The goal of this cross-sectional observational study is to examine potential relationships between the blood and gut microbiota of patients with obesity before and after weight loss surgery (WLS) and evaluate potential ethnic differences in the blood and gut microbiotas before and after the WLS.

The main aims / objectives of this sub-study are:

• Aim 1. Compare the relationship between the blood and the gut microbiomes among a sample of (1) pre-WLS and (2) 6-month post-WLS participants.

Hypothesis: Blood bacterial composition will resemble that of the gut microbiome among pre-WLS participants. Because the effect of WLS on the blood microbiome is not known, our post-WLS results will be mostly exploratory.

• Aim 2. Determine racial differences in the blood microbiome of the pre- and post-WLS groups.

Hypothesis2: Ethnic differences will be detected in both the pre- and post-WLS groups.

A subgroup of participants from the main study will be invited to participate in a cross-sectional sub study evaluating the relationship between blood and gut microbiotas. A total of 100 participants will be recruited, 50 participants will be recruited from the "non-completers" and the other 50 participants will be recruited from the "6 months post-WLS" follow-up group of our main project.

Inclusion Criteria:

• 18-60 years old
• Will belong to either Non-Hispanic Whites (NHW) or Non-Hispanic Blacks (NHB) ethnic groups
• "No-WLS" participants will have a BMI >35 kg/m2 (threshold BMI for WLS) whereas "6 months post-WLS" participants will have no BMI requirements.

Exclusion Criteria:

• Having taken antibiotics in the previous 6 months;
• Metformin, proton pump inhibitors, probiotics, or prebiotics in the previous month;
• Currently following a vegetarian diet;
• Pregnancy;
• Having any infection in the previous month; and
• Having a comorbid disease that might alter the blood microbiome composition (e.g., renal failure) or the intestinal permeability (e.g., IBS).

Investigators will recruit in the following manner:

• Non-surgery participants from the "non-completers" group from the main study
• Participants who had bariatric surgery 6 months prior to their enrollment into this sub study, will be recruited from the "early and late completers" in the main study. If additional participants are needed, particularly due to strict ethnic requirements (limited to NHW and NHB), first, invitation emails will be sent to the Weight Wellness Clinic patients, and if recruiting at the expected rate continues to be an issue, advertisements through IRB-approved flyers on social media or in the clinic setting will be posted.