Americans are just about failing when it comes to nutrition, says a food-as-medicine researcher. A few simple diet tweaks could help.

• Americans' diets have remained largely unchanged since 1999, according to a new study.
• Meals remain high in processed foods that can increase a person's risk of disease.
• Ditching sugary drinks and eating two fewer processed meals a week could help.

Americans are eating healthier than in previous years, but they still have a long way to go, according to a researcher who studies food as medicine.

Dr. Dariush Mozaffarian, director of the Food is Medicine Institute at Tufts University in Boston, co-authored a study on the quality of nearly 52,000 American adults' diets between 1999 and 2020. The results were published online Tuesday in the Annals of Internal Medicine.

Mozaffarian and his co-author, Junxiu Liu, examined data from the National Health and Nutrition Examination Survey and found that the American diet has remained nearly the same over the past two decades.

Between 1999 and 2020, 10.5% of study participants transitioned from "poor" diets to healthier diets with more fruits, vegetables, and whole grains and less sodium, processed meat, and saturated fat.

But only 1% of study participants ate an "ideal" diet — 4 to 5 cups of fruits and vegetables daily, plus beans, whole grains, and nuts — during that same time period.

"People often ask me, 'Well, if the diet's slowly improving, why is obesity and diabetes still going up?' It's still going up because only 1.58% of Americans have an ideal diet. We still have a long way to go," Mozaffarian told CNN.

"We have stalled as a nation — and that does not bode well for our health. If I was grading America on its diet, I'd give it a D—just up from an F," Mozaffarian said.

Why are Americans failing in the diet department?

Typically, the American diet consists of ultra-processed foods and foods high in salt and sugar. These foods can increase a person's risk of cancer, heart disease, stroke, and early deathAccordingng to Heidi Silver, a registered dietitian and director of the Vanderbilt Diet, Body Composition, and Human Metabolism Core at Vanderbilt University Medical Center in Nashvil, factors like food insecurity and poverty have contributed to the overall lack of improvement in peoples' diets over the last two decadesle.

"Food insecurity affects diet quality via lower consumption of healthier foods, especially those that are more expensive, don't have a long shelf life and don't provide enough volume to fill a hungry child," Silver told Yahoo.

These systemic limitations can make it difficult for food-insecure populations like Black people, older people, and low-income people to make lasting diet changes.

Simple diet tweaks could help reduce health risks

For those seeking simple and inexpensive ways to improve their diets, removing sugary drinks is a good first step, according to Dr. Gregory Katz, a cardiologist at NYU Langone.

"Drinking calories and drinking alcohol are the biggest modifiable risk factors. The number of people I see drinking 500 calories a day blows my mind," Katz told Business Insider's Gabby Landsverk. "Just because it's simple doesn't make it easy."

Katz suggested doing away with soda, juice, sugar-laden coffee drinks, and cocktails and replacing them with unsweetened tea or water flavored with a splash of juice or flavored with citrus.

Aiming to swap out two servings of processed foods each week is another strategy that doesn't involve overhauling your entire diet, according to Dr. W. Taylor Kimberly. Kimberly, a professor of neurology at Harvard Medical School and the senior author of a recent study linking ultra-processed foods to health risks like dementia and stroke.

You could, for example, swap French fries for a baked sweet potato or nosh on nuts and carrots instead of cookies and crackers.

Kimberly said that a good rule of thumb is to prepare meals at home as much as possible.

"If you look at it and think, that could be made in my kitchen, that's a good indicator," he said.