Old guideline: Not addressed.

2015 guideline: Up to 5 cups a day.

Earlier this year, the federal advisory committee that helps write the Dietary Guidelines for Americans weighed in on coffee for the first time and concluded that drinking up to five cups a day can be part of a "healthy lifestyle." The group wrote that "strong and consistent evidence shows that consumption of coffee within the moderate range...is not associated with increased risk of major chronic diseases."

And the committee didn't just stop there. It also said that consuming as many as five cups of coffee daily was associated with health benefits, such as reduced risk of heart disease and type 2 diabetes.

Those pronouncements are supported by dozens of studies showing that, on average, people who drink coffee are no worse off than those who don’t. They may even be better off, in fact.

But the controversy continues. Some of it has to do with genetics. Scientists have identified at least one part of the human genome that controls whether a person metabolizes caffeine slowly or quickly -- and those who are slow metabolizers may be at higher risk of hypertension and heart attacks the more coffee they drink.

The federal government's influential Dietary Guidelines for Americans, which were released Thursday, are updated every five years, and the debate over saturated fats, red meat, caffeine and salt was especially intense this time around.

The guidelines are the basis of everything from school lunch programs to the diets promoted in bestselling books, but in recent years some scientists have begun to question the one-size-fits-all approach. A growing body of research supports the theory that a person's genetic makeup or microbiome (the organisms that live on or inside of you and help to make you who you are) plays a key role in how food affects the body -- and that the impact can be different from one individual to another. That work supports a more personalized approach to diet, which some researchers argue have argued is the future of nutrition science.

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