Good question. Imagine plants feel pain like other animals and like we do. If our objective is to avoid suffering and environmental damage as much as possible, which one would you choose:

1) Eat animals and plants. Remember the animals you eat also eat plants. This creates maximum suffering and damage.

2) Eat plants only. This creates less suffering and damage than option 1.

To answer your question though, if it's scientifically proven that plants are sentient and feel pain like we do (i.e. suffer) then I would only eat what plants produce (e.g. nuts, legumes, apples, etc) rather than the plant itself (e.g. carrots).