Phosphorus deficiency (hypophosphatemia) is rare and almost never caused by a low diet. It usually comes from medical conditions such as hyperparathyroidism, kidney tubule defects, diabetic ketoacidosis and refeeding after severe malnutrition.
Common symptoms
Loss of appetite
Anemia
Muscle weakness, especially near the hips and shoulders
Bone pain, and rickets in children or osteomalacia in adults
Higher risk of infection
Numbness or tingling
Loss of coordination
Confusion
In refeeding syndrome: breathing failure, heart failure, coma and death
At-risk groups
People with severe malnutrition who start being fed again (refeeding syndrome), including those with anorexia nervosa, excessive alcohol intake, very low body weight or chronic illnesses such as cancer
People recovering from diabetic ketoacidosis
People with hyperparathyroidism or kidney tubule defects
People taking aluminum hydroxide antacids for 3 months or longer
People with rare genetic phosphate disorders such as X-linked hypophosphatemic rickets
Very low birthweight preterm infants
When to see a doctorLow phosphate almost always points to an underlying medical condition, so see a doctor rather than self-supplementing. Anyone recovering from severe malnutrition, anorexia or prolonged fasting needs medically supervised refeeding, because refeeding syndrome can be life threatening.