Translation:You will have to eat with less sugar starting today.
What happens if you change sugar with salt: You will have to eat with less salt starting today.? The meaning in spanish is that you have to put less sugar (salt) i your meals, it is not excatly no to eat sugar as a thing.
Other mistake in the translation is the use of 'starting', the meaning is quite the same, but if you use starting the sentence in Spanish should be 'Tú tendrás que comer con menos azúcar empezando hoy.'. I think the translation into English is 'You will have to eat with less sugar from today'
Okay I'm going to invent a term here. This is what I would call an "explicative translation". What you want is what I would call a "normative translation". Explicative translations are very helpful when you are reading the Spanish and saying, " okay what does this word mean? What is its function?" Normative translations would be saying this is an what American might typically say who was in a good mood this morning when he woke up and was on his best behavior.