Asthma
and Diet
By Kate Jackson
Today’s Dietitian
Vol. 7 No. 5 P. 32
There’s still little consensus about the influence
of diet on asthma. But since the proposed interventions are harmless,
are they worth a try?
In recent years, a flurry of research studies have
explored any number of proposed connections between dietary intake
and asthma symptoms. The medical literature is rife with theories
that certain foods or nutrients exacerbate asthmatic inflammation
and bronchial hyperreactivity, while others reduce inflammation
and thus promote easier breathing. For the most part, though, they’re
little more than hypotheses or promising topics for more substantial
research.
Scientists eagerly turn their energies toward exploring
diet as a modulator for the disease, however, because although excellent
medical treatments are available to people with asthma, nutritional
strategies would be a boon to the 15 million Americans believed
to suffer, particularly children—the fastest growing segment
of the asthmatic population.
In the United States, asthma is the most common
chronic illness of childhood and a leading cause of hospitalizations
and school absences. During the past 15 years, its incidence is
estimated to have increased 150% in preschool-aged children and
74% in school-aged children. Although hard and fast evidence is
difficult to come by, some voices argue that those alarming statistics
have at least something to do with the quality of diet in American
children. Numerous studies have explored a link between asthma and
the consumption of—among other dietary substances—antioxidants
and other vitamins, selenium, fish oils and other forms of fatty
acids, salt, and dairy products. Although the research so far is
not of a depth and breadth to be compelling, it’s persuasive
enough to at least suggest that inadequate nutrition may increase
inflammation in the airways and thereby contribute to bronchial
hyperreactivity. Despite the paucity of significant controlled studies
with clear findings, many experts are encouraged enough to research
further, and some clinicians are going so far as to make simple
dietary recommendations for people with asthma.
Why Intervene?
Why promote dietary intervention in the absence of hard facts? Simply
because most commonly proposed dietary strategies for ameliorating
asthma symptoms are not only harmless but generally sound nutritional
tactics for all individuals, whether or not they have breathing
disorders. Furthermore, they parallel guidelines offered for the
prevention of cancer and heart disease and so may be of benefit
beyond their influence on the airways.
Still, there’s little consensus about the
influence of diet on asthma in general or even with respect to particular
food substances or components. Some clinicians insist that food
can make a difference while others are holding out for more data.
But there is agreement about one thing: While nutrition therapy
should never substitute for traditional asthma care, it might be
beneficial as an adjunct to the best possible medical care, and
… it can’t hurt.
The Range of Opinions
At one end of the spectrum of opinion is Alan D. Harsch, MD, assistant
professor of pediatrics, division of pediatric pulmonary medicine,
Emory University School of Medicine, and pediatric pulmonologist
at Children’s Healthcare of Atlanta, who suggests that nutrition
contributes in only a limited way to asthma. “Most of the
interest in the idea of nutritional approaches come from a time
when we weren’t very good at treating asthma, so people gravitated
toward other approaches to control it.”
Today, he says, there are excellent medical therapies
and so less need to find an alternative. There’s no danger
in the nutritional approaches, he concedes, but he doesn’t
see sufficient evidence that they do much good. Nevertheless, he
says, “I encourage my patients who are interested in that
approach to consider it but caution them about thinking that anything
is going to work better than traditional medicine.”
At the other end of the range of opinions are Amy
Lanou, PhD, and Clifford Bassett, MD. “I believe there’s
a connection between asthma and nutrition,” Lanou says cautiously.
Nutrition director for the Physicians Community for Responsible
Medicine and author of Healthy Eating for Life for Kids, she adds
that “asthma is so multifaceted that it would be impossible
to say that it’s the only cause or modulator of the disease,
but it’s fairly clear at this point that there are a variety
of ways that nutrition can interact in at least some individuals
with asthma.”
Bassett, medical director of allergy and asthma
care at The Long Island College Hospital in New York, says there’s
accumulating research evidence between the prevalence of asthma
and dietary factors. He points to studies linking vitamin E intakes
with reduced incidence of asthma, the consumption of fatty acids
and fish oils as well as calcium from food to a reduction in wheezing
and cough, selenium intake to the protection of the lungs, and elevated
iron in newborn blood from the umbilical cord to reduced asthma
and eczema. Dietitians, he speculates, may use these findings to
positively impact their clients’ health.
A voice somewhere in-between belongs to Sue Moores,
MS, RD, nutrition consultant in St. Paul, Minn., and a national
spokesperson for the American Dietetic Association, who is both
skeptical and optimistic. “For every study that said something
good about milk, for example, I’ve seen something not good
about milk, so I’d be suspect of anyone who offered definitive
answers when it comes to a food’s impact on asthma,”
she says. Nevertheless, she believes research is strong enough to
at least indicate a link. “How strong and how direct that
link is, that’s what’s up in the air. But we’d
be remiss as dietitians to totally negate that food may have a role.”
The Food-Asthma Connections
Although there has been a great number of mostly small studies exploring
potential interactions between food and asthma, research, for the
most part, has centered on the following topics:
Antioxidants
A number of scientists have looked at the role of antioxidants in
lung function and concluded that individuals who consume abundant
quantities of fruits and vegetables reduce their risk for respiratory
illness. Study results have been equivocal. Spanish researchers
in 2001 reported in Allergy their findings of a case control study
of 118 asthma patients and 112 healthy subjects showing no evidence
of a link between blood levels of micronutrient or antioxidant levels
and asthma. As with most aspects of the diet-asthma connection,
other studies have reached the opposite conclusion. For example,
British researchers reported in 2001 on the protective effect of
dietary antioxidants, specifically those contained in apples and
red wine, as well as selenium.
