The other option is to directly measure basal metabolic rate while sleeping. That might be easier to do as a home thing these days. Barnes had to get people to go to the testing centre and then be scared stiff by complicated apparatus. They got all panicky and screwed up the test.

But if there's some way of measuring BMR while sleeping in your own bed and you can do it every day for a week until you stop getting nervous, that looks like it would be sound.