Lactose intolerance (LI), also known as lactose malabsorption is the most common type of
carbohydrate malabsorption. It is associated with the inability to digest lactose into its
constituents, glucose and galactose, due to low levels of lactase enzyme activity (1-2). At
birth, lactase activity is at the highest and it declines after weaning (1-2). The unabsorbed
lactose is metabolized by colonic bacteria to produce gas (hydrogen (H2) and methane (CH4))
and short chain fatty acids. Symptoms related to LI appear 30 minutes to 2 hours after
consumption of food products containing lactose. Related symptoms include: bloating,
cramping, flatulence and loose stool (1-2, 17-18).
Highest rates of LI are found in the Asian populations, Native Americans and African
Americans (60-100%), while lowest rates are found in people of northern European origin
(including northern Americans) (3-4).
The diagnosis of LI based on patients' symptoms is sometimes problematic, since these
symptoms are not specific and may differ from one patient to another. Breath hydrogen test
have been advocated as the best diagnostic tool for the assessment of LI (15-16). During the
test, subjects are sampled for hydrogen levels of breath samples at base line and every 30
minutes after the administration of 50 grams of oral lactose, for a total period of 180
minutes. A breath sample with > 20 ppm above baseline is considered positive for LI (15-16).
There are no established treatments for LI, other than almost complete avoidance of lactose
rich dairy products. Avoidance of dairy products is a major concern since its outcome may
result in a dietary calcium intake that is well below recommended dose of 1,000 mg per day
for men and women and 1,300 mg for adolescents (8-10). For this reason different course of
action needs to be considered instead of a complete exclusion of dairy products by LI
Two possible interventions in the case of LI are the supplement of commercially available
lactase (tablets) or the addition of probiotics.
The consumption of lactase enzyme as a food supplement may assist in restoring adequate
levels of the enzyme needed for hydrolysis of lactose, especially for patients with low, or
non existent levels of lactase. On the other hand, lactase products are problematic since not
all lactase preparations are of the same concentration. Moreover, it is difficult to asses
the amount of lactase tablets needed in order do fully hydrolyze lactose in each dairy mill
Probiotics are live microorganisms that are commonly used in order to prevent or treat a
disease. The current definition by the Food and Drug Administration and the World Health
Organization is "Live microorganisms which, when administered in adequate amounts, confer a
health benefit on the host." These microorganisms are a heterogeneous group, they are
nonpathogenic and produce beta- galactosidase or lactase intracellularly that may assist in
the digestion of lactose (11).
Studies have shown that people with lactose intolerance tolerated the lactose in yogurt
better than the same amount of lactose in milk. The assumption was that the presence of
lactase producing bacteria in the yogurt, especially Lactobacillus acidophilus, contributed
to the digestion and absorption of lactose (5-6, 13).
It was also found that the presence of Lactobacillus bulgaricus and Streptococcus
thermophilus alleviate lactose intolerance through their ability to produce lactase enzyme
Finally, in another study it was found that consumption of milk containing Bifidobacterium
longum resulted in significantly less hydrogen production and flatulence as compared to the
consumption of control pasteurized milk (12).
Based on the mentioned data, the investigators speculate that the administration of
probiotics may assist with the consumption of dairy products containing lactose. Therefore,
the aim of this study is to evaluate the effect of probiotics on patients with LI.