The jury is still out on dairy. Whether or not milk is good or bad for you is always up for hot debate, but there is enough evidence on the negative side of the spectrum to justify cutting it out, if only for a while to see if you feel any better.
Some of the main arguments for milk consumption are turning out to be unprovable at best. We've been taught that we need the calcium from milk for healthy bones, especially women. Yet, the countries with the lowest consumption of milk have the lowest rates of osteoporosis. As a matter of fact, calcium is available in lots of sources outside of milk, like salmon and greens. Calcium and milk consumption has also never been demonstrated to reduce the risk of fractures.
So why avoid it?
Let's start with the least of the problems, lactose intolerance. It's not necessarily bad for you, but it makes you feel like crap. If you are intolerant (and most people in the world are to a certain degree), you can experience gas, cramps, and diarrhea. Not fun. You may actually be intolerant and not even realize it until you stop drinking milk for a while.
Next, casein intolerance. What the heck is casein? It's a milk protein that is similar in structure to gluten. Gluten can destroy your gut lining and lead to auto-immune disease. Some opponents of dairy say that casein wreaks the same kind of havoc as gluten does.
Third, and we're getting more serious now, is that milk has been linked in several studies to cancer. If you want to know the specifics, look into betacellulin, a compound in milk that may cause the growth of cancer cells. This may be mitigated by drinking full fat milk, but the effects seem more pronounced in lowfat and nonfat milk.
Finally, insulin. For some reason, milk induces an insulin response that is greater than most other carbohydrates. And if you don't know what that means, insulin causes your body to store sugar as fat. More insulin, more sugar (energy) locked away as fat. If you keep insulin in your blood, you'll need to take more energy in rather than use what you've got, because it's "locked away" by insulin. This will cause more insulin to be released. It's a vicious cycle.
So, is milk DEFINITIVELY bad? No. Is it suspect enough to warrant personal testing? You bet. So for the duration of the Challenge, you'll lay off dairy. If you have any, it's going to be yogurt. And we do recommend the full fat kind.