Archive for the ‘Basics of Nutrition Research’ Category

Evidence for Nutrition Recommendations: DHA & Prostate Cancer

Sunday, January 20th, 2013

A reader sent me a link to this study, DHA inhibits differentiation of prostate fibroblasts into myofibroblasts and tumorigenesis, and asked me if it changed my recommendations that vegans (under age 60) don’t need to supplement with DHA every day.

The study is in vitro and animal research, and indicates that DHA can prevent prostate cancer growth. I told him that it did not change my recommendations and he asked me to make a blog post to explain why.

Creating nutrition recommendations is not something that should be taken lightly. The United States government calls upon the National Academy of Sciences to make nutrition recommendations for the nation. This is done through the Institute of Medicine’s Food and Nutrition Board and the recommendations are referred to as the Dietary Reference Intakes (DRI).

All known essential nutrients are given a DRI. In most cases, these are based on a large body of research and arrived at by a panel of experts in the area. The research they have reviewed for most nutrients has been based on acute symptoms of deficiency and toxicity; they are rarely based on long-term, chronic disease prevention. This may be changing as more research becomes available and acute deficiencies are no longer the problem they once were.

So, with that background, a very good reason would be needed for me to overrule the Institute of Medicine and set my own “DRI.” But because the DRI are not set with vegans in mind, we have to fill in the gaps and most of my recommendations are to get vegans in compliance with the spirit of the DRI.

The study on DHA and prostate cancer, mentioned above, is only a test-tube and animal study. The results may or may not translate for humans, and even if they do, there is no way to know how much humans need to take to achieve such results or if there are negative side effects from taking whatever level of DHA we might determine is appropriate. The Food and Nutrition Board would not make recommendations based on one in vitro or animal study. There are many studies looking at DHA intake and levels in humans and associated diseases and these studies are fraught with confounding variables with no clear answer as to how much DHA humans should be taking on a regular basis to prevent overall chronic disease.

Some vegan RDs do not think it’s necessary to recommend DHA for vegans; I choose to do so, but err on the conservative side. The Food and Nutrition Board has not created a DRI for DHA, but given that studies have shown that vegans have much lower levels of DHA in the blood than your average person, I recommend DHA to make sure that we are not at a disadvantage compared to non-vegans. If you want to see the reasoning behind my DHA recommendations, you can read it in Omega-3 Fatty Acid Recommendations for Vegetarian.

For more information on the types of studies that provide more evidence for nutrition recommendations than others, please see my article Basics of Nutrition Research.

In conclusion, I try not to supersede the Food and Nutrition Board in formulating nutrition recommendations and I do not change recommendations based on in vitro or animal studies.

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Sad Story of Fish Oil and Small Sample Sizes

Thursday, January 17th, 2013

Interesting, short post by Kevin Drum about fish oil, sample size, and publication bias:

The Sad Story of Fish Oil and Small Sample Sizes


“Small studies do a poor job of reliably estimating the effects of medical interventions. For a small study [snip] to get published, it needs to show a big effect — no one is interested in a small study that found nothing.”


“It’s still possible that fish oil has a slight beneficial effect, but it’s unlikely.”

Even if fish oil does not reduce all-cause mortality, it does not change my recommendations regarding DHA supplementation in vegans because it’s one thing to say that supplementing with DHA to increase DHA blood levels above average does not improve health, and another to say that there are no problems with having much lower than average DHA levels.

Thanks, Matt.

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Basics of Nutrition Research

Tuesday, June 7th, 2011

If you’ve ever thought that nutrition research has no rhyme or reason to it, this article should help clear up the different types of studies and what they are useful for:

Basics of Nutrition Research