For a diabetic patient looking to gain weight safely, I recommend choosing an unsweetened whey protein isolate, pea protein, or soy protein isolate. These options are high in quality protein but very low in carbohydrates, which helps prevent blood sugar spikes. To support weight gain, you can increase the calorie content by mixing the protein powder with healthy fats, such as a spoonful of almond butter, ground flaxseeds, or unsweetened soy milk, rather than using high-carb mass gainers. Please consult your physician or a registered dietitian to tailor a plan specific to your health needs.