1. Introduction
Legumes are defined as the immature, germinated, or mature edible seeds of legume plants (Fabaceae) [
1]. The primarily consumed legumes are dry beans, dry peas, lentils, chickpeas, cowpeas, fava beans, and pigeon peas, which are grouped as mature legumes, green beans and peas, which are considered immature legumes, and sprouted or germinated beans and peas, which are considered sprouted legumes [
2]. Soybeans and peanuts are usually excluded, because of their higher lipid content [
1]. Legumes are an important part of a daily diet because of their nutritional and health benefits [
3]. They are a good dietary source of protein, fiber and folate, are very low in saturated fatty acids, cholesterol, and sodium, and contain many non-nutritive bioactive components [
4]. Consuming 0.5 cup/day (87.5 g) of mature legumes increased fiber, protein, folate, zinc, iron, and magnesium intake and decreased saturated and total fat intake in US adults according to the nation-wide, cross-sectional National Health and Nutrition Examination Surveys (NHANES) 1999–2002 [
5]. Based on their nutritional benefits, the current Dietary Guidelines for US Americans consider mature legumes as a food group with a weekly recommendation of 1.5 cups (equivalent to 37.5 g cooked mature legumes/day) for non-vegetarians and 3 cups (equivalent to 75 g cooked mature legumes/day) for vegetarians [
6]. In addition to their nutritional benefits, daily mature legume consumption may have disease prevention benefits, specifically, preventing or managing obesity, metabolic syndrome, cardiovascular diseases, and colorectal cancer, as concluded by several meta-analyses [
4,
7,
8,
9,
10]. In NHANES 1999–2002, dry bean consumption was associated with low body weight, decreased systolic blood pressure, and a smaller waist circumference in US adults [
11].
The most recently published legume consumption data for US adults are from the NHANES 1999–2002 two-year cycles, in which 7.9% of US adults consumed mature legumes [
5] and 11.1% consumed dry beans on a given day [
11]. An earlier study using the Continuing Survey for Individual Intakes (CSFII) 1994–1996 data reported that 14% of the US adults consumed dry beans on two given days [
12]. Given the health benefits of regular legume consumption published in the last 15 years, we hypothesized that legume consumption increased in US adults, counteracting the previous trend of a consistent decline in legume consumption. Thus, the objective of this report was to evaluate current legume consumption patterns in US adults. To accomplish our objective, we used data from the 2011–12 and 2013–14-year cycles of NHANES, as more recent NHANES data have not been released yet. To have an estimate of more recent legume consumption, we conducted, in fall 2017, a cross-sectional, online survey of families around Corvallis, Oregon [“Beans, Lentils, Peas (BLP) Nutrition Education Online Parent Survey”]. The BLP survey complemented the findings of the NHANES survey, as the BLP survey asked for consumption of legume groups and their primary dish types during the last month, whereas NHANES provided legume consumption data from 24 h food records for two non-consecutive days as food codes, some of which did not specify legume group and dish type.
3. Results
To identify the characteristics of legume consumers, we compared any legume consumers and non-consumers (
Table 1). In the NHANES surveys, age-associated legume consumption had a bell-shaped curve with the highest proportion of legume consumers between the age of 46 and 55 years and the lowest between the age of 18 and 25 years. A similar bell-shaped curve was observed in the 2017 BLP survey. There were no overall gender differences between legume consumers and non-consumers in the NHANES and BLP surveys; however, the age-associated bell-shaped curve was more distinct for men versus women in the NHANES surveys. People of Hispanic descent (Mexican and other Hispanic) had the highest proportion of legume consumers in the NHANES surveys, whereas a smaller proportion of non-Hispanic black and white people consumed legumes. Education level had a significant effect on legume consumption, with consumers in the above and below high school categories being overrepresented. Caloric intake was higher in legume consumers than in non-consumers. Household income did not significantly affect legume consumption. Characteristics were similar for total and mature legume consumption (results not shown).
