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...

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…