Aim: To test the effects of a fiber-blend containing snack prototype in an escalating dose regimen (from 1 to 3 servings per day over a period of 6 weeks) on the configuration and gene content of the gut microbiota of overweight and obese participants (BMI 25-35 kg/m2), while consuming a controlled diet that contains quantities of saturated fats in the upper tertile and quantities of fruits and vegetables in the lower tertile of consumption in the NHANES database (high saturated fat-low fruit and vegetable; HiSF-LoFV). Changes in the representation of bacterial genes involved in carbohydrate utilization in the microbiomes of participants will be correlated with changes in plasma biomarkers at the end of each escalating dose phase by comparing features of their pre- vs post-treatment plasma proteomes and metabolomes.

Design: Participants will be asked to continue to consume their habitual diet (free diet phase) for 1 day prior to being provided with a HiSF-LoFV diet in the form of packed-out meals and snacks to consume for the following 62 days. Ten days after starting to consume the HiSF-LoFV diet, participants will supplement this diet with a fiber-blend containing snack (~10g fiber/serving) once daily for a total of 14 days; the energy contribution from the HiSF-LoFV diet will be reduced accordingly to maintain energy needs during this time and the remainder of the study. For the next 14 days, the diet will be supplemented with two of the same fiber-blend containing snacks per day, followed by 14 days in which the snacks will be consumed three times daily. Subsequently, a 'wash-out' phase of ten days in which the HiSF-LoFV diet is consumed without any of fiber snack supplementation will conclude the study. Stool, urine and blood will be sampled periodically throughout.

Inclusion Criteria:

• BMI ≥25.0 and ≤35.0 kg/m2

Exclusion Criteria:

• Previous bariatric surgery
• Significant organ system dysfunction (e.g. diabetes, severe pulmonary, kidney, liver, or -cardiovascular disease)
• Cancer or cancer that has been in remission for less than 5 years
• Major psychiatric illness
• Inflammatory gastrointestinal disease
• Pregnant or lactating women
• Use of medications that are known to affect the study outcome measures
• Use of medications or supplements known to affect composition of the gut microbiota within the last 30 days (e.g. antibiotics)
• Bowel movements less than 3 times per week
• Vegans, vegetarians, and those with allergies, aversions, or sensitivities to foods provided in the study
• Persons that are not able to grant voluntary informed consent
• Persons who are unable or unwilling to follow the study protocol or who the research team deems not an appropriate candidate for the study.