The inability of individuals to degrade and digest the disaccharide lactose leads to a state known as lactose intolerance. A large proportion of the world population suffers from lactose intolerance. This often results in symptoms such as bloating, nausea, vomiting, diarrhea and abdominal cramps. It has also been reported that a prime reason for the inflammatory bowel disease (IBD) is the consumption of milk by lactose intolerant individuals. Generally, a person may be called lactose intolerant if he breathes hydrogen>20ppm or his blood glucose level increases by <1.12 mmol/L after an intake of 50gm of lactose. There are increasing reports of the beneficial effects that the probiotic products may provide to alleviate the problem of lactose intolerance. Although, there remains certain ambiguities in their proper use due to lack of knowledge among the common people. e.g., individuals with lactose intolerance are able to digest the yoghurt lactose with greater efficiency as compared to the utilization of milk lactose. But the reasons were unknown for such discrepancies in response to the same substrate. In absence of feasible treatment regimes, the earlier efforts to combat the problem involved avoiding lactose containing dietary products.
Source of lactose in the diet:
Since a large number of the human population suffers from the ailment, the obvious question arises is the lactose containing diets indispensable. Lactose is a disaccharide sugar molecule (made from a single molecule each of glucose and galactose) that forms an inseparable part of milk and other milk based products. For a complete human diet, milk plays an integral part. Therefore, methods of lactose utilization need to be developed rather than removing it from the parts of the nutrients.
The problem and reason behind lactose intolerance:
It has been observed that the individuals suffering from lactose intolerance lack the enzyme, lactase. Lactase is a glycosidic hydrolase and belongs to the β-galactosidase family of enzymes that is required to convert lactose into glucose and galactose which can be absorbed into the bloodstream after their passage through the small intestinal wall. The lactase protein is encoded by the gene LCT. Although the LCT gene is expressed quite effectively in infants, it becomes dormant in adults due to weaning. In some adults the gene has been found to harbor mutations causing lactose persistence (ability to utilize lactose). The effect is brought about in an autosomal dominant manner where mutation in a single allele is sufficient to produce the effect. Also, some scientists have established that a transcription factor MCM6 sits on the promoter of LCT gene and actively regulates its transcription. Mutations in MCM6 have been linked to lactose intolerance.
In persons lacking active lactase, the undigested sugar goes into the colon in an intact form where it is acted upon by the colon residing bacteria. These bacteria can metabolize the lactose with a number of gaseous end products like carbon dioxide, hydrogen, etc. which is the reason behind many of the associated symptoms of lactose intolerance. There are also end products of fermentation and unutilized sugars that causes increased osmotic pressure in the colon. According to the researchers, Scrimshaw and Johnson there are several other factors besides the lactase deficiency and its derivative effects that might add to the complexity of the diseased state. Some of the factors according to their study include age, ethnicity and possibly sex coupled with the factors like the ingredients of the meal taken alongwith lactose, the amount of lactose intake at a specific point in time, the transit time through the gastro-intestinal tract and the speed of gastric emptying. There are also possibilities of probable interactions or cross talks among these factors which may only elevate the severity of the condition.
Solution to lactose intolerance with probiotics:
So, what can be the solution to the problem of lactose intolerance? People have tried doing away with lactose containing dietary products but that is not a permanent and wise solution considering the fact that those food supplements are quite necessary for our health. Among others the β-galactosidase enzyme in the form of drugs or encapsulations has been tried. But due to the extreme conditions within the human GI tract it does not met with the due success. Even if it provided relief, it was only for a brief period and the solution seemed to be transient in nature. However, researchers like Gallagher have long before demonstrated that the people suffering from lactose maldigestion for some unknown reason were able to utilize yoghurt lactose but not the milk lactose. It also resulted in lower hydrogen breath. Gradually it was found that the probiotic bacteria present in the yoghurt could exert such beneficial trait. Milk containing L. acidophilus has shown similar results. Several of the non-pathogenic bacterial strains, e.g., S. thermophilus, L. bulgaricus could produce lactase. This effect is well demonstrated both in children and adults. Therefore, the probiotics could be an obvious choice by the ailing individuals. In such host they could exert the action of their lactase along the gut lumen to facilitate digestion and alleviate lactose intolerance. This has been well shown in both adults and children. Infection of the intestine caused by Giardia lambia could result in lactose intolerance among children and probiotics have been used to restore the activity of lactase in such children. Besides, the effect brought about by the bacterial β-galactosidase, there are other beneficial results obtained by the activity of probiotics in bringing lactose tolerance within the host. They also provide delayed gastric emptying and reduced time of orocecal transit and at times both. Also, since the microbes are able to delay the passage of lactose through the GI tract, the lactase deficient people get more time to digest lactose. This can be explained by the finding that yoghurt with no probiotic lactase can effectuate a prolonged transit time to some extent. Probiotics containing fermented products could cause delayed gastric emptying due to higher viscosity and a lowered pH as compared to normal milk.
However, it is noteworthy to mention that the bacterial lactase has the highest activity at pH of 6-8. But within the human body it has to encounter a wide array of pH. Nonetheless, it has been found that bacterial lactase can resist these differences in pH and a good enough amount of it remains active. Some researchers have found that the lactases from certain strains of bacteria are more effective. Efforts should be made to identify, isolate and characterize the probiotic β-galactosidase that can withstand a wider range of pH and still remain active. Through genetic engineering it is also possible to produce more robust lactase producing strains. In any case probiotics seem to be the only hope in lactose intolerance alleviation at present. The US National Institutes of Health has successfully carried out different clinical trials on the use of probiotics in lactose intolerance.
Photo Credit striatic @ Creative Commons – http://www.flickr.com/photos/striatic/