The overall purpose of the study is to investigate whether three weeks of intermittent fasting (alternate-day fasting, (ADF)) result in a more pronounced "metabolic shift" towards the use of ketone bodies than three weeks of Western diet. The investigators will use state-of-the-art PET/CT tracer techniques and well-established steady state kinetics methods for glucose and fatty acids. The study results will provide new insights into the physiological basis of the potential cardio-protective effects of ketone bodies during ADF and will determine whether ADF can help prevent and treat heart failure. Ketone bodies are produced in the liver as an alternative fuel when blood glucose levels are low, as can be seen with various types of diets or after strenuous exercise. The energy produced by breaking down ketone bodies has been shown to require less oxygen than breaking down glucose and fatty acids. In a previous study, the investigators observed that ketone bodies act as a kind of "super fuel" for the heart and improve the heart's energy utilization. It is still unknown how high ketone levels are needed to see these cardio-protective effects. As patients with insulin resistance and/or heart failure have a lower glucose uptake in cardiac tissue, and as energy production by the breakdown of fatty acids is oxygen-demanding, an elevated level of blood ketones can therefore potentially reduce the morbidity seen in patients with type 2 diabetes and ischemic heart disease. PET/CT is a non-invasive well-established imaging modality suitable for tracking the fate of metabolites, as most substances or metabolites can be labeled by a suitable PET isotope. PET has sufficient spatial and temporal resolution to enable direct quantification of e.g. uptake and oxidation rates and has been successfully used by the investigators' department to assess heart efficiency, oxygen consumption, and fatty acid metabolism. Currently, the investigators are in the process of validating the PET tracer 11C-beta-hydroxybutyrate (11C-3-OHB) as a radio tracer for human studies. The tracer will be able to detect changes in biodistribution and kinetics of ketone bodies during both Western diets and ADF. The subjects must go through two study periods of each 3 weeks in which the intervention is western diet (no restrictions) and intermittent fasting (fasting every other day), respectively. After both study periods, there will be an examination day with PET scans and various laboratory examinations.
Age range
55 Years – 70 Years
Sex
ALL
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Change in cardiac uptake and metabolism of hydroxybutyrate
Timeframe: The PET/CT scan will be performed on the study day after each 3-week study period (day 22 and 51).
Change in myocardial perfusion and flow reserve
Timeframe: The PET/CT scan will be performed on the study day after each 3-week study period (day 22 and 51).
Change in insulin sensitivity in skeletal muscle, liver and adipose tissue
Timeframe: The clamp will be performed on the study day after each 3-week study period (day 22 and 51).
Change in cardiac uptake and metabolism of fatty acids
Timeframe: The PET/CT scan will be performed on the study day after each 3-week study period (day 22 and 51).
Change in cardiac uptake and metabolism of glucose
Timeframe: The PET/CT scan will be performed on the study day after each 3-week study period (day 22 and 51).
Change in cerebral perfusion
Timeframe: The PET/CT scan will be performed on the study day after each 3-week study period (day 22 and 51).