Dietary Data Brief No. 49Dietary Intake and Sources of Flavonoids by Adults in the U.S.

What We Eat in America, NHANES 2017-2018

Sebastian RS, Goldman JD, Moshfegh AJ.

Publication Details

National dietary guidance encourages intake of fruits and vegetables in part due to their potential health-promoting effects (1). Flavonoids, a large family of compounds made by plants, may play a role in conferring these benefits. Studies have found that intake of flavonoids is related to lower incidence of many chronic diseases, including cardiovascular disease, diabetes, and cancer (2–5). Flavonoids fall into six distinct classes based on their chemical structure: anthocyanidins, flavan-3-ols, flavanones, flavones, flavonols, and isoflavones (6). This report provides intake estimates and top food group contributors to flavonoids among adults 20 years of age and older using dietary data collected in What We Eat in America (WWEIA), NHANES 2017-2018.

Highlights

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On any given day, 99% of adults consume foods and/or beverages containing flavonoids, albeit in small amounts for most. Intake does not vary by gender.

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The median flavonoid intake of non-Hispanic Asian adults is higher than that of all other race/ethnic groups.

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Adults in the highest category of family income have higher median flavonoid intake relative to those with lower incomes.

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Tea accounts for 91% of flavan-3-ol intake and 75% of total flavonoid intake. It is also among the top sources of flavonols and flavones.

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Berries and grapes - eaten alone, as juices, and in mixtures - are the top food contributors to anthocyanidin intake.

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Oranges and orange juice account for over two-thirds of flavanone intake.

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Soy-containing nutritional products are the primary source of isoflavone intake.

Who consumes flavonoids, and does intake vary by gender?

Overall, nearly all (99%) of adults consume foods and/or beverages containing flavonoids on any given day. For most, intakes are very low (see Statistical notes on page 7).

Mean and median flavonoid intakes among males and females 20 years of age and older are shown in Figure 1 (see definition of “median” on page 6). Within each age group, the median intake estimates do not vary by gender (p>0.001).

Figure 1. Total flavonoid intake (mg) among U.S. adults 20+ years, by sex and age, 2017-2018.

Figure 1

Total flavonoid intake (mg) among U.S. adults 20+ years, by sex and age, 2017-2018.

Does flavonoid intake vary by race/ethnicity or family income?

Total flavonoid intakes among adults by race/ethnic group are presented in Figure 2. The median intake of non-Hispanic Black adults is lower than that of non-Hispanic White adults, and the median intake of non-Hispanic Asian adults is higher than that of all other groups (p<0.001).

Figure 2. Flavonoid intake (mg) among U.S. adults 20+ years by race/ethnicity, 2017–2018.

Figure 2

Flavonoid intake (mg) among U.S. adults 20+ years by race/ethnicity, 2017–2018. a,b,c Medians with different letters were significantly different from one another (p<0.001; See Statistical notes on page 7).

As shown in Figure 3, median intake of flavonoids is greater among adults in the highest income category relative to those in either the lowest or the middle income category (see definition of family income as a percentage of poverty level on page 6)

Figure 3. Flavonoid intake (mg) among U.S. adults 20+ years by family income, 2017-2018.

Figure 3

Flavonoid intake (mg) among U.S. adults 20+ years by family income, 2017-2018. a,b Medians with different letters were significantly different from one another (p<0.001; See Statistical notes on page 7).

What is the intake of flavonoid classes among U.S. adults?

The mean and median intake of flavan-3-ols, flavonols, anthocyanidins, flavanones, flavones, and isoflavones are shown in Figure 4. Flavan-3-ols account for nearly 80% of total flavonoid intake.

Though some flavonoid classes are consumed by nearly all adults on any given day, for others, a large percentage of adults consume none at all. For example, whereas 99 percent of adults have non-zero intake of flavonols, only 45 percent consume any isoflavone-containing foods.

Figure 4. Flavonoid class intake1 (mg) among U.S. adults 20+ years, 2017-2018.

Figure 4

Flavonoid class intake1 (mg) among U.S. adults 20+ years, 2017-2018. 1 The percentage of adults reporting each flavonoid class on the intake day are as follows: flavan-3-ols, 93%; flavonols, 99%; anthocyanidins, 63%; flavanones, 58%; flavones, 86%, isoflavones, (more...)

What are the top contributors to total flavonoids, flavan-3-ols, flavonols, and anthocyanidins?

As shown in Table 1, black and green tea provide 91% of flavan-3-ol intake. Because this class comprises the majority of flavonoid intake (see Figure 4 on page 3), tea is the top contributor to flavonoids among U.S. adults, accounting for 75% of total intake overall (54% from black, 20% from green). Table 1 shows that tea also contributes approximately one-third of daily intake of flavonols. Vegetables, particularly onions and dark greens, are high in flavonol content as well. These foods are common ingredients in mixed dishes. Berries – eaten alone or as a component of foods such as nuts and seed-based trail mixes and flavored milk and other dairy drinks- account for over half of anthocyanidin intake. Grapes and grape- based products, including juice and red wine, are the other top dietary sources of this class.

Table Icon

Table 1

Food and beverage groups that are top contributors (account for 5% or more of total intake) of flavan-3-ols, flavonols, and anthocyanidins, adults 20+ years, 2017–2018.

What are the top contributors to flavanones, flavones, and isoflavones?

The main contributors to flavanones reflect the fact that this class is found exclusively in citrus fruits (Table 2). Dietary sources of flavones include vegetables, which are consumed alone or in mixed dishes. Hot peppers have high flavone content, and explain why condiments and sauces are top contributions to intake of this class. Green tea is also a notable source of flavones. Isoflavones are found exclusively in products containing soy in some form, e.g., soy protein isolate and tofu.

