Please see the drop-down menu under Food Topics in the top navigation bar for links to pages on other food topics.
Know how. Know now.
From border to border in Nebraska, UNL Extension is making an incredible impact on the success of our state — its youth, its families, its farms and ranches, its communities, its economy. Please check these websites for more "know how, know now" information.
Metabolic Food Disorders
Metabolic food disorders are one example of a food intolerance and are not the result of a disorder of the immune system. Metabolic food disorders result from a genetically-inherited defect in the ability to metabolize a food component or a genetically-inherited sensitivity to a food component that affects some critical metabolic process. Lactose intolerance and favism serve as good examples of metabolic food disorders.
- Lactose intolerance occurs because of an inherited deficiency of the enzyme, β-galactosidase, in the intestinal mucosa.
- Favism results from an inherited deficiency in the enzyme, glucose-6-phosphate dehydrogenase, in the erythrocytes, which causes a heightened sensitivity to several naturally occurring oxidant compounds found in fava beans.
Lactose intolerance is one of the most common types of metabolic food disorders. This intolerance is a result of a genetic deficiency that affects the ability of the digestive enzyme, β-galactosidase (lactase), to break down lactose into its component monosaccharide subunits, glucose and galactose.
Lactose must be hydrolyzed into the component monosaccharides in order to be absorbed by the epithelial cells of the small intestine. The undigested lactose then passes from the small intestines into the colon where bacteria metabolize the lactose and produce metabolic by-products such as CO2, H2O, and H2.
This bacterial metabolism in lactose sensitive individuals causes abdominal cramping, flatulence, and frothy diarrhea. These symptoms may vary in sensitive individuals depending on the activity level of the β-galactosidase and the amount of lactose ingested.
Lactose intolerance affects approximately 6-12% of Caucasians worldwide; however, it is much more prevalent in certain ethnic groups and races such as Greeks, Arabs, Jews, African-Americans, Hispanics, Japanese, and other Asians where as many as 60-90% of individuals in these populations are lactose-intolerant. Lactose intolerance can affect people of all ages, starting as early as age three, and steadily worsens with increasing age. Most lactose-intolerant individuals can usually tolerate modest amounts of lactose in the diet; however, most sensitive individuals avoid all products containing lactose.
Favism is another example of a metabolic food disorder in which hemolytic anemia can result from the consumption of fava beans or by the inhalation of pollen from the Vicia faba plant.
People with favism have an inherited deficiency of the enzyme, glucose-6-phosphate dehydrogenase (G6PDH) in their red blood cells. G6PDH is needed to maintain a balance of the reduced form of glutathione and nicotinamide adenine dinucleotide phosphate (NADPH) which are needed to prevent oxidative damage to the red blood cells.
Fava beans contain oxidants such as vicine and convicine that can cause oxidative damage in red blood cells. The genetic deficiency in G6PDH increases susceptibility to the oxidative compounds in fava beans.
Currently, the only treatment for favism is strict avoidance of fava beans and inhalation of pollen from fava bean plants.
Favism is a common metabolic food disorder that affects approximately 100 million people worldwide, although there is some debate whether or not this number underestimates the total number of people with the potential to develop or experience favism as many people throughout the world are not exposed to fava beans or pollen but may still have the genetic deficiency. Increased prevalence is observed in areas where consumption of fava beans is common such as in the Mediterranean, Middle East, China, and Bulgaria. Currently, the only treatment for favism is strict avoidance of fava beans and inhalation of pollen from fava bean plants.