Hi there,
I too have T2 diabetes and purchased a Fitbit soon after I was diagnosed, hoping that it would help me track calories in and calories out. My goal is to put my diabetes into remission by eliminating visceral fat (from the liver and pancreas), which I hope to achieve by losing a large amount of bodyweight as fast and as safely as possible.
Unfortunately I’ve found that the ‘calories out’ function of Fitbit can be very inaccurate, even without the complications associated with diabetes and the effects of common diabetes medications. In my case the ‘calories out’ figure in the Fitbit app can be inflated by as much as 1000 Kcal per day. I am not certain of the reasons behind this level of inaccuracy.
I have tested it by tracking my calorie intake and weight loss in detail and calculating my real world calorie deficit weekly using a spreadsheet. The spreadsheet is based on the fact that 1Kg of body fat, when burned, equates to 7,700 Kcal (7.7 calories per gram of body fat). Simply put, if you lose half a kilo of body weight in a week, that means you ‘burned’ approximately 3,850 more calories than you ate that week, indicating an average gap between calories in and calories out of around 550 calories per day.
Diabetes complicates things because, for example; the diabetes medication Metformin will slightly block the absorption of glucose from the small intestine, and an SGLT2 inhibitor like Dapagliflozin will cause excess glucose to be expelled via the urine. The effects of these medications mean that not all calories consumed are ‘burned’; some calories may be blocked and some may be dumped. The spreadsheet approach is based on real world results, and is very useful in determining what changes need to be made to food and exercise in future weeks based on the experience of past weeks. Real world weight loss experience accounts for all diabetes factors – burning, blocking and dumping.
Where the Fitbit app really shines is in tracking the amount and quality of exercise over time, but not so much for accuracy when it comes to calories burned. If you would like a pretty good estimate of how many calories you’re burning per day then try a BMR calculator. There are lots of these online though the most accurate ones are based on the Katch-McArdle (aka Cunningham) formula. To use these you will need to know your percentage body fat. Smart bathroom weighing scales (which can be quite cheap) can estimate your percentage body fat. Many models of scale can also estimate how much visceral body fat you’re carrying, which is critical information if you’re attempting to put your T2 diabetes into remission.
The BMR calculator on the website I’ve linked below produced figures for me which matched my spreadsheet calculations to within 100 calories per day, averaged over a week. If only there was an option in the Fitbit app that combined general exercise tracking in terms of weekly activity levels with the Katch-McArdle formula, rather than attempting to track the calories burned with every step and wrist movement.
Best of luck in kicking diabetes’ **ahem**!
https://barbend.com/bmr-calculator-for-fat-loss-muscle-gain/
