1. Introduction
Micronutrient deficiency, known as “hidden hunger”, is one of the most critical nutritional problems affecting the health of children and adults currently, as well as being one of the most prevalent public health issues worldwide [
1]. While the dietary requirement for micronutrients is quite small, deficiencies can have negative impacts on health that will ultimately result in death if untreated [
2]. Micronutrient deficiencies can not only affect the immune system and function, but also hamper development and result in metabolic disorders [
3]. Some research suggests that dietary diversity has a favorable impact on micronutrient adequacy, and is positively associated with health status across age groups [
4,
5,
6]. Some studies have documented that a diverse diet is associated with micronutrient adequacy, and leads to positive health outcomes [
7,
8,
9]. A diverse diet also decreases the risk of being stunted and underweight [
10,
11]. Lack of dietary diversity is a serious problem globally, and is most prevalent in the poorest households [
12]. In summary, it is critical to assess micronutrient adequacy and diet diversity in vulnerable populations.
It is estimated that more than 2 billion individuals around the world are suffering from micronutrient deficiencies, particularly vitamin A, iodine, iron, and zinc [
2]. Furthermore, there is a high prevalence of micronutrient deficiency in developing countries [
6,
13]. China is one of the most economically dynamic countries, with complex lifestyles and dietary habits [
1], in which major changes in the country’s population and socioeconomy have resulted in significant challenges to nutrition and health [
6]. Undernutrition and micronutrient inadequacy are still concerning problems in China, especially among rural residents living in poverty [
5]. Health-related illnesses resulting from energy and nutrient deficiencies, such as low body weight and anemia, are adverse consequences of the insufficient food supply and unbalanced dietary habits in low-income areas [
14,
15].
China is one of the largest developing countries that is experiencing significant transitions in multiple areas of society, including poverty levels and dietary habits [
16]. From 2012 to 2019, the rural poor population in China declined from 98.99 million to 5.51 million [
17]. Gansu Province lies in northwest China. It is predominantly an agricultural region, and had 31 impoverished counties until 2019 [
18]. Smallholder farmers live in impoverished counties with insufficient infrastructure, development, medical and health services, and fresh fruits and vegetables. When food is available, many low-income households consume strictly cereal-based diets lacking in vegetables, fruits, and dairy, thus increasing the risk of micronutrient deficiency [
19,
20]. Both Dongxiang and Han Chinese are the dominant ethnic groups in the two regions studied. The Dongxiang Chinese, a distinctive minority group living in Gansu Province of China, are unique in their living environment, lifestyles, and dietary behaviors, compared to their extensive Han counterparts. The limited available evidence suggested that Han rural students grow faster in chest circumference, height, weight, and body mass index (BMI) than their Dongxiang counterparts [
21], and blood lipids and BMI were significantly higher among the Dongxiang than Han Chinese [
22]. This suggested that nutritional imbalance may be especially common in this group.
In addition to the adequacy of each nutrient, it is essential to assess the overall healthiness and diversity of the diet, since the diet contains a wide range of foods that provide a comprehensive profile of nutrients instead of individual nutrients or foods [
11]. It has been reported that the dietary diversity score (DDS) among adults in southwest China was 5.2 (on a scale of 9) [
23]. Some studies have explored the dietary diversity status of Chinese children and adults, the factors that influence dietary diversity, and the connection between micronutrient adequacy and dietary diversity [
5,
6,
24]. Few studies, however, have investigated the association of DDS with micronutrient adequacy in Han and Dongxiang smallholder farmers, especially in low-income rural areas of northwest China. This study aimed to evaluate the dietary diversity and nutrient intake among Han and Dongxiang smallholder farmers, as well as to investigate the association between dietary diversity and nutrient intake. The study also explored associated factors with mean adequacy ratio (MAR) among farmers in low-income rural areas of Gansu Province in China.
4. Discussion
The present study assessed the dietary diversity and nutrient adequacy among smallholder farmers in Gansu Province. The DDS, based on nine food groups, was adopted to assess dietary diversity. NAR and MAR indicators were used to measure the probability of nutritional adequacy. Additionally, the present study demonstrated that dietary diversity was positively associated with most dietary micronutrient intake.
The mean DDS was 3.81 in this study, which was lower than the DDS reported in other studies (5.20 in Zhang et al., 4.46 in Yin et al. [
23,
31]). Variations in the results of DDS may arise from the different study samples and different measurements of DDS [
32]. Yin et al. conducted their study among elderly people, partly from urban areas [
31], where it is more convenient to access a variety of foods than in rural areas. In the present study, participants were from rural areas, where access to diverse foods was more costly than in urban areas [
33]. Studies have also reported that DDS was directly related to income [
34,
35,
36], supporting the present study’s findings that the smallholder farmers’ DDS differed based on different household monthly incomes. The majority of participants were smallholder farmers with very low incomes, and thus, most participants had a lower DDS in the present study, which is in line with the findings of previous studies [
37,
38,
39]. Some studies have demonstrated that lower education levels predict lower DDS [
23,
40,
41], and our study concluded that most of the population born in the 1950s–1970s in areas of poverty had limited opportunity to receive a high level of formal education.
