Type 2 Diabetes and Intake

¶ … Type 2 Diabetes

and intake of Fruits and Vegetables

Diabetes Mellitus has become one of the major chronic diseases affecting more than 220 million people around the world. [WHO, 2009] In Australia too the incidence of diabetes is on the rise with current estimates indicating that more than 1.7 million people are affected by the condition. Of these more than 85 to 90% are type 2 diabetes and on an average 275 people are diagnosed with diabetes everyday. [Diabetes Australia, (2010)] What is more alarming is the increasing prevalence of type 2 diabetes among younger generation. However, it is believed that healthy eating habits, active lifestyles and effective blood glucose control can help prevent up to 60% of type 2 diabetes cases. [Diabetes Australia] Healthy eating, in particular, regular consumption of fruits and vegetables have been regarded as highly protective of type 2 diabetes. This paper focuses on several studies pertaining to this association between fruits and vegetables intake and its effect on Type 2 diabetes. A brief overview and analysis of the studies would provide more insight into this important health topic.

Sargeant et.al (2001)

Sargeant et.al (2001) is one of the rare cross sectional studies to analyze the relationship between the frequency of fruits and vegetable intake and glycosylated Hemoglobin HbA1C levels. This study was conducted from 1993 to 1998 and all the subjects were asked to complete a comprehensive Health and Lifestyle questionnaire. The study subjects were recruited from the European Prospective Investigation into Cancer (EPIC Norfolk ) database. A total of 6089 subjects who completed HbA1C assessment were asked to answer the health and lifestyle questionnaires. Statistical analysis including variance analysis (ANOVA), t-tests comparisons and chi-square tests were performed on the gathered data.

It was deduced that participants who reported very low or no consumption of fruits and vegetables had the highest mean HbA1C values of 5.49 (0.67) among men and 5.40 (0.63) among women. The similar ratios for those reporting high consumption (5 or more times per week) are 5.34 (0.75) for men and 5.31(0.64) for women. Plasma vitamin C levels are also significantly different between the high and low consumption groups for both sexes. 50.9 (18.1) vs. 33.9 (19.2) for men and 61.3 (19.0) vs. 41.7 (23.3) for women. The mean HbA1C values calculated based on the vegetable consumption also reflected a similar pattern. The HbA1C values for those consuming five or more times was 5.36 (0.71) vs. 5.49 (0.60) for the low or no consumption group. Overall it was obvious that participants with the least intake of fruits and vegetables had the highest mean HbA1C values. Even after adjusting for dietary supplements, age, BMI, alcohol and smoking habits, etc. The differences in HbA1C was significant at 5.35 (0.01) for the high consumption group vs. 5.47 (0.05) for the low or no consumption group. Overall, this cross sectional study suggests that fruits and vegetables have a positive effect on glucose metabolism. The higher plasma vitamin C levels (50.9 (18.1) vs. 33.9 (19.2)) and dietary fiber levels (20.1 (6.2) vs. 13.3 (4.8)) in the high consumption group suggests that these may have a role to play. [Sargeant et.al (2001)]

The study authors did not find a significant difference in HbA1C values even after adjusting for vitamin C and dietary fibers and so Vitamin C and dietary fibers could not clearly explain the results. The authors conclude that other components in fruits and vegetables (flavanoids and other secondary metabolites) may be involved in the protective role. This study is significant because of the large sample size and for the proven association between fruits and vegetable intake on reducing glycosylated Hemoglobin levels which is a marker for type 2 diabetes.

Montonen Et.al (2005)

This cohort study recruited participants from the Finnish mobile clinic health examination survey. In all, a total of 4304 men and women aged between 40 and 69 from 30 different communities in Finland were followed up for a period of 23 years. In this population group, the researchers studied the effects of different foods such as Green vegetables, fruits and berries, oil and margarine and poultry and their effect on the incidence of type 2 diabetes. Dietary patterns were gathered using dietary history interview by trained interviewers. Cox Model was used to calculate the relative risk RR for the different quartiles of consumption of the different food items. The following were the data for the RR of developing diabetes between the highest and lowest consumption. 0.69 (95% confidence interval (CI)1/40.50 -- 0.93; P. For trend (P)1/40.02) for green vegetables, 0.69 (CI1/40.51 -- 0.92; P1/40.03) for fruit and berries, 0.71 (CI1/40.52 -- 0.98; P1/40.01) for margarine and oil, and 0.71 (CI1/40.54 -- 0.94; P1/40.01) for poultry. [Montonen Et.al (2005)] The study also revealed that RR for consumption of potatoes was high at RR = (1.42). This study clearly shows an inverse relationship between the prudent diet choice of green vegetables, fruits and berries, oil and margarine and poultry with the risk of developing T2D. The only major shortcoming of the study is that there is no way of identifying diabetics undergoing only dietary therapy in its subject pool. This would have affected the estimation of the relationship between food intake and diabetes risk.

