Something more accessible and potentially more valuable would be to go to a doctor and get a "Composite Metabolic Panel" (CMP) blood test.
This test will give you hard, scientific data on various components of your blood that are perhaps more important than whether or not you are burning more calories than you consume.
The CMP will give you 14 specific data points in regards to how your body is functioning. Getting this test performed periodically (quarterly for those with chronic manageable illness; semi-annually for those who have no apparent illness) can help you to understand "when something is going wrong". It's better to know early and to be able to apply corrective action or treatment, then it is to allow conditions to manifest in disease.
Some health challenges that a CMP can help you to "head off at the pass" include diabetes, kidney and liver problems, hypertension, and improper electrolyte and fluid balance.
Besides, most health insurance policies will cover a CMP if it is indicated for diagnostic purposes in response to "a complaint". Just asking for a CMP for the sake of knowing is probably not a justification for ordering this test.
I get a CMP quarterly, and have done so for nearly 13 years. I know just how healthy I really am. And, I am really healthy for a guy who has survived and thrived despite HIV for just about 26 years now.
Aloha and Be Well!