Rapid weight loss can causes

• Telogen effluvium

  A common condition that can cause widespread hair loss on the scalp. It's usually caused by nutrient deficiencies from restrictive dieting or weight loss surgery. 

• Hormonal imbalance

  Weight loss procedures can disrupt the balance of hormones that are important for hair follicle health. 

• Intermittent fasting

  Short periods of food deprivation can trigger a stress response that can inhibit hair growth. 

• Low protein intake

  Hair is made from keratin, a protein that's formed from amino acids found in dietary protein. Low-protein diets can cause amino acid deficiencies that stall hair growth. 

Symptoms 

• Hair loss that begins about 3 months after the initial weight loss

• Hair loss that lasts about 6 months