That's backwards too, or should I say, that's an opinion that is not supported by better science. If you keep your saturated fat as low as they say to (7%?) you can't possibly get in all the nutrients you need from food. Regina Wilshire showed this in her blog and it was very interesting.

If you keep your saturated fat low, that means you have to fill in with inferior fats. But mono oil might not be so bad.

The goodness of fat goes like this:

best for humans - = saturated
next best = monosaturated
not so good = polyunsaturated

It's because saturated fat is also used to make our hormones and all our machinery running properly. Next best is monosaturated because it's almost saturated. The problem with polyunsaturated fat is, it oxidizes easily in us and before we eat it, and oxidized fat is bad.

Most low carb writers think that the big 3 bad things are wheat, fructose, and vegetable oil (polyunsaturated fat).