The sour cabbage slivers you pile on your hot dog don't appear to have any nutritional cred, but hear us out. Sauerkraut is fermented, and fermented foods have probiotic powers, meaning they naturally crank up levels of good bacteria in your gut. "That improves digestion and keeps your GI tract healthy," says Lamm. Sauerkraut is also low in calories and high in immune-boosting vitamin C. If you're not a fan, load up on its spicy Korean cousin, kimchi. Research on the probiotic effects of packaged foods is mixed, so to ensure you get the gut-boosting benefit, stick to raw or homemade sauerkraut.