According to the data from the Di@bet.es study, which is part of the National Diabetes Strategy, the prevalence of type 2 diabetes among Spanish population is 13.8%. Diabetic patients suffer from several short and long term complications, which are related to a significant worsen of quality of life and a substantial increase in death rate.

In this sense, it is important to prevent the development of Type 2 diabetes. Therefore, it is of high relevance to identify and to treat prediabetic subjects prior to the development of the disease. Many strategies have been implemented to reverse this situation, such as changes in diet and lifestyle, among others. However, it is hard to achieve changes in lifestyle and despite the use of some drugs in this phase of the disease, the problem continues growing.

For this reason, new strategies to combat the development of type 2 diabetes are been investigated, such as the use of probiotic formulations. However, at the moment, few studies evidence the effect of probiotics on glycemic regulation. Therefore, an interesting opportunity arises according to the potential ability of probiotic formulation for the control of prediabetes.

Considering this background, the main objective of this research is to assess the effect of a new probiotic formulation on glycemic control, insulin resistance and the composition of the fecal microbiota in prediabetic subjects.

This study is designed as a 12-week, double-blind, randomised, placebo-controlled parallel study. It is focused on prediabetic overweight / obese men and women between 18 and 70 years old.

All participants attend the Nutrition Intervention Unit of the Center for Nutrition Research in the University of Navarra for the screening visit and 4 more times during the intervention (week 1, 4, 8 and 12 of study).

• Screening visit: evaluation of the inclusion criteria.

Volunteers who meet the inclusion criteria are provided with a stool collection kit and a 72 h food record questionnaire. Moreover, they are randomly assigned to one of the two intervention groups:

Control group: placebo supplemented; Experimental group: probiotic supplemented.

• Clinical investigation day 1 (day 1): The volunteer attend the Nutrition Intervention Unit in fasting state. Each volunteer is asked to provide the stool sample and the 72-hour food record questionnaire. Then, anthropometric, body composition and blood pressure measurements are taken and the gastrointestinal symptoms questionnaire is completed. After that, volunteer is provided with the capsules of the study for one month. Finally, fasting blood samples are collected and then an oral glucose tolerance test is carried out and blood samples are taken at 30, 60, 90 and 120 minutes after the ingestion of the glucose solution.
• Clinical investigation day 2 (week 4): The volunteer attend the Nutrition Intervention Unit in fasting state. The gastrointestinal symptoms questionnaire is completed and the adherence to the study and to the capsule consumption is assessed. After the measurement of anthropometric, body composition and blood pressure a blood sample is collected. Finally, volunteer is provided with capsules for the next month.
• Clinical investigation day 3 (week 8): The volunteer attend the Nutrition Intervention Unit in fasting state. The gastrointestinal symptoms questionnaire is completed and the adherence to the study and to the capsule consumption are assessed. After the measurement of anthropometric, body composition and blood pressure, a blood sample is collected. Finally, the stool collection kit, 72h food record questionnaire and capsules for one month are given to the volunteer.
• Clinical investigation day 4 (week 12): The volunteer attend the Nutrition Intervention Unit in fasting state. Each volunteer is asked to provide the stool sample and the 72-hour food record questionnaire. Then, anthropometric, body composition and blood pressure measurements are taken and the gastrointestinal symptoms questionnaire are completed. Finally, fasting blood samples are collected and then an oral glucose tolerance test is carried out and blood samples are taken at 30, 60, 90 and 120 minutes after the ingestion of the glucose solution.

One month later, the online version of the gastrointestinal symptoms questionnaire is send to each volunteer in order to asess any gastrointestinal symptom after stopping capsule consumption.

Inclusion Criteria:

• Men and women aged between 18 and 70 years.
• Prediabetic subjects: glycosylated hemoglobin (HbA1c) between 5.7% and 6.4%.
• Body Mass Index (BMI) between 25 and 39.9 kg / m2.
• No weight changes (± 3 kg) during the last 3 months.
• The subjects must be in general physical and psychological conditions in accordance with the objective of the study.
• Subjects must be able to understand and sign the informed consent.

Exclusion Criteria:

• To be in continuous pharmacological / hormonal treatment, especially those that could affect blood glucose concentration.
• Suffering from a chronic metabolic disease, or from a systemic intestinal, liver or kidney disease: type 1 or 2 diabetes, severe dyslipidemia, uncontrolled thyroid function disorders, cirrhosis, inflammatory bowel disease, etc.
• Subjects suffering from severe hyperlipidemia, severe hypertension or hypothyroidism without treatment or treated for less than 3 months.
• Presence of relevant functional or structural abnormalities of the digestive system, such as malformations, angiodysplasia, active peptic ulcers, chronic inflammatory diseases or malabsorption.
• Subjects who have undergone gastrointestinal surgery with permanent sequelae (for example, gastroduodenostomy).
• Chronic treatment with stomach protectors.
• Subjects suffering from some type of cancer or being in treatment for it or with a period less than 5 years since its eradication.
• Presence of some type of mental impairment such as depressive pathology, anxiety or untreated bipolar disorder. They will be able to participate if they have stable treatment for at least 3 months prior to the begining of the trial.
• Allergy or intolerance to any food or food group that is likely to manifest during the study.
• Be on a special diet (Atkins, vegetarian, etc.) during the 3 months prior to the start of the study.
• Weight variations (± 3 kg) during the last 3 months.
• Suffering from eating disorders or eating restrictive behaviors (score on the EAT-26 questionnaire equal or greater than 20).
• Subjects who have undergone surgical treatment for obesity.
• Being pregnant or breastfeeding.
• Abuse of alcohol (more than 14 units in women and 20 units in men) and / or drugs.
• Show poor collaboration or, in the opinion of the investigator, have difficulties in following the study procedures.
• Take some type of nutritional supplementation that can affect blood glucose and / or microbiota. If they take it, in order to be included in the study, they will have to stop the supplement, with a washout period of at least 14 days before starting the study.
• People who are positive for Covid-19 will not be able to participate in the study.