A while ago the medical definition of obesity became a certain Body Mass Index (BMI). Thirty or higher, to be specific. And the body mass index is a remarkably crude formula. It’s just the mass (in kilograms) divided by the height (in meters) squared. Since I’m six feet tall (that’s 1.8288 meters), the cutoff for a BMI of 30 is (depending on how you round the inputs) 100 kilograms even. This morning, when I woke up, I weighted 99.9kg, classifying me as “overweight.” Then I drank a glass of water and was 100.1kg, classifying me as obese. The moral of the story is, of course: don’t drink water because it will make you fat.