I think BMI is calculated with a formula like: BMI = weight (kg) / [height (m)]2
(BMI of about 20 is good; less than 18 is underweight; over 25 is obese)
Our heart, bones, and most organs work well when our BMI is right. High BMI can mean excess deposits of fats and carbonhydate compounds which cause 'mal-functioning' of our body (like engines full of gunks).
Other 'hidden' deposits like 'too much' food stored in refrigerators, 'too many clothes/shoes/books/--things--', 'canned/conserved/pickled/... foods and so on are all 'excess', chemicals contaminated and/or energy wasters.
Eat fresh and just enough!