Villegas et.al (2008)

This population-based prospective cohort study analyzed 64,191 women in the age group of 40 to 70 drawn from the Shanghai Women's Health Study (SWHS) database. The participants were evaluated for their intake of vegetables and fruits using baseline food frequency questionnaires. (FFQ) The dietary information was again gathered at the follow up survey. During the follow up after 4.6 years 1608 participants reported diagnosis of diabetes. The researchers applied the Cox proportional hazards model to understand the association between fruit and vegetable intake and the incidence of type2 diabetes. Confounding variables such as age, BMI, WHR, total energy, meat intake, smoking status, physical activity etc. were adjusted for.

The relative risk (RR) comparing the lowest intake of vegetables across the various intake levels of vegetables was found to be 1.00, 0.74, 0.68, 0.72, and 0.72 (P-trend < 0.001) . The RR comparing the lowest intakes of fruit across the various intake levels was 1.00, 0.76, 0.79, 0.87, and 1.05 (P-trend 0.30). After adjusting for antioxidants, fiber, magnesium, etc. The RR for T2D across the different quintiles of vegetable consumption were 1.00, 0.71, 0.63, 0.63, and 0.56 (P-trend

Anne et.al (2008)

Anne et.al (2008) studied the intake of fruits and vegetables and the related plasma Vitamin C levels and tried to ascertain if Plasma vitamin C level could be associated with the risk of T2D. This prospective population-based study also utilized the (European Prospective Investigation of Cancer -- Norfolk) EPIC database and a total of 21,831 subjects were recruited. Semi-quantitative food frequency questionnaires were used to gather data pertaining to the participants' intake of fruits and vegetables. The study participants were between 40 and 75 years of age (male and female). Their plasma vitamin C levels were measured at baseline and they were regularly followed up to analyze their fruit and vegetable intake. This exhaustive longitudinal study began in Feb 1993 and ended in Dec 2005. During this period a total of 735 clinical cases of diabetes were identified. Statistical analysis of the gathered information revealed some interesting facts. After adjusting for demographic and anthropometric variables it was found that the odds ratio of diabetes and the Plasma vitamin C levels was 0.38 (95% confidence interval, 0.28-0.52) clearly suggesting that Plasma vitamin C level is inversely associated with the risk for T2D. Similarly the Odds ratio of diabetes and highest intake levels of fruits and vegetables was 0.78 (95% confidence interval, 0.60-1.00) implying that fruits and vegetables intake have a protective effect. This study had a large sample size and so the results can be generalized across the population.

Bazzano et.al (2008)

A longitudinal cohort study by Bazzano et.al (2008) focused on the relationship between the consumption of fruits, vegetables and fruit juices on the development of Type 2 Diabetes. This study which began in 1984 followed 71, 346 healthy, non-diabetic, nurses over a period of 18 years and their dietary information was collected every 4 years using the Semi-quantitative Frequent food questionnaire. During the entire follow up period, a total of 4529 nurses in the subject pool reported as being diabetic. The Cox regression model was used to study the linear trends. The multivariate adjusted hazard ratio (HR) was 0.99 [95% CI 0.94 -- 1.05]) for a total increase of three servings of fruits and vegetables together. However, the Multivariate Hazard ratio for an increase of three servings of fruits alone was (0.82 [0.72 -- 0.94]) suggesting a positive protective effect of consuming whole fruits. Also the hazard ratio indicated an inverse relation with a one serving increase in consumption of green leafy vegetables HR (0.91 [0.84 -- 0.98]). However, the study results showed a positive relation between consumption of fruit juices and the risk for developing T2D as indicated by the higher hazard ratio (1.18 [1.10 -- 1.26]).

