It is widely believed that heating up food kills all its enzymes and nutritious value, so one should prefer eating their food raw.
But practically speaking, taking only raw food will deprive you of essential nutrients like protein, calcium, iron, and certain vitamins like B-12, since they are mainly obtained from animal sources, which can't be consumed completely raw.
Skipping meals/fasting: Skipping meals, in order to lose weight is a disastrous thing to do, as it ultimately slows down your metabolism, and may even lead to unexpected hunger pangs, thereby inducing overeating later on.
Avoiding fats: It's the same rule as with carbohydrates. Not all fats are bad. Healthy fats, as in nuts, seeds, yogurt, olive oil, and milk must be taken.