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Assuming you are not lactose intolerant, does milk have any specific negative effects on you during heavy exertion?

We're not talking about milk calories or fat related to weight loss. Does milk itself contain components that would affect your performance, to an extent that milk should be avoided?

For example, say someone participates in a high-school marching band where they practice drills outdoors for 6-8 hours a day, 5 days a week during practice season. This is outdoors during the summer, with temperatures in the 80s-90s Fahrenheit. I've heard that milk "curdles" in your stomach during long periods of heavy exertion and can cause nausea. This seems implausible to me.

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Hmmm......interesting; never heard of that before. – Kneel-Before-ZOD Jul 22 '14 at 5:11
Never heard about the curdling part, but it's commonly advised not to drink milk during exercise because of nausea. This should be interesting... – LarissaGodzilla Jul 22 '14 at 7:29
This is a subjective answer, but milk affects me because I am allergic to the casein protein in milk - casein gives me asthma symptoms. My chest tightens, I cough, breathing is difficult. – Josh Jul 22 '14 at 14:36
Yes, casein sensitivity or lactose intolerance would connect to any milk consumption, not just during physical activity. Specifically, coaches at a local high school here in the US recommend limiting or eliminating milk during training. However, no one knows exactly why, they've just always done it that way. It seems unfounded to me, and so far, Google has turned up nothing scientific to support it. – Chris Vesper Jul 22 '14 at 15:46
up vote 1 down vote accepted

One possible risk is that milk can thicken your phlegm (although it doesn't actually make you produce more), which may create difficulty as you begin to breathe more heavily, because you'll have to either breathe through the phlegm or cough it up and spit it out.

More speculative, while I don't see the milk simply "curdling" in your stomach, you might run into mild symptoms similar to lactose intolerance due to your body directing blood away from your stomach, meaning less of the milk is being digested.

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The milk almost certainly curdles in your stomach. Not to say this is a bad thing. I eat farmer's cheese (acid curdled milk) all the time. I think this is part of why milk "fills you up" more than other liquids: it is becoming a solid in your gut. This is all speculation, of course. – Steven Gubkin Jul 23 '14 at 16:49

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