April 2012 Issue

Demystifying Lactose Intolerance — Successful Treatment Begins With an Accurate Diagnosis
By Densie Webb, PhD, RD
Today’s Dietitian
Vol. 14 No. 4 P. 14

Lactose intolerance is arguably one of the most misunderstood and misdiagnosed digestive conditions. Consumers as well as RDs know that lactose intolerance can cause gas, cramps, bloating, and diarrhea. But these symptoms are also common to many other digestive disorders, including irritable bowel syndrome, celiac disease, and inflammatory bowel disease.

While clients may find it easy to point a finger at dairy and hope that removing all dairy products from their diet will solve the problem, RDs need to take a closer look at the clinical presentation before assuming lactose intolerance is the accurate diagnosis.

Lactose Intolerance Defined
At the National Institutes of Health (NIH) Consensus Development Conference on Lactose Intolerance and Health in 2010, lactose intolerance was defined as a syndrome of diarrhea, abdominal pain, flatulence, and/or bloating occurring after the ingestion of the milk sugar lactose. The symptoms result from lactose malabsorption, a decreased ability to digest lactose due to a deficiency of the enzyme lactase, which breaks down lactose into glucose and galactose. Lactose is normally digested in the small intestine, but when lactase levels are low, lactose is transported intact to the colon where intestinal bacteria ferment the disaccharides and cause the hallmark symptoms.

The overwhelming majority of infants in every racial and ethnic group produce lactase sometime after weaning, but most will experience a genetically programmed decrease in the digestive enzyme, known as lactase nonpersistance.

The rate of lactase activity loss varies according to ethnicity. For example, Chinese and Japanese infants generally lose 80% to 90% of lactase activity within three to four years after weaning, while white Northern Europeans may take up to 18 to 20 years for lactase activity to reach its lowest level.1 Congenital lactase nonpersistence, the result of two autosomal recessive genetic disorders, is rare.2

Although the NIH states there’s a lack of reliable estimates of the prevalence of lactose intolerance in the United States, a study in Nutrition Today found that in this country, 12% of those surveyed self-reported being lactose intolerant. Lactase nonpersistance is thought to affect more than 70% of the world’s adult population.        

Diagnosing Lactose Malabsorption
“There’s a lot of misunderstanding about the actual diagnosis of lactose intolerance,” says Robin Plotkin, RD, LD, a culinary and nutrition communications expert based in Dallas, Texas. “Many people self-diagnose.”

A hydrogen breath test prescribed by a doctor is considered the best diagnostic test to determine if lactose malabsorption (also referred to as maldigestion) exists. Before the test, it’s recommended that patients fast for 12 hours and avoid laxatives or stool softeners for one week and antibiotics for one month. During the test, the patient breathes into a balloon-type container and then drinks a flavored liquid usually containing 50 g of lactose (equivalent to the lactose found in 1 qt of milk). Breath samples are collected, usually every 15 minutes, over a two-hour period. Normally, breath contains a minimal amount of hydrogen, but if hydrogen levels rise 12 ppm or more compared with baseline measurements, lactose malabsorption may be the cause. The test isn’t foolproof, however, because as many as 20% of those with lactose intolerance don’t exhale excess hydrogen.1

The NIH states that a clinical diagnosis of lactose intolerance requires both documented lactose maldigestion and the presence of symptoms—for example, the onset of gastrointestinal symptoms following a blinded, single-dose challenge of lactose that doesn’t occur when the person ingests a placebo. Many people who self-report lactose intolerance show no evidence of lactose malabsorption.

Alleviating Symptoms
For clients who’ve been diagnosed with lactose intolerance, no cure exists. But there are several strategies or interventions available that may help them deal with the condition.

Reduced-lactose dairy products: Several products are on the market, such as Lactaid, Horizon Organic, and Dairy Ease lactose-free milk, in which the lactose is “predigested” (hydrolyzed). Lactaid also makes lactose-free ice cream, yogurt, cottage cheese, and eggnog, and Yoplait makes a lactose-free yogurt. These products typically contain between zero and 2 g of lactose per serving.

Also available are lactase enzyme tablets, such as Lactaid, Lacto Digest, Source Naturals, and Nature’s Way, designed to help digest the lactose in dairy once they’re consumed. However, an NIH research review concluded there’s a lack of evidence showing that these products actually reduce symptoms.3

Probiotics: Probiotics contain microbial or yeast lactase and are a widely used intervention for lactose intolerance. However, the NIH has determined there isn’t enough research available to claim that probiotics can help lactose digestion.3 In addition, there’s a huge variability in lactase activity in different probiotics products, so some may be more effective than others.1

Colonic adaptation: Some research suggests that the routine ingestion of lactose increases the amount of lactose tolerated.2 But others have found no evidence of this.1 Overall, adults and adolescents who’ve been diagnosed with lactose malabsorption generally can tolerate at least 12 g of lactose in a single dose (the amount in 1 cup of milk).4

Consume with meals: Individuals with lactose malabsorption can tolerate larger amounts of lactose with meals and if small servings (1/4 to 1/2 cup) are distributed throughout the day.

Chocolate milk: Some research has suggested that chocolate milk may be better tolerated than unflavored milk.5

Goat’s milk: Often, goat’s milk is suggested as a dairy alternative for those who are lactose intolerant. However, lactose is the major free carbohydrate in goat’s milk, although in a slightly lower amount. Goat’s milk contains about 9 g of lactose per cup compared with roughly 12 g per cup in cow’s milk.6

— Densie Webb, PhD, RD, is a freelance writer, editor, and consultant based in Austin, Texas.


