For decades, many dietary recommendations have revolved around consuming a low percentage of your daily calories from fat. It has been widely thought that doing so would reduce your chance of having coronary heart disease. Most of the evidence for that recommendation has come from epidemiologic studies, which can be flawed.
Use of these types of studies happens far more often than we would like, leading to dietary guidelines that may not be based on the best available evidence. But last week, the government started to address that problem, proposing new guidelines that in some cases are more in line with evidence from randomized controlled trials, a more rigorous form of scientific research.