How were our modern nutrition guidelines developed?

The Seven Countries StudyIn the year 1958, an American scientist called Ancel Keys started a study called the Seven Countries Study, which examined the association between diet and cardiovascular disease in different countries.
The study revealed that the countries where fat consumption was the highest had the most heart disease, supporting the idea that dietary fat caused heart disease.
The problem is that he intentionally left out:

• Countries where people eat a lot of fat but have little heart disease, such as Holland and Norway.
• Countries where fat consumption is low but the rate of heart disease is high, such as Chile.

Basically, he only used data from the countries that supported his theory, a process known as cherry picking.
This flawed observational study gained massive media attention and had a major influence on the dietary guidelines of the next few decades.