Increases in the levels of sex steroids due to pregnancy or oral contraceptive steroid use are known to decrease significantly the rate at which caffeine is eliminated from the body. An investigation has now been made into whether the changes in sex steroid levels that occur during normal menstrual cycling also affect the rate of caffeine elimination, especially whether hormonal shifts in the luteal phase are associated with slower elimination of caffeine. Repeated 24-hour caffeine elimination studies were conducted during the follicular and luteal phases of the menstrual cycle in 10 healthy women. Comparisons of the follicular and luteal phases revealed that systemic clearance of caffeine was slower in the luteal phase, although the t1/2 did not differ. The slowing effect was related to the proximity to onset of menstruation and to levels of progesterone. The evidence suggests that caffeine elimination may be slowed in the late luteal phase, prior to the onset of menstruation. Such a reduction would lead to increased accumulation of caffeine with repeated self-administration during the day, but the effect may be too small to be of clinical significance in the majority of women.
Subcutaneous adipose tissue (SAT) dysfunction is key in defining high-risk individuals in obesity. A change in adipose tissue water fraction with weight loss may reflect improvement in blood flow or changes in microstructure of adipose tissue. Single-voxel STEAM Magnetic Resonance Spectroscopy (MRS) and chemical shift encoded-based water-fat separation are non-invasive methods to assess the water fraction and proton density fat fraction (PDFF) of adipose tissue. The present work aims to investigate the feasibility of MRS and water-fat separation to quantify PDFF and evaluate the changes in SAT water fraction in persons with obesity undergoing an 8-week weight loss intervention.
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