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Friday, July 07, 2006

Low-Fat Dairy Study Sparks Ignorance by Dairy Haters

One of the hardest things to do in the world of medicine is to determine the role that any one particular food plays in overall health.

Most of these longitudinal epidemiological studies are compromised by trying to tease out one food's effects in the huge range of diets, lifestyles, locations, occupations, and overall health of the respondents. Even the best of these, which may be The Nurses' Health Study, has run afoul of the changing notions of what makes for good health. The nurses, who keep detailed diaries of their food intake along with other habits, couldn't know at the beginning of the study in 1976 that trans fats may be an issue to keep track of. There would have been probably no way to do so if they had.

So I try not to jump on any individual study that proclaims the advantages or disadvantages of milk. I've seen too many of these studies either invalidated or moderated by subsequent reports.

For that reason, I don't set much store in a recent study published in Diabetes Care 2006 Jul;29(7):1579-84., A prospective study of dairy intake and the risk of type 2 diabetes in women, by Liu S, Choi HK, et al.

As Reuters reported, Low-fat dairy may lower women’s diabetes risk: Preliminary research shows trend, mirrors results shown for men:

[Liu and his colleagues] therefore looked for the relationship between type 2 diabetes and dietary levels of dairy foods and calcium in 37,183 women in the Women’s Health Study. A total of 1,603 women developed diabetes during an average follow-up of 10 years.

“The most important finding is that women who consumed more low-fat dairy foods tended to experience a lower risk of type 2 diabetes in a period of 10 years,” Liu told Reuters Health.



However, Liu and colleagues caution that further studies are needed to confirm their observations “before public health measures to increase dairy consumption can be recommended for prevention of type 2 diabetes.”


This is medicine at its best. A major long-term study on a population so sizable that comparisons can be made, followed by a caution that even so the results are still preliminary and no general public changes in diet can yet be called for.

So what's the problem?

This. Milk - It Does a Body Good? by Regina Wilshire on commonvoice.com.

Wilshire appears to lack all understanding of how a study such as this operates. The only way to separate out the effects of one particular food or medicine or physical routine is to try to control all the rest of the variables. This is absolutely standard in any epidemiological study. But to Wilshire, this somehow invalidates the results:
When I first started to read through the data, I was struck by just how many confounding factors they "adjusted" to reach their significant findings!

• BMI
• smoking status
• physical activity
• family history of diabetes
• alcohol consumption
• history of hypertension
• use of hormones
• high cholesterol



They didn't add IF you're normal weight, don't smoke, are active, don't have a family history of diabetes, drink in moderation, don't have a family history of high blood pressure, aren't using hormones and don't have high cholesterol. Basically, they forgot to add the findings apply to those who are in good health!

Which begs the question - was it the inclusion of dairy or was it an overall better dietary and lifestyle pattern that kept these women in good health?

No it doesn't. Controlling for confounding factors doesn't limit the study to just people in wonderfully good health. It just tries to set one factor against a neutral background.
I hate to say it, but this isn't science. If you ask me, it seems more like a manipulation of data to promote the dairy industry and the consumption of milk and dairy products.

I hate to say it, but Wilshire has let her bias toward milk overcome any understanding of how science works. To her, apparently, if a study comes out in favor of milk it must be wrong.

What is most bothersome is that she may be right for the wrong reasons. As I said in the beginning, and as Liu himself said, one study, even a good study, is not proof, and is most definitely not the last word. There may not be a connection between low-fat dairy foods and lowered risk of diabetes, or the connection may be weak and not applicable to most. If there is a connection, however, than those with lactose intolerance who still consume dairy have to have this important piece of knowledge. It indicates that taking lactase if you are lactose intolerant to retain dairy in the diet is a good road to health.

That is the real issue. Bias for or against a food, especially a hot-button one like milk, should never get in the way of understanding the underlying science. If you don't know enough about medicine to make a knowledgeable critique, don't spread fear and ignorance around the net.

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5 comments:

Anonymous said...

Hi Steve,

Your post on dairy/diabetes prompted me to do some further research. I was curious how big this finding really was when put into perspective. My search for some answers led to a brief article, which as an afterthought we opted to publish. You can view the article on our site at http://www.godairyfree.org/index.php?option=com_content&task=view&id=526&Itemid=154. I would love your feedback on the topic.

Thanks again for keeping such a great site and blog!

Steve Carper said...

Hi, Alisa. I was just about to post a link to your article when I read this. Great minds and all that!

I think the study shows once again that eating an overall healthy diet is by far the best thing you can do for your health. Once you've achieved a state of healthy eating that you can maintain permanently - not a "lose-weight-by-not-eating diet" but that old-fashioned but excellent low-fat, low-sugar, lean protein, lots of fiber, fruits, vegetables, and whole grains diet - any individual food or supplement provides only incremental improvement. (Unless you have a specific condition you must adjust for.)

It's inarguable that tweaking that diet with a number of small improvements would provide extra benefits - if you knew exactly which of the hundreds of possible tweaks were precisely right for you. It's easy to go overboard with worry that you're doing exactly what's right, especially when the advice about what's right changes so often.

Lactose intolerant folks certainly would not be harmed by eating low-fat dairy foods that they could tolerate, with any additional lactase added as necessary.

As you say in your article, though, those who choose or need to avoid milk can still have low risks of diabetes just by eating sensibly and exercising regularly. These studies are guidelines: not mandates.

But swallowing bad science is like swallowing bad food. If you're lucky, you'll only vomit!

. said...

You conveniently left the following out of your critique of my blog post:

"Hey, I like dairy - I eat natural cheese, whole milk yogurt and occassionally even enjoy some good homemade ice cream - but do I need to include dairy to prevent diabetes? No"

If I was so anti-dairy, do you think I'd consume dairy?

And, I stand by my contention that one simply does not need to include dairy - whole or low-fat - to prevent diabetes. If you'd taken time to read other posts you'd realize my position is that a nutrient-dense diet is what we should be eating...if that includes dairy, great; if not, that's OK too. Overall quality of one's diet is what matters - not any one specific food.

Steve Carper said...

I critiqued the comments about study methodology that were purely and simply wrong. I critiqued the ridiculous paranoia that makes every positive mention of dairy a "manipulation of data."

Of course, good health is possible whether one eats dairy or not. I've been saying that in my books and web material for 20 years. I've also encouraged people with lactose intolerance not to believe the scare tactics of the anti-dairy crowd. And I decry the simple-minded ignorance of those who think that all dairy must be avoided after a diagnosis of LI. Dairy can be part of a lactose intolerant's diet, if he or she chooses.

If you had gotten the science right, I wouldn't have posted a word. But anything you say that's right after a blunder that big is suspect. You don't get partial credit on believability.

. said...

By any chance - Have you read the full-text of the study?