One low-calorie vegetable is allowed with both lunch and dinner. Choices include spinach, chard, chicory, beet greens, tomatoes, celery, fennel, onions, red radishes, cucumbers, asparagus, and cabbage. Most of the veggies are packed with vitamins and other nutrients, which is particularly important on such a restrictive diet. Spinach, for example, is rich in fiber, vitamins A and C, and iron, and even contains some protein. Veggies mustn't be topped with oil, butter, or sauce.