Vitamin B12 deficiency can cause symptoms such as fatigue, weakness, and nerve-related problems, but it is not usually a direct cause of weight gain. Weight gain is more often related to diet, physical activity, or other metabolic factors. Maintaining a balanced diet and regular exercise may help manage body weight. Consult a doctor to monitor your vitamin B12 levels and guide proper treatment.

Vitamin B12 deficiency can sometimes cause weakness, mouth ulcers, or digestive discomfort. A balanced diet with foods rich in vitamin B12, such as dairy products, eggs, and fortified foods, may help improve levels. Proper treatment may require supplements if the deficiency is confirmed by tests. Consult a doctor for evaluation and appropriate treatment.