Potential downsides of high-carb diets include risks of weight gain and increased blood sugar levels, particularly from consuming large amounts of refined carbohydrates. Such diets can lead to energy crashes and cravings for more carbs, perpetuating a cycle of overeating. High-carb diets may also contribute to inflammation and negatively affect metabolic health. Balancing carbohydrate intake with protein and healthy fats is essential for maintaining energy levels and overall health.