# Xert - Fat & Carbs - Connect IQ

High-level question:

does it show how much was used or how much to refuel to have optimum performance?

Reading the forum I have assumed likely answer could be used but …

If I apply 101 guidelines and simple formulas:

• Energy (kcal) = Power (watts) * Time (hours) * 3.6
• 3.75 kcalories per 1g of carbohydrate
• replace 25% of the calories you’ll burn (assumes a gross metabolic efficiency of 24-25%)

With the above device [Energy] / [3.75] * [25%] (or in simple math [calories] divided by [16]) I get VERY close to Xert’s realtime carbs calculation.

Thus this leads me to think the algorithm is super smart and is actually advising me how many carbs to put back into my body.

Thoughts? Or just dumb luck that my math adds up?

You burn a combination of fat and carbs, and you only need to replace the carbs on the bike. The ratio between carbs and fat depends on your fitness signature and the power you produce.

I did not understand why you would take 25% in the calculation. If 25 % is the efficiency, you should divide on 25% to calculate how much you need to eat (as 75% will be “wasted” by your body).

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Ideally, the data field does both - it shows how many carbs we estimate you’ve burned through, which you can use as a refuelling guide. If you’re riding an endurance event, you should use the data field to limit your carb usage to no more than ~100g/hr, since that’s about the upper limit of carb intake for most athletes.

As a side note, assuming Gross Efficiency of 25% is probably a bit of an overestimation - a more realistic value would be close to ~19-20%

Thanks all for responding. Maybe math aside, what is your answer to this?

(Actual numbers)

• Situation 1: 2.5 hour road race: 2,272 calories, 122 fat grams, 262 carbs grams
• Situation 2: 3.75 hrous of zone 2: 2,999 calories, 297 fat grams, 40 carbs grams

The above makes sense, as intensity increases the carbs get used up for energy and when intensity is lower body starts burning fat.

My question is rooted here: would you follow Xert’s estimates and refill with specified carb grams? So this would mean:

• Situation 1 you would target to take in 262 carbs during the race
• Situation 2 you would target to limit and take in 40 carbs of gram during a Z2 ride

The more I experiment with this the more I find whatever Xert tells me to eat in carbs feels right .

My ultimate driving reason to ask this: I don’t want to overeat, want to continue to improve fitness and keep lean.