We are what our bacteria eat

Serena Galiè
About the Author

Graduated in Biotechnology and passionate about scientific dissemination, I have carried carrying out a doctoral thesis in Nutrition and Metabolism, at the Faculty of Medicine, in Reus. My main interest is the gut microbiota and its relationship with human nutrition and health. At the same time, I collaborated as a freelance editor with "Microbiologia Italia", an Italian webpage for scientific dissemination on the microbiological world. Despite my passion for traveling and getting to know new cultures and places, I am left with a broken heart between Italy and Spain, where I have lived for more than 6 years.


Today, on July 1, I will defend my doctoral thesis. This thesis is about my research on the effects of nuts and the Mediterranean diet on gut microbiota, BMI and blood sugar levels. In this blog I will highlight some of my research and how this may help you to improve your diet.

A long time ago, Hippocrates said “We are what we eat”. But a new revolutionary idea in medicine is pointing out the major role of gut microbiota in our health status and, more importantly, how diet influences its overall wellbeing.

During the last decade, there has been a lot of effort from the scientific community regarding the potential prebiotic effect of certain foods in humans. Prebiotics are not more than the best feeding for those good bacterial fellows in our gut. They mainly include dietary fibers, which are complex carbohydrates that our bodies cannot digest well, but that are great food for our gut bacteria. Nuts are one example of prebiotic food, other than being related to beneficial role in prevention of cardiometabolic diseases, such as heart problems, high blood pressure and diabetes. However, the potential prebiotic effect of this “superfood” in human metabolic health has rarely been explored in comparison to an overall healthy and controlled dietary pattern such as the Mediterranean diet, whose beneficial role in cardiometabolic health is pretty well known.

In the last 4 years, my research has been focused on understanding the role of those bunch of microorganisms cohabiting with us in the gut, how they contribute to our health and how they are influenced by either consumption of a Mediterranean diet or a normal diet supplemented with nuts. This experiment was called METADIET, and it was a randomized clinical trial.  50 volunteers with both metabolic syndrome and obesity were enrolled in this study, and they were randomly divided into two groups. The first group had to eat according to the Mediterranean diet for two months. The other group could just eat whatever they usually ate, but they also had to eat 50 grams of mixed nuts each day. After two months followed a month of rest where participants could just eat whatever they wanted. And then, the groups switched for another two months, so now the second group ate according to the Mediterranean diet, and the first group ate the nuts.

Our first observations revealed that the Mediterranean diet exerted greater beneficial effects in contrast to nuts supplementation in ameliorating the classical biomarkers of cardiometabolic risk factors, like insulin and glucose levels, as well as insulin resistance. We did not see very big differences between the two types of diets in terms of overall microbial ecosystem, but if we zoomed in on single genera or bacteria we did see some effects of the Mediterranean diet. For instance, we found a previously unknown bacteria species from Lachnospiraceae family called Lachnospiraceae NK4A136 group, that seemed to contribute to participants’ health. In fact, this same bacteria was also correlated with the decreased insulin levels observed after Mediterranean diet, as well as with cholic acid contained in participants’ feces, which is an indicator of the functional metabolism of gut microbiota and commonly related to metabolic health. For the nuts diet, we found that patients enrolled in this nutritional intervention were not experiencing any improvement in their metabolism, but we did find some effects of this diet on the gut bacteria.

Therefore, yes nuts are able to modulate gut microbiota composition towards the predominance of the good guys in the gut, but they do need the co-existence of a healthy dietary pattern like Mediterranean diet to actually exert their potential health benefits. Thus, introducing them in your daily habits is not enough in the context of cardiometabolic disorders prevention. Better is to pay attention to eat vegetables, consume olive oil, abandon refined grains and maybe have a journey to a Mediterranean country.

Today, on July 1, I will defend my doctoral thesis. This thesis is about my research on the effects of nuts and the Mediterranean diet on gut microbiota, BMI and blood sugar levels. In this blog I will highlight some of my research and how this may help you to improve your diet.

A long time ago, Hippocrates said “We are what we eat”. But a new revolutionary idea in medicine is pointing out the major role of gut microbiota in our health status and, more importantly, how diet influences its overall wellbeing.

During the last decade, there has been a lot of effort from the scientific community regarding the potential prebiotic effect of certain foods in humans. Prebiotics are not more than the best feeding for those good bacterial fellows in our gut. They mainly include dietary fibers, which are complex carbohydrates that our bodies cannot digest well, but that are great food for our gut bacteria. Nuts are one example of prebiotic food, other than being related to beneficial role in prevention of cardiometabolic diseases, such as heart problems, high blood pressure and diabetes. However, the potential prebiotic effect of this “superfood” in human metabolic health has rarely been explored in comparison to an overall healthy and controlled dietary pattern such as the Mediterranean diet, whose beneficial role in cardiometabolic health is pretty well known.

In the last 4 years, my research has been focused on understanding the role of those bunch of microorganisms cohabiting with us in the gut, how they contribute to our health and how they are influenced by either consumption of a Mediterranean diet or a normal diet supplemented with nuts. This experiment was called METADIET, and it was a randomized clinical trial.  50 volunteers with both metabolic syndrome and obesity were enrolled in this study, and they were randomly divided into two groups. The first group had to eat according to the Mediterranean diet for two months. The other group could just eat whatever they usually ate, but they also had to eat 50 grams of mixed nuts each day. After two months followed a month of rest where participants could just eat whatever they wanted. And then, the groups switched for another two months, so now the second group ate according to the Mediterranean diet, and the first group ate the nuts.

Our first observations revealed that the Mediterranean diet exerted greater beneficial effects in contrast to nuts supplementation in ameliorating the classical biomarkers of cardiometabolic risk factors, like insulin and glucose levels, as well as insulin resistance. We did not see very big differences between the two types of diets in terms of overall microbial ecosystem, but if we zoomed in on single genera or bacteria we did see some effects of the Mediterranean diet. For instance, we found a previously unknown bacteria species from Lachnospiraceae family called Lachnospiraceae NK4A136 group, that seemed to contribute to participants’ health. In fact, this same bacteria was also correlated with the decreased insulin levels observed after Mediterranean diet, as well as with cholic acid contained in participants’ feces, which is an indicator of the functional metabolism of gut microbiota and commonly related to metabolic health. For the nuts diet, we found that patients enrolled in this nutritional intervention were not experiencing any improvement in their metabolism, but we did find some effects of this diet on the gut bacteria.

Therefore, yes nuts are able to modulate gut microbiota composition towards the predominance of the good guys in the gut, but they do need the co-existence of a healthy dietary pattern like Mediterranean diet to actually exert their potential health benefits. Thus, introducing them into your daily habits is not enough in the context of cardiometabolic disorders prevention. Better is to pay attention to eat vegetables, consume olive oil, abandon refined grains and maybe have a journey to a Mediterranean country.