Type 2 diabetes is a condition which appears to be very much on the rise in terms of prevalence. This, inevitably, has led some to seek to find what factors might cause and also help prevent this condition. Earlier this month one of my blogs focused on some research which linked consumption of foods that tend to disrupt blood sugar levels with an increased incidence of type 2 diabetes. The potential mechanisms that might explain such an association are explained in the blog post which you can read here.
Today sees the publication of another study looking at the association between food and risk of type 2 diabetes. In this study the focus was fruits and vegetables [1]. This study was a ‘meta-analysis’ and pooled the results of six separate studies each of which assessed the relationship between diet and type 2 diabetes risk over several years. In all, some 225,000 individuals were followed for an average of 13 years. Here, in summary are the findings from this study.
Higher fruit consumption was NOT associated with a reduced risk of type 2 diabetes
Higher total vegetable consumption was NOT associated with a reduced risk of type 2 diabetes
Higher fruit and vegetable consumption was NOT associated with a reduced risk of type 2 diabetes
Higher consumption of green leafy vegetables WAS associated with a reduced risk of type 2 diabetes – eating an additional 122 g of green leafy vegetables (about a portion and a half for the UK) each day was associated with a 14 per cent reduction in risk of type 2 diabetes
The first thing to say about this study is that it was what is called ‘epidemiological’ in nature, which means it can only really tell us about associations between things, and not necessarily that one thing is causing another. So, green leafy vegetables might be associated with a reduced risk of type 2 diabetes, but may not be actually reducing diabetes risk. Why? Well maybe those who eat more green veg are more physically active, and this is the explanation. Generally, the interpretation of data from the studies used in this meta-analysis took into account common so-called ‘confounding’ factor. However, this practice is inherently imprecise and even when well done still leaves us unable to draw any firm conclusions about causality.
However, assuming the green leafy do reduce the risk of type 2 diabetes, how do they do it. The authors of today’s study speculate that it might be related to green leafy vegetables relatively high content of one or more of four elements:
- antioxidants (such as beta-carotene and vitamin C)
- polyphenols (plant chemicals which have antioxidant action)
- magnesium
- alpha linolenic acid (a form of omega-3 fat)
All off these ideas have some merit, I think.
However, one thing that the authors did not consider is the influence of the food types examined on blood sugar balance. The fact of the matter is that green leafy vegetables tend not to causes spikes in blood sugar levels (they are of low glycaemic index). And even when eaten in quantity their glycaemic load (their tendency to disrupt blood sugar levels) is low.
The same cannot necessarily be said for the other food groups examined in today’s study. Some fruits (e.g. bananas) have reasonably high glycaemic indices and can be quite disruptive to blood sugar levels. The same is true for starchy vegetables (notably, potatoes).
So, it is possible the certain elements within green vegetables (e.g. antioxidants and magnesium) might help to reduce the risk of diabetes. However, it might also be the case that the relationship here is, at least in part, down to the fact that the more green vegetables someone eats, the lower the potential there is for eating more blood sugar disruptive and diabetes-inducing foods.
References:
1. Carter P, et al. Fruit and vegetable intake and incidence of type 2 diabetes mellitus: systematic review and meta-analysis. BMJ 2010;341:c4229
