Genetics plays a very large factor in fat and cholesterol metabolism, and one that I think explains the variance in success with the ketogenic diet.

e.g. FTO, PPARG, APOA5, FABP2, and APOE.

Essentially, not everyone processes fat the same way, and for some, especially those with APOE4/4, a high fat diet may actually be deleterious to health.

People with the right genes will have great success with ketogenic diets... but convincing their friends to join in might not have the outcome they expect.