Effect of a Low-calorie Diet with a Prebiotic Supplement on Health of Overweight-obese Subjects.

The main objective of this project is to evaluate the effect of prebiotic supplementation on weight loss and other physiological and metabolic parameters related to excess weight in overweight/obese adult men and women, as well as to determine the changes in the gut microbiota associated with these changes. Specific objectives are focus on evaluate the effect of the intervention on the following parameters:

* Weight and body composition.
* Changes in the gut microbiota (metagenomics).
* Changes in urinary and serum metabolites.
* Complete blood count, routine biochemical variables related to glucose and lipid metabolism, as well as liver health parameters.
* Specific markers involved in obesity pathology (insulin, leptin, adiponectin, and cytokines MCP1, TNF, CRP, and IL10).
* Satiety-related variables using a visual analog scale.
* Adherence to the assigned intervention, both to the hypocaloric diet and to the supplement provided in the study.
* Physical activity level.
* Changes in gastrointestinal health through self-reported questionnaires.
* Mental health and quality of life of participants through self-reported questionnaires.
* Chronotype of participants through a self-reported questionnaire. For this purpose, a randomized, double blind parallel study has been designed.

Target sample size is 156 subjects.

Participants will be allocated in two groups for 8 weeks:

* Experimental group (n=104): hypocaloric diet + prebiotic supplement.
* Placebo group (n=52): hypocaloric diet + placebo supplement.

Participants will visit nutritional intervention unit at week 1 and week 8. At week 4 they will receive a phone control call.

Volunteers who wish to participate in the study will be interviewed by phone to verify that they meet the main inclusion criteria. Volunteers who meet the main inclusion criteria will be invited to an information and screening visit to resolve any doubts. Volunteers who agree to participate in the study will sign the informed consent and will be randomly allocated to one of the two arms of the study and will be provided with any required material.

During the intervention, volunteers will attend 2 Clinical investigation visits. The first one will be carried out on the first day of the study and the last one will take place at the end of the 8 weeks. In both visits anthropometric and body composition measurements, blood pressure, stool and blood, urine and stool samples, as well as data about dietary, physical activity, sleep and gastrointestinal symptoms will be taken.

Inclusion criteria

* Men and women aged 18 to 70 years.
* Volunteers with overweight or obesity (BMI: 25.0-39.9 kg/m²) and body fat percentage \> 30% for women / \> 20% for men.
* Stable weight (+/- 5%) in the last three months prior to the start of the study.
* Normal physical examination and vital signs, or clinically insignificant findings for the experiment (those not related to metabolic health).
* Subjects must be able to understand and be willing to sign the informed consent form, agreeing to comply with all study procedures and requirements.
* Continued pharmacological/hormonal treatment will be allowed as long as it does not affect the study parameters and the dosage has been stable for at least 3 months. Exclusion will apply to treatments with insulin or any drug with hypoglycemic effects.
* Willingness to undergo each of the procedures involved in the study (including consuming a sweetened yogurt).
* Availability to attend the two in-person clinical evaluation sessions at the scheduled times and locations.

