Which causes more constipation: calcium carbonate or calcium citrate?

Excessive intake of either calcium carbonate or calcium citrate may cause constipation.

Calcium carbonate is more commonly used and, when consumed, helps increase bone mineral density and prevent osteoporosis. Calcium citrate is typically used to treat conditions associated with calcium deficiency—such as disorders affecting bones, teeth, and nerve function. Both calcium carbonate and calcium citrate are classified as food additives, characterized by their ability to act as bulking and solidifying agents in foods. Under normal circumstances, moderate consumption does not adversely affect the body nor cause constipation. However, because both compounds have relatively low bioavailability and are not fully absorbed by the human body, undigested residues may accumulate. Excessive intake can thereby increase gastrointestinal (GI) tract burden, slow GI motility, lead to excessive accumulation and prolonged retention of food in the intestines, and ultimately result in constipation.

It is recommended to consume foods containing calcium carbonate and calcium citrate in moderation, and to include ample fresh fruits and vegetables in the diet to meet normal nutritional requirements and help prevent constipation.