There’s a lot to say here, but let’s make it really simple:
Carbohydrates are glucose. Glucose in your bloodstream causes the pancreas to produce insulin. Insulin is a storage hormone causing all excess glucose to be stored as fat.
The above two sentences are IT. The keys, the root of understanding the Paleo Diet. But don’t go overboard with this idea and cut out carbs all together. You need carbohydrates. Glucose is the gasoline for your body – it is the fuel that drives most metabolic processes. But, we really don’t need too much of it. Remember, once the liver and muscles are full of glycogen (the stored form of glucose) the excess, glucose in the bloodstream will likely be stored as fat. So how much glucose do we need?
Remember those weird words? Monosaccharides, disaccharides, and polysaccharides? Well, saccharides means sugars. And what is a “mono-“ saccharide? Mono=1 – one sugar. These are most of our “good carbohydrates”: vegetables and fruits. And what are “di-“ and “poly-“ saccharides? MORE THAN ONE sugars. These are most of our complex carbohydrates and starches – grains, refined sugar, processed foods etc. So what does this mean? Eating complex carbohydrates (such as grains and starches), refined sugars, and processed foods result in more glucose in the bloodstream. More glucose in your bloodstream will result in more insulin production telling your body to store food as fat and will eventually snowball in to more serious health problems. Believe it or not, obesity is just a symptom of worse things underneath.
From “Paleo Science 101″ by Cliff Hodges.