The further a society drifts from the truth, the more it will hate those who speak it. ... In a time of deceit, telling the truth is a revolutionary act. George Orwell

Saturday, August 21, 2010

No benefit of veg and fruit consumption in t2 diabetes!

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 Fig 4 Hazard ratios for incidence in diabetes type 2 for highest versus lowest intake of fruit and vegetables combined. Weights are from random effects analysis

Newly published meta-study in BMJ:

Fruit and vegetable intake and incidence of type 2 diabetes mellitus: systematic review and meta-analysis

Quote:

Results Six studies met the inclusion criteria; four of these studies also provided separate information on the consumption of green leafy vegetables. Summary estimates showed that greater intake of green leafy vegetables was associated with a 14% (hazard ratio 0.86, 95% confidence interval 0.77 to 0.97) reduction in risk of type 2 diabetes (P=0.01). The summary estimates showed no significant benefits of increasing the consumption of vegetables, fruit, or fruit and vegetables combined.

I have to add a comment:
   There is only one supposedly significant, positive correlation found in this study - the one with green veg (hazard ratio 0.86).  It is possible [but see also (*)] that the significancy results from pooling four separate studies together. When you look at the individual studies on FIG5 : three are only marginally positive, that is their error estimates touch 1.0, while one large study [39] (Women’s Health Study) shows the hazard ratio of 1.0 which indicates no effect.

This paper  [37] (Nurses' Health Study data) is also interesting because it is one of the largest and longest of its kind. Again, no benefit overall from vegetable consumption and miniscule benefit from greens alone. It also shows this interesting graph:


Note (*): There is a discrepancy in the data. The resulting hazard ratio may also turn out to be not statistically significant for green vegetables, since the overall P=0.18 as per FIG.5 while at the same time it is written as P=0.01 in the abstract for the same result. Given the wide spread 0.77-0.97, my guess is that the abstract figure of 0.01 may be a typo, but I am not 100% sure.

7 comments :

Peter said...

Some nice observational plots again. I like them. Fruit juice (retch in the corner!)...

Peter

Stan (Heretic) said...

Hi Peter,

Yes, it does nicely confirm our bias! 8-:)

Did you notice the original BBC heaelth article headline, based on this study, saying:

"Green leafy veg 'may cut diabetes risk'"

How objective! For some reason they they don't seeem to print something like this:

"Drinking fruit juice may increase your diabetes risk by 50%".

I am beginning to believe in The Conspiracy...

Drs. Cynthia and David said...

Thanks for this. It seems much more likely there is benefit from what they don't eat than from what they do, but the study doesn't seem to be designed to pick up on that data. Presumably eating more greens means eating less pasta, etc. At least that's what it means in our household!

Another observation I would offer is that it's surprising, or it should be, that there is no "healthy eating" effect on the correlation. Presumably, the "healthy eaters" choose vegies, fruits, low fat/whole grain everything, avoid meat, and probably even exercise more. So you would expect perhaps extra superior benefit in terms of diabetes prevention, not no benefit at all.

Cynthia

Stan (Heretic) said...

Hi Cynthia,

I agree about the mechanism - the greens must displace the higher glycemic food out of the diet. I just like you was still expecting to find some small benefits, similar to older studies but I guess this time the authors became more cautious in how far they dare stretching their data.

Interestingly, if you look at the individual studies listed the direct univariately-calculated correlations tend to be so small that when they applied corrections for age, smoking etc - then what was left was below the noise.

This was the case with the two very large studies (Women's and Nurses'). One reason is that in my humble opinion, those studies were intentionally designed that way so as to minimize the potential for embarassing findings.

That is in a stark contrast with the China Study when the original researchers inadvertently, or due to political inexperience, failed to exclude the real important factors such as added animal fat or wheat (separately from other carbs) and other. Once you allow inclusion of the dietary variables that matter, then you get immediately the raw correlations close to or above 50% as you can see in my recent blog posts!

Very large correlation factors are extremely difficult to obfuscate using multivariate or any other mathematically legitimate analysis, even if you try very hard, especially if you had to reverse the sign of almost every result! 8-:)

Probably the best way of hiding the facts is to publish the original data in some obscure low volume proceeding priced at 800$, then write a popular book of the same title as the study, claiming it be based on the original data but so full of nonsense that people would just give up on the whole thing and never look at the original raw data set. 8-:)

Best regards,
Stan (Heretic)

David Isaak said...

Interesting stuff.

I have to say, however, that I think most of this might be explained by the fact that it is pretty silly to have a sweeping category called "fruits and vegetables" in the first place. Any methodology that doesn't distinguish between a potato and a stalk of broccoli, or between a banana and a salad, is going to give meaningless results.

"Fruits and vegetables" is about as good a category of food as "red things." Let's see: beef, apples, strawberry soda pop, tomatoes, salmon, watermelon...

I think people should eat more healthy fruits and vegetables and less unhealthy fruits and vegetables.

Stan (Heretic) said...

Hi David,

I am not convinced.

If some vegetables were really healthy and some not, it would have come out on some studies rather than producing zilch.

How do you define or find a "healthy" vegetable?

Are potatoes supposed to be less healthy than broccoli only because it has more starch? I doubt that. For a person with no metabolic disease eating potatoes is quite OK, it provides complete aminoacids and does not contain any of the known phytotoxins unlike most green vegs. (Sorry - none except in the green sun-exposed parts and the peels).

We are omnivorous, but suitability of the food isn't only about how little carbohydrates they may contain. Carbohydrates in plants may be the least of the problem, for us.

Our "omnivorous-ness" does not mean that plants ought to be our main food.

I always believed in moderation. On my food photos you will always find that it is of mixed orign: of animal AND plant! I do not exclude any food from my plate, just change proportions.

Regards,
Stan

Advin Charles said...

Diabetes are very harmful disease for health. It is also very danger for human life. This is good explain about the consumption in t2 diabetes.


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