When following the cabbage soup diet seven day plan, a multi-vitamin is recommended by Catherine at the Cabbage-Soup-Diet website. Healthline reports a multi-vitamin is encouraged, although the creator of this diet is unknown and many versions exist. This diet is not nutritionally balanced according to Healthline.
Due to the low amount of protein, complex carbohydrates, vitamins and minerals in the cabbage soup diet, Katherine Zeratsky, R.D., L.D. of Mayo Clinic recommends staying on the diet no longer than one week. She also states that adherents of the diet may feel weak or tired due to the lack of proper nutrition.