This study clearly suggests that consumption of green leafy vegetables and whole fruits have a protective effect against diabetes while intake of fruit juices carry a greater risk of developing T2D. One of the main drawbacks of the study include the fact that the FFQ used is relatively old (never changed during the follow up period) and it does not differentiate between canned food from fresh food which may have totally different nutrient profiles.

Song Et.al (2005)

This cross sectional study by Song et.al (2005) analyzed the association between flavanols and flavones, two important dietary flavanoids, on the development of T2D. The research subjects include 38,018 female health professionals from the Women's Health Study (WHS) survey database. The women were all above 45 years of age and they filled in a comprehensive semiquantitative food frequency questionnaire in 1993. The subjects were followed up for an average of 8.8 years, a period in which 1,614 developed type 2 diabetes. From the gathered information, the researchers calculated the relative risk RR of Type 2 diabetes based on the dietary intake levels of flavanols and Flavones and flavanoid rich foods. It was observed that there was no direct association between the different flavones and flavanols such as quercetin, kaempferol, myricetin, apigenin, etc. And T2D. However, the researchers found an inverse relationship between apple consumption and T2D. Multivariate trend analysis indicated (RR = 0.72, 95% CI: 0.56, 0.92;p = 0.006 for trend) a 28% reduced risk for T2D among the female subjects who consumed more than one apple a day. A similar effect was also observed for tea but at a higher consumption of 4 cups (

This study however has some drawbacks. Firstly the calculation of flavanoids intake levels based on the questionnaire may be inaccurate which may explain the absence of any significant association. Statistical collinearity in the study made it difficult to analyze the individual effects of the various flavanoid compounds. Also, particular flavanoid subgroups such as catechins and isoflavones could not be analyzed at all due to the limitations of the available food composition database. Lastly, the very small sample of 384 people for whom plasma concentrations of HbA1C, CRP, or IL-6 were estimated might not have provided the accurate effects and may not be reflective of the true correlation with the flavanoid intake.

Rob et.al (2002)

This prospective cohort study analyzed the association between different dietary patterns and the risk of T2D. Participants were 42,504 male health professionals in the U.S., and were recruited from the 1986 Health Professionals Follow-up Study. All the participants were in the age group of 40 to 75 years. The study subjects were followed over a period of 12 years and questionnaires were sent to them every 2 years. During this period 1321 subjects were identified with diabetes. Dietary information was gathered using a 131-item semiquantitative food-frequency questionnaire in 1986, 1990, and 1994. The subjects were classified into the prudent dietary pattern (vegetables, fruit, whole grains, fish, and poultry) or the western dietary pattern (meat, French fries, high sugar drinks eggs, etc. ] It was found that the relative risk RR of T2D for the prudent dietary pattern was less at 0.84 [CI, 0.70 to 1.00]) while the similar value for western dietary pattern was (relative risk, 1.59 [CI, 1.32 to 1.93]; P < 0.001). The study also indicated that the combination of western dietary pattern 1.96 [CI, 1.35 to 2.84]) and low physical activity 11.2 [CI, 8.07 to 15.6]) led to an increase in risk for T2 D. The study concluded that the prudent diet characterized by vegetables, fruits and whole grains carry a slightly lower risk for developing T2D while the risk was significantly amplified in the western diet pattern. However this study did not specifically find any protective role for fruits and vegetables but pointed out that whole grains have this effect. The shortcomings of the study include the relatively approximate calculations of diet and the resulting errors. Furthermore, the blood glucose level as a confirmation of diabetes was not possible in this study due to the huge sample size.

