Is eating food from fast food such as macdonalds, kfc, etc. Cause pimples?

Acne and food. Acne is usually caused from increased oil or sebum production under hormonal influences. Greasy foods are not typically linked to acne flares. A well balanced diet with exercise is always a good idea. See a dermatologist for acne treatment.
No. There have actually been some scientific controlled studies and there have discredited this widespread idea. Acne follows the skin getting greasier (more sebum) at puberty & this is how the idea got started; there's also a tendency to blame things that people like (fast food) when bad things happen. Think about healthier eating choices to stay fit & trim.. All acne is manageable today; ask ur dr.