In the NHANES, legume consumption frequency in US adults was low and showed a downward trend from 2011 to 2014 of 18.5% to 13.7% on a given day (
Table 2). The downward trend was primarily due to a decrease in dry bean consumption from 10.0% to 6.5%. The primary legume groups consumed were dry beans and green legumes; chickpeas and lentils were consumed by about 1% of participants on any given day. Very few NHANES participants consumed cowpeas (0.27%), dry peas (0.20%), sprouted legumes (0.13%), pigeon peas (0.02%), or fava beans (0.01%) on a given day. The primary dry bean types consumed were reported as pinto beans (23.1% of total dry bean frequency), followed by refried beans (14.0%; usually pinto beans), black beans (13.7%), red kidney beans (8.3%), baked beans (7.2%; usually navy beans), red beans (4.5%), and white beans (2.4%); the remaining dry bean types contributed each to less than 2.0% of the total dry frequency. The dry bean type was not specified for 21.3% of the total dry bean frequency, which were primarily soups and bean dishes combined with rice or meat.
The results from the BLP survey were similar to those of the NHANES (
Table 2). In NHANES, 5.6% (2011–2012-year cycle) and 4.0% (2013-2014-year cycle) of participants ate legumes on each day of data collection compared with 4.9% of participants in the 2017 BLP survey. Similar to NHANES, the most consumed legume types in the BLP 2017 survey were dry beans followed by green legumes, chickpeas, and lentils. Sprouted legumes (21.7%), dry peas (18.9%), and cowpeas (14.0%) were eaten during the last month by less participants.
Legumes were mainly consumed as side or main dish (both primarily dry beans and green legumes) by NHANES participants (
Table 3). Other dish types of legume intake were soups (primarily dry beans and lentils), dips (primarily chickpeas as hummus and dry bean dips), and salads (primarily sprouts and green legumes). Breakfast items (0.13%), baked goods (0.13%), snacks (0.03%), and desserts (0 respondents) were rarely a source of legume consumption. A declining trend over time was observed for using legumes as soup and main dish. Results in the BLP survey were similar to those in NHANES (
Table 3), as the primarily reported dishes containing legumes were main and side dishes and, to a lesser extent, soups, dips, and salads. Breakfast items (1 respondent), baked goods (1 respondent), and desserts (0 respondents) were rarely a source of legume consumption.
Lentils and dry beans were consumed at higher quantities than green legumes and chickpeas (
Table 4). The caloric-adjusted median cooked consumption levels of the less consumed legume groups were 126.0 g/day for pigeon peas, 116.9 g
/day for dry peas, 95.5 g/day for fava beans, 50.5 g/day for cowpeas, and 28.0 g/day for sprouted legumes in NHANES. We did not observe any change in consumption between 2011 and 2014 for consumption of legume groups, except for lentils, the intake level of which increased over time. The monthly average intake in legumes in the 2017 BLP survey is lower than the 2-day average intake in NHANES, which reflected the low consumption frequency of most legume groups. In the 2017 BLP survey (
Table 4), 4.9% of participants ate at least 1 cup/day of cooked mature legumes, 16.8% at least 0.5 cup
/day of cooked mature legumes, and 38.5% at least 37.5 g/day of cooked mature legumes during the last month. In comparison, 2.2% (2011–2012) and 1.8% (2013–2014) of NHANES participants ate at least 1 cup/day of cooked mature legumes, 7.1% (2011–2012) and 5.3% (2013–2014) at least 0.5 cup/day of cooked mature legumes, and 14.0% (2011–2012) and 10.7% (2013–2014) at least 37.5 g/day of cooked mature legumes during the 2 days of survey, after adjusting for caloric intake.
