It's the worst-kept of secrets that many people in the United States have terrible diets, with overly large portions that contain enough fat, sugar and salt to push obesity and other health problems to epidemic levels. Outside our borders, you may be aware of the Mediterranean Diet and its cardiovascular benefits, or perhaps the health benefits of the Japanese way of eating.

But what about the rest of the world? Largely there has been a void of comprehensive information, with the exception of news about food security and occasional crises in impoverished and developing parts of the world.

Now a team of researchers has completed the arduous task of assembling information on the diets of 88.7 percent of the global adult population from 325 surveys, and assessing whether diets have improved or worsened between 1990 and 2010.

Overall, the news is not good. While some people — older folks, women and those in some developed nations — have increased their consumption of ten healthful foods and substances, that improvement has been surpassed by increased consumption of seven unhealthful foods, particularly among younger generations, men and middle-income and poor nations, according to the study published Wednesday evening in the journal The Lancet Global Health.

(Mozzafarian, et al./Lancet)

"International food programs have traditionally focused on food security and micronutrient deficiency, but the diet-related health burdens due to non-communicable chronic diseases (NCDs) are now surpassing those due to undernutrition in nearly every region of the world," the authors wrote.

The 10 healthful foods were whole grains, fruits, vegetables, fish, nuts and seeds, beans and legumes, milk, dietary fiber, polyunsaturated fat and plant omega. The unhealthful foods were sugar-sweetened beverages, unprocessed red meats, processed meats, saturated fat, trans fat, cholesterol and sodium.

[Read more: Salt intake is too high in 181 of 187 countries]

"There are just really striking changes going on in the world in nutrition in recent decades," said Dariush Mozaffarian, dean of the Friedman School of Nutrition Science and Policy at Tufts University, who participated in the study funded by the Bill and Melinda Gates Foundation and the Medical Research Council. For poor countries, he said, it will no longer be sufficient to simply supply calories in the form of starchy staples to prevent starvation. "We have to adjust our entire approach to feeding the planet," he added.

In their paper, the authors wrote that "it has been estimated that, by 2020, nearly 75% of all deaths and 60% of all disability-adjusted life years will be attributable to [non-communicable diseases] and most of the key causes of these conditions are dietary or strongly diet-related."

Most high-income nations and some middle-income countries, by contrast, "are actually showing reductions  in consumption of unhealthy foods. Together with the increasing consumption of healthy foods, these results could at least in part explain the observed reductions in blood pressure, blood cholesterol, and cardiovascular mortality in the USA, Canada, and western Europe. Yet, despite the improvements in dietary patterns in these high-income nations, our findings show that they are still among the worst in the world, especially for consumption of unhealthy foods."

(Mozzafarian, et. al/Lancet)