There are many reasons for low blood phosphorus, which are mainly related to decreased phosphorus intake, increased phosphorus excretion and phosphorus loss, and hyperparathyroidism. 1. Decreased intake of phosphorus: low blood phosphorus can be caused by prolonged picky eating or intake of a single type of food. 2. Increased excretion of phosphorus: When certain renal tubular diseases, such as Fanconi syndrome, lead to reabsorption disorders in the proximal tubules of the kidney, low blood phosphorus may also occur. 3. Phosphorus loss: hypophosphatemia may occur in certain patients with gastrointestinal diseases such as diarrhea and burns. 4. Hyperparathyroidism, when the parathyroid glands increase their secretion, can also lead to low blood phosphorus. There may be other reasons for low blood phosphorus, it is recommended to consult a specialist in time, complete the relevant examinations, and give targeted treatment and therapy after clarifying the cause of the disease.