The authors, led by Patrice Carter at the University of Leicester, say there is a need for further investigation into the potential benefits of green leafy vegetables.
In the last two decades there has been a dramatic increase in the number of individuals developing type 2 diabetes worldwide.
Diets high in fruit and vegetables are known to help reduce both cancer and heart disease, but the relationship between fruit and vegetable intake and diabetes remains unclear, say the authors.
The researchers also note that previous research found that in 2002, 86% of UK adults consumed less than the recommended five portions of fruit and vegetables per day, with 62% consuming less than three portions. The study says that "it was estimated that inadequate consumption of fruit and vegetables could have accounted for 2.6 million deaths worldwide in the year 2000."
Patrice Carter and colleagues reviewed six studies involving over 220,000 participants that focused on the links between fruit and vegetable consumption and type 2 diabetes.
The results reveal that eating one and a half extra servings of green leafy vegetables a day reduces the risk of type 2 diabetes by 14%. However, eating more fruit and vegetables combined does not significantly affect this risk. Only a small number of studies were included in the meta-analysis and the benefit of fruit and vegetables as a whole for prevention of type 2 diabetes may have been obscured.
The authors believe that fruit and vegetables can prevent chronic diseases because of their antioxidant content. Green leafy vegetables such as spinach may also act to reduce type 2 diabetes risk due to their high magnesium content.
The authors argue that "our results support the evidence that 'foods' rather than isolated components such as antioxidants are beneficial for health … results from several supplement trials have produced disappointing results for prevention of disease."
In conclusion, they believe that offering tailored advice to encourage individuals to eat more green leafy vegetables should be investigated further.
In an accompanying editorial, Professor Jim Mann from the University of Otago in New Zealand, and Research Assistant Dagfinn Aune from Imperial College London, are cautious about the results and say the message of increasing overall fruit and vegetable intake must not be lost "in a plethora of magic bullets," even though green leafy vegetables clearly can be included as one of the five portions of fruit and vegetables per day.