[My limited knowledge and reading of this is reflected here]
There are genetic, dietary and lifestyle factors. Genetically and historically, people were used to famines and lower availability of food. So the body evolved to store up whenever food consumption increases. This applies to large parts of the population in Africa too.
With affluence and affordability improved drastically in the last few decades, people tend to eat more and richer food, which forces the body to store as fat. This triggers Type 2 diabetes, hypertension and heart disease. Diet wise, the consumption of dairy is quite high (not as high as some developed countries though) - significantly higher than consumption in the past. This combined with genetics makes things worse, and a lot of lacto-vegetarians also tend to suffer from the lifestyle diseases mentioned above.
