The Fasting Study - Unraveling the Mechanistic Effects of Prolonged Fasting in Humans.

Rationale: Elevated levels of plasma triglycerides are increasingly recognized as an important causal risk factor for cardiovascular disease and associated pathologies. Lowering plasma triglycerides may therefore be a therapeutic target to lower cardiovascular disease risk. Lipoprotein lipase (LPL) is the enzyme that catalyzes the hydrolysis of plasma triglycerides into fatty acids on the capillary endothelium, thereby lowering plasma triglycerides and stimulating the uptake of these fatty acids into cells. Angiopoietin-like 4 (ANGPTL4) is produced by fat cells and promotes the unfolding and inactivation of LPL, leading to decreased hydrolysis of plasma triglycerides. The role of ANGPTL4 in regulating LPL is especially important during fasting. However, as most studies are performed in animal models, little is known about the effects of fasting on adipose tissue metabolism in humans, and specifically on ANGPTL4 and its relationship with LPL.

Objectives: The key objective of this study is to determine the effect of a prolonged fast on ANGPTL4 gene and protein expression in subcutaneous adipose tissue, the key organ involved in lipid metabolism. Additionally, the effect of a prolonged fast on LPL gene expression, LPL protein expression, and on LPL activity in subcutaneous adipose tissue will be examined. To explore the systemic effects of a prolonged fast, the investigators will also measure ANGPTL4 levels in plasma, and ANGPTL4 and LPL gene expression in circulating immune cells (PBMCs). The secondary objective of this study is to obtain a more holistic view on the changes occurring upon a prolonged fast, by examining the effects of fasting on whole genome expression, post-transcriptional changes, and on markers of metabolic status. The combined results of all measurements will ultimately lead to a better understanding of the mechanistic effects of a prolonged fast and the metabolic functioning in humans.

Study design: The Fasting Study is a single arm intervention study in healthy men and women. The investigators will examine the effects of a fed state, which is 2 hours after the last food intake, versus a prolonged fasted state, which is 26 hours after the last food intake. Adipose tissue biopsies and blood samples will be taken 2 hours after the last meal and 26 hours after the last meal. The 24 hours between sampling points are chosen to prevent effects of the circadian rhythm.

Study population: The study population will consist of 24, 40-70 years old men and women with a BMI of 22-30 kg/m2, selected from the surroundings of Wageningen through the mailing list for potential study research subjects of the division of Human Nutrition and health of Wageningen University. If needed, additional recruitment of research subjects will take place by flyers and posters, or advertisements in local newspapers.

Intervention: All research subjects will start with the consumption of a standardized meal (ad libitum). Directly thereafter the intervention begins, which is a fasting period of twenty-six-hours, during which research subjects are not allowed to eat or drink anything except for water, which the research subjects may consume ad libitum. The investigators will take the first blood samples and adipose tissue biopsies two hours after the consumption of the standardized meal. This is the fed state: the point in time where the body is physiologically fed, based on the average time for plasma free fatty acids to drop. Twenty-four hours after the "fed state", research subjects are in the prolonged fasted state, and the investigators will take the final blood samples and adipose tissue biopsies. The time period of twenty-four-hours between sampling points is chosen to prevent the effects of circadian related changes on our outcome measures.