What foods contain casomorphins? A guide to dietary opioid peptides

November 24, 2025 •

4 min read

Casein, the primary protein in cow's milk, can release opioid-like peptides called casomorphins during digestion. These compounds can bind to opioid receptors in the brain, producing feelings of pleasure and comfort. Understanding which foods contain casomorphins can be crucial for those with sensitivities or digestive issues.

Quick Summary

This article explores the dietary sources of casomorphins, focusing on dairy products like cheese and milk, as well as other potential plant-based sources. It details how these peptides are formed during digestion and the differences between A1 and A2 milk, providing a comprehensive overview for the health-conscious consumer.

Key Points

Dairy is the primary source: The most significant sources of casomorphins are dairy products, including milk, cheese, and yogurt.
Cheese concentrates casomorphins: As cheese is a concentrated milk product, it contains higher levels of casein and, consequently, higher concentrations of casomorphins compared to liquid milk.
A1 vs. A2 milk matters: Cow's milk containing the A1 beta-casein variant releases more of the potent beta-casomorphin-7 (BCM7) during digestion than milk with the A2 variant.
Soy and wheat have similar compounds: Other foods, including soy and wheat, produce different opioid-like peptides (soymorphins and gliadorphins) that can also affect opioid receptors.
Effects depend on individual health: The degree to which casomorphins affect an individual depends on their digestive health and whether the peptides can cross the intestinal barrier.

Understanding Casomorphins

Casomorphins are opioid peptides formed from the breakdown of casein, a protein found in mammalian milk. During the digestive process, enzymes cleave the casein protein into smaller fragments, some of which are casomorphins. These peptides can then interact with the body's opioid receptors, creating mild, opiate-like effects. This mechanism is believed to have an evolutionary purpose, helping to ensure that infant mammals continue to nurse. However, in some individuals, particularly those with conditions like irritable bowel syndrome (IBS) or certain neurodevelopmental disorders, these peptides can cause various adverse effects.

Dairy Products with Casomorphins

The most well-known dietary sources of casomorphins are dairy products, and their concentration can vary significantly. Generally, the more processed or concentrated the dairy product, the higher the casomorphin content. Cheeses are a prime example, as they are a concentrated source of casein.

Common sources include:

Cheese: Hard cheeses, like cheddar and gouda, and soft blue cheeses, like gorgonzola, tend to be particularly high in casomorphins. A study found that Gorgonzola cheese contained the highest concentration of casomorphin-7 among several cheeses tested.
Cow's Milk: The content of casomorphins in milk depends heavily on its genetic origin. Milk from cattle with the A1 beta-casein variant is more prone to releasing the potent beta-casomorphin-7 (BCM7) during digestion than milk from A2 variant cows. Most conventional milk from European breeds contains a mix of A1 and A2 beta-casein.
Yogurt and Fermented Milk: The fermentation process can influence casomorphin levels. While some studies have found casomorphins in yogurt digests, others suggest they may be degraded during fermentation, making results inconsistent.
Infant Formula: Cow's milk-based infant formulas, which use whey and casein as protein sources, have also been shown to contain casomorphins after enzymatic digestion.

Non-Dairy Foods and Other Sources

While dairy is the most direct source, other foods can also yield opioid-like peptides or influence casomorphin activity.

Soy Products: Soybeans contain proteins that can be digested into peptides called soymorphins, which also exhibit opioid-like activity.
Wheat (Gluten): Grains containing gluten, such as wheat, barley, and rye, can produce gliadorphins (or gluten exorphins) during digestion. These peptides are also resistant to digestive enzymes and can interact with opioid receptors.
Spinach: This leafy green vegetable can release opioid peptides called rubiscolins upon digestion.
Rice: The digestion of rice albumin can produce oryzatensin, an opioid antagonist.
Human Milk: Casomorphins are also found in human milk, particularly in colostrum, and may play a role in infant development and mother-infant bonding, though the human version is much weaker than bovine casomorphins.

Navigating A1 vs. A2 Milk

The distinction between A1 and A2 milk is significant for understanding casomorphin release. A1 milk, which is the most common variety in Western countries, contains a specific amino acid sequence that easily breaks down to release BCM7 during digestion. A2 milk, produced by certain cow breeds (like Guernsey and Jersey) and all other mammals including humans, contains a different amino acid sequence that resists this cleavage, resulting in a much lower release of BCM7. Many individuals with dairy sensitivity find A2 milk easier to digest due to this difference.

