Summary: Lactose intolerance is an inability to hydrolyze milk sugar (lactose) which mainly occurs due to deficiency of lactase enzyme. Lactose intolerance is affected by age and genetic factors and increases with increasing age. Lactose intolerance is divided into three major classes: primary lactose intolerance, secondary lactose intolerance, and inherent deficiency of lactase enzyme. The clinical symptoms include: stomachaches, stomach muscles contractions, flatulence, and tympanites. Lactose intolerance differs from allergy to milk. This inability in hydrolysis of milk sugar is identified in different individuals by means of various tests such as lactose intolerance test, hydrogen breath test, urine acidity test, and so on. In general, lactose is present in two categories of dairy and non-dairy products. Todays, the patients suffering from this disease are recommended to avoid consuming milk and dairy products with high lactose content and instead use other dairy products like yoghurt that have negligible amount of lactose. Such individuals can also benefit from enzyme delactosed products, lactose supplement pills, foods enriched with calcium and vitamins and other alternative products.

Key Words: Milk, Lactose Intolerance, Lactase Enzyme

Introduction

While carbohydrates constitute a major portion of our diets, lactose merely account for 10% of the carbohydrate in the diet of adults [1]. Lactose intolerance is an inability in metabolism of lactose, the sugar found in milk and other dairy products [1, 2, 3 & 4]. Lactase is an enzyme which is produced in our body only in the small intestine and its presence is necessary for digesting lactose. The people whose bodies do not produce sufficient lactase suffer from lactase deficiency and are not able to digest lactose [5].

History: Lactose intolerance along with chronic diarrhea was first described in 1958 by Durand in infants, and at the same year, Houlzel et al. (1958) stated that lack of lactose absorption is the cause of patients’ diarrhea and use of lactose tolerance test in temporary malabsorption of sacarids during diarrhea of infants was demonstrated in 1962. The first observation of lactose desorption was depicted in 1963 for the first time [1 & 6].

Cause: If sufficient lactase for digestion of the lactose present in food does not exist, lactose will remain in intestine and causes water retention by the small intestine. As a consequence, the person might experience tympanites and stomachaches usually 30 minutes after eating lactose-bearing foods [5]. Disaccharides are unable to get absorbed and pass through the wall of small intestine into the blood circulation. As a result, in absence of lactase, the lactose of the consumed food remains intact and enters the large intestine. Activity of intestinal bacteria quickly leads to metabolism of lactose and large amount of gas is generated as a result of fermentation (a mixture of hydrogen, carbon dioxide, and methane) giving rise to a series of stomachaches including stomach muscles contraction and tympanites [1].

Symptoms

Fundamental clinical symptoms including nausea, muscular contraction, tympanites, diarrhea, and flatulence are dependent on extent and intensity of lactose intolerance [1, 2, 3, 4 & 5].

Lactose intolerance is divided in three following classes:

  • Primary lactose intolerance: occurs when an offspring is stopped from receiving mother’s milk in societies where consumption of dairy products is not prevalent. This state occurs in many Asian and African countries.
  • Secondary lactose intolerance: results from intestinal diseases caused by intestinal parasites, celiac disease, surgery or radiation. Once the damage of the intestine cells improves, these cells will regain the ability to generate lactase. In certain cases, generation of lactase enzyme might be stopped for ever [1 & 5].
  • Inherent deficiency of lactase enzyme: a genetic disorder which prevents from enzymatic production of lactase and is diagnosed in infants at the beginning of birth [1]. This sort of lactose intolerance is rarely observed [5].

Many individuals who have reported problems associated with lactose intake do not suffer from lactose intolerance [1]. Lactose intolerance is affected by age and genetic factors and is intensified by increasing age [4].

Conventional Tests in Diagnosing Lactose Intolerance
1.Lactose intolerance test                                  2.Hydrogen breath test

  1. Urine acidity measurement test 4.Living tissue macroscopic test
  2. Lactose intolerance test: first, a blood sample is taken from the patient. This blood samples is taken from the tip of patient’s finger for measuring blood sugar. The patient then drinks solution of milk. If the patient is able to hydrolyze the patient’s sugar, his/her blood sugar content increases after one hour. If the blood sugar content doesn’t increase, it is a sign that lactose hasn’t been decomposed into glucose and galactose.
  4. Hydrogen breath test: the patient is normally advised to avoid taking foods that contain bran in order to reach the lowest level in breathing. An initial sample of patient’s breath is taken and then s/he then drinks a solution of milk. Patient’s breath hydrogen content is measured at 15 minutes, 30 minutes until 2 hours afterwards. If hydrogen content in patient’s breath does not increase significantly, his/her body is able to hydrolyze lactose. In case of failure in lactose hydrolysis, its metabolism is accomplished by large intestine bacteria and amount of hydrogen gas rises. The same test is done for carbon dioxide.

  1. Urine acidity measurement test: As other tests are difficult and almost impossible to carry out on offspring, this test is used for diagnosing lactose intolerance in neonates. Taking into account that large intestine bacteria produce lactic acid and other acids as well as gas production, these compounds can be detected in neonates’ urines and presence or absence of lactose intolerance in them can be inferred.

  1. Microscopic test of living tissue: this method is for special cases in which samples are directly taken from patient’s intestine.

 

Differences between lactose intolerance and allergy to milk

  1. Allergy to milk happens because of allergy to milk proteins whereas lactose intolerance is associated with inability to decompose lactose in the digestion system. 2. Allergy to milk is often observed in babies whereas lactose intolerance is common in higher ages. 3. Allergy to milk not only affects digestion system but also influences skin and respiratory system. Lactose intolerance mainly affects digestion system and leads to symptoms such as tympanites and diarrhea. 4. Allergy to milk can threaten life, but lactose intolerance is not dangerous though disturbing.

