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Purpose of review 

Conventional knowledge holds that saturated fat is the primary dietary driver of increases in low-density lipoprotein-cholesterol (LDL-C), and that high LDL-C seen among some persons consuming low-carbohydrate, high-fat diets is driven by increased saturated fat intake. This simple paradigm cannot account for the lipid patterns, nor for the magnitude of effect, observed in ‘lean mass hyper-responders’ on low-carbohydrate diets. The Lipid Energy Model (LEM) provides an alternative explanation for LDL-C increases seen in persons without obesity who adopt ketogenic diets and makes testable predictions, including that acute overfeeding, including increased saturated fat consumption, would decrease LDL-C levels.

Recent findings 

This study reports data from an n = 1 experiment, performed in duplicate, in which the subject consumed three ketogenic diets for 5 days that varied in caloric content: weight-maintenance (2278 kcal/day), hypo-caloric (1135 kcal/day), and hyper-caloric (4116 kcal/day). Consistent with the LEM, LDL-C and apolipoprotein B increased following caloric restriction and decreased following overfeeding, despite increased saturated fat consumption. Data from a case series of 24 individuals who underwent similar protocols similarly found that overfeeding on a ketogenic diet decreased LDL-C.

Summary 

This n = 1 study and associated case series provide data that short-term overfeeding can lower LDL-C in the context of carbohydrate restriction.

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Each of us an n=1 experiment waiting to be documented

Measure vldl next time. More important risk factor than ldl.

It will inherently be lower as well, as high fat ketogenic diets lower triglycerides as well and vldl is directly connected to triglyceride levels.

There's at least one genotype that can't handle high fat diets, hyper fat absorbers. A high fat diet for these people would promote obesity, diabetes, CVD, etc. And their blood work would get worse. For this genotype a low fat diet is advisable.

But for everyone else, it doesn't matter much. Healthy people meticulously regulate fat intake by various means. Low fat absorbers just poop most of the fat out. Really, for most people, (besides trans fats) it just doesn't matter much as long as you have a good balance of (mono)(un)saturated fats and get your essential omegas.

What most people could use more of is fiber and vegetables. Very solid way to lower trigs and cholesterol and it works regardless of genotype.

Can someone ELI5?

They fed one person a couple high fat diets and it lowered cholesterol a little bit.

That's not anyone. That person is a LMHR (lean mass hyper-responder). His LDL went from 225 on "normal" diet to 280 eating fewer calories and to 190 eating higher calories. (And they discuss 20+ people with similar results.)

Not only does this provide evidence of the LEM (lipid-energy model), but it also shows how variable LDL is. I've had LDL change in 3 days. (Fasting 4.5 days caused my LDL to increase significantly; eating high calorie, high saturated fat -- cups of cream -- caused my LDL to plummet.)

And it is yet more evidence that eating higher saturated fat can DECREASE LDL, not increase it.

Actually, fiber and vegetables cause me all kinds of issues. IBS, constipation, you name it. I think most people should be on a low fiber and vegetable diet.

Maybe just worry about yourself and avoid prescriptions for others.