To compare legume consumers by cooked consumption level, we switched from “any legume” to “mature legume” consumption level, as dietary recommendations only exist for the latter. To identify characteristics that differentiate among mature-legume consumers, we compared marginal consumers (<37.5 g cooked mature legumes
/day), recommended consumers (37.5–87.49 g/day), and beneficial amounts consumers (≥87.5 g
/day). In NHANES (
Table 5), young adults (18–35 years) ate less mature legumes, whereas older adults ate more mature legumes. Non-Hispanic white people ate lower amounts of mature legumes, whereas Mexicans and non-Hispanic Asians ate more mature legumes with intermediate amounts more prevalent for other Hispanics. Participants with >high school education or a higher income ate less mature legumes, whereas participants with <high school education and low income ate higher amounts. The caloric intake (
Table 5) decreased with increased mature legume intake to levels below that of non-legume consumers (
Table 1).
Higher mature legume intake was linked to a greater legume variety (
Table 6). All mature legume consumers utilized dry beans and green legumes, although to different extents (higher in the recommended and disease prevention mature legume consumers versus the marginal low intake group). Recommended mature-legume consumers added chickpeas to their diet, and beneficial amounts legume consumers added lentils to their diet. Regardless of mature legume consumption level, mature legume consumers preferred the same dish types for the same legume groups (
Table 6), which were dry beans for main dish or soup, green legumes or fava beans for side dish, chickpeas for dips, sprouted legumes for salad, and lentils, dry peas, or cowpeas for soup.
4. Discussion
The primary finding of both of our surveys (NHANES 2011–2014 and BLP 2017) is that daily legume consumption in US adults is rare, as less than 5% of participants in both surveys reported that they ate legumes each day. Approximately one-third of participants did not consume legumes within a month. In the companion study (BLP), we learned that primary reasons why people did not consume legumes were that people disliked their taste and texture, experienced digestive discomfort, or were concerned about their high carbohydrate content [
20]. Consistent with the literature [
5,
12], non-consumers were more likely to be young adults or of non-Hispanic descent; however, neither age nor ethnicity appeared to play a role in their decision to not consume legumes [
20]. In contrast, the lower price of legumes, especially during the winter months when other vegetables were more expensive, played a role in legume consumption and may explain in part why legume consumers were more likely to be of lower socio-economic status, as also observed in the literature [
12]. Furthermore, legumes were a less expensive and a more environmentally sustainable protein source than meat and an alternative protein source for vegetarians, all of which were provided as reasons for consuming legumes in the BLP study [
20].
We stratified mature legume consumers based on current US dietary recommendations for non-vegetarians, which are 1.5 cups/week of cooked mature legumes (equivalent to 37.5 g/day), which is equivalent to the recommendation of the healthy Mediterranean-style eating pattern [
6]. With the same consumption level, Mitchell et al. [
5] showed that 1.5 cups/week of mature legumes were insufficient to alter the nutrient profile, specifically the fiber and cholesterol content of the diet, and thereby did not provide health benefits. Instead, they proposed a cut-off of 0.5 cup/day of mature legumes (equivalent to 87.5 g/day), which we used as second cut-off. Approximately one-third of mature-legume consumers consumed mature legumes below the current dietary recommendations (marginal consumers). In other US studies, the median mature legume or dry bean consumption level usually falls into this category [
17,
21,
22], which is consistent with our findings. Historically, dry legumes were not a staple in the US diet [
2]. Mature legume consumption in the US was low in the 1960s, with 10 g per person, and bottomed out in the 1984, with 6 g per person [
2]. Mature legume consumption increased by 1991 to 11 g per person, primarily due to an increase in consumption of other legumes than dry beans and has been stable since then [
2]. Globally, the US is 100th out of 174 countries in legume consumption. In 2011, the leading legume consumers were Niger with 96 g per person and day, Rwanda with 82, United Arab Emirates with 66, and Cameroon, Nicaragua, and Tanzania with 56, 55, and 54, respectively [
2].
