too far from what an adult might need without a workout (assuming vaguely 400+800+800 for the three meals).

The purpose of this worked-out example is to illustrates the difficulty of attempting to reach 3200 calories in a day.

If I did this route daily, it would be simple enough. Rather than the daily ~2000, I'd aim to consume ~3200 calories daily.

But, in full humility, admiration, and respect for those who can climb three mountain ranges racing one day and still be expected to repeat the feat on the following day, I need a day to rest.

What do you do if you ride a day and rest the next? Is it more sensible to increase your caloric intake to, in this example, 2600 daily, or would you alternate between 3200 and 2000?

I am not trying to lose weight. More importantly, I'm hoping to avoid that the caloric deficit would come from losing muscles.

If you choose option 1 (a regular diet), where does the deficit on the training days come from?

If you choose option 2 (an irregular diet), is the human digestive system able to handle the stress of this fluctuation? Or is the secret really to drop the quality of the food and eat, say, cakes or chocolate bars, and then a thousand extra calories become a small volume of food. In that case it seems a spreadsheet would be necessary—to avoid that the outlandish number of calories do not come with an equally spectacular amount of saturated fats. Few would complain of the opportunity to indulge in extra slices of cakes and chocolate bars. The trouble then is the accompanying (saturated) fat. Even if it's not the objective, one of the nice side effects of a workout is to develop a larger heart muscle and larger-flow arteries. It doesn't help if that happens while both become surrounded with fat deposits.

Update

• Part of the problem is fear that my hunger triggers may be entirely off. They only signal a very slight extra hunger on riding days, which may mean a slow, inadvertent, and gradual muscle loss. The combination of potentially being hard to measure (slow) yet cumulative (gradual) muscle loss is what makes it worrisome.

• Judging by the very existence of hitting the wall, it's not that hard to exhaust the carbs stored in the body. I understand that these carb stores increase with exercise, but meanwhile what mechanism does the body use to average out? Are fat stores really capable of building up and getting used in a short-scale cycle?

• I'm not a doctor or sports nutritionist, but less than 90 minutes of cycling every two days is not a huge amount of riding. That's less than many people's cycle commute. You body has mechanisms for storing energy, so just eat normally every day. Sep 28, 2020 at 1:23
• My cyclocomputer tells me that my ride used 1200 calories. From riding less than 90 minutes, the number seems outlandishly high What kind of bike? How fast are you going? 800+ cal/hr is in fact on the high side - that's probably averaging outputting 220-240W to your pedals for 90 min. On a road bike on level ground, depending on how aero you are that'd likely have you going over 20 mph/30 kph - the entire time. In my experience, most guesses that things like cycling computers make for "calories burned" tend to be on pretty high side. Sep 28, 2020 at 1:49
• Does that include your basal metabolic needs or is it just the extra "spent" on the exercise ?
– Criggie
Sep 28, 2020 at 2:44
• Most fitness watches / bands highly exaggerate calories burned, some as much as 50%. Take the figure with a pinch of salt. It’s simple enough to make a spreadsheet and using basic calculations you can work out your TDEE, Base rate and more. Sep 28, 2020 at 10:56
• @Sam for the calorie count, what happens if you start a ride on the device but don't go anywhere? If it still goes up, it's including basal metabolic rate, which a general activity/lifestyle device is more likely to do than a bike computer Sep 28, 2020 at 14:19

Either is fine - in fact on this timescale there's not much difference.

My suggestion:

I suspect that what's most satisfying for your body and your desire to measure will be somewhere between the two - probably something like 2300 Cal on your off days and 2900 on your riding days. This should be quite achievable - a handful of cheese added to your pasta example and another energy bar on your riding days and you're well on the way.

Reasoning:

The human body is very good at averaging out calories burnt and calories taken in. This is easily demonstrated: the recovery eating phase lasts several hours (though tapering fast especially regarding glycogen), and carb loading (not needed for up to 90 minute efforts) happens the day before the ride. You'd see a weight fluctuation if you weighed yourself daily, but that happens anyway and hydration would affect that too.

If you're trying to maintain your weight and muscle mass, with that sort of level of riding, you should be fine with a sensible balanced diet eaten to hunger - tracking your calorie intake isn't necessary, but if you want to do it, that's fine, except that your estimate of your requirements may not be perfect.

Your body can store enough glycogen for that much effort, so losing muscle mass to fuel your rides really isn't an issue, especially as you're snacking. If you're worried, some small protein intake during/after the ride would do no harm (even just the little bit you get from energy bars with nuts in, for example). I sometimes do a 75 minute early morning fasted ride (32km, just under 800 Cal which seems like a good estimate - yours seems high but not implausibly so). In that case I start a protein drink towards the end, which seems to help my recovery in terms of muscle fatigue/aches.

I take your uneven pattern much further - every couple of weeks I do an all-day or even all-weekend ride, and then you really can't take in what you burn (Strava says 8000 Cal for Saturday's 400km). The excess hunger lasts 1-3 days, but my weight recovers in a similar timescale (when I first started distance riding there was a permanent drop after each long ride, but as I didn't get weaker in the gym I don't think it came from muscles). Yes there's some energy-dense junk food in there, but that's optional; I happen to like chocolate.

