The paleo diet is based on the core idea that our bodies are not equipped to deal with the developments of modern food types. Proponents believe that we should get our nutrition from a diet that mirrors that of our ancestors because modern developments in processed foods have quickly outgrown our natural ability to evolve with them. The paleo diet outlines foods that our ancestors did eat, and foods that we should categorically avoid. So why exactly should we be eating like our ancestors?
Our eating habits are changing - that is a fact. Just as modern society has shown massive developments in technology and our way of living, so too have our eating habits evolved. The problem here is that our bodies are being left behind. They have not had the chance to evolve to our new ways of consumption and are poorly equipped to process these new food types. This can be directly attributed to huge increases in diseases, such as diabetes and cardiac-related illness.
A second, obvious reason for changing how we eat is the simple issue of weight. As a society, we have never been more obese. This may, in part, be attributable to a more sedentary lifestyle with more and more people working in office jobs, but there is no doubt that our eating habits have contributed massively to this problem. In the US, almost 2/3rds of the population is considered overweight. This issue is not just a problem; it is an epidemic, and one that is not being addressed. A paleo diet would naturally counter many of these problems as it is far more difficult to put on weight eating a paleo diet than it is one with huge amounts of processed foods.
The issue mentioned above is particularly relevant. Processed foods are almost entirely new to our systems, and our bodies really struggle to deal with them. Processed convenience foods that are high in sugar and saturated fats are particularly harmful, as countless studies have shown. Our over-reliance on these processed foods is directly attributable to societies growing health issues, not only in our susceptibility to disease but our growing weight problem. A diet that focuses on healthy eating, like the diet of our ancestors, removes so many of these issues in one fell swoop. For these reasons, it is hard to make an argument against eating more like our ancestors.