I've been using an Apple Watch for 6 months and I notice the calories it shows are often way inflated compared to what I calculate myself. So I'm not really sure if I can actually trust the data to adjust my diet. Is this a known issue or is it just my watch acting up?
It's not really a systematic overestimation, it's just that the formula it uses (based on your heart rate, your weight, your age) is very generic and it can't know all the details of your personal metabolism or the quality of your movements. So yeah, the numbers can be off by 20-30% compared to reality, but it's not the watch that's "messing up" - it's just the limits of the technology.
For diet, it's better to use those numbers as a general trend rather than absolute truth. If you see that you're burning "500 calories" according to your watch, count on 350-400 instead to be safe, and adjust based on your actual results after a few weeks.
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