Original researchNutrition-related knowledge and its determinants in middle-aged and older patients with type 2 diabetes
1. Introduction
Diabetes affects more than 425 million people worldwide, of which one-third are people older than 65 years. This number is expected to rise to 693 million in 2045 [1]. In Portugal, in 2015, the Portuguese Society of Diabetology reported a prevalence of diabetes of 13.3% (20–79 years old). The prevalence increases to 25% between the ages of 60 and 79 years old [2]. For 2030, the World Health Organization estimates diabetes as the 7th leading cause of death [3]. Besides mortality, diabetes has a huge impact on morbility, with neuropathy, nephropathy, retinopathy, amputation and cardiovascular disease as major chronic consequences [2]. Type 2 diabetes (T2D) is the most common type of diabetes, accounting for 90–95% of all cases [4]. Dietary modification is considered a cornerstone of effective T2D self-management [5]. The goals of T2D dietary management are to attain ideal blood glucose and blood lipids levels, to prevent, delay, and control diabetes-related complications, and to improve health through a healthy diet [6]. While numerous factors potentially influence the adoption of a healthy diet, nutrition-related knowledge is necessary to achieve this goal [7].
Although some studies conducted in T2D patients had found deficits in nutrition-related knowledge [5], [8], [9], [10], [11], [12], [13], [14], [15], most of them were conducted in countries outside Europe [8], [9], [10], [12], [14], [15] and only two were conducted in Western Europe [5], [13]. Furthermore, few studies have analyzed the determinants of nutrition-related knowledge in T2D patients [9], [11], [14], [15] and most of them only focused on educational level. To our knowledge, this is the first study in Portugal that focused on these two issues.
The aim of the present study was to analyze nutrition-related knowledge and its determinants in Portuguese middle-aged and older patients with T2D.
2. Methods
2.1. Study design
This was a cross-sectional study conducted in the cities of Vila Real and Maia, Portugal. Study protocol was approved by the local health ethics committee in accordance with the Declaration of Helsinki. All patients gave written informed consent before participation. Appropriate standard procedures were implemented to guarantee data confidentiality and protection.
2.2. Participants
A total of 116 middle-aged and older patients with T2D were recruited from primary health care centers by their family doctors in a consecutive basis according to the following inclusion criteria: aged between 50–80 years old; T2D diagnosed for at least six months; non-smokers; independent living in the community; without major changes in gait or balance; diabetes comorbidities under control; willingness to participate in this study.
2.3. Nutrition-related knowledge assessment
Nutrition-related knowledge was assessed using the Portuguese modified short version [16] of General Nutrition Knowledge Questionnaire (GNKQ) [17]. In order to adapt the GNKQ to the Portuguese population, the Translation into Portuguese, Cultural Adaptation and Linguistic Adaptation was performed [16]. The final version of the questionnaire consists of three sections, each one addressing a different area of knowledge: dietary recommendations (DR; 1 multiple choice question; 0–6 points); sources of nutrients (SN; 8 multiple choice questions; 0–34 points); and diet-disease relationship (DDR, 5 multiple choice and 4 open-ended questions; 0–16 points). Differences between original questionnaire and the one used in our study are presented in Table 1. The participants answered on a range of different scales such as ‘more, equal, less, don’t know’, ‘yes, no, don’t know’, ‘rich, poor, don´t know’, ‘agree, disagree, don´t know’. Some questions related to diet-disease relationships are open-ended and require participants to list diseases related with diet-related lifestyle factors. Correct responses from each section were added giving an overall score out of 56 points. A higher score reflects a higher knowledge level.
Table 1. Differences between General Nutrition Knowledge Questionnaire (GNKQ) and Portuguese modified short version of GNKQ.
| GNKQ | Portuguese modified short version of GNKQ | |
|---|---|---|
| Section 1 | 3 multiple choice and 1 open-ended question | 1 multiple choice question |
| Section 2 | 21 multiple choice questions | 8 multiple choice questions |
| Section 3 | 10 multiple choice questions | No questions — lack of internal consistency and item validation |
| Section 4 | 5 multiple choice and 5 open-ended questions | 5 multiple choice and 4 open-ended questions |
2.4. Sociodemographic characteristics
Sociodemographic characteristics were obtained through a set of questions at the end of the questionnaire: gender (male; female), age (<65; ≥65 years), personal monthly (net) income (<500 €; 500–1000 €; >1000 €), living situation (living alone; living with others), education level (years of school; ≤4 years; 5–9 years; >9 years), marital status (married or with domestic partner; single, divorced or widowed).
