I understand that short-chain fatty acids (a product of fermentation of fibre within the colon) suppress cholesterol synthesis in the liver by lowering levels of LDL and triglycerides in the blood.
How does fibre lower levels of LDL and triglycerides?
There is more to fibre than "roughage".
Dietary Fiber, by it's definition is undigestible fiber, thus it's main form of action is in the form of a physical cleaner, binding to fat molecules, and cleaning your intestinal system (think of a scrub running through your intestine system). Thus, it indirectly lowers your fat intake and decreases LDL and triglycerides.