http://www.gnolls.org/1763/why-humans-crave-fat/

http://universe-review.ca/R10-35-metabolic.htm

it’s because animal fat is the primary constituent of the evolutionary human diet. “Low-fat” diets just make us crave fat more keenly—and anti-animal-fat propaganda makes us binge on unsatisfying substitutes.

Fruit Isn’t Enough: Leaving The Equatorial Forests Humans are (mostly) fruit-eating chimpanzees who have become meat-eating, predatory omnivores, most likely due to the pressures of massive and continual climate change throughout the Pleistocene. Our continually shifting environment strongly selected for physical adaptations and behavior that let us survive outside the equatorial tropical forests of Africa.

How did this happen?

Well, first we had to adapt to eating something besides fruit, because fruit is only available year-round in tropical forests. We needed to eat something available year-round on the savanna and plains, in wet and dry seasons, in cold and warm seasons.

We needed to eat meat.

Fortunately we had a head-start: chimpanzees already eat meat.chimpanzees already eat meat.

Please read the article before post an answer, Or crossread it! The quote is just to give you a short view to the article. The article is more complex and have some nice discussion on the why we eat fruits and why we eat fat and meat.