Dispelling nutrition myths, ranting, and occasionally, raving

The no tomatoes, plenty of cookies diet

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Air settle plate photo by Kathie Hodge on Flickr. Used under a Creative Commons Licence.

An interesting study was published a few weeks ago and I ignored it because I was all like, “this isn’t news, I blogged about it months ago”. Then, when I finally got around to looking at the study, and going back to look at my blog post, I realised that I had been writing about unpublished research that I hadn’t read. Now that I’ve read it I have a few more thoughts.

One, the authors do not express surprise that ice cream doesn’t have a large impact on blood sugar. In fact, quite the opposite. Phew!

The article, Personalized nutrition by prediction of glycemic responses could really be several studies. In the first study of 800 individuals in Israel, mostly women (60%), and mostly overweight (54%) or obese (22%), they looked at the effect of a number of standardized breakfasts on blood sugar. They found that there was considerable variability between individuals but fairly consistent responses by each individual. For example, Sue showed high blood sugar after eating potatoes and this happened every time she ate potatoes, but Sally showed little change in blood sugar each time she ate potatoes.

The next “phase” of the study looked at the effects of individualized “good” diets in comparison to individualized “bad” diets in 100 participants. The effect that each of these diets had on individual blood glucose responses and on gut bacteria was examined. In this week-long phase, it was found that a “good” diet had less impact on blood sugar and also had a positive effect on the gut microbiome. That is, foods that had less effect on blood sugar also appeared to encourage the growth of microbes that were associated with lower weights and discourage the growth of microbes that were associated with overweight and obesity. Foods that caused spikes in blood sugar encouraged the growth of microbes associated with obesity and discouraged the growth of microbes associated with lower weights.

I certainly think that the connection between diet, the human microbiome, and health conditions is an extremely interesting area of research well worth exploring. However, I’m still reluctant to jump to any conclusions based on this research.

While the researchers referred to diets as “good” and “bad” this is certainly not a positive way to approach food. I’d also like to caution that glycemic response is not the only factor in determining a healthy diet. There are many nutrients that we need to obtain from food and let’s not forget those pesky calories. Just because ice cream has a limited effect on blood sugar doesn’t mean that we should eat more of it.

This research does seem to point toward the fact that we are all individuals and what works for one person when it comes to a healthy diet may not work for another. Again, this research focussed on glycemic index which is just one tool that people can use in developing healthy eating habits. It’s premature to state that we can start developing bespoke diets based purely on individual glycemic responses to foods.

This research also only looked at a certain subset of a certain population. Commonly consumed foods may have an impact on how individuals reacted to foods in this experiment. We can’t say for certain that the results of this experiment are applicable to all persons of all weights from all populations. For example, we might see quite different responses, to the same experiment, in native North Americans.

It’s certainly premature to be making probiotic recommendations based on the results of this research. As the researchers themselves mention, they found some strains of microbes to be associated with lower body weight that had been associated with obesity in other research. As trendy as probiotic supplements may be there is a distinct likelihood that even if the strains you’re getting are truly beneficial that they’ll never make it alive to where you want them to be.

A final caution, this study only looked at a week of participants following these “good” and “bad” diets. It’s easy to follow any diet for a week. However, we don’t know if participants enjoyed the diets they were prescribed or if they felt they would be unsustainable over the long-term. We also don’t know what health benefits, if any, the “good” diets would yield over the long term.

Sorry, you can’t proclaim that tomatoes are sabotaging your diet just yet. The good news is: you don’t have to eat them if you don’t like them.


Author: Diana

I'm a registered dietitian from Nova Scotia, living and working in Ontario, Canada. My goal is to help people see food and nutrition from a different perspective and understand that nutrition and health are not necessarily a result of personal choice.

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