pizza is high in carbohydrates and it is therefore not healthy to eat in typical american quantities.

fats, especially saturated fats, are the fuel that your body is actually genetically designed to run on as the primary fuel. not carbohydrates, these are secondary.

no matter how much you weigh,
- eating fewer than 50g of carbs per day will trigger weight loss.
- eating 50g to 100g, for most people, will maintain bodyweight.
- eating over 100g of carbs is almost definitely certain to cause weight gain, diabetes, and/or heart disease.

the sedentary lifestyles most americans live calls for perhaps only 900 to 1200 calories, again depending on weight and the size of your frame. you will maintain bodyweight if you do not overeat relative to caloric intake.

however.

if you get all 1200 (for example) of your calories from foods loaded with carbohydrates, and you ALSO consume ANY fats, you will NOT convert those fats to energy. you will store them and they will cause insidious weight gain, and eventually, cardiovascular diseases or chronic/permanent cardiovascular damage.

https://en.wikipedia.org/wiki/Ketosis
https://en.wikipedia.org/wiki/Glycolysis