It's difficult to say exactly why you're having problems (we'd need a slew of other information), but lactose
intolerance is a possibility. The good news is that if you are lactose intolerant, there are many solutions
available to ease your stomach difficulties.
Despite all the hype, lactose intolerance (LI) is worth paying attention to, particularly if you fall within a group that is traditionally predisposed to it. People with this condition suffer from gas, bloating, diarrhea and stomach pain after ingesting dairy products containing a certain amount of lactose. It is not an all-or- nothing affliction: For many, the effects depend on the amount of lactose ingested. Fully 70% of those of African descent, and 80% of those of Asian and Middle Eastern descent develop some degree of LI. People of Northern European descent are much less likely to develop the condition.
The reduction in the enzyme lactase is the cause: Approximately 50% to 70% (depending on the research you read) of humans lose the enzyme as they grow older. Lactase is required to break down the lactose in milk and most other dairy products into glucose and galactose. Without this breakdown, the lactose reaches the large intestine undigested; a colony of bacteria then descends on it, producing gas, intestinal rumbling and diarrhea.
If you have problems after drinking milk, one solution is to simply drink a small quantity at a time - an eight-ounce glass usually won't create problems for most people. You can also drink sweet acidophilus milk, which has bacteria cultures added to it, without any loss of taste or consistency. We recommend the sweet version, because plain acidophilus milk is sour-tasting. Yet another solution is to buy a lactase product that can improve lactose digestion; these include drops to be added to milk, and lactase pills and tablets to be taken right before eating dairy. Reduced-lactose milks are another option.
A lactose-intolerant person must be wary of many other products, as well. These include anything made with dry milk, nonfat dry milk, dry whey, concentrated whey, whey protein concentrate, dairy- product solids or dried dairy blend. If these ingredients sound familiar to you, they should: They're found in many packaged foods and most frozen foods, like pies, muffins, cookies, cream soups and frozen pancakes. Cereal is also a surprising source of nonfat dry milk and whey.
Whatever your solution of choice, you'll probably need to experiment with how much milk you can drink at one time (or how much to eat), when and how many lactase pills or drops will reduce your symptoms, and which products agree with your palate and digestive system. Unfortunately, once the symptoms start, it's better to suffer and let them run their course; slowing the process down with medication will usually only prolong your discomfort.
There are many solutions to the problems you're having with shakes, such as trying different kinds of protein blends (i.e. whey protein isolate or soy), finding a low-lactose product, or taking a lactase product with the supplement - if you are indeed lactose intolerant.
Finally, though lactose intolerance is prevalent, there are many other disorders that can cause similar intestinal distress. You can be tested for LI to confirm that you're not needlessly avoiding certain foods. Try keeping a food diary so a doctor can find possible patterns and more easily reach a diagnosis.