2.5. Data analysis
Categorical variables are presented as proportions (number and percentage) and continuous variables as means and standard deviations (SD). One-way analysis of variance (ANOVA) was performed to assess differences in nutrition-related knowledge score among the different levels of sociodemographic characteristics. All statistical analysis were performed using Statistical Package for the Social Sciences, version 20. The level of statistical significance was set at p < 0.05.
3. Results
3.1. Participant’s characteristics
3.2. Nutrition-related knowledge
Nutrition-related knowledge total score and by section is presented in Table 3.
Table 3. Nutrition-related knowledge scores (total and by section).
| Mean (SD) | Percentage of correct answers | |
|---|---|---|
| Total score (0–56 points) | 28.6 (7.5) | 51.1% |
| Dietary recommendations (0–6 points) | 4.8 (0.9) | 80.0% |
| Sources of nutrients (0–34 points) | 17.2 (5.8) | 50.6% |
| Diet-disease relationship (0–16 points) | 6.6 (2.0) | 41.3% |
Results from each question are presented in Fig. 1. Questions on general dietary recommendations, dietary behaviors to reduce cardiovascular disease and cancer are the items with higher proportion of correct answers. On the other hand, health problems related with lower intake of fruit, vegetables and fiber and knowledge about antioxidants vitamins presented the lower proportion of correct answers.
Fig. 1. Percentage of correct answers in each question of the Portuguese modified short version of General Nutrition Knowledge Questionnaire.
3.3. Determinants of nutrition-related knowledge
Results of the analysis between sociodemographic characteristics and nutrition-related knowledge are presented in Table 4.
Table 4. Analysis between sociodemographic characteristics and nutrition-related knowledge.
| Characteristics | Sample | Total nutrition-related knowledge score (0–56 points) | Dietary recommendations section (0–6 points) | Sources of nutrient section (0–34 points) | Diet-disease Section (0–16 points) | |
|---|---|---|---|---|---|---|
| n | % | Mean (SD) | Mean (SD) | Mean (SD) | Mean (SD) | |
| Age | a | b | ||||
| <65 years | 55 | 47.4 | 30.15 (7.50) | 4.87 (0.88) | 18.60 (5.85) | 6.71 (2.05) |
| ≥65 years | 61 | 52.6 | 27.28 (7.30) | 4.77 (0.92) | 16.02 (5.55) | 6.49 (1.96) |
| Gender | ||||||
| Male | 61 | 52.6 | 28.82 (6.68) | 4.95 (0.76) | 17.21 (5.30) | 6.69 (1.79) |
| Female | 55 | 47.4 | 28.44 (8.40) | 4.67 (1.02) | 17.27 (6.39) | 6.49 (2.23) |
| Education level | c | d | e | |||
| ≤4 years | 61 | 52.6 | 25.39 (6.76) | 4.66 (0.91) | 14.70 (5.08) | 6.03 (1.85) |
| 5 to 9 years | 29 | 25.0 | 31.21 (6.83) | 5.07 (0.96) | 19.21 (5.10) | 6.93 (2.07) |
| >9 years | 26 | 22.4 | 33.38 (6.39) | 4.92 (0.74) | 21.00 (5.45) | 7.54 (1.88) |
| Marital status | ||||||
| Single, divorced or widowed | 19 | 16.4 | 27.42 (7.79) | 4.63 (1.42) | 16.79 (5.63) | 6.00 (2.16) |
| Married or with domestic partner | 97 | 83.6 | 28.88 (7.47) | 4.86 (0.76) | 17.33 (5.87) | 6.71 (1.96) |
| Living situation | ||||||
| Living alone | 9 | 7.8 | 28.50 (5.33) | 4.80 (1.23) | 17.14 (4.22) | 6.58 (2.28) |
| Living with others | 107 | 97.2 | 30.22 (7.67) | 5.00 (0.87) | 18.44 (5.93) | 6.78 (1.99) |
| Personal monthly income | f | g | ||||
| <500 € | 53 | 45.7 | 27.53 (7.24) | 4.81 (0.88) | 16.34 (5.55) | 6.38 (2.14) |
| 500–1000 € | 36 | 31.0 | 27.64 (7.21) | 4.72 (1.03) | 16.31 (5.22) | 6.61 (2.04) |
| >1000 € | 27 | 23.3 | 32.15 (7.61) | 4.96 (0.76) | 20.26 (6.24) | 7.00 (2.00) |
- a
Significant differences between participants with <65 years and ≥65 years (p = 0.040).