We also found that Han Chinese appeared to have higher odds of DDS than Dongxiang Chinese, which is consistent with a previous study among adults in southwest China [
23]. This suggests that Dongxiang smallholder farmers have a less diverse diet than their Han peers. No significant difference between DDS and sex was found in our study, which is inconsistent with a previous study [
23,
42], possibly since there were more males than females in the present study. In this study, we also found that DDS significantly differed by weight status. Previous studies have shown that obese individuals have higher DDS values than normal-weight individuals [
34,
42], and the present study reported a higher DDS among overweight participants than in those who were underweight and normal weight. A possible explanation is that individuals with higher DDS are likely to have unhealthy diets [
33]. Smallholder farmers are less nutritionally literate, and some of them consume adequate types of food but also excessive amounts simultaneously, thus indicating that dietary interventions and nutrition education are necessary.
Imbalanced dietary practices are more common in underdeveloped areas of Gansu Province. A monotonous diet usually means unhealthy eating habits, and some studies have related the DDS to higher rates of obesity [
23,
43] and poor nutrient adequacy [
44,
45].
The adequacy rates for some micronutrients, such as calcium, vitamin A, vitamin C pyridoxine, and riboflavin, in smallholder farmers were low. The imbalance of micronutrients may have a large burden on smallholder farmers’ health, increasing the risk of chronic diseases. Among the nutrients assessed in this study, deficiency in vitamin A intake was the most common. Given that vitamin A has a major role in multiple aspects of health, such as immune function and eye and skin health, dietary interventions to address the insufficient intake of this nutrient should be implemented, such as increasing intake of organic and dark green vegetables [
46]. Moreover, deficiency in riboflavin and pyridoxine results in homocysteine accumulation, which is related to cardiovascular disease, hypertension, and cognitive impairment [
6]. Vitamin B complex intake deficiency may be related to low intake of whole grains, legumes, vegetables, fruits, and some animal foods [
47]. Furthermore, dairy products are the most abundant origin of calcium, yet they are consumed at relatively low level, especially in rural areas of poverty in northwest China [
48]. Vitamin C is a potent water-soluble antioxidant that not only protects immune cells in the innate system by fighting ROS and regenerating oxidized glutathione and vitamin E, but also regulates B and T-lymphocyte differentiation and proliferation through gene regulation in adaptive immunity [
49]. Participants’ vitamin C intake, however, was inadequate in the present study. Therefore, it is necessary to increase vegetable and fruit intake. We also found that out of the 14 micronutrients assessed, ten were significantly different between the Han and Dongxiang Chinese, suggesting that dietary interventions for ethnic minorities should be enhanced in the future.
In addition, a positive correlation was also found between DDS and NAR in most micronutrients, which is in accordance with previous findings [
5,
23,
50]. Zhang et al. estimated the dietary diversity and nutrient profile of adults in southwest China, and showed a positive correlation between NAR values of most nutrients and DDS. Meng et al. demonstrated a positive association between DDS and nutrient adequacy in children aged 3–17 years in China. Similarly, higher DDS was directly associated with adequate nutrient intake. Participants with high DDS in the present study had higher adequacy rates for intake of most micronutrients (vitamin A, vitamin E, riboflavin, niacin, calcium, zinc, phosphorus, and selenium), with Pearson correlation coefficients in the range of 0.15 to 0.71. Moreover, the DDS was associated with the MAR, showing a significant increase in the high DDS group, which is consistent with a previous study [
29]. Despite this, the high DDS group did not perform well for vitamin A, calcium, and pyridoxine intake, which showed that mean NARs were below 50% of EAR. These findings emphasize the need for increasing food diversity to acquire adequate nutrients. Consuming a variety of food groups including fruits, vegetables, dairy, and other healthy food groups will ensure adequate intake of nutrients [
45,
51]. Given that essential nutrient content varies among foods, the dietary guidelines suggest that people should consume a variety of foods.
To the best of our knowledge, the present study is the first to assess the relation of dietary diversity status and nutrient adequacy in poor rural areas of northwest China. Most of the previous studies are primarily focused on the dietary diversity of children and urban areas, but not on individuals living in poor and remote rural areas, especially among Han and Dongxiang smallholder farmers. Our study fills the gap by providing a comprehensive evaluation of dietary diversity, nutrient adequacy, and their relation in remote rural areas in Gansu Province. An important strength of this study was the use of paired sampling in Han and Dongxiang Chinese, allowing us to compare the dietary diversity and nutrient intakes in these two ethnic groups.
This study also has some limitations. First, a cross-sectional study could not determine causality. Second, it was conducted only in two counties of one province, and the data were limited to rural populations, thus it does not represent the urban populations. Additionally, the sample size was small, so the findings may not be generalized to a large population. Third, the three-day dietary recall also had limitations in terms of assessing nutrients and due to the absence of biochemical tests, we could not offer more precise results on micronutrient levels. Fourth, the language barrier of the Dongxiang Chinese may have affected the accuracy of the information collected by the questionnaire.