The idea is that before the development of agriculture, we ate mainly meats and veggies. Foods high in carbs weren't a part of our diet. As we know, in response to carbohydrates insulin is released so that our bodies can absorb glucose. The central idea is that the chronic increase in insulin and other hormones are what is leading to our chronic health problems, such as diabetes and obesity. Put another way, it is thought that our body doesn't process carbohydrate as efficiently as proteins and therefore removal of carbs is a diet optimal for health.
So, in a nutshell, Paleo diet is all about eating meat, fish, vegetables and fruit, excluding dairy or cereal products and processed food.
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