Potential answers are in the American Journal of Clinical Nutrition (2012). I quote:
For hypertension, coronary heart disease, and stroke, there is convincing evidence that increasing the consumption of vegetables and fruit reduces the risk of disease. There is probable evidence that the risk of cancer in general is inversely associated with the consumption of vegetables and fruit. In addition, there is possible evidence that an increased consumption of vegetables and fruit may prevent body weight gain. As overweight is the most important risk factor for type 2 diabetes mellitus, an increased consumption of vegetables and fruit therefore might indirectly reduces the incidence of type 2 diabetes mellitus. Independent of overweight, there is probable evidence that there is no influence of increased consumption on the risk of type 2 diabetes mellitus. There is possible evidence that increasing the consumption of vegetables and fruit lowers the risk of certain eye diseases, dementia and the risk of osteoporosis. Likewise, current data on asthma, chronic obstructive pulmonary disease, and rheumatoid arthritis indicate that an increase in vegetable and fruit consumption may contribute to the prevention of these diseases. For inflammatory bowel disease, glaucoma, and diabetic retinopathy, there was insufficient evidence regarding an association with the consumption of vegetables and fruit.
It bothers me that vegetables and fruits are lumped together: they’re not the same.
All of my diets—Advanced Mediterranean, Low-Carb Mediterranean, and Ketogenic Mediterranean—provide plenty of fruits and vegetables.
Diabetic Mediterranean Diet 
Effect of increased potassium intake on cardiovascular risk factors and disease: systematic review and meta-analyses
It would be interesting to know to what extent the benefits of vegetable consumption arise from the additional potassium they provide?
We have an RDA for both magnesium and potassium but it’s frequently the case that folks only get around half the RDA. There is also some debate about whether the RDA for magnesium and potassium are either adequate or optimal.
I agree, Ted.
Not exactly overwhelming evidence that increasing fruit and vegetable consumption has any real positive impact considering the number of times ‘possible’, ‘probable’, ‘might’ and ‘may’ appears!
It is more likely that an increased consumption of fruit and vegetables displaces other ‘foods’ that do have a negative impact on health.
In fact, studies have been done which show a complete absence of fruit and vegetables (or at least the so-called ‘phyto-nutrients’ they contain) has no negative impact on health markers – quite the opposite. Other studies have indicated that any benefits of fruit and vegetable consumption are optimized by as little as two servings per week. So much for five-a-day!
Yes, Alex, there are lots of waffle words used in nutrition science reporting.