Legume consumption patterns of marginal mature-legume consumers were weekly to monthly and lacked legume group variety, as they consisted of dry beans as main or side dish, green beans or peas as side dish or both. The primary dry bean types consumed in NHANES were pinto beans, black beans, kidney beans, and navy beans, which is similar to previously reported studies [
5,
12,
17]; however, our findings suggest that black bean consumption has increased over the last decades. When asked for reasons for their low legume consumption, consumers cited problems with finding and preparing tasty recipes that include legumes; however, they did not question the health benefits of legumes, whereas non-legume consumers did [
20]. In the Polyp Prevention Trial, participants remarked that it was difficult to choose legume-containing dish options, when eating in social situations [
23]. This may explain in part why younger adults, non-Hispanic white people, and people at higher income to poverty ratio were over-represented in the marginal consumer group. Concerning is that dietary energy intake levels were higher in marginal mature-legume consumers than in non-legume consumers, which suggests that low legume consumption may do harm rather than benefit consumers. Marginal mature-legume intake levels were in line with the common nutritional concept of mature legumes, as part of the vegetable requirements. For example, the federal school meal regulations for receiving reimbursements requires 0.5 cups/week of mature legumes as part of the vegetable requirements [
24]. This makes sense, as US dietary recommendations for mature legumes have been alternating over the last decades, between providing specific recommendations for legume consumption and including legumes in the vegetable recommendations [
6,
23], which can cause confusion in consumers. Similarly, the healthy Mediterranean-style eating pattern groups legumes as part of the vegetable group [
6].
Another one-third of mature legume consumers ate mature legumes above current dietary recommendations, but below intake levels required to observe nutritional and health benefits [
5]. Therefore, we defined them as recommended mature-legume consumers. Consistent with current US dietary recommendations and various Mediterranean-style plans, legume consumption patterns of recommended mature-legume consumers were typically weekly and included dry beans, green beans or peas, and chickpeas. A subset of recommended mature-legume consumers added lentils and sprouted legumes on a weekly basis to their legume mix. Recommended mature-legume consumers were a transitional group, as they in some aspects resembled more marginal mature-legume consumers, whereas in other aspects, they resembled more beneficial amounts mature-legume consumers. For example, when asking for reasons for their legume consumption pattern, they cited similar challenges as low legume consumers with finding and preparing healthy dishes with legumes [
20]. In terms of age, demographics, income to poverty ratio and education levels, recommended mature-legume consumers were more similar to beneficial amounts of mature-legume consumers, whereas regarding ethnicity they were more similar to marginal mature-legume consumers. In regards to caloric intake, recommended mature-legume consumers had intermediate caloric intake; higher than marginal mature-legume consumers but lower than beneficial amounts mature-legume consumers, supporting the notion that recommended mature-legume consumption may be insufficient to provide the full nutritional and, thereby, health benefit.
Approximately a quarter of mature-legume consumers, or 15% of the total population, ate mature legumes at levels required to achieve nutritional and, thereby, disease prevention benefits, as supported by multiple population studies and meta-analyses, including ours [
4,
7,
8,
9,
10]. We defined them as beneficial amounts mature-legume consumers. Legume consumption patterns of beneficial amounts legume consumers were typically daily or 3–4 times a week, which is consistent with US dietary recommendations for vegetarians, Dietary Approach to Stop Hypertension (DASH) plans, and Mediterranean-style plans that promote heavily legumes as partial replacement of animal-originating protein foods [
6,
25]. Regularly consumed legumes included dry beans, green beans or peas, chickpeas and lentils. A subset of this consumption group added sprouted legumes and dry peas on a weekly basis to their legume mix. Adding more lentils to the diet was the primary change from recommended to beneficial mature-legume consumption levels.
