|
|
Issue 1, November 2003
Food For Thought!
Kate Wighton, Science Journalist
Biochemistry, Imperial College of Science Technology & Medicine
wighton@jyi.org
Discuss this article!
 |
Figure
1. Peanuts and peanut-containing foods are commonly known
sources of food allergies. Source: Scott Bauer/United
States Department of Agriculture.
(Click to view enlarged image) |
Along
with Lord of the Rings, David Blaine in a box and the Atkins diet,
food intolerance is fast becoming the next big thing. A recent study
published in the medical journal The Lancet suggests that 19.4%
of the British population believe they have a food intolerance,
when in fact the actual prevalence is 1.4%.
Food Intolerance and Food Allergy – What's the difference?
Finding a concrete definition of food intolerance/allergy is difficult.
Many people perceive them as the same thing. "It’s difficult
to get actual definitions of food intolerance and allergy,"
says Tanya Wright, a dietician who has worked and published material
on this subject. "Even experts can’t give clean-cut
definitions; therefore if professionals cannot offer definitions
it’s very hard for anyone else to know the difference."
Generally, food intolerance refers to an adverse reaction to a food
that causes feelings of discomfort, such as nausea, bloating or
migraine. Food allergy involves the antibody immunoglobulin E (IgE)
recognizing a food as "foreign." The ensuing immune responses
vary from local swelling to life-threatening anaphylactic shock.
Although
the definitions of food intolerance and food allergy are cloudy,
these appear to be the most widely accepted:
Food Intolerance
Food intolerance is the general term used
to describe a range of reproducible adverse responses to a
specific food or food ingredient which can occur whether or
the not the person realizes they have eaten the food. The
general term includes allergic reactions that by definition
involve the immune system (such as celiac disease), adverse
reactions resulting from enzyme deficiencies (such as lactose
intolerance), pharmacological reactions (such as caffeine
sensitivity), and other non-defined responses. Food intolerance
does not include food poisoning from bacteria and viruses,
mold, chemicals, toxins, and irritants in food, nor does it
include food aversion (dislike and subsequent avoidance to
foods).
Food Allergy
An allergic reaction to a food is an inappropriate
reaction by the body’s immune system to the ingestion
of a food that in the majority of individuals causes no adverse
reactions. Allergic reactions to foods vary in severity and
can be potentially fatal. In food allergy, the immune system
does not recognize as safe a protein component of the food
to which the individual is sensitive (such as some proteins
in peanuts). This component is termed the allergen. The immune
system then typically produces immunoglobulin E (IgE) antibodies
to the allergen, which trigger other cells to release substances
that cause inflammation. Allergic reactions are usually localized
to a particular part of the body and symptoms may include
asthma, eczema, flushing and swelling of tissues (such as
lips), or difficulty in breathing. A severe reaction may result
in anaphylaxis (as with severe peanut allergy), in which there
is a rapid fall in blood pressure and severe shock.
Source:
www.studentbmj.com/Judith Buttriss, Science Director, British
Nutrition Foundation |
How do you know if you have a food intolerance?
Debbie, a schoolteacher from Oxford, England, had been feeling unwell
for some time. As she explains, "It was January 2002, I had
bad sickness and diarrhea and was referred to a hospital consultant
in March but due to the waiting list the appointment was not until
August." Exasperated with this long wait and not wanting to
feel ill on her summer vacation, Debbie decided to buy a food intolerance
home test kit she had seen in her local pharmacy, for the cost of
about £200 (US$340). The test procedure was simple: send a
blood sample and the results would come back in two weeks. Also
included in the price of the test was a one-hour consultation with
a dietician to discuss the test results.
"The
results of my test showed that I was intolerant to gluten, wheat,
cow’s milk, and soya," Debbie says. "They recommended
that I cut these, as well as oats and rye, from my diet."
Even though she was not intolerant to the latter two foods, the
dietician informed her that if she had intolerance it was usually
easier to detect if "the whole lot were cut out of the diet."
"By
August," Debbie says, "I had been completely off all
the suggested foods for one month and was feeling better."