- b
Significant differences between participants with <65 years and ≥65 years (p = 0.016).
- c
Significant differences between participants with ≤4 years of school and >9 years of school (p < 0.001) and between ≤4 years of school and 5–9 years of school (p = 0.001).
- d
Significant differences between participants with ≤4 years of school and >9 years of school (p < 0.001) and between ≤4 years of school and 5–9 years of school (p = 0.001).
- e
Significant differences between participants with ≤4 years of school and >9 years of school (p = 0.003).
- f
Significant differences between participants with a personal monthly income <500 € and >1000 € (p = 0.026).
- g
Significant differences between participants with a personal monthly income >1000 € and <500 € (p = 0.012) and between >1000 € and 500–1000 € (p = 0.020).
4. Discussion
Our results showed important deficits regarding nutrition-related knowledge in this population, with 41% of participants scoring below 28 points. Age, years of school and personal monthly income were observed as determinants of nutrition-related knowledge.
Higher nutrition-related knowledge enables individuals with T2D to make healthier food choices [5]. According to our search, this is the first study conducted in Portugal that specifically evaluated nutrition-related knowledge in T2D patients. Studies conducted in T2D patients in other countries focused on other issues beyond nutrition-related knowledge (for example: glycemic control, diabetes complications, physical activity, etc.) and used different evaluation methods: group interviews [8], [12] and questionnaires evaluating diabetes knowledge [5], [10], [11], [13], [14], [15]. We just found one study that specifically assessed nutrition-related knowledge in T2D patients, using a 25-item nutrition knowledge scale designed for a community of Hispanics living in United States [9]. Despite the different methodological approaches, these studies also revealed nutrition-related knowledge deficits in this population.
We did not find studies in T2D patients that used GNKQ. However, studies conducted in other populations, in community setting, using GNKQ [18], [19] found a better performance in DR section and lower in DDR as in our study. Increasing availability of nutrition information in the media can justify the awareness on DR section [20], which leads participants to be closer from dietary guidelines [7]. Regarding DDR, according to Rolstad et al. [21], the length of the questionnaire can increase response burden. Since DDR is the final section of our instrument, it may have influenced its score. Furthermore, results may have been conditioned by type of questions design, since there are some open-ended questions that required participants to report one or more diseases instead of choosing multiple choice answers [22]. Effectively, our participants were best able to give a correct response to multiple choice questions than open-ended ones. Despite the lower score in DDR, our participants had a higher proportion of correct answers in two questions from this section: dietary behaviors to reduce cardiovascular disease and cancer. Although the association between a balanced diet and cancer and cardiovascular diseases had been well recognized worldwide since 1950 [23], opposite findings to our study had been found in previous studies conducted with general population [24], [25], where participants had poor knowledge about the link between fruit and vegetable intake and cancer.
On the other hand, throughout our questionnaire, the link of health problems with lower intake of fruit, vegetables and fiber and the knowledge about antioxidants vitamins presented the lower proportion of correct answers.
Fruits and vegetables are recommended mainly due to their high concentration of dietary fiber, vitamins (especially vitamins C and A) minerals (especially electrolytes) and phytochemicals (especially antioxidants) [26]. Low intake of fruits and vegetables are associated with cardiovascular diseases, high blood pressure, hypercholesterolemia, osteoporosis, many types of cancers, chronic obstructive pulmonary diseases, respiratory problems as well as mental health [27]. Consistent with our findings, Doherty et al. [8] revealed that the knowledge about the health effects of fruits was not clear, after interviewing 30 patients with T2D. Also Ranasinghe et al. [12] illustrated that individuals with T2D considered fruits unhealthy thanks to its sweet taste, in a cohort of 50 patients.
Lack of knowledge in the link between fiber intake and health is alarming as dietary fibers are known to have a protective effect against stroke, diabetes, obesity and several gastrointestinal diseases such as: constipation, hemorrhoids, colon cancer, gastroesophageal reflux disease, duodenal ulcer, diverticulitis [28]. They are also associated with lower all-cause mortality in individuals with T2D [29].
