Lactose intolerance is a gut acting condition which is the body's own "omics" test whether it has too much weight. because there is a lactose intolerant gene - which will make a body own gene system give up on the entire process - it may be regarded as a self-determining thing under most circumstances, with an opt-out clause in extreme cases. the problem, of course, is that modern diets are extreme cases in a large number of scenarios.
Instead of seeing lactose intolerance as a signal, it should be regarded as a response - which will trigger in endless variations depending on the weight and condition of the gut biota. The lactose intolerance genes give the possessors a very low opt-out threshold, and the inverse - with a very high lactose tolerance - a very high opt-out threshold. the key here is how much additional weight does the person carry in terms of excess fat. because of this, patient's should be looked at in terms of their own weight history. it also means that at the point of adolescent, a large number of people will balloon up rather than engage in lactose intolerance.
The key is fat that the body does not use, but that the gut biota does use. remember that the inner and outer intestine does not generally get larger, except by storing fat in its length. the normal course is to develop lactose intolerance after some period of time after weaning away from milk. However, in the northern European and descendants, a mutation gave the individuals a high lactose tolerance.
However, the control is how much weight the individual stores - with relatively high weight retention occurring to delay or offset the lactose tolerance. That is, the individual gains weight rather than suffer lactose intolerance. Eventually, most individuals will go into lactose intolerance, which has noted will act as a "sticky" point.