row of cows being milked

Some people experience gastrointestinal distress from drinking cow’s milk, a problem that can be eliminated by consuming lactose-free milk, which is readily available in retail outlets across the commonwealth. However, not all people find relief from that change.

For about 20 years, some medical professionals and researchers have blamed the digestive issues connected to regular milk on proteins.

Milk is considered a major source of high-quality protein, providing about 38% of the solids-not-fat portion of milk and 21% of whole milk energy. Ninety five percent of the proteins in milk can be divided into two major categories — serum proteins (found in whey) and casein proteins.

Proteins are long chains made up of amino acids. The protein chains are “snipped” by enzymes during digestion into shorter amino acid chains known as peptides. The arrangement of the amino acids in the protein chains, as well as how the proteins are broken up during digestion, determines how they act, biologically, in a myriad of chemical reactions.

A1 and A2 are names for just two of the casein proteins. The only difference between the two is that the No. 67 amino acid in their chains is different. When each is digested, the peptide segments created by enzyme action at that 67th amino acid result in how A1 and A2 work in the body.

When the A1 casein protein is split, there is a resulting peptide known as the BCM-7 peptide. It is not produced with the breakdown of the A2 protein.

That difference is what causes issues, according to proponents of A2 milk and available research.

Some research has been conducted and published in credible journals to indicate that consuming milk that contains the A1 protein does create digestive problems in some people, but the research on benefits of A2 milk is inconclusive. Few human studies have been conducted.

Results of one study found that humans that ingest milk containing both A1 and A2 proteins may take longer to digest the proteins, a situation that would cause bloating and abdominal pain. The journal Nutrition reviewed research related to A2 proteins and found that while this result is confirmed the majority of additional research was conducted using rodents.

It is possible that the A1 protein creates digestive issues in some people, just as lactose may, but not enough research on humans — large-scale experiments — has been done to provide conclusive evidence.

Researchers at University of Vermont say there are many more proteins that vary in cow’s milk that may be at play and possibly contributing to the small percent of gastric issues. According to one professor, her team examined two types of cows and found over 40 proteins that were different between them. It is possible that any one of those could be causing differences in symptoms.

I often say, jokingly, that all things in life can be explained by a bell curve, but I also believe there is some truth to that statement.

A bell curve is a graph that shows the distribution of a set of chosen values. When drawn, it resembles the shape of a bell. Using the statistics applied to the bell curve of a normal distribution, approximately 68% of the human population would have no symptoms when drinking milk containing A1 protein, and only 5% would have serious issues and symptoms. The only way to know if this is a correct representation would be to conduct appropriately designed research.

The Pennsylvania Milk Marketing Board supports experimentally-designed research to examine any claims of nutritional or health related issues or benefits associated with the consumption of dairy products. Valid and reliable research helps the industry grow and improve its consumer offerings.

We also support efforts of our Pennsylvania processors, manufacturers and retail outlets to provide dairy-based alternatives such as lactose-free and A2 milk so that all individuals have access to nutritious dairy beverages.

I can be reached at 717-210-8244 or by email at to discuss any questions and concerns.

Carol Hardbarger is the secretary of the Pennsylvania Milk Marketing Board.


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