Dispelling nutrition myths, ranting, and occasionally, raving


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Prebiotic vs probiotic

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I came across this short but confused and confusing article a few weeks ago. The article is referencing a study on the effect of prebiotics on maternal weight gain (in rats) during pregnancy. Fairly straightforward until I read the statement: “Dr. Raylene Reimer gave prebiotics – found in food like yogurt or sauerkraut – helped to reduce fat in pregnant rats who were on a high fat and sugar diet.” See my confusion? Either the study involved prebiotics, which are fibre, or the study involved probiotics, which are bacteria (found in cultured and fermented foods such as the ones given in the example).

I found the actual journal article on the study to find out if the research had involved prebiotics or probiotics. It was prebiotics. So, the author of the news article was correct in stating “prebiotics” but confused about what prebiotics actually are. No wonder so many people confuse the two when talking about prebiotics and probiotics. And, to be fair, the terms are incredibly similar.

My trick for remembering the difference between the two? “Pre” means before, and I always think of prebiotics as being what probiotics need before they can grow. Before you can have a healthy gut microbiome, you need food for that bacteria to flourish. That food is the fibre (like that found in grains, vegetables, fruits, nuts, and seeds).


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Eat for your microbes: lose weight fast, gain control of your blood sugar in only one week!

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Photo by Pacific Northwest Laboratory on flickr. Used under a Creative Commons Licence.

I know that I really shouldn’t comment on this research without reading the actual journal article but that hasn’t been published yet and I can’t resist jumping into the fray. Is there a fray? Not really. I just keep seeing people retweeting this and everyone seems all excited about the possibility of these individualized and I need to put a little rain on the parade.

The article starts off sounding great. Who doesn’t want a bespoke diet? Considering the number of people who have asked me as a dietitian to “just tell me what to eat” I think that most people want someone to hand them a nice little meal plan. Of course, most meal plans would be “bespoke” in a sense as any professional worth their credentials is going to tailor the menu to the client. But, I’m not here to quibble about what exactly makes a meal plan bespoke.

So, apparently the researchers looked at how different people react (in terms of blood sugar) to the consumption of different foods. They found a wide range of responses and linked those responses to the types of gut microbes residing in the participants digestive tracts. Then in another study (of only 20 participants) each participants was given a unique diet to control blood sugar and one that was designed to increase blood sugar. Unfortunately, the diets aren’t described in the article so it’s hard to say how much they differed for each participant. There’s also no explanation as to how this ties in to the earlier research looking at the microbiome. In a shocking turn of events, on the diets designed to control blood sugar some (again the article doesn’t indicate how many) participants blood sugar levels returned to normal. On the “bad” diets they had blood sugar spikes that “would be described as glucose intolerant” according to one of the researchers. Essentially, they exhibited diabetes or similar conditions.

The article then goes on to say that this research somehow shows that calories aren’t the only player when it comes to weight loss. What? I thought the research was looking at blood glucose levels. There was no mention of weight change in participants. While I certainly agree that there are many other factors at play, in addition to calorie consumption when it comes to weight management, I fail to see how this research examined this issue at all.

What makes me a little more leery about this study is that the researcher says it’s surprising that ice cream (for example) doesn’t cause huge blood sugar spikes, and that buttered bread has less impact on blood glucose than unbuttered bread. Have these people not heard of glycemic load before? Of course blood glucose responses are going to be mitigated when high carbohydrate foods are consumed with fat or protein. That’s why it’s important to look at how people are consuming foods rather than examining the effect of specific foods in isolation.

I’m trying to withhold full judgement until the research is published. I think that the human microbiome is a fascinating emerging area of research. However, on the basis of this article all I’m envisioning are more scam diet books urging people to eat for their microbes.


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Follow Friday: @americangut

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I’m just finishing up a short course on the human microbiome on coursera. While we’re only just beginning to scrape the surface of our understanding of how microbes affect our health it’s a fascinating subject. Did you know that bacteria that are beneficial in your gut may be harmful if they’re found in another part of your body? Obviously your diet can transform your gut microbiome but what effect does it have on your health? It seems that exercise also affects the composition of your gut microbiome. In turn, your microbiome may impact your hormones and neurotransmitters.

You can get in on the ground floor of human microbiome research by supporting the American Gut Project. By pledging your support you can get a kit to send them samples of your microbes. In turn, you’ll receive an analysis of your microbes and see how they compare to others in the study. Despite the name, citizens of countries other than American are welcomed to participate as this can help to provide a larger picture of the human microbiome. The analysis is not intended to diagnose any medical conditions, it simply shows you the prevalence and variety of microbes in your gut at a given moment in time (and other areas of your body depending how much you pledge). However, you’re contributing to some really exciting research that will hopefully lead to greater insight into what your microbiome may mean for your health and well being.


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Are apples the key to curing obesity?

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A few weeks ago the media was reporting that apples may provide the cure for obesity. I was a little more sceptical. I mean, how many overweight and obese people do you know who eat apples? Probably lots. If apples were capable of curing obesity everyone would be thin.

My first concern was that this research was conducted on mice. That means that it may (likely) is not translatable to humans. A couple of things to consider: these mice were fattened up by being fed a very specific high-fat diet. Obesity is a complex condition with myriad factors. Unless the reason for people being overweight is due to consuming a similar diet to these lab mice, it’s quite likely that they will not respond to this weight loss treatment in the same manner as the mice. I also wondered how much apple the mice were fed. How much apple would humans need to consume to see similar results? Here’s where it gets crazy: the mice did not eat the apples. Yep, that’s right. We have no idea how much apple would be beneficial to humans as we don’t know how much would be beneficial to mice. Rather than feeding the apples to the mice, the researchers made a slurry of apple compounds and mouse faeces. They found increased levels of certain bacteria that are commonly found in the faeces of slim mice in the cultured faeces of obese mice. Their results were not statistically significant. They showed a trend toward increased levels of some bacteria and butyric acid, and decreased levels of other bacteria in the faeces-apple slurries of obese mice but none of the changes (save the decreased bacteria) were large enough to be statistically significant.

It’s impossible to say whether or not eating apples (how many, how frequently) would have similar effects on the fecal microbiomes of mice or humans. We also don’t know if these microbial changes do occur if they would result in weight loss. Without knowing this, it’s a ridiculously huge leap to suggest that consuming apples could be a treatment for obesity. This didn’t stop the authors from concluding that:

These results suggest that dietary fibre and phenolic compounds remaining in apples after IVD might help to prevent metabolic disorders driven by an altered microbiota in obesity, and potentially protect from an obesity-disturbed balance of microbiota.

It also didn’t stop the media from publishing articles with headlines like: “An apple a day could keep obesity away: Granny Smiths promote friendly bacteria helping us feel fuller for longer” and “Granny Smith apples can help prevent the damage of obesity“.

I do think that research into our microbiomes is going to provide insight into many illnesses and conditions. However, our individuals microbiomes are extremely variable. Suggesting that this research using mice will translate to obesity treatments for humans. It’s also extremely unlikely that consuming one healthy food will negate the effects of an overall unhealthy diet. That being said, apples are nutritious and it’s certainly not going to hurt you to have an apple a day.