Bananas and sweet potatoes can lose weight together. Banana contains starch, protein, vitamin B, vitamin E and vitamin C, while sweet potato is rich in starch and vitamin A. Eating both foods at the same time can easily affect gastrointestinal digestion, cause abdominal distension, and may be accompanied by gastric acid reflux. Excessive consumption can easily lead to food staying in the stomach for too long, resulting in stomach toxicity, and even serious chronic poisoning.