Introduction

Lactose is a disaccharide, which means it is composed of two saccharides (sugars) joined together. Lactose Intolerance (LI) is the inability to digest significant amounts of lactose due to a shortage of the enzyme lactase, which is normally produced in the small intestine and its function is to separate the two sugars from each other. Lactase breaks down the lactose, the main sugar in milk, into two smaller sugars glucose and galactose to be absorbed in the bloodstream. LI is the most common disorder in the world, although it may be claimed that humans where never made to be lactose tolerant.

In a normal digestive system all the food we eat is broken down into smaller and simpler ‘bits and pieces' by the help of the enzymes that are present in our saliva, stomach and the digestive tract. This helps the body to absorb the food, take out the nutrients, proteins, carbohydrates and what ever is needed to maintain itself. Lactase breaks down milk sugar (lactose) into the simpler form of sugar called glucose and galactose that can then be absorbed into the bloodstream.

It is not quite clear why there has to be a special carbohydrate (sugar) in milk. Some writers hypothesize that lactose solubility may be matched best with milk synthesis and expression, and it may provide appropriate energy while minimizing osmotic load. As far as is known, lactose has no special nutritional importance for adults. It is the most important source of energy during the first year of a human’s life, providing almost half the total energy requirement of infants.

Lactose has several applications in the food industry. It is used, for instance, in sweets, confectionery, bread and sausages because of its physiological properties: lactose provides good texture and binds water and colour. Lactose is only about one third as sweet as sucrose (normal sugar) and less than half as sweet as glucose.

To be absorbed, lactose needs to be hydrolyzed (broken down) in the intestine by a ß-galactosidase, lactase-phloritzin hydrolase, generally called lactase (read article explaining how lactase functions and how sugars are absorbed). Lactase is found most abundantly in the jejunum (at the beginning of the small intestine), and it specifically only hydrolyses lactose. It is found at the tip of the intestinal villi (see Figure 1) and is therefore more vulnerable to intestinal diseases that cause cell damage than other sugars, which are located deeper.

Lactase: enzyme found in microvilli cells of small intestine that hydrolyzes lactose.

Pharmaceutical preparations of fungal or yeast-derived lactase have been developed for the treatment of lactose maldigestion. There is evidence that these preparations increase lactose digestion and alleviate symptoms, but different preparations seem to vary in their effectiveness, and they do not help all subjects. One case report on allergy to supplemental lactase enzyme (Lactaid and Lacteeze) has been published in the Journal of Allergy and Clinical Immunology (Volume 97, Issue 6, Pages 1414-1416).

Terminology of Lactose Intolerance

The following are terminology differences and possible confounding terms about lactose intolerance:

• Lactose maldigestion & lactose malabsorption: are terms to describe a poor lactose hydrolysing capacity without symptoms.
• Hypolactasia, lactase non-persistence, lactase restriction: means that there is low lactase activity in the jejunal mucosa.
• Normolactasia, lactase persistence: when there is persistent lactase activity comparable to the neonatal period
• Lactose Intolerance: should only be used for a clinical entity, describing symptomatic lactose maldigestion (20% of hypolactasic individuals.