Control Mechanism of Lactose Intolerance

As of today, no methodology has been developed for producing stable lactase. Bradner & Hargrove proposed four rules and principles for this respect:

1-Prevention from consumption of lactic diets; 2-use of substitutes for replacement and absorption of nutritious compounds; 3-adjustment of absorbed calcium; utilization of enzymatic substitutes [1]

 Lactose is mainly present in two large sets of foods:

  • Dairy Products: major dairy products including milk, cheese, yoghurt, butter, sour cream, ice cream, kefir, and dairy beverages [1].

Nutritional value of dairy products: Prevention from milk consumption aimed at preventing from lactose intolerance symptoms can lead to calcium deficiency in the diet. Dairy products are the main source of calcium in human’s diet. Calcium is required for building strong bones, teeth and other essential roles in body. Lactose enhances absorption of calcium, phosphor, magnesium, and zinc. Milk protein has a high quality and is rich in water-soluble vitamin riboflavin. Other vitamins and minerals are also found in milk but at a lesser amount [5].

Table 2: Examples of lactose level in different dairy products [1]

Dairy Product Lactose content (grams)
Simple and low-fat yoghurt (240 ml) 5
Low-fat yoghurt (240 ml) 11
Swiss cheese (28 grams) 1
Ice-cream (120 ml) 6
Cottage cheese (120 ml) 3-2

More suitable dairy products for patients suffering from lactose intolerance

  • Unskimmed milk: the fat content of milk delays stomach depletion, and as a result, the milk lactose will enter the intestine gradually.
  • Coffee-milk: the coffee added to milk enhances the activity of lactase enzyme, restrains the activity of bacteria generating gas as a result of lactose fermentation, decelerates stomach depletion, and consequently, leads to improvement of milk tolerance in such patients.
  • Yoghurt: yoghurt is better accepted in the respective individuals due to possession of acid lactic bacteria. In addition, yoghurt regulates secretion of stomach acid and causes stimulation of lactase enzyme secretion cells of the intestine. Yoghurt leaves the stomach later due to its semi-solid state helping better tolerance compared to milk [4].
  • Dairy beverages: among such beverages, whey and yoghurt juice which contain more than 60-90% of milk ingredients besides less lactose [11 & 12].
  1. Non-dairy Products

When words such as whey, whey, dry milk powder, and so on are used in the labels of products, those products do contain lactose. Actually, lactose is considered as a commercial additive which is used for flavoring, texture improvement, and adhesive properties. Lactose is present in foods like processed meat (sausages, hot dogs, etc.), meat juice powder, margarine, breakfast cereals, French fries, bakery and confectionary products, frozen desserts, instant products such as instant cafes, dried fruits, medicines, fast foods, food substitutes (soups), and protein supplements [1 & 5].

Byproducts

Products with low lactose content or free from lactose have been produced in dairy industries for the consumption of lactose intolerant patients. Lactose-free milk is produced by passing the milk through fixated enzymes over a carrier. In Finland, the products with label HYLA have hydrolyzed lactose. In another method, bacteria such as lactobacillus and acidophilus are used for milk fermentation, similar to the method deployed in yogurt. Herbal milks and their derivatives are sources absolutely free from lactose (soybean milk, rice milk, almond milk, nut milk, pistachio milk, barley milk, cannabis milk and so forth) [1].

Lactase Substituent Supplements

Enzymatic supplements of lactose like the lactase produced in human’s small intestine are generated by aspergillus fungi. Beta-galactasoidase enzymes in tablet form are available in different countries around the world at different dosages without any prescription. This enzyme acts effectively in acidic environment such as the conditions in human’s intestine. Unfortunately, high acidity causes denaturation of this enzyme. Therefore, it shall not be used in an empty stomach. Furthermore, the enzyme will have no effect if it doesn’t reach the small intestine on time. The respective enzyme is also generated by Kluyveromyces yeasts. The enzymes generated by this yeast need long time for operating and are also destroyed in mild acidic environment. This genus is less common than the enzyme produced by aspergillus and is mainly utilized for producing low-lactose products. Lactase enzymatic supplements have an advantage to stopping consumption of dairy products as there is no need to add calcium for supplying adequate calcium especially in children [1 & 5].

Discussion and Conclusions

Today, different methods have been provided for lactose intolerant patients to benefit from dairy products. Devising more novel methods requires further research in this scope.

References

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  2. Sandra Bastin, M.N.S., lactose intolerance. Coopérative extension service, University of Kentucky. 1997.
  3. Tuula H. Vesa, Marteau, P. and Korpela R., lactose intolerance. Journal of the American College of Nutrition, 2000. 19(2): 165-175.
  4. Firouz Ezhieh, Hassan Elyasi, Lactose Intolerance, Post-Specialization Dissertation, Shahid Beheshti Faculty of Medical Sciences, 1993

7) Carroccio A, Montalto G, Cavera G, Notarbatolo A . 1998. Lactose intolerance and self-reported milk intolerance: relationship with lactose maldigestion and nutrient intake. Lactose Deficiency Study Group. J Am Coll Nutr 17 (6): 631–6.

8) Heyman, M. B., 2006.  Lactose intolerance in infants, children and adolescents.  American Academy of Pediatrics, 118 (3): 1279-1286.

9) Rusynyk RA, Lactose intolerance. J Am Osteopath Assoc. 2001. 101: 2-10.

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