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Trends in Dietary Carbohydrate, Protein, and Fat Intake and Diet Quality Among US Adults, 1999-2016

Educational Objective
To understand the components of a healthy diet and trends in dietary intake among US adults.
1 Credit CME
Key Points

Question  What were the trends in carbohydrate, fat, and protein intake among US adults from 1999 to 2016?

Findings  In this nationally representative serial cross-sectional study that included 43 996 adults, there were decreases in low-quality carbohydrates (primarily added sugar) and increases in high-quality carbohydrates (primarily whole grains), plant protein (primarily whole grains and nuts), and polyunsaturated fat. However, 42% of energy intake was still derived from low-quality carbohydrates and the intake of saturated fat remained above 10% of energy.

Meaning  The macronutrient composition of diet among US adults has improved, but continued high intake of low-quality carbohydrates and saturated fat remain.


Importance  Changes in the economy, nutrition policies, and food processing methods can affect dietary macronutrient intake and diet quality. It is essential to evaluate trends in dietary intake, food sources, and diet quality to inform policy makers.

Objective  To investigate trends in dietary macronutrient intake, food sources, and diet quality among US adults.

Design, Setting, and Participants  Serial cross-sectional analysis of the US nationally representative 24-hour dietary recall data from 9 National Health and Nutrition Examination Survey cycles (1999-2016) among adults aged 20 years or older.

Exposure  Survey cycle.

Main Outcomes and Measures  Dietary intake of macronutrients and their subtypes, food sources, and the Healthy Eating Index 2015 (range, 0-100; higher scores indicate better diet quality; a minimal clinically important difference has not been defined).

Results  There were 43 996 respondents (weighted mean age, 46.9 years; 51.9% women). From 1999 to 2016, the estimated energy from total carbohydrates declined from 52.5% to 50.5% (difference, −2.02%; 95% CI, −2.41% to −1.63%), whereas that of total protein and total fat increased from 15.5% to 16.4% (difference, 0.82%; 95% CI, 0.67%-0.97%) and from 32.0% to 33.2% (difference, 1.20%; 95% CI, 0.84%-1.55%), respectively (all P < .001 for trend). Estimated energy from low-quality carbohydrates decreased by 3.25% (95% CI, 2.74%-3.75%; P < .001 for trend) from 45.1% to 41.8%. Increases were observed in estimated energy from high-quality carbohydrates (by 1.23% [95% CI, 0.84%-1.61%] from 7.42% to 8.65%), plant protein (by 0.38% [95% CI, 0.28%-0.49%] from 5.38% to 5.76%), saturated fatty acids (by 0.36% [95% CI, 0.20%-0.51%] from 11.5% to 11.9%), and polyunsaturated fatty acids (by 0.65% [95% CI, 0.56%-0.74%] from 7.58% to 8.23%) (all P < .001 for trend). The estimated overall Healthy Eating Index 2015 increased from 55.7 to 57.7 (difference, 2.01; 95% CI, 0.86-3.16; P < .001 for trend). Trends in high- and low-quality carbohydrates primarily reflected higher estimated energy from whole grains (0.65%) and reduced estimated energy from added sugars (−2.00%), respectively. Trends in plant protein were predominantly due to higher estimated intake of whole grains (0.12%) and nuts (0.09%).

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

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Article Information

Corresponding Authors: Zhilei Shan, MD, PhD, Department of Nutrition, Harvard T. H. Chan School of Public Health, 665 Huntington Ave, Boston, MA 02115 (zshan@hsph.harvard.edu); Fang Fang Zhang, MD, PhD, Friedman School of Nutrition Science and Policy, Tufts University, 150 Harrison Ave, Boston, MA 02111 (fang_fang.zhang@tufts.edu).

Accepted for Publication: August 12, 2019.

Author Contributions: Drs Zhang and Bhupathiraju had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Drs Zhang and Bhupathiraju contributed equally.

Concept and design: Shan, Rehm, Hu, Mozaffarian, Zhang, Bhupathiraju.

Acquisition, analysis, or interpretation of data: Shan, Rehm, Rogers, Ruan, Wang, Hu, Zhang, Bhupathiraju.

Drafting of the manuscript: Shan, Rehm, Rogers.

Critical revision of the manuscript for important intellectual content: Rehm, Ruan, Wang, Hu, Mozaffarian, Zhang, Bhupathiraju.

Statistical analysis: Shan, Rehm, Rogers, Ruan, Wang.

Obtained funding: Hu, Zhang.

Administrative, technical, or material support: Hu, Zhang.

Supervision: Hu, Mozaffarian, Zhang, Bhupathiraju.

Conflict of Interest Disclosures: Dr Rehm reported receipt of personal fees from Nestec Ltd and the Dairy Management Institute. Dr Hu reported receipt of grants from the California Walnut Commission and personal fees from Metagenics, Standard Process, and Diet Quality Photo Navigation. Dr Mozaffarian reported receipt of grants from the Gates Foundation; receipt of personal fees from GOED, Nutrition Impact, Pollock Communications, Bunge, Indigo Agriculture, Amarin, Acasti Pharma, Cleveland Clinic Foundation, America’s Test Kitchen, and Danone; scientific advisory board membership from Elysium Health (with stock options), Omada Health, and DayTwo; and receipt of publication royalties from UpToDate; in addition, Dr Mozaffarian reported holding patents US8889739 and US9987243 listing Dr Mozaffarian as a coinventor for use of transpalmitoleic acid to prevent and treat insulin resistance, type 2 diabetes, and related conditions as well as reduce metabolic risk factors. No other disclosures were reported.

Funding/Support: This work is supported by National Institutes of Health grant R01 MD011501 to Drs Shan, Rehm, and Zhang; National Institutes of Health grant K01 DK107804 to Dr Bhupathiraju; and the Young Scientists Fund of the National Natural Science Foundation of China grant 81703214 to Dr Shan.

Role of the Funder/Sponsor: The study funders had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.

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