Lactose Intolerance: A Diagnostic Fad

Reading time: 4 – 7 minutes

Just as clothing styles come in and out of fashion, diagnoses go through fads as well. While this is rarely true of diagnoses issued by traditional healthcare practitioners, health-related Internet sites (particularly those promoting alternative medicine) and some practitioners of alternative medicine may be susceptible to these diagnostic trends. One such fad diagnosis is lactose intolerance, which is sometimes blamed for everything from hyperactivity to joint pain.

Pouring milk splashImage credit: Pouring milk splash via Shutterstock

In reality, the prevalence of lactose intolerance in the U.S. is difficult to assess accurately. Still, it is likely much lower than suggested based upon self-report, according to the National Institutes of Health [1]. In part, this is because individuals have a tendency to misinterpret any gastrointestinal upset following a dairy-containing meal as evidence of lactose intolerance [2]. Most people, however — even those with lower-than-normal lactase levels — do not report gastrointestinal upset after being exposed to lactose in a blind challenge, explains the NIH.

Blind (Food) Challenge: exposure of an individual to a food without their knowledge. The blind challenge helps to prevent an individual’s preconceptions from influencing their response or perceived response to a food.

Lactose intolerance results from insufficient production of the enzyme lactase (LCT), which the small intestine uses to help break down lactose, or milk sugar. Lactose is a disaccharide, meaning it’s made up of two smaller sugar units called monosaccharides. The small intestine can absorb monosaccharides, but disaccharides (and larger combinations of monosaccharides, called polysaccharides) have to be digested into their monosaccharide building blocks before they can be absorbed. The digestive tract uses a wide variety of enzymes to accomplish this task. Digestive enzymes are very specific in their function; the enzyme responsible for breaking down lactose, for instance, can’t digest sucrose (table sugar). Sucrase, the enzyme that breaks down sucrose, is similarly incapable of digesting lactose. As such, a person must produce lactase in order to digest lactose.

Lactase: the digestive enzyme that helps break down lactose in the gut.

In those individuals with true lactose intolerance, the absence of appropriate quantities of lactase means that lactose passes undigested into the large intestine. There, native flora (naturally-occurring bacterial species) of the gut break down the lactose to provide for their own energy needs. This results in the accumulation of a large amount of gas, which is a waste product of bacterial lactose digestion. The gas leads to the sensations of bloating and cramping, and can result in flatulence. Undigested lactose in the large intestine can also cause diarrhea.

Most people make lactase in appropriate amounts early in life; without lactase, babies would be incapable of digesting breast milk (which is actually higher in lactose than cow’s milk). Some ethnic groups produce less lactase after the age of weaning, leading to lactose intolerance that begins in childhood. This lactose intolerance persists throughout adulthood, and is most common in individuals of African, Hispanic (non-European), Native American, and Asian descent. Europeans are much less likely to develop lactose intolerance post-babyhood. Further, there’s some evidence to suggest that lactose intolerance increases with advancing age [3], though there isn’t a significant body of data supporting this.

Despite the trend among alternative health practitioners to diagnose patients with lactose intolerance (and to blame that lactose intolerance for a variety of other physical symptoms) [4], lactose intolerance isn’t the sort of malady that underlies other health problems. Those with lactose intolerance have one specific set of symptoms (bloating, cramping, diarrhea, and flatulence after consuming dairy), and the symptoms can be avoided entirely by taking lactase supplements (available over-the-counter) along with dairy-containing food.

The NIH points out that increased education regarding the nature of lactose intolerance and the relatively narrow scope of its symptoms — as well as the fact that it’s a benign and easily alleviated digestive malfunction — could help to prevent needless avoidance of dairy by those who incorrectly assume they are lactose intolerant. While dairy isn’t essential to the human diet, it’s nevertheless an excellent source of calcium, which can otherwise be difficult to incorporate into the diet apart from supplementation. Further, most dairy in the U.S. is fortified with vitamin D, in which many Americans are deficient, and which is required for the uptake of calcium from the gut.


  1. NIH Lactose Intolerance Conference — Panel Statement, February 22–24, 2010. National Institutes of Health (NIH) Consensus Development Program. Accessed 2012 Feb 13.
  2. Saltzman et al. A randomized trial of Lactobacillus acidophilus BG2FO4 to treat lactose intolerance. Am J Clin Nutr. 1999 Jan;69(1):140-6.
    View abstract
  3. Stefano et al. Lactose malabsorption and intolerance in the elderly. Scand J Gastroenterol. 2001 Dec;36(12):1274-8.
    View abstract
  4. Pupillo, J. Got a little milk?: AAP report recommends some dairy products for lactose intolerant patients. AAP News 2006; 27:12.
About the Author

Kirstin Hendrickson, Ph.D., is a science journalist and faculty in the Department of Chemistry and Biochemistry at Arizona State University. She has a PhD in Chemistry, and studied mechanisms of damage to DNA during her graduate career. Kirstin also holds degrees in Zoology and Psychology. Currently, both in her teaching and in her writing, she’s interested in methods of communicating about science, and in the reciprocal relationship between science and society. She has written a textbook called Chemistry In The World, which focuses on the ways in which chemistry affects everyday life, and the ways in which humans affect each other and the environment through chemistry.