Cafestol is a naturally occurring diterpene found in unfiltered coffee beans. Unlike most other coffee components, cafestol is not readily absorbed by the human body and can accumulate in the bloodstream. While research is ongoing, the potential health effects of cafestol are still being investigated.
Some studies suggest that cafestol may have antidiabetic properties. A study published in Pure found that cafestol increased glucose uptake in human skeletal muscle cells and glucose-stimulated insulin secretion in vitro. The researchers also found that cafestol supplementation in mice fed a high-fat diet helped to delay the onset of type 2 diabetes. https://pubmed.ncbi.nlm.nih.gov/28763212/
However, other studies have shown that cafestol may increase LDL cholesterol levels, also known as "bad" cholesterol. This is because cafestol inhibits the reabsorption of bile acids in the intestine, which leads to increased production of LDL cholesterol by the liver.