Huge question mark over Xert's fat calculations

Was considering experimenting with a combination of TrainerRoad’s plans and Xert’s fat loss calculation for mild, possibly safe? weight loss during build which I’m about to start next week.

Went out for a 3 hour endurance ride this morning to see what it came up with - it gives 241g fat. I was expecting a good figure as I was reasonably good at keeping my HR down for a lot of the ride until maybe later I perhaps started touching tempo.

Here’s my issue - 241g of fat converts to 2169calories. The ride itself was 2207KJ. Breakfast was a few eggs and slice of bread (500cals?).

Anyone think the numbers for the fat use are overblown badly and can’t be relied upon for anything meaningful?

That’s pretty high, and you’d have to have a pretty massive fat oxidation rate to achieve that.

For a pure endurance ride, you are probably looking at between 50-65g of fat per hour, which is around 350-450 calories per hour. You’ll burn a bit of glycogen as well but that’s ok.

I would ignore Xert’s calculation and just go by a generic calculation instead.

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Also YMMV, having done the whole weight loss thing during build, I’d advise against it. I’ve gone from 205 -> 155 over the past 4 years and I’ve had the best success doing the following:

  1. Heavy focus on weight loss during the off season (basically I go on vacation in October, don’t ride for that 2 weeks, and then as soon as I’m back, it’s time to focus on dropping some fat)
  2. Moderate focus on weight loss during base
  3. Maintenance focus during build (fuel your workouts!)
  4. Eat to feel during peak
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Yes! Agree with all of it and that’s my general sort of approach too, but I reckon I can lose a kilo a month (ie 2 kilos during the 8 weeks build) and get away with it. To do that I wanted to get some idea of fat usage via Xert but doesn’t look reliable unfortunately. Will just run a small to medium sized deficit depending on what the workout was that day.

I’m not quite sure how Xert’s fat algorithm works, but I’m guessing it is looking at HR as a % of maxHR to estimate where energy is coming from. So it is worth looking at what value of maxHR is entered into Xert, and how you calculated this.

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Interesting, that could be it. I couldn’t find any setting for maxHR just now when I poked around though.

If you’re one that blessed with a high threshold power and small high intensity energy store, the model will presume you’re not going to consume valuable carbs at very low intensities relative to your threshold power. Those with greater capacity and thus more power above threshold, by virtue of having that power, will rely more on carbs than those with smaller capacity. The model also doesn’t account for basal metabolism which may require considerable carbs. HTH


What are you doing to focus on fat loss? I’m in that boat now and am interested.

Caloric deficit while maintaining protein recommendations based on your weight

How well dialled in is your Xert fitness signature particularly your Peak Power? My understanding is that the Fat/carb estimations are heavily based on your LTP (as defined by Xert). If your signature is out then the Fat/Carbs will be miles out. Also what was your Carb grammage?