There are a few potential side effects associated with the cabbage soup diet. These include: 1) Feeling lightheaded or dizzy. 2) Feeling nauseous or sick. 3) Excessive gas. 4) Diarrhea. 5) Constipation. If you experience any of these side effects, stop the diet and speak to your doctor. Cabbage soup is not right for everyone, and it's important to make sure it's safe for you before starting it.