Learn Spanish (Latin America): Para un cuerpo saludable, debes evitar el azúcar. - For a healthy body, you must avoid sugar.

When you use deber to state an obligation or give advice, the action verb that follows it always stays in its infinitive (unconjugated) form. That is why we say debes evitar (you must avoid), not debes evitas.

Why do we use Para at the beginning of this sentence instead of Por?

Para is used here because it points to a goal or an objective. In this case, the goal you are aiming for is un cuerpo saludable (a healthy body).

Why is it el azúcar when the English translation just says "sugar" without "the"?

In Spanish, when you talk about a general concept or an entire category of things, you must include the definite article (el, la, los, or las). Because this sentence is about sugar in general, it requires el.

Does debes mean "you must" or "you should"?

It can mean both! Depending on the context, debes acts as a strong obligation ("you must") or firm advice ("you should"). If you wanted to sound softer, you would use the conditional form deberías, but debes is perfectly normal for giving firm health advice like this.