> Scientists know surprisingly little about how much energy we burn throughout our lives. That’s because such data require so-called doubly labeled water studie

> Scientists know surprisingly little about how much energy we burn throughout our lives. That’s because such data require so-called doubly labeled water studies, an expensive test in which people drink “heavy” water with unusual versions of hydrogen and oxygen that can be chemically traced. Scientists measure the amount of these “isotopes” excreted in urine, blood, or saliva over 24 hours for 1 week or more to calculate how much energy individuals use on average in a day. I remember an article a while back on HN or Reddit about drinking heavy water. Interesting it’s a way to measure energy consumption.