The bioaccessibility, metabolism, and excretion of lipids composing spent coffee grounds (SCGs) were investigated. An analysis of mycotoxins and an acute toxicity study in rats were performed for safety evaluation. Total fat, fatty acids, and diterpenes (cafestol and kahweol) were determined in SCGs and their digests obtained in vitro. A pilot repeated intake study was carried out in Wistar rats using a dose of 1 g SCGs/kg b.w. for 28 days. Fat metabolism was evaluated by analysis of total fat, cholesterol, and histology in liver. The dietary fiber effect of SCGs was measured radiographically. The absence of mycotoxins and toxicity was reported in SCGs. A total of 77% of unsaturated fatty acids and low amounts of kahweol (7.09 µg/g) and cafestol (414.39 µg/g) were bioaccessible after in vitro digestion. A significantly lower (p < 0.1) accumulation of lipids in the liver and a higher excretion of these in feces was found in rats treated with SCGs for 28 days. No lipid droplets or liver damage were observed by histology. SCGs acutely accelerated intestinal motility in rats. SCGs might be considered a sustainable, safe, and healthy food ingredient with potential for preventing hepatic steatosis due to their effect as dietary fiber with a high fat-holding capacity.

Relatively little is known about the influence of sex and the circadian rhythm on gastrointestinal transit. However, these factors could have an important impact on aspects such as digestion, oral absorption of drugs or the clinical manifestation of gastrointestinal diseases, among others. Remarkably, preclinical models have scarcely taken these factors into consideration. In this study, we assessed the gastrointestinal transit of young adult Wistar Han rats of both sexes, under normal and inverted light cycle. To do this, serial radiographs were taken for 24 h (T0–T24) after intragastric barium administration and subsequently analysed to construct transit curves for each gastrointestinal region. Under a normal light cycle, transit curves were similar, except for a slower transit in females compared with males from T8 to T24. Under the inverted cycle, there was a significant acceleration in stomach emptying (similar in both sexes), emptying of the small intestine (even faster in females) and filling of the caecum and colon (which was also even faster in females). This study confirms, using X-ray non-invasive methods for the first time, that both sex and circadian rhythm (probably through its effect on behaviour) influence gastrointestinal transit in laboratory animals.

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