While this study only claims an association, not cause, it seems obvious to me.
Many studies have linked the meals served at fast-food outlets to obesity, but is there a relationship between the number of restaurants in a country and the girth of its population?
To answer this question, an international team of health experts looked at the number of Subway restaurants per 100,000 people in 26 economically advanced countries. They also considered other factors, including the number of men and women over 15 with a high body mass index, gross national income, a country's Gini coefficient (an indicator of income inequality), urbanisation, motor-vehicle and internet use.
The conclusions, ..., are clear: the density of Subway's outlets is positively associated with the prevalence of obesity across 26 advanced economies in both men and women. Even after adjusting for the other factors, countries with the highest density of Subway restaurants (such as the United States and Canada) have a higher prevalence of obesity than countries with a low density (like Norway and Japan).
The authors suggest that the rapid global market integration and trade liberalisation promoted by organisations such as the World Trade Organization -- which contribute to an increase in exports of domestic goods, imports of foreign products and the opening of markets to foreign investment -- have also played a large part in expanding waistlines. The growth and power of transnational food companies, supermarkets and fast-food restaurants encouraged by such policies has had a dramatic impact on global diets. [emphasis mine]
If a human mass extinction happens, many won't survive it.
Will they be the thick or the thin?