Exclusion criteria

* Volunteers undergoing pharmacological treatment if the treatment is not stable (at least 3 months before the start of the study), with exclusion of treatments:
* That alter gastrointestinal function.
* Stomach protectants.
* Hypoglycemic drugs.
* Insulin (under no circumstances).
* Subjects with relevant functional or structural abnormalities of the digestive system, such as malformations, angiodysplasias, active peptic ulcers, chronic inflammatory or malabsorption diseases, hiatal hernia, reflux, etc.
* Subjects who have undergone surgical interventions with permanent sequelae in the digestive system (e.g., gastroduodenostomy) or bariatric surgery.
* Suffering from any chronic metabolic disease or obesity-related disease, or any systemic intestinal, liver, or kidney disease: type 1 or 2 diabetes, severe dyslipidemia, uncontrolled thyroid dysfunction, cirrhosis, inflammatory bowel disease, untreated anemia, etc. (non-alcoholic fatty liver will not be an exclusion criterion).
* Exceeding the alcohol consumption limit for the corresponding sex (more than 14 units per week for women and 20 units per week for men).
* Pregnant, breastfeeding, or planning to become pregnant.
* Taking nutritional supplementation (weight loss supplements, fiber supplements, probiotics, multivitamins, etc.) that contains compounds that may affect the study outcomes, unless the person is willing to stop these supplements during the 8-week intervention period and ensures a minimum washout period of 30 days before baseline measurements.
* Having donated blood in the 14 days prior to the start visit.
* Subjects with any type of cancer or undergoing cancer treatment, or who have not been free of cancer for at least 5 years since eradication.
* Subjects with an allergy to any component of the study product or any other food that interferes with and complicates following the study protocol.
* Subjects with any cognitive and/or psychiatric impairment.
* Subjects who are expected to have poor cooperation or, in the investigator's opinion, have difficulty following the study procedures.
* Subjects currently undergoing treatment for weight loss/body composition modification.
* Subjects who are taking or have taken antibiotics within 30 days before the initial visit.

Eligibility Criteria:
Inclusion Criteria:

* Men and women aged 18 to 70 years.
* Volunteers with overweight or obesity (BMI: 25.0-39.9 kg/m²) and body fat percentage \> 30% for women / \> 20% for men.
* Stable weight (+/- 5%) in the last three months prior to the start of the study.
* Normal physical examination and vital signs, or clinically insignificant findings for the experiment (those not related to metabolic health).
* Subjects must be able to understand and be willing to sign the informed consent form, agreeing to comply with all study procedures and requirements.
* Continued pharmacological/hormonal treatment will be allowed as long as it does not affect the study parameters and the dosage has been stable for at least 3 months. Exclusion will apply to treatments with insulin or any drug with hypoglycemic effects.
* Willingness to undergo each of the procedures involved in the study (including consuming a sweetened yogurt).
* Availability to attend the two in-person clinical evaluation sessions at the scheduled times and locations.

Exclusion Criteria:

* Volunteers undergoing pharmacological treatment if the treatment is not stable (at least 3 months before the start of the study), with exclusion of treatments:
* That alter gastrointestinal function.
* Stomach protectants.
* Hypoglycemic drugs.
* Insulin (under no circumstances).
* Subjects with relevant functional or structural abnormalities of the digestive system, such as malformations, angiodysplasias, active peptic ulcers, chronic inflammatory or malabsorption diseases, hiatal hernia, reflux, etc.
* Subjects who have undergone surgical interventions with permanent sequelae in the digestive system (e.g., gastroduodenostomy) or bariatric surgery.
* Suffering from any chronic metabolic disease or obesity-related disease, or any systemic intestinal, liver, or kidney disease: type 1 or 2 diabetes, severe dyslipidemia, uncontrolled thyroid dysfunction, cirrhosis, inflammatory bowel disease, untreated anemia, etc. (non-alcoholic fatty liver will not be an exclusion criterion).
* Exceeding the alcohol consumption limit for the corresponding sex (more than 14 units per week for women and 20 units per week for men).
* Pregnant, breastfeeding, or planning to become pregnant.
* Taking nutritional supplementation (weight loss supplements, fiber supplements, probiotics, multivitamins, etc.) that contains compounds that may affect the study outcomes, unless the person is willing to stop these supplements during the 8-week intervention period and ensures a minimum washout period of 30 days before baseline measurements.
* Having donated blood in the 14 days prior to the start visit.
* Subjects with any type of cancer or undergoing cancer treatment, or who have not been free of cancer for at least 5 years since eradication.
* Subjects with an allergy to any component of the study product or any other food that interferes with and complicates following the study protocol.
* Subjects with any cognitive and/or psychiatric impairment.
* Subjects who are expected to have poor cooperation or, in the investigator's opinion, have difficulty following the study procedures.
* Subjects currently undergoing treatment for weight loss/body composition modification.
* Subjects who are taking or have taken antibiotics within 30 days before the initial visit.