Trends in Dietary Carbohydrate, Protein, and Fat Intake and Diet Quality Among US Adults, 1999-2016.
Level 4 - case-series / case-control
Serial cross-sectional survey analysis of nationally representative sample (NHANES)
PubMed 31550032 · doi:10.1001/jama.2019.13771
What was done
A serial cross-sectional analysis evaluated nationally representative 24-hour dietary recall data from 9 NHANES cycles (1999–2016) among 43,996 US adults aged 20 years or older (weighted mean age 46.9 years, 51.9% women). The primary outcomes were trends across survey cycles in macronutrient intake (and their subtypes/food sources) as percentages of total energy, and diet quality measured by the Healthy Eating Index 2015 (HEI-2015, score 0–100).
What was found
Between 1999 and 2016: - Total carbohydrates decreased from 52.5% to 50.5% of energy (difference, -2.02% [95% CI, -2.41% to -1.63%]; P < .001). - Low-quality carbohydrates decreased from 45.1% to 41.8% of energy (difference, -3.25% [95% CI, -3.75% to -2.74%]; P < .001), largely due to decreased added sugars (-2.00% of energy). - High-quality carbohydrates increased from 7.42% to 8.65% (difference, 1.23% [95% CI, 0.84% to 1.61%]; P < .001), primarily driven by whole grains (+0.65%). - Total protein increased from 15.5% to 16.4% (difference, 0.82% [95% CI, 0.67% to 0.97%]; P < .001), and plant protein increased from 5.38% to 5.76% (difference, 0.38% [95% CI, 0.28% to 0.49%]; P < .001), driven by whole grains (+0.12%) and nuts (+0.09%). - Total fat increased from 32.0% to 33.2% (difference, 1.20% [95% CI, 0.84% to 1.55%]; P < .001), with increases in both saturated fatty acids (11.5% to 11.9%; difference, 0.36% [95% CI, 0.20% to 0.51%]) and polyunsaturated fatty acids (7.58% to 8.23%; difference, 0.65% [95% CI, 0.56% to 0.74%]) (all P < .001). - Overall HEI-2015 score increased from 55.7 to 57.7 (difference, 2.01 [95% CI, 0.86 to 3.16]; P < .001).
Why it matters
This study establishes long-term national trends showing modest dietary improvements in the US population—particularly reduced added sugars and increased whole grains and polyunsaturated fats—while highlighting that low-quality carbohydrates and saturated fats still make up an excessive share of daily caloric intake.
Limits
Dietary intake was measured via self-reported 24-hour recalls, which are susceptible to recall bias and underreporting. The repeated cross-sectional design cannot track within-individual changes over time, and a minimal clinically important difference for the HEI-2015 score is not established.
Cited by
- context Americans consume almost a pound per person per day of sugar and refined starch flour.