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Table 2

Food and beverage groups that are top contributors (account for 5% or more of total intake) of flavanones, flavones, and isoflavones, adults 20+ years, 2017–2018.

Definitions

Family income (as percentage of poverty level)

the ratio of family income to poverty expressed as a percentage. The Department of Health and Human Services’ poverty guidelines were used as the poverty measure to calculate the ratio (7).

Food groups

In general, food/beverage groups listed as food sources of total flavonoids/flavonoid classes correspond to the 2017–2018 WWEIA Food Categories (see definition and link below). Some WWEIA categories were divided into smaller groups to underscore foods exceptionally high in a particular flavonoid class. For example, foods in the WWEIA category “Blueberries and other berries” were split into three groups- “blueberries”; “cranberries”; and “blackberries, raspberries” because berries are a top contributor to anthocyanidin intake. (Note: “Strawberries” is a separate WWEIA category.) In other cases, multiple WWEIA categories were merged to create a new group.

Median

The middle value within a set of data values for a given variable. Half of all values are less than the median, and half of all values are greater than the median. In a symmetric distribution, the mean and median are similar. In a right-skewed distribution, the mean can be much larger than the median.

Percentile

Value below which a certain percentage of the values in a data set are found, e.g., if a value of 200 is at the 75th percentile, 75 percent of the values are below 200, and 25 percent are above 200. The median is analogous to the 50th percentile for a given set of data values.

Skewed distribution

a set of values for a variable that when plotted form an asymmetric, or non-normal (i.e., not bell-shaped) curve. Flavonoid intake distributions exhibit a right skew, characterized by a large proportion of zero/low intake observations and a long right tail reflecting a relatively small proportion of very high intake observations.

Total flavonoids

Summative total of the following flavonoid classes: anthocyanidins, flavan-3-ols, flavanones, flavones, flavonols, and isoflavones. Excludes the contribution of dietary supplements.

WWEIA Food Categories

A scheme applied to classify each food and beverage reported in WWEIA, NHANES into one of approximately 165 mutually exclusive categories (www.ars.usda.gov/Services/docs.htm?docid=23429).

Data source

Estimates in this data brief are based on one day of data from WWEIA, NHANES 2017–2018 (8). Day 1 dietary data were collected in person using the 5-step USDA Automated Multiple-Pass Method for the 24-hour recall (9). A total of 4,742 individuals age ≥20 years (2307 males and 2435 females) provided complete and reliable dietary intake data. In the race-specific analysis (page 2), non-Hispanic individuals who were multi-racial or of a racial group other than those listed (n = 236) were excluded. Similarly, individuals who did not report family income (n = 558) were excluded from the income-based analysis (page 2). Intakes of flavonoids were calculated using the 2017–2018 versions of the Database of Flavonoid Values for USDA Food Codes (10) and USDA’s Food and Nutrient Database for Dietary Studies (11).

Statistical notes

The figure below shows the intake distribution of total flavonoids among adults, and the mean, median, and selected percentiles of that distribution. (See definitions of “total flavonoids”, “median” and “percentile” on page 6). Flavonoids are highly concentrated in some plant foods, but low or absent in others. Individuals who consume foods in the former group have high intakes, while those who do not have relatively low intakes, resulting in highly skewed intake distributions. (See definition of “skewed distribution” on page 6.) Strong right-skewness as displayed here can cause means to be much larger than medians.

Distribution1 of total flavonoid intake by U.S. adults 20+ years, 2017-2018.

Distribution1 of total flavonoid intake by U.S. adults 20+ years, 2017-2018

1 Mean (red line), and selected percentiles shown. Intakes above 1000 mg/d not displayed.

SOURCE: WWEIA, NHANES 2017-2018, day 1, adults 20 years of age and older.

Because flavonoid intake distributions did not meet all assumptions for parametric testing (i.e., data did not show a normal distribution), nonparametric testing were employed to detect differences in intake between population groups. Specifically, median intakes were compared using the quantile test described in (12).

Sample weights were applied in all analyses to produce nationally representative estimates.

References

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7.
U.S. Department of Health and Human Services, Office of the Assistant Secretary for Planning and Evaluation. Poverty guidelines. https://aspe​.hhs.gov/poverty-guidelines. Accessed March 6, 2023.
8.
Centers for Disease Control and Prevention, National Center for Health Statistics. NHANES Questionnaires, Datasets, and Related Documentation. https://wwwn​.cdc.gov/nchs/nhanes/. Accessed March 15, 2023.
9.
USDA Food Surveys Research Group. AMPM - USDA Automated Multiple Pass Method. www​.ars.usda.gov/nea/bhnrc/fsrg/ampm. Accessed February 2, 2023.
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11.
USDA Food Surveys Research Group. FNDDS Documentation and Databases. www​.ars.usda.gov/fsrg/fndds/download. Accessed February 2, 2023.
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Pan Y, Caudill SP, Li R, Caldwell KL. Median and quantile tests under complex survey design using SAS and R. Comput Methods Programs Biomed. 2014;117(2):292–297. doi:10.1016/j.cmpb.2014.07.007. [PMC free article: PMC5708173] [PubMed: 25123100] [CrossRef]

Sebastian RS, Goldman JD, and Moshfegh AJ. Dietary Intake and Sources of Flavonoids by Adults in the U.S.: What We Eat in America, NHANES 2017-2018. Food Surveys Research Group Dietary Data Brief No. 49. October 2023.