1. Lomer MCE, Parkes GC, Sanderson JD. Review article: lactose intolerance in clinical practice—myths and realities. Aliment Pharmacol Ther. 2008;27(2):93-103.

2. Suchy FJ, Brannon PM, Carpenter TO, et al. NIH Consensus Development Conference Statement: Lactose Intolerance and Health. NIH Consens State Sci Statements. 2010;27(2):1-27.

3. Wilt TJ, Shaukat A, Shamliyan T, et al. Lactose intolerance and health. Evid Rep/Technol Assess. 2010;192:1-410.

4. Savaiano DA, Boushey CJ, McCabe GP. Lactose intolerance symptoms assessed by meta-analysis: a grain of truth that leads to exaggeration. J Nutr. 2006;136(4):1107-1113.

5. Jarvinen RMK, Loukaskorpi M, Uusitupa MIJ. Tolerance of symptomatic lactose malabsorbers to lactose in milk chocolate. Eur J Clin Nutr. 2003;57(5):701-705.

6. Is goat’s milk lower in lactose than cow’s milk? Academy of Nutrition and Dietetics website. http://www.eatright.org/Public/content.aspx?id=6442459036. Accessed February 14, 2012.


Optimizing Nutrient Intake
Clients who believe they’re lactose intolerant or have been diagnosed with lactose malabsorption often are deficient in calcium and vitamin D.1

The National Institutes of Health (NIH) concluded that long-term milk avoiders have lower bone mineral content than milk drinkers. A 2007 study in Pediatrics suggested that the self-imposed restriction of dairy foods due to a perceived milk intolerance as early as age 10 is associated with lower spinal bone mineral content.2 The same has been found in adolescents.3,4

The NIH identified self-restriction of dairy foods due to self-diagnosis of lactose intolerance as a public health problem.5 “People think they must completely avoid any and all dairy products,” says Robin Plotkin, RD, LD, a culinary and nutrition communications expert based in Dallas, Texas. “But in doing so, they miss out on key nutrients that dairy provides.”


Practical Tips
The good news is that lactose-intolerant clients can consume dairy products. To ensure clients get the nutrients they need, RDs can provide lists of foods low in lactose and suggest clients do the following:

Start with small amounts. Recommend clients drink 1/4 to 1/2 cup of milk as part of a meal or a snack. If they experience no symptoms, they can gradually increase servings to 1 cup. Any more than that, and the likelihood of symptoms increases.

Try chocolate milk and yogurt. Research shows they may be better tolerated than other dairy products.

Include low-lactose cheeses. These include cheddar, Swiss, Colby, Monterey Jack, and mozzarella, which have less than 1 g of lactose per serving.

Sample lactose-free dairy products. They taste the same as other dairy products, although they’re generally more costly.

Take supplements. Clients who avoid dairy products completely due to a clinical or self-diagnosis must replace missing nutrients, especially calcium and vitamin D. If dairy products aren’t an option, recommend clients try fortified soy, almond, and/or rice milk, or calcium (1,000 to 1,300 mg) and vitamin D (600 to 800 IUs) supplements at age-appropriate levels. Suggest chewable calcium and vitamin D supplements for clients who have difficulty swallowing pills.


1. Savaiano DA, Boushey CJ, McCabe GP. Lactose intolerance symptoms assessed by meta-analysis: a grain of truth that leads to exaggeration. J Nutr. 2006;136(4):1107-1113.

2. Matlik L, Savaiano D, McCabe G, VanLoan M, Blue CL, Boushey CJ. Perceived milk intolerance is related to bone mineral content in 10- to 13-year-old female adolescents. Pediatrics. 2007;120(3):e669-e677.

3. Parson TJ, van Dusseldorp M, van Der Vliet M, van de Werken K, Schaafsma G, van Staveren WA. Reduced bone mass in Dutch adolescents fed a macrobiotic diet in early life. J Bone Miner Res. 1997;12(9):1486-1494.

4. Du XQ, Greenfield H, Fraser DR, Ge KY, Liu ZH, He W. Milk consumption and bone mineral content in Chinese adolescent girls. Bone. 2002;30(3):521-528.

5. Wilt TJ, Shaukat A, Shamliyan T, et al. Lactose intolerance and health. Evid Rep/Technol Assess. 2010;192:1-410.

— DW


Lactose Lexicon
Lactase nonpersistence (lactase insufficiency): This is a drop in lactase activity that occurs with age. Lactase activity in the small intestine of adolescents and adults is a fraction of that in infants.

Lactose malabsorption (lactose maldigestion): This occurs when a large portion of a dosage of lactose isn’t absorbed in the small bowel and is transported to the colon. Lactose malabsorption is best diagnosed with hydrogen breath tests. The presence of lactose malabsorption doesn’t necessarily translate into symptoms.

Lactose intolerance: This happens when malabsorbed lactose produces symptoms (eg, diarrhea, abdominal discomfort, flatulence, bloating). The presence of symptoms and their severity are determined by the quantity of lactose ingested.

— DW


Lactose and Calcium Content of Common Foods

Dairy Products

Calcium Content (mg)

Lactose Content (g)

Milk, whole (3.25%), 1 cup



Milk, reduced fat, 1 cup



Yogurt, plain, low fat, 1 cup



Ice cream, vanilla, 1/2 cup



Cottage cheese, creamed (small curd), 1 cup



Cheddar cheese, 1 oz



Swiss cheese, 1 oz



Source: Heyman MB; Committee on Nutrition. Lactose intolerance in infants, children, and adolescents. Pediatrics. 2006;118(3):1279-1286.