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Milk With This Kind of Protein

What's in it: A protein called A1 casein

The science: If you're lactose intolerant, any type of dairy will lead to, shall we say, gastrointestinal distress. But there's evidence that A1 casein protein can trigger inflammation on top of an urgent need for a bathroom. (Cow's milk usually has both A1 and A2 casein.) In a small study in Nutrition Journal, subjects drank milk that had both A1 and A2 and milk that only had A2. The milk with both proteins was associated with higher levels of inflammation markers and more stomach symptoms, suggesting that A1 was the problem.

One more thing: Not everyone is sensitive to A1. Like lactose intolerance, which is more common among African-Americans, Asian Americans and Latinos, according to the National Institutes of Health, it varies. If milk that contains both proteins doesn't sit well with you, try one of the growing number of milks that only has the A2 type.