Comparison of Casomorphin Sources


Food Type	Protein Source	Notable Peptides	Typical Casomorphin Release	Notes
Cheese	Concentrated Bovine Casein (A1, A2 mix)	BCM5, BCM7	High	Concentration process significantly increases casein and peptide potential. Higher in hard and blue cheeses.
Conventional Milk	Bovine Casein (A1, A2 mix)	BCM7	Medium	Contains a mix of A1 and A2 variants, leading to moderate BCM7 release in the gut.
A2 Milk	Bovine Casein (primarily A2 variant)	Weaker peptides (e.g., BCM9)	Low	The proline at position 67 prevents easy cleavage into BCM7.
Human Milk	Human Casein (A2 type)	hBCM7	Very Low	Significantly weaker opioid activity and higher susceptibility to degradation.
Soybeans	β-conglycinin β-subunit	Soymorphins	Varies	Digestion produces different opioid peptides (soymorphins).
Wheat	Gluten (gliadin, glutenin)	Gliadorphins	Varies	Digestion produces gluten exorphins, not casomorphins, which act on opioid receptors.
Spinach	RuBisCo	Rubiscolins	Varies	Releases opioid peptides (rubiscolins) after digestion.

The Controversial Effects of Casomorphins

The physiological impact of dietary casomorphins remains a subject of scientific debate. Some researchers suggest that casomorphins can cross the intestinal wall and enter the bloodstream, potentially affecting immune and neurological function. This has led to speculation about their role in various conditions, although the evidence is controversial and not fully substantiated. The European Food Safety Authority concluded in 2009 that the relationship between BCM7 and non-communicable diseases had insufficient data to demonstrate a causal link. For individuals with a healthy digestive system, the peptides are likely broken down further before causing any significant systemic effects. However, for those with intestinal permeability issues, the absorption of these peptides is a greater possibility.

Conclusion

Casomorphins are naturally occurring opioid-like peptides released during the digestion of casein protein, predominantly found in dairy products. The concentration of these peptides is highest in concentrated dairy foods like cheese, and the specific genetic variant of beta-casein (A1 vs. A2) significantly influences the type and quantity of casomorphins released. While dairy is the primary source, other foods like soy and wheat also produce opioid peptides. While an evolutionary explanation exists for their presence, their impact on adult human health is complex and controversial. For those with sensitivities, opting for A2 milk or non-dairy alternatives may help mitigate potential effects.

Frequently Asked Questions

A1 milk, which is common in many European breeds of cattle, releases the peptide beta-casomorphin-7 (BCM7) upon digestion, which has stronger opioid effects. A2 milk, found in Jersey and Guernsey cows, contains a different protein structure that prevents the formation of BCM7, leading to a much lower casomorphin content.

All dairy products derived from milk containing casein will have the potential to form casomorphins during digestion. However, the concentration varies based on the product and the type of milk used. Highly concentrated products like cheese have higher potential, while the fermentation process for products like yogurt can sometimes degrade the peptides.

While the term 'casomorphin' is specific to milk casein, other foods, particularly some plants, can produce different opioid-like peptides. Soybeans produce soymorphins, and wheat contains gliadorphins, both of which can bind to opioid receptors.

The mild, pleasurable, and rewarding effects caused by casomorphins binding to opioid receptors in the brain can contribute to cravings for dairy products, particularly cheese, which is a concentrated source.

The health effects of casomorphins are a topic of debate and depend largely on the individual's sensitivity and digestive health. While some studies have suggested links to certain health issues, the European Food Safety Authority has stated there is insufficient evidence to confirm these claims.

For those sensitive to casomorphins, options include choosing dairy products made from A2 milk or opting for non-dairy alternatives entirely. Plant-based milks made from nuts, rice, or oats do not contain casein and therefore do not produce casomorphins.

Studies suggest that heat treatments like pasteurization may alter protein digestion, potentially affecting the release of casomorphins. However, research has shown that the beta-casein variant (A1 vs. A2) is a much more significant factor in determining BCM7 release than the heat treatment process itself.