Most tests for parasites come back negative because live parasites cannot be eliminated. Most of what you see is only pin worms that will come out on the outside of the body at night to lay their eggs. If we have one parasite, it's mostly concurred around the zone here that you have at least six different kinds. If you can find a medical doctor who will admit 99% of the population world wide has parasites, good luck. If you get on and stay on a good parasite killer, you're probably going to see parasites. Then colon cleansing will rid you of the eggs as well as the adult parasites there and in the liver. The bug eggs will go through the digestive tract through the blood stream to the liver.
If you have a sluggish liver when you can't tolerate fats --if you do some liver flushes-- you will have a lot of fat coming out of the liver. But that shouldn't go on for very long. It shouldn't be long before you can tolerate some fat again, but make it only saturated animal far or some of the good plant oil fats and butter, not unsaturated fat or stuff you buy in the store for cooking.
The companies who make herbal cleansers you'll find on the market usually do have an inferior product. I'd say it's best to find a good master herbalist and buy their products which is usually in liquid form. http://www.oldfashionedspices.com
is a reputable herbalist I used that netted me about 10# of parasites and liver stones out of only the liver after around 140 liver flushes.
Any type of drugs or OTC drugs, too, will cause the liver to slow down. My liver was on the verge of shutting down when I started flushing it out. Over time the functioning ability of it will came back, but it took me several years of persevering and working on things, so patience is needed.