Yes at normal portions. Rutabaga root grades A on total FODMAPs and clear on polyols, GOS and excess fructose, with fructans the only subgroup at a moderate mark. That profile is why swede mash is a standard potato substitute on low FODMAP plans, and it is a genuinely better pick than cauliflower mash, which is high in mannitol. The limit is quantity: fructans accumulate, so a side portion behaves very differently from a bowl of swede eaten as the whole meal.

Only if you count the portion honestly. Cutting rutabaga into fries or noodles turns a side vegetable into the bulk of a plate, and people routinely eat three or four times the amount they would have eaten mashed. The grades describe the vegetable, not the serving, and the moderate fructan mark is the one that compounds. If low-carb swaps have coincided with new bloating, the swap is worth logging by weight rather than by dish for a week.

You can, and shredded raw swede turns up in slaws and juices, but raw is the harder version for a sensitive gut. Cooking breaks down some of the fibre and deactivates much of the enzyme that converts the plant's glucosinolates into their goitrogenic breakdown products, so a large daily raw intake is the only scenario where the brassica goitrogen question becomes practical, and mainly if your iodine intake is already low. Raw also means a bigger volume of unbroken plant matter for the same weight, which tends to show up as gas.

No. Rutabaga is a brassica, in the cabbage family, and grades A for nightshade. That makes it one of the more useful potato replacements on a nightshade elimination, since it roasts, mashes and fries in roughly the same way without bringing glycoalkaloids with it. It is also clear on gluten, lactose, dairy protein and histamine content, so it survives most eliminations at once.