Learn Hardcore Japanese: ama mono wo takusan taberu to hutorimasu. - If you eat a lot of sweets, you will gain weight.

The particle を marks the direct object of the verb 食べる. In 甘い物を食べる, 甘い物 (“sweets” or “desserts”) is what’s being eaten, so を shows it is the object.

What role does たくさん play in this sentence? Is it modifying 甘い物 or 食べる?

Here たくさん is an adverb meaning “a lot,” and it modifies the verb 食べる. So たくさん食べる means “eat a lot.” If you wanted to modify a noun, you’d say たくさんの甘い物.

How does the particle と function here? It looks different from たら or ば.

と after a verb in dictionary form expresses a general, inevitable consequence: “Whenever/if you do X, Y always happens.” So 食べると太ります means “If/when you eat (a lot), you (inevitably) get fat.”

Could you use たら or ば instead of と? What’s the nuance difference?

Yes.

たら: たくさん食べたら太ります is “if/when you eat (in that situation) a lot, you’ll get fat,” somewhat more situational.
ば: 食べれば太ります is also possible but sounds a bit more hypothetical or formal.
と is best for stating a general rule or natural law.

Why is 太ります in the polite -ます form? Can it be plain form?

Using ます (太ります) makes the sentence polite. In casual speech, you’d drop the ます and say 甘い物をたくさん食べると太る. Use polite vs. plain based on your audience.

I noticed it’s written 甘　物 without the い in 甘い. Is that a mistake?

Yes—i-adjectives require their okurigana (い). The correct spelling is 甘い物 (あまいもの). The example’s spacing is just for separating words; always include い.

Is 甘い物 the same as お菓子? Which should I use?

They overlap in meaning:

甘い物 literally “sweet things” (desserts, sweets).
お菓子 means “snacks/candy/pastries.”
You can use either: お菓子をたくさん食べると太ります is perfectly natural.

Why do we say 太る instead of 太くなる for “get fat”?

太る is the standard verb for “gain weight” or “get fat.” 太くなる (“become thick”) is usually used for objects or body parts (e.g. “the rope got thicker”). For a person’s weight gain, always use 太る.