12 February 2007

Enzymes and allergies

Can eating too much of a certain food lead to a reduction in the enzymes that metabolise it, and consequent allergies? DietDoc investigates.

I recently received a rather interesting question from one of my readers about enzymes and allergies.

The question went like this: "In eating certain foods over and over again, we use up the enzymes needed to digest and metabolise them. An adaptation develops wherein the person copes with the chronic stress by becoming addicted and consequently allergic to that particular food!"

Needless to say, the reader was totally confused by this piece of pop science.

I then realised that many people may be in the dark about how allergies develop and how they can be treated. So let's have a look at this bizarre statement to see what the real scientific facts are about enzymes and allergies.

Many enzymes
The human body produces many enzymes to digest the foods we eat. In most cases, a human being will continue to produce digestive enzymes for his or her entire life no matter what foods are eaten over and over again. The enzymes don't get used up because we produce them afresh every day.

Human beings also certainly don't get "addicted" to certain foods because their enzyme levels may have fallen. This is nonsense!

People also don't get allergic to a food because they are addicted to it. This would mean that every person in the world who is addicted to chocolate would supposedly develop an allergy to chocolate and then of course stop eating chocolate – this does not happen as we full well know. Chocoholics go on eating their favourite food for years and never stop being able to digest it.

Enzyme deficiencies
When certain individuals are born, they lack some of the digestive enzymes required to digest certain foods. The best-known example is probably lactose enzyme deficiency. All types of milk produced by humans and animals (cow's milk, goat's milk etc.) contain lactose, or milk sugar.

If you are born with what is called 'primary lactose intolerance', then you lack the enzyme called lactase that is necessary for the digestion of lactose. In such a case, you cannot digest lactose in milk and may develop symptoms such as abdominal cramps, diarrhoea, foul-smelling stools and growth failure in infants. Such individuals should avoid the intake of large quantities of cow's or goat's milk for the rest of their lives.

However, unless severely affected, most adults with primary lactose intolerance can still drink approximately one cup of milk a day without developing symptoms. Fermented milk products, such as yoghurt, have a low lactose content because most of the milk sugar has been used up during the fermentation process. This means that patients with primary lactose intolerance can usually consume moderate amounts of yoghurt without any negative effects.

Some people are born with lactase enzyme, but tend to lose the ability to produce sufficient quantities of the enzyme as they get older. This condition is called 'secondary lactose intolerance', which is common in many African, Indian and Asian populations. Interestingly, these populations have developed a variety of fermented milk products such as yoghurt, kumis, maas, or kefir, which they can use without developing symptoms.

Metabolic disorders
Other deficiencies of metabolic enzymes can also occur, but are usually rare – for example, a child can be born lacking the enzyme to metabolise galactose (another type of sugar), which leads to galactosemia.

Other patients can't metabolise certain amino acids (maple sugar urine disease patients who are unable to metabolise the branched chain amino acids or phenylketonuria patients who cannot metabolise an amino acid called phenylalanine).

All of these conditions are so-called inborn metabolic disorders where the child is born without one of its metabolic enzymes.

Metabolic disorders such as galactosemia or phenylketonuria are not caused by eating foods over and over again, but by the absence at birth of a vital metabolic enzyme.

Wheat and other allergies
So what about other allergies to foods such as wheat, nuts, soya, seafood, etc? At first glance it would seem that the statement made above, is correct. Most people will eat these foods for many years and then suddenly develop an allergy to wheat or nuts or soya or seafood. Is this not a case of an enzyme getting used up?

No, it is a case of the body's immune system producing minute amounts of protective substances, such as immunoglobulins, because it erroneously assumes that the food or one of its components is harmful (when it actually is not harmful).

Over time, the level or "titre" of these protective substances in the body rises until it reaches a critical level and this is when the person develops a full-blown hypersensitivity reaction to the offending food. Note that "no enzymes have been used up" and no one has become "addicted" to the trigger food. This is a biological reaction that can occur in our bodies no matter what we eat.

Once a patient has experienced a full-blown allergic reaction to a food, he or she can be classified as 'hypersensitive' or 'allergic' to that food and should carefully avoid eating foods that contain the allergen.

Get expert assistance
If you should suffer from a milk, wheat, nut, soya, seafood or any other allergy, intolerance or sensitivity, then it is a good idea to consult a clinical dietician to help you work out a diet that excludes the offending foods, but which is still balanced.

For example, if you or your child are milk intolerant and need to exclude milk and most dairy products from your diet, then a dietician will assist you in selecting a diet that avoids these foods, but is not deficient in calcium or high-quality protein.

Don't just cut out a food or a whole food group because you think you may be allergic. Until you have been tested and there is proof that you are sensitive or intolerant to a specific food, this type of self-diagnosis can be potentially harmful and lead to nutrient deficiencies.

If you suspect that you may be reacting negatively to certain foods, go for a medical checkup and if the symptoms are not being caused by other conditions (e.g. skin rashes caused by eczema or fungal infections, bloating and diarrhoea caused by irritable bowel syndrome, etc), then ask your doctor to send you for allergy tests.

If you test positive for one or more foods, consult a dietician to help you with your exclusion diet. To find a dietician in your area, you can visit the Association for Dietetics in SA website at: and click on "Find a Dietician".

I hope that this will help you to understand what food allergies are all about and that it is not that our enzymes get used up (except in the case of 'secondary milk intolerance'), or that we develop allergies to foods we are addicted to, but rather that some people lack certain enzymes at birth and other people develop hypersensitivity to foods because of a reaction of the immune system.

Text copyright: Dr I.V. van Heerden (DietDoc)
12 February 2007

(Mahan et al. (2000). Krause's Food, Nutrition & Diet Therapy, 10th Edition, WB Saunders Co, USA)
Read more:
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Dr Morris is the Principal Allergist at the Cape Town and Johannesburg Allergy Clinics with postgraduate diplomas in Allergology, Dermatology, Paediatrics and Family Medicine dealing with both adult and childhood allergies. obesity and diabetes societies and runs a trial centre for new drugs.

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