What is the reason why experts explain that 'diet reduces basal metabolism but makes you healthy'?

Dieting has the problem of rebounding, as soon as you quit, your weight is restored. Professor Adam Collins of the Faculty of Nutrition , Surrey University , England explains the theory that 'basal metabolism falls when dieting', which is often said to be the cause of such rebound.

Dieting may slow metabolism – but it doesn't ruin it
https://theconversation.com/dieting-may-slow-metabolism-but-it-doesnt-ruin-it-154620

Basal metabolism refers to 'calories burned while resting for a long time'. In order to lose weight, you basically need to burn more calories than you consume, so the higher the basal metabolism you consume just by resting, the better your diet.

However, when you are on a diet, not only unnecessary fat but also muscles that burn calories are lost. It is a fact that when 1 kg of muscle is lost, the basal metabolism of 15 to 25 kcal is reduced, so the basal metabolism is reduced. Furthermore, according to Professor Collins, when the calorie intake decreases, the body minimizes weight loss, so a system called 'reducing metabolism' works. It has been suggested that this metabolic-killing system starts within just three days of starting a diet and persists after the end of the diet. This series of processes is the mechanism by which rebound occurs.

It is a fact that basal metabolism falls and rebound is likely to occur when dieting as described above. However, Professor Collins argues that 'the loss of basal metabolism due to dieting is good in the long run.'

The biggest change that occurs in the body when you lose weight is 'loss of body fat.' The decrease in body fat is also described as 'fat loss', but in reality, the phenomenon of fat cells shrinking occurs. When fat cells shrink, the body interprets it as 'zero energy storage' and reduces the production of the hormones 'leptin ' and ' incretin' that suppress appetite. By reducing the amount of leptin and incretin that suppress appetite, you will feel strongly that you are hungry, and you will end up eating too much.

The reason Professor Collins describes it as 'a good thing in the long run' is that the overall metabolism becomes healthy. For example, excessive swelling of fat cells may make it impossible to remove excess sugar and fat from the body, and the sugar and fat content in the blood continues to increase, eventually leading to diabetes and cardiovascular disease. In some cases, the risk of Professor Collins argues that it is important to go on a diet and shrink fat cells on a regular basis to prevent this situation.

Professor Collins said, 'Diet does not ruin your metabolism, but rather helps it to work well.' On the other hand, 'If your metabolism goes down, take some measures.' If you don't, you'll rebound. ' As a measure to prevent rebound, muscle training is recommended, citing research that muscle training minimizes the decrease in metabolism. He also pointed out that muscle training has a function of suppressing appetite and a function of helping to burn fat, and commented that 'it may help to lose weight in the long term.'