Adults in the United States have reduced their intake of refined carbohydrates and increased their intake of complex carbohydrates, plant protein, and polyunsaturated fat from 1999 to 2016, a study in JAMA reports.

Nutrition researchers performed a serial cross-sectional analysis of 24-hour dietary recall data taken from the National Health and Nutrition Examination Survey. Only adults aged ≥20 years who completed ≥1 valid dietary recall during the 9 cycles of the survey from 1999 to 2000 and 2015 to 2016 were enrolled (n=43,996). Energy intake from consumption of major macronutrients and macronutrient subtypes was the primary outcome of the study. Other outcomes included sources of carbohydrates and proteins as well as overall diet quality assessed by the Healthy Eating Index 2015.

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Results show that there was a significant decline in the estimated energy from consumed carbohydrates in US adults from 1999 to 2016 (52.5% to 50.5%, respectively; difference, −2.02%; 95% CI, −2.41% to −1.63%; P <.001 for trend). Conversely, there was an increase in the percentage of energy intake from total protein (15.5% to 16.4%; difference, 0.82%; 95% CI, 0.67%-0.97%; P <.001) and total fat (32.0% to 33.2%; difference, 1.20%; 95% CI, 0.84%-1.55%; P <.001).

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Additionally, there was a significant decrease in the estimated energy intake from low-quality carbohydrates from 1999 to 2016 (45.1% to 41.8%, respectively; 95% CI, 2.74%-3.75%; P <.001 for trend). In this same time frame, respondents reported an overall 1.23% increase in estimated energy from high-quality carbohydrates (95% CI, 0.84%-1.61%; P <.001), a 0.38% increase in plant protein (95% CI, 0.28%-0.49%; P <.001), a 0.36% increase in saturated fatty acids (95% CI, 0.20%-0.51%; P <.001), and a 0.65% increase in polyunsaturated fatty acids (95% CI, 0.56%-0.74%; P <.001).

The researchers also noted an increase in healthy eating patterns from 1999 to 2016 as evidenced by a noticeable increase in the overall Healthy Eating Index for US adults (55.7 to 57.7, respectively; difference, 2.01; 95% CI, 0.86-3.16; P <.001 for trend). Changes in energy intake from carbohydrate sources reflected increased estimated energy intake from whole grains (0.65%) and decreased estimated energy from added sugars (−2.00%). Increased intake of whole grains (0.12%) and nuts (0.09%) contributed to the trends in plant protein consumption. 

Limitations of the 24-hour self-reported dietary recall survey include the potential measurement error as well as its cross-sectional nature. 

The researchers concluded that “the macronutrient composition of diet among US adults has improved, but continued high intake of low-quality carbohydrates and saturated fat remain.”

Disclosure: Several study authors declared affiliations with the pharmaceutical industry. Please see the original reference for a full list of authors’ disclosures.


Shan Z, Rehm CD, Rogers G, et al. Trends in dietary carbohydrate, protein, and fat intake and diet quality among US adults, 1999-2016. JAMA. 2019;322(12):1178-1187.