The short answer is: bribes. How does anything get done? But there's more to the story.
Sugar was losing, and it got desperate
Back in the 1960s, people were seriously freaking out about heart disease. In just one decade, the death rate from the condition rose nearly 25%, and everyone was trying to figure out how to curb it.
Diet surely played some role, and since the 1950s, scientists had been scrutinizing the two major suspects: fat and sugar. By the early 1960s, evidence was beginning to suggest that folks with high-sugar diets were getting heart disease, even if they didn't eat much fat. This had the sugar industry -- represented by the Sugar Research Foundation (SRF), which today is the National Sugar Association -- concerned, to say the least. They devised a plan.
The authors of the exposé discovered that the sugar industry “identified a strategic opportunity for the sugar industry: increase sugar’s market share by getting Americans to eat a lower-fat diet.” In the business world, "market share" usually means percentage of total dollars people spend on a product. But the sugar folks weren’t talking about total dollars -- they were talking about total calories.