Regardless of the type, to get the best quality, select winter squash that are blemish-and bruise-free, with an intact stem and heavy feeling for their size. Naturally low in fat and calories, the winter squash family delivers significant nutritional benefits.For example, one cup of baked butternut squash is rich in vitamins A (from beta carotene), B6, C, and E, as well as magnesium, potassium, and manganese.aturally low in fat and calories, the winter squash family delivers significant nutritional benefits. For example, one cup of baked butternut squash is rich in vitamins A (from beta carotene), B6, C, and E, as well as magnesium, potassium, and manganese.