Based on the findings of several major studies, it has been revealed that special diets are only successful in exceptional cases. Good results are only attained in the long-term, almost exclusively, through a complete change in diet (or a surgical procedure). In the following article, which I wrote after my training in Harvard Medical School in Boston, I have summarised the most important basic principles of a modern change in diet. For more detailed information on the Glycemic Index, please refer to section G.