POP Study: dietary habits and gut microbiome of the Spanish population

The microbiota can be defined as the conjunction of living microorganisms that can be found in a concrete place, such as the gut, skin, vagina, etc. These microorganisms contain not only bacteria but also fungi, viruses, etc. (2). Among the different human body sites, the gut corresponds to one the largest locations, as it measures approximately 400 m², in which your microbes relate with you and the environment (22).

Gut microbiota is important because it ferments the fiber and starch that are present in your diet and it uses them to produce several components that are beneficial for your health such as:

• Short chain fatty acids or SCFAs: the more common ones are propionate, acetate and butyrate and they serve as food for the cells present in our colon, known as colonocytes. Correct feeding of this cells allows for a correct functioning of our gut barrier (12; 23)
• Vitamins: some examples are vitamin K, B5, B9 and B12. We are not able to produce these vitamins by ourselves, so we obtain them thanks to our microbes. Vitamin K has a role in producing the elements that we need for blood clothing (21). Vitamins B5 and B12 are relevant for normal brain function (12).
• Antimicrobial agents: they are substances that help to kill, or at least prevent from growing, possible harmful organisms that may enter our body (1).

Microbiota is also involved in the proper development of our immune system by allowing us to distinguish between “our bacteria” and “foreigners”, and it serves as physical barrier against pathogens (12).

There are several things that can affect your microbiota, such as age, gender, the place where you live, with who and even your lifestyle (6). However, among them, diet seems to be one of the most relevant and easier to modify.

As a country bordering the Mediterranean Sea, Spain has traditionally followed the Mediterranean diet (MD). This diet is rich in plant-based foods such as fruits, legumes, whole grains, vegetables, and nuts. It emphasizes healthy unsaturated fats, primarily from olive oil, and includes frequent fish consumption, moderate intake of dairy products and fermented beverages, and a low intake of meat and meat-derived products (5).

Despite its benefits, adherence to the Mediterranean diet (MD) in Spain appears to have declined over time, shifting towards a more Western dietary pattern. This shift is characterized by a decrease in the consumption of whole grains and an increase in processed foods, sugar, saturated fat, and animal protein (15; 25; 26). This type of diet has been pointed out by some organizations as the cause of morbidities and health problems worldwide (9) that may be consequence, at least in part, of the loss of microbiota equilibrium known as “dysbiosis”.

POP study is a prospective and longitudinal study that was carried out at the Vall d'Hebron University Hospital in Barcelona. Healthy volunteers aged between 18 and 75 years from different regions of Spain participated in the study. It started in December 2020 and it is still active nowadays.

1. Which are the objectives of the study?

The main objectives of the study are:

• To obtain an overview of the dietary habits of the Spanish population.
• To analyze the relationship between diet and gut microbiota, which means to understand how food choices can modify our microbiome and how these changes can affect our health.
• To study how other factors such as demographic and anthropometric characteristics relate to microbiota composition and diversity.
• To compare this information with that of patients suffering from certain diseases in order to identify what has happened in their microbiome and try to restore it towards a profile considered "healthy" (work currently in progress).

2. Study design

We recruited participants from the 17 autonomous communities of Spain, as well as from the cities of Ceuta and Melilla, through advertisements on social media (Facebook, Twitter, Instagram). Each participant provided three stool samples and completed three digital food frequency questionnaires over the course of a year (at baseline, 6 months, and 12 months) to assess habitual diet.

• Questionnaires collected information on diet, lifestyle, and anthropometric measurements.
• Stool samples were processed to obtain microbiome data.

To date, we have recruited 1,017 volunteers from various regions of Spain, forming the "POP" cohort. Dietary information is available for virtually all participants. However, due to budget limitations, bacterial analysis has been performed on a random subset of 680 baseline fecal samples, while fungal analysis has been completed on 98 samples. We are currently actively working to secure additional funding to sequence the remaining samples.

3. General results

3.1. Population characteristics and dietary habits

• Geographical distribution: people from all autonomous communities participated, grouped into four large regions: Mediterranean, Interior, North and Islands.
• Age and gender: the cohort included adults aged 18 to 75, with a balanced representation of men and women.
• Main dietary patterns:
  • With age, there was an increased consumption of healthy foods such as whole grain bread, nuts, and fruit, although alcohol intake also rose.
  • Women exhibited higher quality diets (more fruit, vegetables, fish, whole grain bread, and non-alcoholic beverages), while men consumed more prepared meals and alcoholic beverages.
  • The Interior region showed a healthier dietary pattern, including a higher consumption of legumes, compared to the Mediterranean region.
  • Overall, the Spanish diet met global recommendations for fruits, vegetables, and fiber, but fell short of the recommended levels for legumes, nuts, whole grains, dairy, and calcium, in addition to excessive consumption of red/processed meats and sugary beverages.

3.2. Microbiome and diet

• A higher intake of fruit, vegetables, and nuts was associated with greater microbial diversity, while the consumption of refined grains was linked to lower diversity.
• We developed an index comparing the microbiota of healthy volunteers in the study with that of 321 patients with inflammatory bowel disease (IBD). The results showed that a diet low in fruit, nuts, and vegetables, along with a high consumption of sugary beverages, promotes a microbiota profile more similar to that observed in patients with IBD.
• Microbiome data allowed us to predict consumption habits of key foods such as coffee or nuts, among others.

4. Conclusions

The POP study represents the first large-scale analysis in Spain exploring the relationship between diet, personal factors, and gut microbiome using metagenomic techniques. The results reinforce the importance of following national dietary guidelines, showing that a higher intake of fruits, vegetables, and nuts not only increases microbial diversity but also promotes a microbial profile distinct from that observed in patients with IBD. Additionally, the project has developed an interactive platform that allows participants to access their dietary and microbial profile, fostering citizen involvement in science.

Those who wish to delve deeper into the scientific results can consult the publication at:

Finally, we would like to express our sincere gratitude to all the volunteers who have altruistically participated in this project. Their involvement has been key to advancing knowledge about the relationship between diet, microbiota, and health in the Spanish population.

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