According to the World Health Organization's body mass index (BMI) classification standard, the normal weight of an adult with a height of 1.8 meters is generally between 60 kg and 82 kg. Obviously, in order to keep in good shape, his weight has been below normal.
Even if a professional dietitian provides food matching, it may not fully meet the needs of the body. In addition, wearing a corset for a long time may also cause pressure on the internal organs and spine, causing potential health problems. Moreover, excessive dependence on waist girdling may lead to muscular atrophy of abdominal muscles and waist, increasing the risk of injury.
In the long run, this extreme physical management may have a negative impact on his health. I suggest you try to communicate with him, raise your concerns, encourage him to seek professional advice and find a healthier and more sustainable way to manage his body!