As it often does, the BBC health news item (CALL TO RETHINK CHILDHOOD BMI TESTING (Sunday, 29 June 2008) misses the point.
While anyone can see if someone is carrying excess fat by inspection of the unclad waist and ideally waist girth measurement, BMI is invaluable as an objective measure of weight-for-height – but how can weight or BMI ever be a measure of fitness?
Weight-for- height reflects the aggregate of lean mass and fat mass.
Except in body builders, athletes, the lean mass is as much a factor of hormone balance (anabolics- androgens, vitamin D, growth hormone) and water balance as it is of exercise.
Fat mass is far more a reflection of calorie intake than of calorie expenditure – physical excercise.
So regular measurement of height, weight and waist girth is crucial at all ages for monitoring both fat mass – the major marker of the risk of the obesity diseases from early puberty, infertility and type 2 diabetes to cardiovascular disease, cancer and weightbearing osteoarthritis – and lean mass. Low lean mass for height (the LMI- lean mass index) reflects reflects low protein-exercise levels and thus risk of future frailty- fractures.
Hence the increasing problem of fatness frailty in those who are pampered by abundance of food, transport and physical leisure – especially in postmenopausal women, especially those on oral estrogen-progestin hormone therapy- apparent “normal” BMI but increasing girth and fat mass while lean- muscle- mass declines inexorably. These are the patients we see in practice every day, in whom weight and BMI is especially misused, in whom doctors dismiss a weight gain of say 1/2kg a year while this may mask a fat gain of 2.5kg a year while 2kg of lean mass a year is being lost.
These are the patients in which doctors (who should know better) negligently continue to ignore that the older patient often has excess estrogenic:androgen balance if not frank androgen deficiency syndrome; and/or negligently deny the patient metformin prescription until she has frank diabetes and obesity!
There are thus two distinctly separate imperatives at all ages but especially in young schoolchildren, when habits are being set: monitoring of fat mass- which must be regulated by prescription of metformin supplement (or equivalent natural weight-insulin resistance reducers) to tolerance long term if all else fails so as to halve the inexorable progession to overweight, metabolic syndrome and diabetes; and enforcement of minimum exercise standards to promote both physical and mental health.