As for your worry about the stress of fluctuating intake - yes, it's fine. Most of our human ancestors had no choice (could they afford much more than rice/potatoes/bread every day, with meat once a week - or what could they gather in season, how often did they hunt successfully) and anyway couldn't measure their calorie intake. Your bowel movements might settle into a new pattern, but I wouldn't expect so much as a mild stomach ache

• To address your update in brief: glycogen responds quickly, fat less so, but it will be used well ahead of burning your own muscles. For this level of training, with a bit of a snack on the ride, you have no need to report Sep 28, 2020 at 14:17
• But if you ignore my modest workout, the question remains. Suppose you have the time and the fitness to go on alternate days on the ride that consumes 8000 calories. Even if you've been training for years, your glycogen is gone long before you finish the ride. The question then is do you a- carry along 8000 worth of energy drinks (that would be quite a load) or b- your body somehow supplies the energy by breaking up something.
– Sam
Sep 28, 2020 at 14:33
• That's what fat is for (its evolutionary benefit is that it's an energy store) but you're right that there's a limit to how far you can draw on it. What happens is that you slow down to the rate that your ability to burn fat (and whatever calories you consume) will support. This can be improved by fasted training, but as a baseline you'll still be able to ride, struggling a bit with hills Sep 28, 2020 at 16:21

This is a difficult question to answer without being a sports nutritionist, however my advice would be to worry less about daily totals and focus more on timings of when you take in calories.

I focus on trying to eat for recovery from my workout and to be fuelled for my next workout. For example

1. If i've been on a shorter (90mins or less) easy ride, i won't do anything special, just eat my normal daily diet.
2. If i've gone for a shorter hard ride but am NOT riding the next day, I'd take a recovery drink after, but no other changes.
3. If i've gone for a shorter hard ride and will be riding the next day, I'd take a recovery drink AND increase my calorie intake for the rest of the day
4. If i've got a big (over 2 hours hard, or maybe 4-6 hours endurance pace) ride the next day i'll eat a larger main meal the evening before AND (if possible) a larger breakfast on the day AND a larger meal to recover afterwards.

As for hitting the 3000+kcal per day - well strange as it sounds that is as much part of training as riding the bike once you start riding bigger volumes. You need to adjust from eating 3 meals a day to potentially 4-5 meals a day.

Alternative energy

If you want to avoid hitting the wall, you could look into using ketones. They are the alternative energy source produced by your body once our 2000 calories of glycogen stores are depleted. Ketones are produced by breaking down fat stores in our body. But because our modern diets are very carb-heavy, our bodies rarely have to produce ketones, and so switching from using glucose to ketones as a source of energy does not happen instantly. But you can buy 'ketone oil', and by familiarizing your body with this alternative energy source, allegedly your body can make the switch faster.

Getting enough calories

You mention the "difficulty of attempting to reach 3200 calories in a day." Body builders regularly have to get 3000+ calories a day. They often use "mass gainer" protein shakes, which often have 800+ calories per serving. I personally drink "meal replacement" shakes, specifically Huel, because they have a more balanced nutrition profile. Another very cheap and very convenient alternative is nuts. A 16oz (450gr) container of peanuts has ~2700 calories. That is something you can snack on throughout the day. Nuts also have a ton of healthy fat.

Calories during ride

I would suggest drinking a sports drink (such as Gatorade) in addition to eating snacks during the ride. Depending on what your snacks are, the carbs (glucose) in the food will not hit your bloodstream as quick as a sports drink will. Also, consider eating a small snack an hour before the ride. One peanut butter and jelly sandwich can easily have 300 calories.

Summary

As others have said, spread your eating out evenly. After all, when you are riding, you are using calories which your body has processed, probably the day before. Try to eat food which is more "caloric-dense". For example, a 16oz (450gr) box of pasta contains only 1600 calories.

Edit

I read your previous question. Eating a bunch of pasta a few hours before a ride is not going to fuel your ride, it's going to make you feel sick. I would suggest switching to a sports drink rather than croissants during the ride (unless you are French, because French cyclists are fueled entirely by croissants and espresso). You can buy Gatorade powder, and mix it in with your water to get precisely the number of calories you want during the ride.

• All super useful information, but... should I eat 3200 calories on the ride day, and 2000 the next, or should I eat 2600 daily?
– Sam
Sep 30, 2020 at 23:00
• Many professional road cyclists are using ketone esters for the reasons stated, but they are extremely expensive, and they're reported to taste vile. I'm not familiar with the use of cheaper ketone oils. However, the standard dose of ketone esters is 120 calories worth for one dose, often taken before a race. If that stuff actually works, I'd expect you'd need that much of the ketone oil. That would probably bring the price up, and the ketone oils I see on Amazon are not cheap. Oct 1, 2020 at 21:53