Of course, it's not good for a girlfriend to be too thin. A girlfriend BM≤ 18.5 is just too thin. How to calculate? Body mass index equals weight/height/height. For example, my height 168cm and my weight are 54kg. My body mass index is 54 ÷1.68 ÷1.68 =19.1,so I am not too thin. Too thin girls are prone to anemia, lack of certain nutrients, and lack of protein. In severe cases, hair loss and dull skin will occur. So, as a boyfriend, do you want to fatten her up? That's only half right. It is best to increase muscles, need to supplement enough protein and physical activity, and it is best to have strength training. Eat some chicken breast, lean beef, egg white, fresh shrimp and fish, all of which are high in protein and low in fat. In addition, you can also eat some protein powder and cooperate with dumbbells, squats, aerobics, swimming and other sports. It is easier to realize that both muscles are long and protein is tall. The worst thing is the "puffiness" of fat, so eating high-sugar and high-fat food is good for you, but it is not only bad for you to gain weight, but also harmful. Let's focus on a particularly easy-to-reach diet, which is to gain muscle and fat. If your girlfriend is thin, no matter how much you eat now, you should add meals, two or three meals, or three meals. Yogurt, milk, cheese, milk powder, melon seeds, peanuts, walnuts, pistachios, almonds, bread, biscuits, oatmeal, noodles, sesame sauce, miscellaneous grains powder, grilled fish fillets, beef jerky, eggs, soybean milk powder and so on are recommended in the diet.