This product has the same amount of fiber you would get in a whole head of lettuce.
The amount of fiber in this product is equivalent to the amount of fiber found in one head of lettuce.
1) This product has the same amount of fiber you would get in a whole head of lettuce.
「この商品には、レタス一個分で摂取する量の食物繊維と同じ量が入っている。」
the same amount of fiber you would get in ... で「…で摂取する同量の食物繊維」
「レタス１個分」は a whole head of lettuce
2) The amount of fiber in this product is equivalent to the amount of fiber found in one head of lettuce.
「この商品の食物繊維量はレタス一玉分の食物繊維量と同量です。」
... is equivalent to ~ で「…は〜と同量・同価値です」という言い方です。
ご参考になれば幸いです！
日本 
