1. Introduction
Hispanics, the largest minority group in the United States (U.S.) [
1], have a higher prevalence of obesity and cardiometabolic disease risk factors relative to other ethnic groups, disproportionately increasing their risk for chronic conditions such as cardiovascular disease and diabetes [
2,
3]. Among women of reproductive age, excess weight gain during pregnancy and failure to lose weight postpartum have been associated with long-term obesity and further risk for chronic diseases [
4]. This is of particular concern for postpartum Hispanic women due to higher pre-pregnancy obesity rates [
5] and the presence of many contributors to excessive weight retention after childbirth [
6].
Several dietary factors are essential for the prevention and management of chronic diseases. Studies have shown that a higher dietary quality is inversely related to chronic disease risk factors such as waist circumference, low density lipoprotein (LDL)-cholesterol, insulin and C-reactive protein (CRP) [
7,
8]. Despite the known benefits of consuming adequate diets, available surveillance data on dietary composition suggest that, as for other ethnic groups, the diet of Mexican-American adults is in need for improvement, as indicated by reports of high intake of solid fats, added sugars, and sugar-sweetened beverages, and low intake of vitamins D and E, calcium and potassium, whole grains, dairy products, dark greens, and highly colored vegetables [
9,
10,
11,
12,
13].
Due to their cholesterol content, the contribution of eggs to a healthful dietary pattern continues to be controversial [
14,
15,
16,
17]. Whereas some studies have identified eggs as part of a “healthful” or “prudent” dietary pattern with greater Healthy Eating Index (HEI) scores [
18,
19], others have identified eggs as components of dietary patterns associated with greater risk for adverse outcomes including overweight and obesity, metabolic syndrome, and insulin resistance [
20,
21]. However, data from prospective cohort studies suggest that egg intake is not associated with increased risk of coronary heart disease, stroke, and mortality, although it may be associated with increased risk of type 2 diabetes [
22,
23]. Eggs are an inexpensive food with high quality protein and a rich source of nutrients including choline, folate, selenium, and vitamins A, B, D, E, and K, and, if fortified, ω-3 fatty acids [
24]. The nutritional value of eggs can be an important contributor to the health of women of reproductive age and to positive pregnancy outcomes particularly in disadvantaged populations with limited access to more costly healthy foods [
24,
25]. Folate, choline and docosahexaenoic acid (DHA), all of which can be supplied by eggs, are important nutrients during reproductive age for their role in the prevention of adverse pregnancy outcomes related to fetal central nervous system development [
25,
26,
27].
The World Agricultural Supply and Demand Estimates Report [
28] shows that the U.S. had an annual per capita consumption of 263 eggs in 2014, while Mexico is reported to have the highest consumption in the Americas with 335 eggs per person/year. Data from the 2001–2002 National Health and Nutritional Examination Survey (NHANES) suggested that eggs accounted for 7% of the servings from meat and beans group among the general U.S. population [
29]. Estimates using NHANES III data suggested that 18.7% of U.S. adults were egg consumers (
i.e., individuals who reported intake of at least one egg-group product in a 24-h recall) [
30]. Compared to non-consumers, egg consumers were less likely to have inadequate intakes of vitamins B12, A, E, and C. Furthermore, relative to other ethnic groups, a greater proportion of Mexican Americans (31.8%) were egg consumers [
30].
Despite the known nutritional content of eggs and their potential benefit towards the health of reproductive-age women, information regarding their contribution to a healthful diet among Hispanic women of reproductive age is limited to a report with a diverse sample of pregnant women, most of them of Caribbean descent [
31]. Thus, the objective of the present study was to compare nutrient intake and dietary quality, as assessed by the Healthy Eating Index 2010 (HEI-2010) [
32], an algorithm that measures conformance to the 2010 Dietary Guidelines for Americans [
33], between egg-consumers and non-consumers among Mexican-American postpartum women.
4. Discussion
This study assessed the contribution of eggs to dietary quality among an understudied group of the population, Mexican-American postpartum women, by comparing nutrient intake and HEI-2010 scores between egg-consumers and non-consumers. This report is of importance because there is limited information regarding contributors to nutrient intake and dietary quality among Mexican-American women of reproductive age. Study findings indicated that egg consumers had greater intakes of energy, protein, fat, monounsaturated fat, cholesterol, total and soluble fiber, vitamin D, riboflavin, vitamin B12, choline, sodium, potassium, and phosphorus, and a modestly higher HEI-2010 score than non-consumers. Similarly, in the only study of its kind conducted in a diverse sample of pregnant Hispanic women, egg consumers had higher intakes of several nutrients including protein, fat, vitamins K and E, cholesterol, total polyunsaturated fatty acids, and DHA [
31]. Comparable information among postpartum women is lacking.
In the current study, a greater proportion of participants (59% or
n = 82) reported consuming eggs than what has been reported for U.S. adults (19%) or Mexican-American adults (32%) using NHANES III data [
30]. A majority of study participants (78%) were immigrants of Mexican origin who had been in the U.S. for 12 ± 7 years [
34,
38,
39]. Several reports indicate that multiple factors that are part of the immigration experience, such as acculturation, generational status, and time in the U.S., are associated with lifestyle modifications often associated with less healthful dietary patterns in part due to immigrants’ lack of familiarity with available foods in their new environment [
40,
41,
42,
43]. However, eggs are a low-cost common protein source in the Mexican diet, as evidenced by the high per capita consumption of eggs in Mexico compared to other countries [
28], which may have made eggs a nutritious and familiar dietary choice among the generally low-socioeconomic status study participants [
34,
38,
39]. Nevertheless, the possibility cannot be ruled out that the methodology used in the current study (three 24-h recalls) may have better allowed to capture individual instances of egg intake than using only one 24-h recall for NHANES.