Beneficial amounts of mature-legume consumers cited digestive health benefits (i.e., high fiber, low cholesterol, and high vitamin content) and their taste and texture as primary reasons for their consumption [
20]. Surprisingly, most of them were unaware that regular legume consumption may prevent obesity and chronic diseases [
20]. Most beneficial amounts mature-legume consumers had mastered preparation of a variety of legume groups, which can explain partly why older adults and Mexicans were over-represented in the disease prevention group. It may also explain why in previous studies, mature legume consumption was higher in the US West and in rural areas [
12]. Another important reason for high legume consumption was cost, as legumes were cheaper than other protein and vegetable sources, especially during times when fresh vegetables were expensive [
20]. The lower legume cost could explain in part why adults of lower socioeconomic status were over-represented in the beneficial amounts group. Despite the fact that disease prevention consumers ate sufficient amounts of legumes, half of them expressed interest in increasing their legume consumption by diversifying their legume group and dish type choices (i.e., obtaining tasty recipes of less popular legume groups and dish types) [
20]. Several BLP respondents responded that they lost body weight when they consumed legumes daily [
20], which is consistent with the lower dietary energy intake of disease prevention mature-legume consumers compared with the other groups in 2011–2014 NHANES and findings in the Legume Inflammation Feeding Experiment (LIFE) study, in which participants lost on average 1 kg body weight per week on a high dry bean (navy, pinto, kidney and black bean) diet over four weeks [
26].
The strengths of this study included a large sample size with a nationally representative sample. The NHANES has carefully controlled protocols and screens 24-h dietary recalls to confirm they are valid and complete; as stated, the NHANES also uses the multiple pass method to obtain dietary intake [
14]. However, NHANES is not without limitations. It is a cross-sectional study, and thus, causality cannot be established. Additionally, two 24-h dietary recalls do not represent one’s habitual dietary intakes; therefore, we queried in the 2017 BLP survey the legume consumption pattern. Additionally, 24-h dietary recalls have several intrinsic limitations. They are memory dependent and over- or under-reporting of intake may occur [
14]. In NHANES, changes in legume related food codes occurred over different year cycles, which made itdifficult to compare yearly consumption over time and, thereby, this can affect the quantification of legume consumption. There is a variety of ways how legumes are grouped in the literature and defined by governments [
1,
5,
6,
12,
15,
17,
18,
19,
27], which also makes comparisons difficult and causes confusion for consumers and scientists alike. We chose to combine mature and immature legumes (excluding high lipid legumes) that were similar in nutrient and disease prevention profile [
17] and disregard USDA guidelines that group members of the botanical legume family into six categories [
6].
There are several limitations to the BLP online survey. The participants were parents or guardians of families in the Corvallis, Oregon, area that were interested in nutrition and health; thus, our ability to generalize the finding from the study could be limited and our findings may be region-specific; however, the observed legume consumption patterns in BLP and NHANES are similar, suggesting the generalizability of our BLP findings. Data collection occurred over a 4-week period in November and December, which may have impacted results; however, based on our survey results, seasonal variability in legume availability was not a consumer concern. To keep the duration of the survey below 10 min, we did not ask for the average caloric intake of participants. Adjusting for caloric intake had little impact on legume consumption quantities and proportion of legume consumption groups in NHANES, and, therefore, is unlikely to have affected results in the BLP survey. Another potential concern is that the BLP survey was not validated; however, categories for legume consumption frequency and amounts and legume group and dish type were adapted from validated NIH surveys [
16,
17] and the FAO guidelines [
18], respectively. To reach a large target population, we chose direct e-mail messages, despite their limitations as unused and incorrect email addresses might have diminished the accuracy of the listserv and survey participation [
28]. We did not use any incentives for participation, which might have resulted in a higher response rate. To preserve the anonymity of the respondents, we did not collect any demographic characteristics related to respondents. Furthermore, in order to keep the BLP survey short and increase the response rate, we did not query in either survey for physical activity level or other food choices of the consumer groups. Hence, we were not able to explore these aspects, which may explain in part some of our results. Thus, subgroups of consumers may differ in their benefits, barriers and preferences for legume consumption, which needs to be explored in future studies.
