Study: Average US Diet is Improving, But Remains Suboptimal for Many

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Analysis of NHANES data from 1999 to 2020 provides some evidence of diet quality improvement but highlights low rates of adults achieving ideal diet quality.

A new study of more than 50,000 people is highlighting the suboptimal quality of the average US diet.

Led by the Food Is Medicine Institute at the Friedman School of Nutrition Science and Policy of Tufts University, results of the study demonstrate more than 1 in 3 US adults surveyed in 2020 had a poor diet quality, which was measured using a validated score from the American Heart Association, with fewer than 2% achieving ideal diet quality.1

“We face a national nutrition crisis, with continuing climbing rates of obesity and type 2 diabetes,” said Dariush Mozaffarian, MD, DrPH, cardiologist and director of the Food is Medicine Institute.2“These diseases afflict all Americans, but especially those who are socioeconomically and geographically vulnerable. We must address nutrition security and other social determinants of health including housing, transportation, fair wages, and structural racism to address the human and economic costs of poor diets.”

As the US grapples with burgeoning obesity and type 2 diabetes epidemics adding to the prevalence of cardiovascular disease, the quality of the US diet has been pointed to as a leading driver of these increase in risk factors. However, despite the renewed interest in diet and nutrition on a population, few studies offer a comprehensive assessment of trends in overall diet quality among US adults.

With this in mind, Mozaffarian and Junxiu Liu, PhD, designed the current study to address these research gaps using nationally representative data. Funded by the National Institutes of Health, the cross-sectional study leveraged data from adults aged 20 years and older who participated in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2020.1

For inclusion in the study, patients needed to at least 1 valid 24-hour diet recall in the dietary interview component of NHANES. In total, 51,703 adults who completed at least 1 valid 24-hour diet recall were identified for inclusion. This cohort had a mean age of 47.0 years and 51.9% were female. Among those with 1 valid 24-hour diet recall, 72.6% provided 2 recalls.1

Investigators several notable trends during the study period. Among those were an increase in older adults (16.3% to 21.7%), a decrease in the proportion of younger patients (53.8% to 43.7%), an increase in the proportion of Hispanic adults (14.0% to 16.1%), and an increase in the proportion of those reporting some college education or more (49.8% to 62.1%). Additionally, investigators pointed out participation in SNAP more than doubled (8.62% to 16.7%), the proportion with government-sponsored health insurance increased (13.2% to 28.1%), and the proportion with private health insurance decreased (67.2% to 58.4%).1

The primary outcome of interest for the study was the proportion of patients achieving targets of the validated AHA 2020 continuous score. Using the AHA score, which awards higher scores based on higher intake of fruits and vegetables, whole grains, fish and shellfish, and nuts, seeds, and legumes and lower intake of sugar-sweetened beverages, processed meat, saturated fat, and sodium, poor diet was defined as less than 40% adherence, intermediate as 40% to 79.9% adherence, and ideal as at least 80% adherence.1

Results of the study suggest the estimated proportion of US adults with poor diet quality decreased from 48.8% to 37.4% (difference, −11.4 percentage points; 95% CI, −16.8 to −5.96 percentage points), the estimated proportion with intermediate quality increased from 50.6% to 61.1% (difference, 10.5 percentage points; 95% CI, 5.20 to 16.1 percentage points), and the estimated proportion with an ideal diet increased from 0.66% to 1.58% (difference, 0.93 percentage points; 95% CI, 0.35 to 1.51 percentage points) (P for trend <.001 for each) from 1999 to 2020. When assessing the outcome continuously, results indicated the mean AHA score increased from 32.8 out of 80 to 36.7 out of 80 during the study period (difference, 3.95; 95% C, 2.28 to 5.62) (P for trend <.001).1

When assessing specific trends in nutrition, results indicated the statistically significant reductions in intake were observed for sugar (86.2 to 63.1 grams per day), sugar-sweetened beverages (1.73 to 1.0 servings per day), fruit juice (0.44 to 0.22 servings per day), refined grains (5.49 to 5.24 servings per day), and milk (0.90 to 0.54 servings per day) (P for trend <.001 for each).1

Investigators highlighted numerous disparities found within their research, including greater improvements in diet quality among younger versus older adults, those with higher versus lower income, those with food security versus food insecurity, and those with private versus no or government health insurance (P for interaction <.05 for each).1

“While we’ve seen some modest improvement in American diets in the last two decades, those improvements are not reaching everyone, and many Americans are eating worse,” Mozaffarian said.2“Our new research shows that the nation can’t achieve nutritional and health equity until we address the barriers many Americans face when it comes to accessing and eating nourishing food.”


  1. Liu J, Mozaffarian D. Trends in Diet Quality Among U.S. Adults From 1999 to 2020 by Race, Ethnicity, and Socioeconomic Disadvantage. Annals of Internal Medicine. Published online June 17, 2024. doi:10.7326/M24-0190
  2. Tufts University. American diets have a long way to go to achieve health Equity. Newswise. June 17, 2024. Accessed June 17, 2024.