What activity level did you select when calculating the TDEE? If you sit at a desk all day, even if you do a 2000 kJ ride, I would still select the sedentary activity level. If you have TR -> Strava -> MyFitnessPal your 2000 kJ from the ride would then be added to the calories burned. If you select a high activity level and then add the kJ from your TR ride you’ll be counting (roughly) the calories burned during the ride plus the extra calories MFP adds based on your activity level, which includes an estimate of your exercise time. Essentially you’d be inflating your estimated calorie burn for the day and if you try to eat that much you’ll gain weight because you’re over.
TDEE calculators are an estimate based on model(s) of size, lean mass, activity level, etc. There are a lot of variables involved and I would consider it a place to start (assuming good data going in), but to find the real number you need to track what you eat, your exercise, and tracking your weight / fat mass. If you are maintaining weight you are eating at your TDEE, if you are losing weight you’re under, and over if gaining weight. If you were chronically under-eating for 6 years you would have been losing weight that entire time or you’ve broken the laws of thermodynamics.
A big benefit of tracking calories is see what you (generic you) really eat and how bad your estimates of calorie content are (happened to me.). I thought i was ‘eating well’ or ‘eating clean’ and just had no clue as to caloric content and density of the foods I was eating. You can ‘eat clean’ and gain weight and eat fast food and crap and lose weight, though it is easier to lose weight and feel full with low calorie dense foods.
Other things to keep in mind are:
- Nutritional information (i.e. calories) can be off by 20%! So its all a bit of a crap shoot and you are never going to have 100% accuracy on food intake, calories burned through exercise, BMR, etc.
- kJ -> kCal calculations assume a certain efficiency. It is not uncommon for Zwift to report about 50 calories less burned during a 60 min ride compared to TR and that difference grows with the length of a ride. That can add up.
- We frequently assume our power meters accurately measure our power output. I see significant differences between my smart trainer and my stages PM and those would effect your exercise burn estimate.