Ketogenic Diet in Healthy Adults With Differing BMI

The goal of this clinical trial is to examine the effect of the ketogenic diet over four weeks on blood lipid levels and risk factors for heart disease in adults with a healthy BMI compared to adults with a body mass index (BMI) in the range for obesity. The main questions it aims to answer are:

* Does the ketogenic diet cause larger increases in "bad cholesterol" (low density lipoprotein-cholesterol) in adults with a healthy BMI compared to adults with BMI in the range for obesity?
* Does the ketogenic diet cause larger decreases in vascular health in adults with a healthy BMI compared to adults with BMI in the range for obesity?

Participants will:

* Consume all of the study food provided and avoid intake of non-study foods during the 28-day diet period
* Visit the metabolic kitchen daily (Monday-Friday) to pick up meals
* Attend 5 fasting visits at the Clinical Research Center for testing

This is a controlled feeding study investigating if four weeks on the ketogenic diet will cause differential alterations in blood lipids and lipoproteins, vascular health as measured by fasting flow mediated dilation (FMD), and mechanistic markers of lipid metabolism in adults with normal weight when compared to adults with obesity. Outcomes will be measured at both the beginning and end of the study on two consecutive days, for a total of four clinic appointments.

Eligibility Criteria:
Inclusion Criteria:

1. Age 25-45 years
2. Fasting direct LDL-C ≤100 mg/dL
3. BMI of 18.5-22 kg/m2 or 30-35 kg/m2
4. Blood pressure \<140/90 mmHg
5. Fasting blood glucose \<126 mg/dL
6. Fasting triglycerides \<350 mg/dL
7. ≤10% change in body weight for 6 months prior to enrollment

Exclusion Criteria:

1. Have type 1 or type 2 diabetes or fasting blood glucose ≥126 mg/dL
2. Prescription of anti-hypertensive, lipid-lowering or glucose-lowering drugs
3. Intake of supplements that affect the outcomes of interest and unwilling to cease during the study period
4. Diagnosed liver, kidney, or autoimmune disease
5. Prior cardiovascular event (e.g., stroke, heart attack)
6. Current pregnancy or intention of pregnancy within the next 2 months
7. Lactation within prior 6 months
8. Follows a vegetarian or vegan diet
9. Food allergies/intolerance/sensitives/dislikes of foods included in the study menu
10. Antibiotic use within the prior 1 month
11. Oral steroid use within the prior 1 month
12. Use of tobacco or nicotine containing products within the past 6 months
13. Cancer at any site within the past 10 years (eligible if ≥10 years without recurrence) or non-melanoma skin cancer with in the past 5 years (eligible if ≥5 years without recurrence)
14. Participation in another clinical trial within 30 days of baseline
15. Currently following a restricted or weight loss diet
16. Previously consumed the ketogenic diet for more than 1 week
17. Prior bariatric surgery
18. Intake of \>14 alcoholic drinks/week and/or lack of willingness to consume no alcohol while enrolled in the study and/or not willing to avoid alcohol consumption for 48 hours prior to test visits
19. Current or past eating disorder
20. Principal Investigator discretion related to the potential participant's ability to adhere to the study requirements including being able to come to the metabolic kitchen to pick-up food five days per week
21. Planning to relocate out of the State College area in the next 2 months
22. Unwilling to refrain from plasma/blood donations during the study
23. Previously diagnosed familial hypercholesterolemia
24. If a potential participant takes thyroid medicine, abnormal thyroid stimulating hormone (TSH) concentration (TSH outside of normal range of 0.5 - 4.5 mIU/L)