More than 640 million people globally now weigh in as obese and the world has more overweight than underweight people, according to an analysis of global trends in body mass index (BMI). A startling increase in rates of obesity in the past 40 years means the number of people with a BMI of more than 30 has risen from 105 million in 1975 to 641 million in 2014, the study found. A BMI score over 25 is overweight, over 30 is obese and over 40 is morbidly obese.