@zand, (sorrry folks this is really going off topic)
I don't think anyone really knows why. So here's a post of speculation with a few facts (ie my thoughts)
I do know that some low carb supporting doctors suggest that1/3 to a quarter see at least some sort of rise in LDL .(that's just a guestimate, based only on what a very few doctors see )
We are all individual, we have variations in our genetic make up which means some people react to something that others don't . For example if you don't have the gene variation that allows people to produce lactase past childhood you will get very ill if you drink milk. This is an interaction between the genes of the individual and the environment .(have a look at
PKU for another very rare but very serious diet/gene interaction. ) Most interactions aren't nearly as clear cut as these
There is a suggestion that some variations of gene called APOE makes people more susceptible to high cholesterol (and to high fat levels in the diet making it worse).
http://www.gbhealthwatch.com/GND-High-Cholesterol-APOE.php (I'm not endorsing the recommendations as they are a bit speculative but it does explain something about the gene variations involved)
It probably isn't the whole answer (lots of genes interact with each other so it almost certainly isn't one gene alone. Secondly it may not just be fat alone , it could be that in eating more fat then, in some cases, other nutrients are displaced from the diet .
Differences before and after adopting any diet must also depend on what the person was eating before.
I've linked to this before, it's long but if you skip to the bottom does show that slight changes in diet seems to have made a difference.
http://www.lowcarbdietitian.com/blo...ery-low-carb-ketogenic-diet-my-own-experience