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Fruit and Vegetable Quantity and Variety Both Matter for the Prevention of Type 2 Diabetes
The recommendation by the World Health Organisation to consume a minimum of 400g or five portions (based on an average portion weighing 80g) of fruits and vegetables (F&V) each day for the prevention of several major chronic diseases, including diabetes, is now widely adopted by health agencies. Furthermore, programmes such as the “five-a-day” programme in the United Kingdom and similar programmes in other countries (e.g. United States) recommend consuming a variety of different F&V.
Clarify the Respective Contributions of the Quantities and Varieties of F&V Consumption
There is compelling evidence for the effectiveness of lifestyle interventions for the primary prevention of diabetes, with promotion of increased F&V intake forming an important part of lifestyle modification1-3. However, the specific role of variety in F&V intake for the prevention of diabetes has not previously been investigated. Given the increasing burden of type 2 diabetes, with a projected rise in numbers with diabetes from 366 million globally in 2011 to 522 million by 20304, it is important to clarify the contribution of both quantity and variety of F&V intake if we are to develop effective dietary public health strategies to prevent the disease.
We designed a study aimed at answering the following questions:
- Is the quantity of F&V intake related to the risk of developing diabetes after accounting for variety of intake?
- Conversely, is the variety of intake related to diabetes risk after accounting for quantity of intake?
Assessing Quantity and Variety of F&V Intake
Using a Food Diary in EPIC-Norfolk
The European Prospective Investigation of Cancer-Norfolk (EPIC-Norfolk) study is a population-based cohort study that recruited 25,639 men and women aged 40-75 years, resident in Norfolk, U.K5. All participants attended a health check in 1993-97. Dietary intake was assessed using a prospective 7-day food diary. We ascertained incident cases of diabetes (n=892) over 11 years of follow-up, and a representative comparison group (random subcohort) of 4,000 participants. After exclusions, the final sample consisted of 653 incident cases of diabetes and 3,166 subcohort participants. Average daily quantity of intake of fruits, vegetables, and F&V combined were computed. Variety of fruit, vegetables, and combined F&V were derived by calculating the total number of different items consumed at least once in a one week period6.
Increasing Variety of F&V, and Increasing
Quantity of Vegetable Intake Decrease Risk of Type 2 Diabetes
In adjusted analyses, and after accounting for variety of intake, participants in the top third for quantity of vegetable intake (compared to bottom third) had a 24% lower incidence of diabetes (95% confidence interval (CI) 3% to 40% lower), while there was no relationship with quantity of fruit intake (9% lower; 95% CI ranging from 29% lower risk to 16% increased risk), and for combined F&V intake there was a borderline lower risk (21% lower incident diabetes, 95% CI 0% to 38% lower).
For variety of intake, fruit, vegetables and combined F&V intake were each strongly inversely related to a lower incidence of diabetes with a reduction of:
- 30% [95% CI: 9% to 47%] for fruit variety,
- 23% [95% CI: 2% to 39%] for vegetable variety,
- 39% [95% CI: 22% to 52%] for combined F&V variety.
These reductions were dependent of the effects of quantity of intake. These analyses accounted for important factors that may be related to diabetes risk or to potential healthier lifestyles among those with greater F&V intake, including age, sex, body mass index, waist circumference, education level, deprivation index, occupational social class, smoking status, physical activity level, family history of diabetes, energy intake and season.
Maximum Benefit in the Prevention of Diabetes
These findings place particular emphasis on recognising the important and independent role of both quantity and variety, and suggest that a diet characterised by a greater quantity of vegetables and a greater variety of both F&V has the potential to reduce the risk of diabetes. Biologically plausible mechanisms include the low energy and high fibre content of F&V, combined with micronutrients and bioactive phytochemicals.
Overall, as well as consuming at least five portions of F&V each day, we should also select these portions from different fruit and vegetable categories in order to gain the maximum potential benefit for diabetes prevention.
- Gillies, C.L., et al., Pharmacological and lifestyle interventions to prevent or delay type 2 diabetes in people with impaired glucose tolerance: systematic review and meta-analysis. BMJ, 2007. 334(7588): p. 299-302.
- Pan, X.R., et al., Effects of diet and exercise in preventing NIDDM in people with impaired glucose tolerance. The Da Qing IGT and Diabetes Study. Diabetes Care, 1997. 20(4): p. 537-44.
- Tuomilehto, J., et al., Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med, 2001. 344(18): p. 1343-50.
- International Diabetes Federation, IDF Diabetes Atlas, Fifth Edition. 2011, Brussels: International Diabetes Federation.
- Day, N., et al., EPIC-Norfolk: study design and characteristics of the cohort. European Prospective Investigation of Cancer. Br J Cancer, 1999. 80(1): p. 95-103.
- Cooper, A.J., et al., A prospective study of the association between quantity and variety of fruit and vegetable intake and incident type 2 diabetes. Diabetes Care, 2012. 35(6): p. 1293-300.