In the current study, energy intake was greater for egg consumers than non-consumers. Considering that participants were overweight or obese, this increased energy intake could be of concern because it could potentially translate into long-term weight gain, even when mean total energy intake was lower than what has been reported among U.S. adult women (7543 ± 59 kJ/day (1803 ± 14 kcal/day) according to NHANES 2009-2010 data [
44]). The greater energy intake among egg consumers could have been in part attributed to greater fat intake. Differences in fatty acid intake were due to greater monounsaturated fatty acids in the diet of egg consumers
vs. non-consumers, which explains the greater, albeit non-significant, HEI-2010 fatty acid ratio score ((polyunsaturated fatty acids + monounsaturated fatty acids)/saturated fatty acids) for egg consumers. Although these differences cannot be solely attributed to the fatty acid contribution from eggs, it is noteworthy that roughly 50% of fatty acids in eggs are monounsaturated [
45]. Regarding polyunsaturated fatty acids, fortified eggs can be an important dietary contributor to ω-3 fatty acids. A study including Mexican pregnant women reported that 20% of total DHA intake was supplied by eggs [
27]. In a diverse sample of pregnant Hispanic women, a greater proportion of egg consumers than non-consumers had DHA consumption in the highest tertile of intake [
31]. In the current study, differences in ω-3 fatty acid intake between egg non-consumers and consumers were not statistically significant. Although as expected in the current study egg consumers had greater dietary cholesterol than non-consumers, intake levels did not exceed current recommendations for cholesterol intake (300 mg/day) [
46].
Adequate protein intake is crucial for women of reproductive age to maintain maternal and fetal tissue accretion during pregnancy and milk production during lactation [
47,
48,
49]. In fact, a recent report [
50] suggested that protein needs for pregnancy may be even higher than current dietary reference intake recommendations of 1.1 g/kg of body weight/day [
46]. In the current study, both absolute protein intake and the HEI-2010 score for total protein foods were greater for egg consumers than non-consumers, although as previously reported the total protein HEI-2010 score was indicative of appropriate consumption of protein-containing foods for all participants [
38]. Intake of animal protein was also greater for egg consumers than for non-consumers, although non-significantly different (data not shown). However, the high-quality nature of egg protein [
24] may provide an additional nutritional advantage to women who incorporate eggs as part of their diet in the postpartum period.
In the present study, egg-consumers had a greater intake of vitamin D compared to non-consumers. According to NHANES 2003–2006 data, eggs were ranked the third main source of vitamin D (after milk and fish/seafood), contributing with about 5% of vitamin D intake among adults in the United States [
51]. This is important considering that it is estimated that between 40% and 80% of U.S. adults, depending on gender and age range, have inadequate vitamin D intake [
52]. Furthermore, results from a meta-analysis study showed that low maternal vitamin D levels during pregnancy are associated with risk of preeclampsia, gestational diabetes, preterm birth and small-for-gestational age [
53].
All participants in the current study had HEI-2010 scores suggesting intake of diets with low quality or in need for improvement (55 ± 14 relative to a maximum score of 100). A report using NHANES data suggested that at the population level HEI-2010 total score was 53 [
54]. Furthermore, participants were not meeting intake recommendations for several nutrients, including fiber, Ca, vitamin E, vitamin C and folate. Egg consumers had a greater HEI-2010 score for total protein foods, and trends towards greater scores for total fruit and empty calories, and lower score for sodium. These differences resulted in a modestly greater total HEI-2010 score for egg consumers.
The main risk associated with egg consumption in the U.S. is salmonellosis, mainly due to consumption of raw or undercooked eggs [
55]. The risk is particularly important during pregnancy since salmonellosis may be transmitted to the fetus, increasing the risk of preterm delivery and intrauterine death [
55,
56]. In a study about food safety, most pregnant women were aware about recommendations to avoid raw eggs; however, they still reported consumption of eggs with runny yolk (35%) and cookie dough containing raw eggs (40%), indicating the need to improve instructions given to this target group [
57]. Nevertheless, the potential benefits associated with their high nutritional quality outweigh risks as long as eggs are properly cooked before consumption.
Prior reports from the current study have documented that participants included a large proportion of women living under disadvantaged socio-economic conditions in neighborhoods with limited food access [
34,
38,
39]. In general, Hispanic households have been documented to have greater food insecurity rates than the general population [
58]. Thus, an additional benefit of egg intake for the target population in the current study as well as other Hispanic subgroups is associated with their low cost. In general, the cost of foods is directly associated with protein but inversely associated with carbohydrate content [
59]. In contrast, relative to other animal sources of protein, eggs are an inexpensive nutrient-dense, high-protein, low-carbohydrate food [
24,
59]. According to the Nutrient Rich Foods Index, developed as an effort to aid consumers select nutritious food choices under financial constraints, eggs are a low cost source of protein, vitamin A, vitamin B12, riboflavin, calcium and zinc, providing excellent nutritional value for the money [
60].
An important limitation of the current report is that dietary assessment was conducted using three 24-h dietary recalls, a method subject to intake underreporting, particularly among women and Hispanic individuals [
61,
62], as indicated by the relatively low energy intake observed in the current study. Although this limitation was addressed by calculating the HEI-2010 scores on an energy-density basis when assessing dietary quality [
32], differences observed in individual nutrient intakes between egg consumers and non-consumers, particularly macronutrients, are likely a result of absolute energy intake and not solely due to egg consumption. Moreover, data from 24-h dietary recalls may not be the best indicator of habitual food consumption, including eggs.
