Is high-carbs consumption during Z2 rides efficient for weight-loss?

Question

I am bit overweight (BMI: 30+, 89kg/170cm), riding regularly 3 times a week, 2hrs/50+km/flat road each time. Rides are mostly in Z2, with occasional Z4 ride (once every 2-3 rides). I enjoy the rides, my main goal here is to gain some fitness, stamina. I see consistent improvement in VO2, FTP (measured with power meter), which is cool, but it also would be nice to shave off some fat.

I used to take very naive approach of simply reducing carbs (and food intake in general to create calories deficit) during the day BUT also almost never fueling during (or before/after) rides (I ride at nights, ~9pm). Just plain water for entire 2hr ride. Now I'm realizing that it wasn't the best approach. Changed it to more balanced box-diet, with better controlled calories intake.

What I still don't really know how to manage is fueling during the rides. I recently bumped into interesting concept (Science-Backed Nutrition Plan for Cyclists | Cycling Science Explained) on how to plan it.

In short (for those who don't want to go through entire YT video), general daily intake of calories is calculated as OEA x FFM

Where:
OEA: optimal energy availability, typically 30-45kcal/kg FFM: fat free mass (can be derived from body fat, measured with DEXA or better scale)

Example:

For 89.5kg with 29.1% body fat FFM = 62.6kg, that is further multiplied by 30kcal/kg (=1878kcal, lower range) or 45kcal/kg (=2817kcal).

That sounds legit. Now, for the ride itself suggested is the intake of 90g of carbs / 1hr, topped up after the ride to reach actual calorie burn.

Example:

• Ride was 2hrs = 180g carbs (=720kcal)
• Estimated kcal burn = 1100kcal
• Topup needed: 1100-720 = 380kcal (suggested is 4:1 carbs:protein ratio for top-up)

That amount of overall sugar sounds insane! For someone who just had bottle of water for these typical 2hrs, it sounds impossible to digest.

QUESTION:

• Does that amount of carb intake sound legit, when we talk about weight loss and other factors mentioned above (rider profile, type of rides, etc.)? Are my calculation correct?
• Alternatively, what are the alternatives (how to fuel for that kind of rides)?

I was checking other topics over here, but answers are either focused on generic cycling choices or general carb intake to avoid weight increase.

Answer 1

I never take in anything like that much, and not pure carbs. I reckon on recovery feeding both in the evening and the next day*. This is what works for me. I'm not trying to lose weight, but was happy to when I started doing proper road rides.

During covid restrictions I was doing something similar to what you're doing, on water alone. If I got over 60km and had a hill towards the end (likely on my way home from the directions I rode in at the time) I'd have a gel or a cereal bar a few minutes before the climb, so 20-40g carbs, 80-150kcal.

As people vary so much, the following is to give you an idea of something that can work for some people.

It's probably fair to treat my long rides (100km+) as mainly zone 2 - except the hills, both up (harder) and down (some long/steep enough to count as full rests rather than active recovery). My shorter rides (up to about 60km) can be zone 3 for significant sections. My routes aren't chosen for their training potential, but to be nice routes, and I live in an area where it's hard to avoid steep (but not massively tall) hills.

Taking Strava numbers and rounding them, I burnt about 4000kcal in 10 riding hours on Saturday, and 400kcal/hour would indeed be 100g_carbs/hour. And I can remember everything I ate. The total during the ride (rounded) was about 2300 kcal and 300g carbs, under 30g carbs per hour. I've added more detail below, as an example.

This is the sort of thing that typically works for me, but I've had a few years (and 85 days of over 200km) to figure out what I need - and that has changed over time. I still need more frequent feeding than a lot of long-distance riders.

Time from start	kcal	g carbs	notes
Before	500	50	estimated, granola & oat milk
1½ hours riding (plus a stop for a puncture)	407	64	Hot chocolate and a mince pie.
4 hours	760	70	Veggie breakfast (carbs estimated from similar elsewhere), coffee
6-ish hours	300	46	Cereal bar and a gel (I missed the planned cafe, which also led to running low on water)
At some point	129	23	Cereal bar
9½ hours	731	88	I must have needed it by this point. Hot chocolate, savoury pastry, and a cake that I couldn't finish. Lots of water.
After			A proper dinner with plenty of carbs (dhal, rice and naan).

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* After a hilly 600km weekend,the recovery feeding takes about 4 days.

Answer 2

I made some corrections to the answer to clarify my stance. In general, take caution that people here don't have formal training in nutrition. That said, 90-120g per hour is the target for people doing races or other long, hard rides. I've found that even in harder group rides, I don't need this much. I think you almost certainly don't need 120g/hr for a 2h zone 2 ride. Interval training also benefits from high carb intake, although keep in mind it takes about 15 minutes for the glucose to hit your bloodstream, so a lot of that is intake before the session.

