Dispelling nutrition myths, ranting, and occasionally, raving


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Can yoghurt prevent diabetes?

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A friend of mine recently shared the news of a new study reporting an association between yoghurt consumption and decreased risk of type 2 diabetes.

The study was actually a meta-analysis of three large studies. Meta-analyses always make me a little nervous due to the ease of cherry picking and interpreting the results to yield the desired effect. The results of a meta-analysis can only be as good as the results of the original studies on which they’re based. I’m not saying this was the case here, just that it’s something to bear in mind when reading about meta-analyses. The researchers do have on their side the fact that all three studies had large sample sizes. After examining the results of these three studies, they added an additional 11 prospective-cohort studies for their meta-analysis.

The researchers controlled for a number of potential confounders. However, there’s always a remaining risk that an unaccounted for confounding variable might be the true reason for any observed effect. While the researchers reported a significant decreased risk of type 2 diabetes in regular yoghurt consumers they were also quick to acknowledge that this does not indicate causation. Yes, people who consume yoghurt appear to be less likely to develop type 2 diabetes than people who don’t. However, the studies all relied upon self-reported food frequency questionnaires and they were observational. It is possible that there is some unaccounted for variable that’s reducing the risk of type 2 diabetes in yoghurt consumers other than the yoghurt.

The researchers do make an interesting suggestion that the probiotics in yoghurt may be responsible for the decreased risk of type 2 diabetes. I do wonder about the validity of this as many yoghurts contain limited live bacteria due to their processing. In addition, it’s unlikely that many probiotics in yoghurt survive the acidic stomach environment to make their way to the intestines. Perhaps it’s the by-products of the bacteria in the yoghurt (e.g. vitamins, lactic acid) that are responsible for decreased risk of type 2 diabetes. Just postulating here. I would love to see a study in which participants are prescribed diets containing either yoghurt with live bacteria, yoghurt without live bacteria, and no yoghurt. Yes, it would take a long time to determine if the yoghurt reduced the risk of type 2 diabetes but other effects could be examined as well and it would be interesting to see what the true effects of  regular yoghurt consumption are on health.


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The vitamin D debate: Won’t someone please think of the children?!

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The latest “study” on vitamin D reached the conclusion that vitamin D does nothing to prevent myriad medical conditions. You may be wondering why I placed study in quotation marks. That’s because it’s not actually a new study. It’s an analysis of the results from a number of randomized controlled trials of vitamin D supplements.

Of course, there are the usual issues with meta-analyses. We don’t know for certain if the authors cherry-picked the studies they chose to look at. We don’t know (without spending substantial amounts of our own time, and probably money) if the original studies were flawed. It’s a good thing that it’s good that this analysis looked at studies using a randomized control model. This avoids the obvious potential confounding factors seen with observational studies. However, I have some doubts that these studies would have been conducted over long enough time-spans to accurately assess the use of vitamin D supplements. After all, they were looking at the effects of vitamin D supplementation on myocardial infarction or ischaemic heart disease, stroke or cerebrovascular disease, cancer, total fracture, hip fracture, and mortality. To truly determine the effects of vitamin D supplementation on these conditions supplementation would have had to begin in childhood and continue until death (or at least very old age).

The authors found that vitamin D did not affect outcomes by more than 15% for any of the above conditions, aside from hip fractures in institutionalized seniors.

I’m inclined to think that we may be expecting far too much from vitamins and minerals. Just because vitamin D probably doesn’t prevent cancer or heart disease doesn’t mean that there aren’t any benefits to be obtained from taking it as a supplement. Perhaps it may prove to be beneficial in mood regulation, cold prevention, or something else less earth shattering than these studies looked at.

Perhaps there is no benefit to taking vitamin D supplements. However, I’m not quite ready to toss my bottle. I know that I can’t meet the currently recommended amount of vitamin D through diet alone. And I’m certainly not getting any from sun exposure this time of year. I don’t think that we should dispose of the current vitamin D recommendations on the basis of one meta-analysis. I’m certainly open to changing my mind but for now I’d like to hedge my bets. I’d rather risk taking a “useless” vitamin D supplement than risk experiencing adverse health consequences from not consuming sufficient vitamin D.

In addition, I worry that research such as this may lead to new parents neglecting to supplement their infants with vitamin D and causing a resurgence in rickets. Just because there’s uncertainty about the long-term outcomes of vitamin D supplementation doesn’t mean that we don’t know the benefits in early childhood.


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Eggs: Nature’s deadliest weapon?

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Another study on eggs and heart disease risk has been published. Well, sort of. It’s a meta-analysis of 16 previously published studies. As soon as I see that an article was based on a meta-analysis I can’t help but question the conclusions it reaches. There are a number of issues to consider when looking at meta-analyses and I feel like there’s a huge opportunity for bias and misinterpretation of results. It’s far too easy to be selective about inclusion of research and implications of results. Oftentimes the original studies are flawed and those flaws are carried through into the meta-analysis but they’re not as apparent when you’re not looking at the entire study. That being said, let’s look at the present meta-analysis.

It appears that the authors don’t have any conflicts of interest (always the first thing to check when looking at research: where did the funding come from?). A quick Google search of each of the authors didn’t reveal any obvious affiliations that could have impacted their research. It doesn’t appear that they had any ulterior motives.

The study actually found no relationship between egg consumption and cardiovascular disease in the general population. Did you catch that behind the headlines suggesting that egg yolks are bad for you?: healthy individuals who eat eggs once a day are no more likely to die from a heart attack or stroke than healthy individuals who don’t eat eggs at all. However, the part that’s getting the most attention is the finding that egg consumption may be associated with an increased incidence of type 2 diabetes and those egg-eaters who have diabetes are at greater risk of dying from cardiovascular disease. Before you start freaking out and getting on the egg-white omelette bandwagon please note the presence of the words incidence and associated. These words tell us that people who regularly eat eggs may be at greater risk of developing type 2 diabetes than those who don’t. It also tells us that people who have diabetes and eat eggs may be at greater risk of dying from cardiovascular disease (CVD). This is assuming that all of the studies they looked at were sound and that all relevant studies were included (big assumptions). However, it doesn’t tell us that eating eggs was the reason for the increased risks. There could have been some other commonality among the egg-eaters that raised their risk for type 2 diabetes and there may have been something other than egg-consumption that increased their risk of dying from CVD.

Now, if you have diabetes, not knowing for certain if eggs may increase your risk of dying from CVD you may want to minimize your consumption of them. Better safe than sorry. And, while most of us can safely consume up to an egg a day, I think it’s important to bear in mind that variety is an important component to a healthy diet.