Sugar - "Pure, White and Deadly" - John Yudkin

(I try to keep it very simple.)

Definitions:
- Sugar: glucose (in starches: rice, flour etc), fructose (in fruits), lactose (in milk)
- Simple carbs: one or two sugar molecules bound together
- Complex carbs: chains of sugars, it can be tens of thousands of molecules long (broken down to simple sugars during digestion)
- Glycemic Index: measure of how quickly carbohydrates are absorbed and converted to blood sugar. The more simple (refined) the carbohydrate, the greater the blood sugar and insulin response.

When native populations added refined carbohydrates and sugar to their traditional diets, their insulin and blood sugar levels increased, leading to the appearance of obesity and the diseases of civilisation (heart disease, diabetes, certain types of cancer...) through the physiological changes of metabolic syndrome (glucose intolerance, insulin resistance, high triglycerides...).

The geographic pattern of obesity incidence is also very similar to that of heart disease and diabetes. This means, that populations with more obese people have a greater number of chronically sick people. So, in theory, the cause must be the same: refined carbohydrates and sugar.

What happens when we eat sugar?
Table sugar is composed of 50% glucose and 50% fructose, one glucose and one fructose molecule bound together. Glucose has no taste, fructose (found in fruits) is very sweet. 

- When we eat white rice, white bread (starches), the carbs are broken down to glucose during the digestion, and they move directly from the small intestine to the bloodstream, causing high levels of blood sugar. In response, the body produces insulin to cope with these high sugar levels.

- When we eat table sugar, as half of it is glucose, this will have the same effect as described for the digestion of starches above. The other half, fructose passes from the small intestine directly into the liver where it is metabolised and is converted to triglycerides (or fat). High triglyceride level is a risk factor for heart disease. On top of this, fructose apparently causes a glucose build-up in the liver. As a result, the pancreas secretes more insulin, and this in turn leads to insulin resistance in the muscles, which can lead to diabetes and heart disease.

To make it simple, because of its half-half composition, sugar is the worst form of carbohydrate. It causes high insulin levels and high triglyceride levels in the blood. These conditions are the perfect breeding ground for chronic diseases.

And another interesting article on how sugar is harming us: 
This is your brain on sugar: UCLA study shows high-fructose diet sabotages learning, memory

Sugar was not part of our daily diet until 100 years ago. Native populations chose fat (fish, meat, eggs) as the most important part of their diet. For more details you can go to the study done by Doctor Weston Price: Nutrition and Physical Degeneration. A wonderful study which cannot be repeated today, as populations are moving towards a "civilized" diet.

And a very short video with Doctor Price and native people. Those natives are an example of how we actually should look like.