In
August, Debbie also saw the hospital consultant, who suggested a
series of tests. These took about a year in total to complete, due
to waiting periods of two to three months between each one. It also
meant re-including the foods into her diet that she had previously
been avoiding. The test results showed some intestinal inflammation,
which the consultant attributed to fat in her diet. He did not believe
that her discomfort was linked to any of the foods suggested by
the home test dietician.
Given conflicting opinions and advice, Debbie tried to do some reading
around the subject herself but with little success. "It was
difficult to get any solid facts as there were many different bodies
of thinking, which made it very hard to get a clear diagnosis,"
she said. "It was pretty much a trial and error method that
I had to adopt to find out what was wrong."
How
is food intolerance diagnosed?
Food intolerance
is notoriously hard to diagnose, as Debbie found out; it involves
a process of skin tests, blood tests, and exclusion diets. Although
these procedures are necessary to achieve a proper diagnosis, they
can be all-consuming. Patients may have to take time off work and
the social implications of being on a strict diet can also be quite
tough.
| The
diagnosis of food intolerance often involves five steps:
|
- History
and clinical analysis
- Clinical
and laboratory test
This stage can involve tests such as the RAST (radioallergosorbent
test), which involves mixing small amounts of the patient’s
blood with food extracts in a test tube. In the case of
an allergy the blood will produce antibodies to the food
extract, recognizing it as “foreign.”
Another test commonly used is the skin-prick test, whereby
food extracts are placed on the patient’s skin. The
skin is then pricked or scratched to see if there is any
swelling or itchiness.
- Diagnostic
exclusion diet
Certain food groups are excluded one at the time from the
patient’s diet. Excluded foods should always be substituted
by foods that would be easily accessible and are of similar
nutritional value.
- Open
food challenges
These involve the patient eating small amounts of a variety
of food groups (e.g., wheat, shellfish) while their body’s
responses are recorded. These are needed to confirm diagnosis
and are used to investigate the severity and development
of the food intolerance.
- Double-blind
placebo controlled food challenges
A rather complex test involving patients eating a small
amount of food without either the patient or clinician knowing
which food is being sampled. This is undertaken by disguising
the food in another dish or putting in an unmarked capsule.
|
Poor
provisions of allergy services
Due to a number
of reasons, in Debbie’s case not being able to see a professional
for some time, people are taking matters into their own hands. This
can have detrimental effects. Although people may eventually identify
the causes for their food complaints, exclusion diets — when
not properly managed by a healthcare professional — can lead
to a decline in an individual’s nutritional health.
Wright believes
this may be due to a lack of services providing diagnosis and treatment
of food intolerance and food allergy. "The provisions for
allergy services are very poor," she says. "There are
long waiting lists for many allergy clinics, for example the waiting
list for allergy clinics in Scotland is up to two years."
Is food intolerance fashionable?
Talk of food,
or to be more specific, diets, constantly surrounds us. Whether
it is via the television, glossy magazines or the Internet, there
is constant discussion of what foods to eat or avoid.
"Recently
food intolerance had almost become ‘trendy,’"
says Wright. "The marketing of intolerance-substitution foods
may also have an effect. The manufacturers of these foods claim
that if you feel tired or run down then you could have a food intolerance,
when in many cases this may not be true."
Whether
it is due to trends, an ill sufficiency of allergy services offering
diagnosis or simply an increase in awareness of this disorder, the
cause of the apparent discrepancy between actual and perceived cases
of food intolerance is uncertain. What is certain is the effect
that it has on sufferers. Food intolerance causes them distress,
from diagnosis, the intolerance itself, and detrimental effects
on their health if it remains untreated.
Discuss this article!
Related
Websites
www.allergyfoundation.com
References
Buttriss,
J., ed. Adverse Reactions to Food. Oxford: Blackwell Science (2001)
Jansen, J.J., et al. Prevalence of food allergy and intolerance
in the adult Dutch population. Journal of Allergy and Clinical Immunology,
93:446-456 (1994)
Wright, T. Food Allergies – Enjoying Life with a Severe Food
Allergy. London: Class Publishing (2001)
Young E., et al. A population study of food intolerance. The Lancet.
343:1127-30 (1994)
Journal
of Young Investigators. 2003. Volume Nine.
Copyright © 2003 by Kate Wighton and JYI. All rights reserved.
|
|