1) Eat more foods and get enough sleep.

2) Pay attention to personal mental health. Tension and pressure at work, obsession with small things in life, and "crazy" study or work beyond human load will make people thin. On the contrary, a happy mental state and harmonious interpersonal relationship will help you gain weight.

3) You should take some time to exercise every day, which will not only improve your appetite, but also make you muscular and strong. The muscles of the human body are "put into use and discarded". If you don't exercise for a long time, muscle fibers will contract and weaken, and people will look thin.