Twins Nutrition Study (TwiNS): Vegan vs. Omnivore

Inclusion Criteria:

* Age 18+
* 1/2 of a pair of twins that will both be participating
* Willing to consume a plant-based diet (vegetables, fruit, whole grains, legumes, etc.)
* Willing to consume meat/eggs (beef, pork/sausage, chicken, eggs) \>= 1 time a day
* Willing to consume dairy (milk, yogurt, cheese) \>= 1 time a day

Exclusion Criteria:

* Weight \< 110 lb
* BMI \>= 40
* LDL-C \> 190 mg/dL
* Systolic Blood Pressure \> 160 mmHg OR Diastolic blood pressure \> 90 mmHg
* Pregnant, lactating or planning to become pregnant during the course of the study.
* Use of any of the following drugs/supplements within the last 2 months:

* systemic antibiotics, antifungals, antivirals or antiparasitics (intravenous, intramuscular, or oral);
* corticosteroids (intravenous, intramuscular, oral, nasal or inhaled);
* cytokines;
* methotrexate or immunosuppressive cytotoxic agents.
* Chronic, clinically significant, or unstable (unresolved, requiring on-going changes to medical management or medication) pulmonary, cardiovascular, gastrointestinal, hepatic or renal functional abnormality, as determined by medical history, Type 1 diabetes, dialysis
* History of active cancer in the past 3 years except for squamous or basal cell carcinomas of the skin that have been medically managed by local excision
* Unstable dietary history as defined by major changes in diet during the previous month, where the subject has eliminated or significantly increased a major food group in the diet.
* Recent history of chronic excessive alcohol consumption defined as more than five 1.5-ounce servings of 80 proof distilled spirits, five 12-ounce servings of beer or five 5-ounce servings of wine per day; or \> 14 drinks/week.
* Any confirmed or suspected condition/state of immunosuppression or immunodeficiency (primary or acquired) including HIV infection, multiple sclerosis and Graves' disease.
* Surgery of the GI tract, with the exception of cholecystectomy and appendectomy, in the past five years. Any major bowel resection at any time.
* Regular/frequent use of smoking or chewing tobacco, e-cigarettes, cigars or other nicotine-containing products
* Regular use of prescription opiate pain medication