Body Mass Index takes a persons height and weight and calculates the mass, it doesn't take into account muscle density which makes it useless for calculating obesity. This might sound like a fundamental flaw but the BMI was never intended to be used to calculate the weight of wealthy Europeans. The BMI was invented in the mid 19th century in Belgium. It's first use was by groups protesting against the military's treatment of its own troops in Africa. The enlisted men were given a tiny ration of food each week and were starved. By comparing the height and weight of the returning soldiers to healthy mean of the same age it could be proved that their treatment was wrong. The BMI was refined in the 1930s during the great depression an American doctor refined the index this time to present evidence of starvation in the South to congress. It is this version of the scale which is used by most health agencies in the world and this version of scale that you can find on the internet. It did fall out of favour for most of the 20th century it became popular again during the 1980s when Oxfam used the scale during the famine in Africa as it was an easy way to present data to political leaders.
It was after this that the BMI was adopted as a way of measuring obesity and it is behind the rise and rise of obesity. But it was never designed to measure obesity it cannot cope with weight of the muscle mass of a healthy person. If you want to look good the best way to do it is to eat properly, that means at least three balanced meals a day, and to train with weight. You may end up weighing more but be thinner muscle weighs more than fat. If you become fit and athletic you may well find you BMI tells you you are overweight. Jessica Ennis won the Heptathlon gold medal at the World Championship in Berlin and is also the BBC Sport Personality of the year. However the BMI scale would say she is obese to be a 'healthy' woman using the BMI would mean someone of Size 0 who would struggle to lift an i-phone to her ear. Any man of average height over 120lbs would also be overweight. A pro rugby player like Johnny Wilkingson would come under the heading of Morbidly Obese. It makes no sense.
So this New Year when you diet forget about the BMI.