Lactose or fructuse malabsorption can be secondary to another medical condition. What does that mean? Mirriam-Webster defines secondary as "Not first in order of occurence or development--dependant or consequent on another disease."
How could lactose malabsorption occur as a consequence of another disease? Well, to review, proper lactose absorption requires:
- production of the enzyme lactase by cells lining the small intestine
- time for the enzyme to break lactose down to glucose and galactose
- time for for the absorption of glucose and galactose
- healthy and large enough absorptive surfaces in the small intestine
There are any number of ways that other medical conditions, untreated, could cause secondary lactose malabsorption:
- Damage to the cells lining the small intestine can diminish lactase production and cause loss of absorptive surfaces. Damage or loss of healthy tissue in the small intestine could be caused by untreated celiac disease, Crohn's disease, a stomach virus, food poisoning, parasites, radiation therapy, a resection, etc.
- Anything that speeds up the rate at which food moves through the gastrointestinal tract (known as rapid transit time) can mean not enough time for lactase to do its work or not enough time for complete absorption of sugars. Picture this as a commuter train rolling through the station too fast to let off passengers! Intestinal transit time can be sped up by certain medications, ulcerative colitis, bile salt malabsorption or other food sensitivites or intolerances, to name just a few. Yes, this means that lactose malabsorption can occur secondary to fructose malabsorption (and vice versa), another reason the FODMAP approach is more effective in managing symptoms for some people than dealing with lactose or fructose malabsorption in isolation.
The scenario is similar for fructose malabsorption, except that fructose does not need to be digested before it is absorbed--there is no enzyme comparable to lactase involved.
The GOOD news about secondary malabsorption of lactose or fructose? If the underlying condition is treated, cured, healed, or in remission, absorption is much improved or even completely restored!