What Foods Contain Intrinsic Factor? The Surprising Truth

December 13, 2025 •

4 min read

Intrinsic factor is a protein produced exclusively within the body, specifically by parietal cells in the stomach lining, and is not found in any food sources. While many foods contain vitamin B12, a substance that intrinsic factor binds to, intrinsic factor itself must be produced internally for proper nutrient absorption.

Quick Summary

Intrinsic factor is a protein synthesized by the stomach for vitamin B12 absorption. It is not present in dietary sources, which instead provide the B12 vitamin itself for the body to utilize.

Key Points

Intrinsic Factor is Body-Made, Not Dietary: Intrinsic factor is a protein produced by the parietal cells in the lining of your stomach, not something you consume through food.
Facilitates Vitamin B12 Absorption: Its primary role is to bind with dietary vitamin B12 to ensure it is absorbed efficiently in the small intestine.
Essential for Nutrient Intake: Without intrinsic factor, the body cannot effectively absorb vitamin B12, even with a B12-rich diet, potentially leading to a deficiency.
Confusion with Vitamin B12: The misconception arises because people often confuse the intrinsic factor (the carrier protein) with vitamin B12 itself, which was once called the “extrinsic factor”.
Deficiency Causes: Conditions that can lead to a lack of intrinsic factor include autoimmune diseases like pernicious anemia and certain types of gastrointestinal surgery.
Focus on B12-Rich Foods: To support proper B12 absorption, consume animal products like meat, fish, and dairy, or fortified plant-based alternatives.

Intrinsic Factor: A Crucial Internal Component

Unlike vitamins and minerals that must be consumed through diet, intrinsic factor is a glycoprotein that your body manufactures internally. Its sole purpose is to bind to dietary vitamin B12 (also known as cobalamin) in the stomach to facilitate its journey through the digestive system. Without this critical protein, the body would be unable to absorb vitamin B12 in the terminal ileum of the small intestine, leading to a deficiency.

The Role of Intrinsic Factor in B12 Absorption

The absorption of vitamin B12 is a complex process that relies heavily on intrinsic factor. The journey begins when you consume food containing B12. Here’s a step-by-step breakdown:

Release of B12: In the stomach, hydrochloric acid and enzymes like pepsin help release vitamin B12 from the food proteins it's bound to.
Binding to Intrinsic Factor: The free vitamin B12 then binds with intrinsic factor, which is secreted by the stomach's parietal cells.
Protection Through Digestion: This newly formed intrinsic factor-B12 complex travels safely through the intestines. Intrinsic factor protects the delicate vitamin B12 from degradation by digestive enzymes.
Ileal Absorption: The complex arrives at the terminal ileum, the final section of the small intestine. Here, specialized receptors recognize and absorb the intrinsic factor-B12 complex into the bloodstream.
Distribution: Once absorbed, vitamin B12 is released from the intrinsic factor and bound to another protein, transcobalamin II, which transports it to body tissues and storage in the liver.

The Confusion: Intrinsic Factor vs. Vitamin B12

The most common reason people search for foods containing intrinsic factor is a misunderstanding. The foods themselves don't contain the factor; they contain the vitamin B12 that the factor helps to absorb. Historically, vitamin B12 was referred to as the “extrinsic factor” because it comes from outside the body (diet), while the internally produced carrier protein was named the “intrinsic factor”. Understanding this distinction is key to comprehending B12 metabolism.

Comparison Table: Intrinsic Factor vs. Vitamin B12


Feature	Intrinsic Factor	Vitamin B12 (Cobalamin)
Source	Produced in the body by parietal cells in the stomach.	Obtained from dietary sources, primarily animal products.
Role	Carrier protein essential for B12 absorption.	Essential nutrient for red blood cell formation and nerve function.
Classification	A glycoprotein.	A water-soluble vitamin.
Storage	Not stored in the body; produced on demand.	Stored in the liver; reserves can last years.
Deficiency Cause	Autoimmune disease (pernicious anemia) or surgery.	Inadequate dietary intake or malabsorption issues.

Foods That Provide Vitamin B12, Which Your Intrinsic Factor Utilizes

Since intrinsic factor is made within the body, the focus should be on consuming foods rich in vitamin B12 to ensure your digestive system has the necessary nutrient to absorb. For those with normal intrinsic factor production, a balanced diet can provide sufficient B12.

Here are some of the best dietary sources of vitamin B12:

Meat and Poultry: Organ meats like liver and kidneys are particularly high in B12, as are beef, pork, and chicken.
Fish and Seafood: Clams, salmon, tuna, trout, and sardines are excellent sources of vitamin B12.
Dairy Products: Milk, cheese, and yogurt contain good amounts of B12.
Eggs: A significant source of vitamin B12.
Fortified Foods: For vegetarians, vegans, or those with dietary restrictions, many cereals, plant-based milks, and nutritional yeasts are fortified with vitamin B12.

What Happens When Intrinsic Factor Is Lacking?

If your body cannot produce enough functional intrinsic factor, you can develop a vitamin B12 deficiency despite consuming enough B12-rich foods. The most common cause is an autoimmune condition called pernicious anemia, where the body's immune system attacks the parietal cells that produce intrinsic factor. Surgical removal of part of the stomach (gastrectomy) or stomach bypass procedures can also lead to a deficiency. Symptoms of B12 deficiency can include fatigue, weakness, nerve problems, and megaloblastic anemia. For more in-depth information on the absorption process and deficiencies, the NCBI Bookshelf provides detailed physiological context.

Conclusion

In summary, the question of what foods contain intrinsic factor is based on a fundamental misunderstanding. Intrinsic factor is a vital protein synthesized in your stomach, not a nutrient found in food. Its production is a prerequisite for absorbing the vitamin B12 that is found in animal products and fortified foods. For those concerned about B12 levels, the correct approach is to ensure adequate dietary intake of B12 or supplementation, especially if an underlying condition affects intrinsic factor production or function. The surprising truth is that you don't eat intrinsic factor; you make it to benefit from the B12 in your food.

Sources

NIH - Physiology, Gastric Intrinsic Factor: https://www.ncbi.nlm.nih.gov/books/NBK546655/
MedlinePlus - Intrinsic factor: MedlinePlus Medical Encyclopedia: https://medlineplus.gov/ency/article/002381.htm

Frequently Asked Questions

No foods contain intrinsic factor. It is a protein produced by the parietal cells in the lining of your stomach. Food contains vitamin B12, which the intrinsic factor binds to and helps your body absorb.

The human body manufactures its own intrinsic factor. It is produced and secreted into the stomach by specialized cells called parietal cells.

Intrinsic factor is a protein made in the stomach that acts as a carrier for vitamin B12. Vitamin B12 (cobalamin) is a nutrient obtained from food. The intrinsic factor is required for the body to be able to absorb the B12 from food.

An inability to absorb vitamin B12 can be due to a deficiency in or lack of intrinsic factor. This can be caused by autoimmune diseases, gastric surgery, or other digestive disorders that disrupt the stomach's ability to produce the protein.

Pernicious anemia is a specific type of vitamin B12 deficiency caused by a lack of intrinsic factor. It is often an autoimmune condition where the body attacks the cells that produce intrinsic factor.

Foods rich in vitamin B12 include animal products such as meat, fish, poultry, eggs, and dairy. For those on plant-based diets, fortified cereals, nutritional yeast, and plant milks are good sources.

The production of intrinsic factor is not dependent on diet; vegetarians and vegans produce it just like meat-eaters do. However, they must rely on fortified foods or supplements to get enough vitamin B12, which intrinsic factor needs to function properly.