I don't believe that these watches or devices give a good indication of calories burned. There is a general formula, but I believe a well trained athlete will be more energy efficient than a novice for example. There are just too many factors in play to make any sort of assumptions with certainty. I log what I eat and drink on long training rides and then take notes after (RPE, how I felt after, etc). I also have Training Peaks set up to show calories expended versus calories consumed on a daily basis (and when I bother to track what I eat). I do this to generally get a feeling if I am eating too much or too little according to my training load. I did find, interestingly, that I wouldn't eat enough on the weekends, and then I would binge at the start of the week. To make things even more complicated, women's nutrition requirements while racing (carbs and hydration) are also different depending on certain hormonal levels. I have done a couple of sweat tests, so I know how much hydration I need in cool and warm conditions. My general rules are as follows: 60 to 70 grams of carbs per hour during long rides and on race day (I am using FarBars now as I have bloating issues with gels).750ml of electrolytes per hour during long rides and runs. I try eat nutritious, colourful food, with around 1.4g of protein per KG of body weight. My macros I aim for are 45% carb, 25% protein and 30% fat. If I want a chocolate, or ice cream, I will eat it, as long as it fits into my macro percentages and fits within my calorie intake for the day. I try keep things as simple as possible.