(For reference for those unfamiliar with zone 2, or Z2, this refers to endurance rides, like long slow distance rides that you'd do in base training. This is about 56-75% of threshold power.)

For a Z2 ride under 2h, I usually don't take any carbs during the ride. For something around 2-3h, I'd want some fuel. For 4-6 hour Z2 rides, I'm trying to get into the habit of at least 30g/hr, including something with protein and fat for variety. At 120g per hour, I could be keeping pace with or slightly exceeding my calorie burn rate during a Z2 ride.

I think your understanding that you should create your calorie deficit outside of the rides is correct. A possible exception is if you choose to do fasted rides (but these are usually 30-60 mins, and probably more like zone 1 or low zone 2). My understanding is that you should do these rides on a limited basis if you choose to do them at all. There's some reading here, although it's aimed more at performance-oriented cyclists.

I haven't listened to the podcast, but TrainerRoad has discussed weight loss on its blog. That includes a link to a YouTube of the podcast, and that should also be available on usual podcast apps.

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A last note is that I don't know how strong the evidence base for 90+g of carbs for intense exercise is. Andy Coggan made comments on the TrainerRoad forum to this effect. I can't remember the specifics. His handle there is currently The_Cog if you want to browse. The TR forum is a generally useful place to seek information on this sort of thing.

Answer 3

Ambitious cyclists often aim for up to 100g of carbs per hour of long and intense cycling. As you point out, this is a lot and can be hard to consume and process, even in the form of easy to digest, pure carbs like glucose or maltodextrin.

From a pure performance point of view you probably don’t need that much (and probably don’t even benefit from it) for two reasons. First of all a 2 or 3 hour ride is still relatively short. Well rested muscles have enough glycogen (as well as the glucose in your bloodstream and glycogen in your liver) to sustain a bit over an hour of intense exercise. That’s the reason why you basically never see anyone eat during <1h races. The second reason is that your power output and therefore calorie consumption is probably not that high, especially during an easy training ride.

That being said, I think you should eat some carbs during >1h rides because it will improve your performance (and training effect) and recovery. It could also be helpful for weight loss if it reduces post-ride hunger and cravings.

Personally on a 2h ride at moderate intensity I feel fine with around 50g of carbs for the whole ride. Without any carbs I feel like shit in the last 40 minutes and my performance drops (as shown by my power meter). On a ride like that I burn around 720kcal per hour, so the vast majority of calories still comes from body fat and glycogen/glucose stores.

For longer rides carb intake becomes really crucial. With enough carbs and caffeine even a relatively untrained person can sustain hours and hours of cycling.

For training rides I wouldn’t over-optimize but instead see it as an opportunity to have some guilt-free soft drink or chocolate bar (pick one with less fat and more carbs).

On a 2 hour ride you burn at least 1000kcal. Even if you eat 400kcal of carbs and snacks during the ride you still end up with a sizeable calorie deficit from the ride alone which should be helpful for weight loss (if you manage to keep your overall calorie intake in check).

Answer 4

I'm sure this isn't what you want to hear, but if you're searching for an evidence-based way of losing weight by controlling your energy budget, then you're not going to find it. If you look through the literature on weight loss, what you see is mostly a proliferation of studies that measure short-term results from behavioral interventions such as restricting how many calories the subjects are allowed to eat. But, with some possible exceptions such as boxers and actors, people don't go on a strict diet with the goal of losing weight for a few months. They're hoping to make a change that will not just be a yo-yo cycle. A review of the literature (Mann 2007) shows that people almost always do regain the weight. In fact, when systematic errors are taken into account, the weight and health outcomes for people who underwent even rigorously supervised dieting are difficult to distinguish from the outcomes of people who didn't.

The best and most rigorous studies also seem to show that the human body actually has a fixed budget for energy output, and that changing the amount of physical activity you do has no effect on your total energy expenditure (science.org article below). Physical activity is actually only a very small slice of the pie when it comes to your calorie expenditure. The bulk comes from other stuff, such as running your brain and your immune system. The evidence from these studies seems to be that those other categories just get automatically reduced a little bit to compensate if you increase your level of physical activity.

Exercise is really, really good for you, but it is not a way of losing weight.

The notion that you need to "fuel" your physical activity is also more of a marketing ploy than anything supported by scientific evidence. Your evening bike rides are being fueled by muscle and liver glycogen, which was stored up from your meals earlier in the day or even the day before.

References:

Mann et al., 2007, "Medicare's search for effective obesity treatments: diets are not the answer," https://sci-hub.se/https://doi.org/10.1037/0003-066X.62.3.220

https://www.science.org/content/article/scientist-busts-myths-about-how-humans-burn-calories-and-why