Jennifer et.al (2008)

This Multi-ethnic population-based study by Jennifer et.al (2008) focused on the effects of specific dietary patterns on the incidence of T2D in a group of 5,011 participants recruited from the Multi-Ethnic Study of Atherosclerosis (MESA) program. The participants include Caucasian, African-American, Chinese and Hispanic Adults in the age group of 45-84. The participants completed a Food frequency questionnaire at baseline and the subjects were screened for incidence of diabetes during the follow up examinations (2002 -- 2003, 2004 -- 2005, and 2005 -- 2007). Empirically derived food patterns were then observed for their association with T2D. It was found that the empirically derived food pattern characterized by fruit, nuts/seeds, green leafy vegetables, whole grains, low-fat dairy had a low hazard ratio 15% lower diabetes risk (0.85 [0.76 -- 0.95]; Ptrend = 0.005) while the dietary pattern characterized by high intake of Red meat, refined grains, high-fat dairy and beans was associated with a 18% higher risk with the hazard ratio of ( SD 1.18 [95% CI 1.06 -- 1.32]; Ptrend = 0.004). There was also an inverse relationship between the low risk food pattern and the risk for diabetes. (0.87 [0.81 -- 0.99]; Ptrend = 0.04). The researchers also found that the interaction between each dietary pattern and the different races were not significant (P > 0.16). This study was complete in the sense that the population base has a good mix of racial and ethnic groups.

Conclusion

There is an increasing incidence of type 2 diabetes not just among the older adults but even among the younger generation. The growing epidemic of diabetes requires a new strategy, one that is prophylactic in approach and aimed at prevention. The general inference that could be gathered from the studies discussed above is that a prudent diet constituting vegetable and fruits and whole grains is an effective choice in minimizing the risk for Type 2 diabetes. Sargeant et.al proved that frequent fruit and vegetable consumption reduced the glycosylated Hemoglobin HbA1C levels, a known marker for T2D. More studies focusing on the HbA1C parameter in conjunction with a vegetarian and fruit-based diet would provide additional verification to the current research results. Montonen Et.al (2005), showed that a dietary choice of green leaves, fruits and berries had an inverse relationship with the risk of developing T2D. Song et.al (2005) reported the beneficial effects of consuming apples while Villegas et.al (2008) concluded that vegetables rather than fruits consumption was inversely associated with risk for T2D. Rob et.al (2002) and Jennifer et.al (2008) both confirmed the protective effect of a prudent diet choice involving vegetables, fruits and whole grains. Bazzano et.al (2008) pointed out that green leafy vegetables and whole fruits had a protective effect while fruit juices carried an increased risk for T2D. Anne et.al (2008) showed an inverse relationship between plasma vitamin C levels and risk for T2D. The implications of this study are that the vitamin C in fruits and vegetables contributes to the protective effect against the development of type 2 diabetes.

There is clear evidence for the protective role of fruits and vegetables in the risk for T2D. Though the exact mechanism of action by which fruits and vegetables provide this protective function is still under study, it is thought that fruits and vegetables relieve oxidative stress and this results in the positive effects on glucose metabolism. It is possible that the phytates, lignans, and isoflavones in vegetables and the 4000 different flavanoid compounds and their free radical properties may be involved in the protective role. Future research in these areas would provide more concrete information related to the mechanism of action by which fruits and vegetables provide protection against Type 2 Diabetes. The inference from the discussed studies is that regular consumption of a diet based on fruits and vegetables has clear positive association with reduced risk for type 2 diabetes. With the growing obesity problem among younger adults there is an urgent need to create awareness about healthy eating styles in schools and colleges. Policy makers should focus on promoting the healthy beneficial aspects of a diet rich in fruits and vegetables as an effective way to counter the growing obesity crisis and as an important natural defense against the onset of Type 2 diabetes.

Evidence Table

Study

Population/setting

Sample Size

Intervention/exposure

Outcome

Results/statistics

Comments

Montonen et al. Eur J. Clin Nutr 2005:59:441-448

Prospective cohort study with a 23-year follow up

Men and women From 30 Finnish communities. All the subjects free from diabetes and other chronic diseases at baseline.

N = 4304

Incident cases = 383

164 males and

219 females

Dietary Food pattern ascertained using Structured interview based on a 100-item food Questionnaire . Subjects classified as prudent or conservative

Incidence of Diabetes verified by use of medication records from the national Social Insurance Institution's register

Adjusted RR

Prudent diet

0.72 (0.53,0.98) p=0.03

Conservative diet

1.40 (1.04,1.87) p=0.02

A clear evidence favoring prudent diet of fruits vegetables, oil, Margarine and poultry as a protective factor against T2D.

Sargeant et.al (2001)

European Journal of Clinical Nutrition: 55 342-348