What is a factor that has contributed to the global increase in obesity?

Bad diet : Obesity is very preventable. Excessive sugar and carbohydrate intake cause high blood sugar levels, which then make your Insulin levels rise. Over time the chronically high Insulin levels lead to Insulin resistance and you will need to make higher and higher levels of Insulin to maintain normal blood sugar levels. Eventually you will have full blown diabetes, heart disease and HTN & obesity.

Too many 2 count: Where to start? Convenience foods, fast foods, commercial advertising for soda etc... Decrease in the importance of sit down family dinners... Obesity is a multifactoral problem with many causes that we have yet to identify. Fixing the obesity epidemic is also going to have to be tackled from several different angles..

Lifestyle.: First, technology has made most of us quite sedentary, and as such we don't expend nearly as many calories as we used to. Second, busy lifestyles tend to beget grab-and-go types of foods, which are generally less healthy and actual relaxed sit-down meals. That's one way to see it.