Obesity or being overweight to an extent of 10 kg(22 lbs)  or more  over your ideal body weight is a disease. Most of us do not realize obesity/overweight to be a disease and consider this as sign of prosperity.
This ignorance is deep rooted in human evolution.
Humans have evolved over millions of year under starvation. From being hunters to being agrarian, food was a luxury. It was never in excess. Our body got used to this starvation. So if any one or someone in the community was obese this meant that  they  were well fed which was equivalent being wealthy.
This led to the common notion that being overweight was sign of prosperity.
After industrial revolution, food became available and in later half of the century became excess.
Markets were flooded with highly-processed food.
Humans were not ready for this. The availability and excess of food lead to bombardment of calories. This was accompanied by increasing sedentary lifestyle brought by mechanization. These factors combined with ignorance about the food and calories we consume resulted in the obesity epidemic of our time.
So once we understand that being overweight is not a sign of prosperity, but beginning of a disease, we as a society will be well equipped to prevent and treat this problem.