Low-carb diets like keto may reduce sugar intake but without adequate hydration or minerals, saliva flow in mouth can drop. "This can increase risk of cavities, periodontal disease, and bad breath," Swati Mohapatra, Chief Dietitian at Bhubaneswar's Manipal Hospital said. Meanwhile, vegan diets may lead to reduction in vitamin B12, calcium, and vitamin D, essential for strong teeth and gums.