The purpose of this research is to determine the role of a type of immune cell in blood, called a non-classical monocytes (NCMs), following consumption of a high-fat meal. Previous studies have found that monocytes are important for blood vessel health. In this study, two different high-fat meals will be used to study the effect of different types of dietary fat on postprandial NCMs. The investigators will characterize NCMs in both fasting conditions and following consumption of two different high-fat meals, and will evaluate whether the type of fat in a meal affects NCMs in blood.

Monocytes are a heterogeneous population of circulating blood cells that contribute to tissue integrity as well as to innate and adaptive immune defense. There are three well-characterized subsets based on their relative expression of surface antigens, cluster of differentiation 14 (CD14) and cluster of differentiation 16 (CD16). Monocytes originate from myeloid precursors in the bone marrow and enter the circulation as classical monocytes (CLMs). CLMs represent a transient cell population with a diverse differentiation potential. CLMs comprise 80-90% of the circulating blood monocyte pool and remain in circulation for approximately one day before either migrating into tissue to repopulate the tissue resident macrophage population or maturing into non-classical monocytes (NCMs). NCMs comprise only 5-10% of the circulating blood monocyte pool but have a much longer circulating lifespan of approximately 7 days. NCMs exhibit conflicting functions as anti-inflammatory caretakers of vascular tissue and as contributors to the pathogenesis of disease.

Metabolic responses to food consumption influence the risk of cardiometabolic disease. Postprandial glycemia and lipemia modulate vascular health by altering endothelial function and inducing oxidative stress, inflammation, and apoptosis. Consumption of a single high-fat meal increases circulating interleukin 6 (IL-6), enhances expression of monocyte adhesion molecules, reduces flow-mediated dilation, and increases markers of oxidative stress in human subjects. Although NCMs are described as vascular housekeepers with distinct motility and crawling patterns allowing them to actively surveil endothelium and scavenge luminal debris, their role in the postprandial state is currently unknown.

To better understand the function of postprandial NCMs following consumption of a single high-fat mixed macronutrient challenge meal, the investigators propose a study following a crossover design in which participants will consume one of two isocaloric high-fat challenge meals spaced two-weeks apart, a high-saturated fat mixed macronutrient challenge meal or a high-monounsaturated fat mixed macronutrient challenge meal. Blood at fasting and at six hours postprandial will be collected and the proportion of NCMs and their integrin expression will be analyzed by flow cytometry while changes in global gene expression will be measured by RNA-sequencing.

Inclusion Criteria:

• BMI 18.5 - 29.9 kg/m²
• have a bank account and social security number or taxpayer identification for financial compensation

Exclusion Criteria:

• Pregnant or lactating women
• Known allergy or hindering intolerance to study meal ingredients
• Systolic blood pressure greater than 140 mmHg or diastolic blood pressure greater than 90 mmHg measured
• Fasting glucose above 105 mg/dL
• Triglycerides above 150 mg/dL
• HDL cholesterol less than 40 mg/dL (men) and 50 mg/dL (women)
• Self-reported history of difficulties with blood drawing procedures including prior fainting or dizziness, or veins assessed as not suitable for four separate venipunctures by licensed phlebotomist
• Diagnosed active chronic diseases for which the individual is currently taking daily medication, including but not limited to Diabetes mellitus, Cardiovascular disease, Cancer, Gastrointestinal disorders, Kidney disease, Liver disease, Bleeding disorders, Asthma, Autoimmune disorders, Hypertension, Osteoporosis
• Recent minor surgery (within 4 wk) or major surgery (within 16 wk)
• History of gastrointestinal surgery, including gastric bypass surgery or resection
• Recent antibiotic therapy (within 4 wk)
• Known gallbladder disease or history of cholecystectomy
• Recent hospitalization (within 4 wk)
• Use of prescription medications at the time of the study that directly affect endpoints of interest (e.g. hyperlipidemia, glycemic control, steroids, statins, anti-inflammatory agents, and over-the-counter weight loss aids)
• Current participation in another research study
• Less than 18 and over 39 years old
• BMI less than 18.5 and above 29.9 kg/m²
• Has HIV/AIDS or another disease that affects the immune system
• Unable to fast for 12 hours
• Gives regular blood donations and is unwilling to stop during the study
• Has monocytosis (>0.8 x 10³/microliter) or other abnormalities in hematologic parameters based on a screening complete blood count (CBC) with differential