Green vegetables linked with reduced risk of type 2 diabetes. How?

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:

  1. antioxidants (such as beta-carotene and vitamin C)
  2. polyphenols (plant chemicals which have antioxidant action)
  3. magnesium
  4. 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

7 Responses to Green vegetables linked with reduced risk of type 2 diabetes. How?

  1. blackdog 20 August 2010 at 4:56 pm #

    Despite the actual data not showing much in terms of a result with regards to fruit and vegetables, the Today programme still hyped up the need for ‘five-a-day’, when in fact this study was about green leafy vegetables imparting protection from NIDDM.

    I despair sometimes of the media and so called spokes persons for the advocates lobby continually conveying an entirely different view from that of the actual data in studies. They always seem reluctant to lose hold of the dogma at the expense of truth. Whilst I find that green leafy vegetables have little to no effect on glucose levels the advocates of all fruit and veg seem blinded to the fact that many are bad for Diabetics and indeed for most, in any quantity.

    As someone who has researched extensively since my partner succumbed to NIDDM, in an effort to avoid harmful drugs, I have been enraged by the unscientific, often dangerous protocols invoked by mainstream medicine. We have achieved Hba1c levels close to normal with recourse to little more than low carb diet, moderate exercise and some supplements. The greatest of the latter being ‘insulin mimetics’ of ALA combined with Evening Primrose Oil at a ratio of 5;3 (100mgs). Our last test was 6.3% which would now be viewed as dangerous if on hypoglycemic agents.

    I also find it unbelievable that Diabetes UK fails to look further into low carb diets when even it’s own research has shown they are of merit. This study shows the low carb ketogenic diet to be of value (http://www.ncbi.nlm.nih.gov/pubmed/16318637?ordinalpos=1&itool=PPMCLayout.PPMCAppController.PPMCArticlePage.PPMCPubmedRA&linkpos=3) There are in fact a number but the cohorts are quite small.

    As you say the confounding factor is always, what did they also eat (or not eat) as well? People who eat vegetables do tend to be those that would not eat lots of bread, cakes, sugar etc. Thanks for your highly scientific and thoughtful posts.

  2. Steve T 20 August 2010 at 6:56 pm #

    I dislike studies like this. Some might think that running out for a bunch of veggies to augment their high carb diet will fend off T2D. Perhaps we should look at it this way – people who eat lots of green leafy vegetables are less likely to consume refined carbohydrates that are known to induce T2D. It’s too easy to draw the wrong cause / effect relationship.

  3. Margaret Wilde 20 August 2010 at 8:42 pm #

    It’s not too difficult to eat 122gm of broccoli.

  4. fredtully 21 August 2010 at 1:57 am #

    122 gms of lettuce is a lot of lettuce. Perhaps the result is more about what was displaced, perhaps carbs.

  5. Jo 21 August 2010 at 1:37 pm #

    I get frustrated when this is translated into the 5 a day message. Because I am not that fond of veges I use to try and reach the target with fruit, which I now know is not healthy. And that is what parents do to get their kids eating 5 a day. You see the phrase, ‘one of your five a day’ on the side of fruit bars and parents buy tons of these thinking they are giving their kids a healthy diet.

  6. dennis 22 August 2010 at 10:03 pm #

    To a physicist the answer to your question is simple – green vegetables have lowest entropy of human foods and therefore help the human body to maintain it healthy, highly ordered, low entropy state.

    In more detail, the human body is a highly ordered ‘low enropy’ system. The only ultimate source of low entropy is the sun. Unlike plants, animals can not use the sun directly to maintain low entropy – they absolutely have to eat low entropy foods to maintain their low entropy – otherwise they will decay and become unhealthy due to entropy (disorder) increase associated with human metabolism. All healthy natural foods have low entropy but green vegetables have the lowest entropy as they are nearest to the sun. Refined, processed and overcooked foods have higher entropy and are therefore not so healthy. Eat natural foods, particularly green veg and low sugar fresh fruits to maintain a healthy, highly ordered, low entropy state – avoid refined, processed and overcooked foods which may provide energy but, due to their higher entropy, will not keep the body in optimum state of repair.

    The reductionist approach of analysing natural food for a magic bullet component is pointless – it is complete whole foods in their natural state which confer health. Only humans, and animals fed by humans, eat unnatural foods and therefore fail to maintain optimum health.

  7. Marcus 27 August 2010 at 10:51 pm #

    I am investigating whether foods that contain cysteine have an influence on T2D. There are warnings for T2D not to take supplemental cysteine( cysteine is capable of inactivating insulin).Cysteine or cystine is found meats ,eggs and vegetables containing Sulpher(thiols) cabbage, broccoli etc.Lettuce is low in thiols.

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