Dietary fibers are generally not degraded by the endogenous digestive enzymes, but rather by the complex ensemble of microorganisms that reside in the human gut [1]. This ensemble, collectively known as the human gut microbiome, plays a key role in breaking down, fermenting, and ultimately converting such dietary fibers into a variety of beneficial metabolites, including most notably, short chain fatty acids (SCFA). These end products of fibers' fermentation affect host metabolism, immunity, and physiology, and have been implicated in multiple diseases including obesity, metabolic syndrome, diabetes, and cardiovascular diseases.

Intermediate fasting, and in particular circadian intermediate fasting (i.e. 16 hours of fasting followed by 8 hours of allowed eating), has been shown to have positive associations with multiple health conditions as obesity, diabetes mellitus, cardiovascular disease, cancers, and neurologic disorders In this study, we will try to answer open questions utilizing the long fasting period during the day to investigate the isolated effect of dietary fiber consumption, uncovering the degradation effect, but not the bulking effect, on the microbiome and the host physiology, and in particular its glucose response.

During the 22 days of the study, participants will wear a continuous glucose monitor, fill a daily food diary, and collect stool and oral samples which will be used for microbiota profiling. Participants will be asked to carry out an intermediate fasting regime, which will include: 16 straight hours of fasting followed by 8 hours which the participants will be allowed to eat. Drinking water is allowed throughout the fasting hours.

The groups will consume 4, 12, 20 grams of the dietary fiber per day, according to the group they were assigned to, while not exceeding the total fiber consumption of 50 grams per day, which is considered a high-fiber diet.

Inclusion Criteria:

Male and Female BMI<28 Age - 18-70

Exclusion Criteria:

Consumption of antibiotics 3 months prior to the first day of the experiment. Consumption of probiotic or dietary fibers supplements 1 month prior to the first day of the experiment.

Practiced in intermediate fasting 1 month prior to the first day of the experiment.

Diagnosis with type 1 or type 2 diabetes. Pregnancy, breastfeeding, or fertility treatments in the last 6 months. Chronic disease (e.g. AIDS, Cushing syndrome, CKD, acromegaly, hyperthyroidism hepatitis, fibromyalgia, etc.).

Cancer and recent anticancer treatment. Psychiatric disorders. Coagulation disorders. IBD (inflammatory bowel diseases). IBS (Irritable bowel syndrome). Alcohol abuse, more than 2 drinks per day for males, and more than one drink for females.

Substance abuse. BMI>28. Daily dietary intake higher than 25 grams per day. History of abdominal surgeries (including Bariatric surgery). Mentally incompetent or lack of judgment