It's not good to eat vegetables that are high in sugars.
It's not good to eat vegetables that have a lot of sugars.
ご質問ありがとうございます。
「糖質」はsugar(s)と言います。食べ物に入っている糖類が様々にありますので、普通に複数形（sugars）にしています。「糖質が多い」はhave a lot of sugarsと言いますが、専門的な言い方はare high in sugarsです。例えば、Bread and pasta are high in carbohydrates.（パンとパスタは炭水化物が多いです。）
ご参考いただければ幸いです。
"It's better not to eat too many high-carb vegetables."
"It's better not to eat too many high-carb vegetables."
"You shouldn't overeat vegetables that are high in carbs."
"For dieting, it's probably best not to go overboard on high-carb vegetables."
"Should I avoid eating too much of high-carb vegetables like onions and carrots?"
"Even with vegetables, you may want to watch your carb intake."
・It's better not to eat too many high-carb vegetables.
better not to で「〜しない方がいい」です。
too many が入るので「食べ過ぎない」がちゃんと出ます。
アメリカ合衆国 
