Airline seats have been one-size-fits-all since the beginning. Today, those 16.5 to 18-inch wide seats are anything but.
According to the World Health Organization (WHO), obesity has more than doubled since 1980. In 2014, more than 1.9 billion adults were overweight, and over 600 million were obese. (WHO defines "overweight" as a BMI greater than or equal to 25 and "obese" as a BMI greater than or equal to 30.)