I think that a lack of physical activity and an abundance of unhealthy foods as entertainment are the causes of obesity in the US. Before the modern era, most jobs involved a good amount of physical labor and people spent a lot of time in their gardens or farms, walked to work, etc. Now we all drive most of the time and often work jobs that are not physically demanding. Our lives are also very demanding and often thinking about what to feed your family is a big source of stress. Fast food and delivery food is often way easier, but the price thing is debatable. I find that eating whatever I want at home is way cheaper than eating out.