Americans still eat too many low-quality carbs and saturated fats, say experts

By Sally Robertson, B.Sc.Sep 25 2019Reviewed by Kate Anderton, B.Sc. (Editor)

A new study has found that although Americans have made improvements to their diet, most adults are still eating too many low-quality carbohydrates and saturated fats.

The study, which was conducted by to researchers at the Friedman School of Nutrition Science and Policy at Tufts University and the Harvard T.H. Chan School of Public Health, looked at dietary habits and how trends have changed over an 18-year period.

Although the researchers identified some dietary improvements, the data revealed that the consumption of low-quality carbs and saturated fats still represents a major problem.

Elena Veselova | Shutterstock

Intake of high-quality carbohydrates is still too low

Intake of low-quality carbs from starchy vegetables, added sugars and refined grains accounted for 42% of the typical daily calorie intake, while the intake of high-quality carbs such as whole grains and whole fruits only accounted for 9%.

Over the 18 -year study period, data showed that total carb intake had fallen by around 2% and  the intake of low-quality carbs decreased by 3%. However, the intake of high-quality complex carbs only increased by 1%.

Total saturated fat intake is too high

Total fat intake increased by 1%, and half of this was accounted for by the consumption of saturated fat. Total intake of saturated fat accounted for 12% of daily calorie intake, which is higher than the recommended guideline of 10%.

Improvements less pronounced in certain groups

The researchers also observed that the dietary improvements that had been made were less pronounced among older individuals, people on a lower income and people with a lower level of educational achievement.

Adults on higher incomes had reduced their consumption of low-quality carbs by 4%, whereas those living below the poverty line had only reduced it by 2%.

Although Americans generally adhered to dietary guidelines more over the study period, no such improvement was seen among people who were aged over 50 years, people with less than a high-school education and people who were living below the poverty line.

The team writes:

US adults with low income and educational attainment experienced a smaller improvement in macronutrient composition and did not improve the overall diet quality in the past 18 years. Further interventions should focus on minimizing these differences.”

Long way to go to get an “A on this report card”

Co-senior author Fang Fang Zhang, a nutrition epidemiologist at the Friedman School of Nutrition Science and Policy at Tufts University, says that although there were some encouraging signs that Americans have slightly improved their diet over time, there is still a long way to go before the situation improves enough to get an “A on this report card.”

He adds that the study does indicate where improvements will need to be made in the future.

"These findings also highlight the need for interventions to reduce socioeconomic differences in diet quality so that all Americans can experience the health benefits of an improved diet."

Looking into specific nutrients

The study looked at consumption trends of specific macronutrients to find out how changes in food sources such as plant-based foods may confer health benefits.

For instance, the majority of protein intake was from meats such as red and processed meats, while protein intake from healthier sources such as wholegrains, legumes, nuts, and seafood all accounted for a significantly smaller proportion.

Co-senior author Shilpa Bhupathiraju, from Harvard T.H. Chan School of Public Health says the research suggests that Americans have an opportunity to diversify their sources of protein to include more seafood, beans, soy products, nuts, and seeds.

Because low-quality carbs are associated with disease risk, taking in higher-quality carbs could mean better health for Americans in the future.”

Zhilei Shan, First Author, Harvard T.H. Chan School of Public Health

Cross-sectional analysis of nationally representative data

For the study, the researchers conducted a cross-sectional analysis of nationally representative 24-hour dietary recall data from the National Health and Nutrition Examination Survey (NHANES), which was carried out between 1999 and 2016.

The team assessed data available for 43,996 adults aged 20 years or older (average age 46.9 years) and used the USDA's Food and Nutrition Database for Dietary Studies (FNDDS) to estimate nutrient intake. To examine the overall quality of diet, the team used the Healthy Eating Index (HEI)-2015, which measures adherence to the 2015-2020 Dietary Guidelines for Americans.

While there were some slight improvements in overall dietary health over the study period, the data revealed that low-quality carbohydrates are still incredibly prevalent in the average person’s diet and that intake of saturated fats remained high.

“From 1999 to 2016, US adults experienced a significant decrease in percentage of energy intake from low-quality carbohydrates and significant increases in percentage of energy intake from high-quality carbohydrates, plant protein, and polyunsaturated fat,” writes the team.

They conclude:

Despite improvements in macronutrient composition and diet quality, continued high intake of low-quality carbohydrates and saturated fat remained.”

The authors suggest that in the future, people should prioritize protein sources such as fresh seafood, plants, grains, and nuts and should only eat processed meats sparingly.