You may have heard that boiling milk helps to remove some or all of the lactose, making the milk more appropriate for people with lactose intolerance. While boiling technically can degrade some lactose, the effect is so minimal as to be nearly inconsequential; if you're lactose intolerant, the milk will still upset your gut.
Lactose
The lactose molecule is a sugar made up of two smaller sugar units, or monosaccharides. These smaller units are called glucose and galactose, and you can absorb them from your small intestine into your bloodstream, and your cells can then take them up to burn for energy. You can't absorb lactose; it's too big. When you consume lactose, therefore, you have to rely upon the enzyme lactase to break it down into glucose and galactose, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Lactose Intolerance
Most people make plenty of lactase and secrete it into their small intestines, meaning they can break down dietary lactose without trouble. Some, however, don't produce sufficient quantities of the enzyme. These individuals have lactose intolerance, and when they consume lactose, it causes a variety of symptoms including bloating and cramping, explains the Mayo Clinic. The primary way to avoid symptoms of lactose intolerance is to avoid lactose in the diet.
Boiled Milk
Enzymes like lactase speed up reactions that could happen otherwise, albeit very slowly. Technically, lactose breaks down when exposed to water, a small amount of acid, and heat. However, this process is incredibly slow, which is why your body depends upon lactase to speed it up. In the strictest technical terms, boiling milk does cause a fraction of lactose in the milk to break down, but there's plenty of lactose remaining, meaning the milk will still cause you symptoms if you're lactose intolerant.
Avoiding Symptoms
Rather than trying to boil milk as a means of removing the lactose, there are other things you can do to keep lactose from causing you trouble. Some manufacturers offer lactose-free milk and dairy products; these have been treated with the lactase enzyme, which removes all of the lactose in the dairy and allows you to consume it without symptoms. Alternately, you can take lactase supplements, which allow you to temporarily digest the lactose you consume.
References
- "Biochemistry"; Reginald Garrett, Ph.D., and Charles Grisham, Ph.D.; 2007
- Mayo Clinic: Lactose Intolerance
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