Regarding the connection between antioxidant vitamins intake and health, our results are in keeping with the study of Parmenter et al. [19], where only 22% of participants have heard about antioxidant vitamins. Scientific findings relating to this term are recent [19] and the mean age of our sample is 65.1 (6.7) years old. Higher dietary intake of antioxidant vitamins was inversely associated with pancreatic cancer risk [30] and may decrease the risk of all-cause mortality [31].
Studies evaluating the determinants of nutrition-related knowledge in individuals with T2D are scarce [9], [11], [14], [15] and mostly centered in educational level [9], [14], [15]. In our study it was observed higher nutrition-related knowledge scores with lower age, more years of school, and higher personal monthly income.
Regarding age, we did not find any study in T2D patients. However, other studies conducted in people without T2D also reported that older people had a lower nutrition-related knowledge [32], [33]. In our study, higher knowledge scores of younger age groups probably reflects the fact that the Portuguese current dietary recommendations are relatively recent [34] and older people have more implemented ideas regarding food, being less receptive to change [19]. Older adults have more difficulties in the use of new technologies that are, increasingly, a major information source [35]. Another possible reason could be the rise of cognitive impairment as population ages [36].
In what concerns education level, our results are consistent with other findings in individuals with [9], [14], [15] and without diabetes [18], [32], [37], [38], [39]. School is a stimulus for more knowledge and for a better understanding of information from different sources such as newspaper, TV, radio, internet, etc. [19]. The importance of educational status is highlighted in a study carried out by Nilsson et al. [40] in which T2D patients with less education had 40% excess mortality compared with those who were highly educated.
The association of nutrition-related knowledge and personal monthly income needs to be analyzed with care, since it is common the use of different methodologies [38]. In many studies, personal monthly income is included in socioeconomic status (SES) that is defined by Adler et al. [41] as a complex construct including economic status (income), social status (education) and work status (occupation). Our findings confirm the conclusion of Parmenter et al. [19] that people with a lower SES (determined by occupational status) seemed to have a lower nutrition-related knowledge. Also, De Vriendt et al. [38] found a similar result, with a higher SES (composed by a higher educational level, non-smoking behavior, and higher occupation status) related to higher nutrition-related knowledge. The fact that less educated people may have lack of resources and difficulties to access to some sources of nutrition information [42] may justify the differences in nutrition-related knowledge according to personal monthly income and years of school.
Regarding gender, and contrary to our results, most studies observed that women had higher nutrition-related knowledge than men [19], [32], [33], [39], [43]. Our finding is not unique [37], and may be related with changes in family structure, with more men cooking and having interest about food contents [19]. It also appears that marital status and living situation are not significant determinants of nutrition-related knowledge as it was shown in the systematic review of Barbosa et al. [44].
Considering the importance of nutrition-related knowledge in glycemic control [45] and weight management [46], the current findings suggest a need for nutrition education intervention in this population. Primary health care system could be a successful context for the implementation of these interventions [47].
This study has few limitations. Analysis were based on cross-sectional data and therefore cannot demonstrate cause-effect relationships. Further research should extend this work by using intervention-design data, preferably from a randomized controlled trial to determine how nutrition-related knowledge influence dietary behaviors over time. The instrument that we used to measure nutrition-related knowledge differ from those used by other studies in T2D and only evaluate declarative knowledge (do not evaluate procedural knowledge). Our sample may not be representative of the wider Portuguese population with T2D, since our data collection was made only in the north of Portugal. Therefore extrapolation of the results beyond this sample needs to be treated with caution.
Despite the limitations, our study also has strengths. The questionnaire used covered three main areas of nutrition-related knowledge (DR, SN and DDR). Besides, through our search, it seems the first study evaluating nutrition-related knowledge in T2D Portuguese patients. We believe that our data are of high clinical importance as it indicates the need for practical dietary education.
5. Conclusions
Middle-aged and older patients with T2D showed alarming nutrition-related knowledge deficits, especially related to the link between health problems and lower intake of fruit, vegetables and fiber and knowledge about antioxidants vitamins. Age, personal monthly income, and years of school were observed as determinants of nutrition-related knowledge. Participants with lower age, higher personal monthly income, and more years of school showed better scores.
The results suggest the need for nutrition education in this population, as this can contribute to dietary changes and therefore to the improvement of health outcomes.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Conflict of interest
The authors state that they have no conflict of interest.
Acknowledgements
The authors acknowledge the support received from all participants of the Diabetes em Movimento Vila Real and Diabetes em Movimento Maia.
Appendix A. Supplementary data
The following are Supplementary data to this article:
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