To gain weight healthily, focus on a consistent calorie surplus with nutrient-dense foods. Eat 5 to 6 meals daily, incorporating lean proteins (chicken, fish, eggs) for muscle growth, complex carbohydrates (oats, sweet potatoes) for energy, and healthy fats (avocados, nuts, olive oil) to boost calories. For supplements, a high-quality whey or plant protein powder can help meet daily protein goals. A daily multivitamin can support overall metabolism. Avoid heavy 'mass gainers' which are often high in added sugars. Please consult a registered dietitian or your doctor to design a personalized plan and ensure these supplements are safe for you.