"Cholesterol levels" is a blunt term to use, there are HDL, LDL (with different particle sizes) etc.
Correlation != causation
"The total body of evidence suggests that attention should
be shifted from the harmful effects of dietary SAFA per
se, to the prevention of the accumulation of SAFA in
body lipids. This shift would emphasise the importance
of reducing dietary CHO, especially CHO with a high
glycaemic index, rather than reducing dietary SAFA"
"A meta-analysis of prospective epidemiologic studies showed that there is no significant evidence for concluding that dietary saturated fat is associated with an increased risk of CHD or CVD"
Although serotonin is well known as a brain neurotransmitter, it is estimated that 90 percent of the body's serotonin is made in the digestive tract. In fact, altered levels of this peripheral serotonin have been linked to diseases such as irritable bowel syndrome, cardiovascular disease, and osteoporosis.