How do i know if i am lactose intolerant?

Lactose intolerance?: Lactose breath testing (objective) or a clinical response to lactase enzyme supplements &/or milk avoidance (subjective decline in the gassiness & diarrhea associated with ingesting lactose) may clarify your concern. Some (particularly children) with suspected lactose intolerance however are intolerance to other milk components. Bleeding, weight loss, significant tenderness is not lactose intol.

Tests: The gold standard for determining lactose intolerance, is the breath hydrogen measurment. This can be done as an outpatient. It involves drinking a known amount of lactose solution and measuring the amount of hydrogen given off in exhaled air over a few hours.

Simple test: Try avoiding all milk products for a week and then try the lactaid brand of milk/cheese/ice cream. If you don't have any problems with those then you are likely to be lactose intolerant. There is also a breath hydrogen test that some GI offices perform to more definitively diagnose the condition.

If slight symptoms..: A person can drink lactose-free milk for 2 weeks (and also avoid lactose foods), and then "normal" milk for 2 weeks, and then lactose-free milk again for 2 weeks, and finally go back to "normal" milk. If a person has gas, bloating, with or without tummy aches when on "normal" milk, but not when on a lactose-free diet, then there is very likely lactose intolerance. There also is a lab test.

Trial and error: Lactose intolerance tends to give you bloating and gas after eating dairy. The best way to see if you're lactose intolerant is to cut Dairy out of your diet and see if the symptoms go away

Easy and obvious...: If milk or milk products (e.g., ice cream, yogurt) cause abdominal cramping and/or diarrhea, you're probably lactose intolerant. Symptoms usually start within minutes to a couple of hours. There's usually a "dose effect" as well: the more milk product, the more severe the symptoms.