Fatty Acids
Asthma is among the growing list of maladies believed to be improved
by increased consumption of omega-3 fatty acids and decreased intake
of omega-6 fatty acids. While too many omega-6 fatty acids increase
the production of cytokines, which cause inflammation and irritate
the airways, abundant omega-3 fatty acids do the opposite.
In one study, Japanese researchers compared pulmonary
function in two groups of asthmatic subjects, one given a supplement
rich in perilla seed oil for four weeks and the other a supplement
rich in corn oil for the same period of time. Their findings revealed
that the group receiving the perilla seed oil, rich in omega-3 fatty
acids, showed better pulmonary function than those receiving the
corn oil, which is rich in omega-6 fatty acids.
Among other scientists exploring the potential of
omega-3s, however, Australian researchers who performed randomized
controlled trials comparing fish oil supplementation with placebo
in patients with asthma found no benefit, as well as no risk, in
such supplementation. On the other hand, another Australian study
comparing normal children with those with asthma pointed toward
a protective effect of a diet with increased omega-3s and reduced
omega-6s, noting that children who ate fresh fish high in omega-3s
were 75% less likely than those who didn’t to have asthma.
Some researchers further hypothesize that an appropriate ratio of
these fatty acids not only improves symptoms but reduces one’s
risk of developing asthma, even suggesting that excessive consumption
of omega-6s contributes to the development of asthma.
Obesity and Lipid Intake
It’s been widely noted that obesity and asthma often coexist
and that both have been on the rise in recent decades. Research
has revealed improved lung function and reduced asthma symptoms
following weight loss in obese patients. University of California,
Los Angeles researchers, writing in the April 2003 issue of the
Annals of Allergy, Asthma, and Immunology, concluded from a review
of literature that nutritional strategies such as the intake of
oils containing gamma-linolenic acid and eicosapentaenoic acid diminishes
the inflammatory process linked to asthma. Evidence suggests, they
conclude, that high body mass index and consumption of dietary lipids
contribute to asthma symptoms and that dietary modification may
decrease symptoms at the same time that it reduces the risk of other
chronic illnesses. It’s also been suggested that trans fats
are damaging to the airways because they instigate the production
of prostaglandins and leukotrienes.
Salt
Some researchers have explored the possibility that high levels
of dietary sodium influence pulmonary function in individuals with
asthma, especially in those with exercise-induced asthma. Researchers
reporting in the August 2004 issue of the Journal of Alternative
and Complementary Medicine on a review of the literature concluded
that studies supporting the notion of reducing dietary sodium to
diminish the symptoms of asthma are promising yet methodologically
limited and not clinically persuasive. More research, they conclude,
is needed.
Milk
Studies surrounding a link between milk and symptoms of asthma have
been equally confounding. Investigations suggest that frequent consumption
of milk by children correlates with a reduction in the risk of asthma
symptoms, with some researchers crediting the magnesium in milk
and others attributing the improved lung function to calcium. While
milk may not be a problem for most children with asthma, it can
aggravate the problem for children who are actually allergic to
it. For that group, it is a good idea to exclude egg and milk protein
from the diet, says Lanou. “There’s no harm in trying
it for any child with asthma, and there are certainly other ways
to get protein and calcium in the diet, methods for which dietitians
can explain.”
Since milk is not harmful, however, to most people
with asthma and may in fact be beneficial, dietitians, says Harsch,
can help dispel the apparent myth that links milk products and mucous
promotion. “We consider it a myth because we have been unable
to prove it,” Harsch says. “The scientific approach
dictates that you should be able to prove a hypothesis by altering
a variable in an experimental situation—for example, how much
milk someone is ingesting and whether that correlates to a change
in mucous production or consistency.”
Despite several studies, no one has been able to
prove it, he explains. He speculates that the myth may arise from
the feeling milk produces in the throat because of its semiviscous
nature. But he admits to a bit of doubt. It’s an extremely
common belief, he says—one that crosses cultures. “The
milk-mucous production belief is fairly universal. Apparently grandmothers
in Siberia and mothers in Africa say it, so you have to wonder if
there could be something to it.” Furthermore, Harsch observes,
people naturally tend to avoid it when they’re congested,
and people very attuned to it—opera singers, for example—tend
to believe it. Still, his patient population is made up of children
who drink large quantities of milk to no apparent ill effect.
Helping Clients
All in all, even in the absence of stronger evidence that diet affects
asthma symptoms, experts suggest that a variety of healthy nutritional
strategies may help, and if they don’t have a direct effect
on asthma symptoms, will at least enhance general health. Among
the suggestions are increasing consumption of fruits, vegetables,
whole grains, foods rich in omega-3 fatty acids such as fatty fish,
walnuts, and flaxseed; and low-fat dairy products, and decreasing
intake of processed foods, foods with preservatives and colorings
for sensitive individuals, and foods containing trans fats—such
as fast food, baked goods, and fatty snacks—and replacing
them with foods containing monounsaturated fats, as well as cooking
and using monounsaturated fats as opposed to trans fat-containing
margarines. If you guide your clients and help them develop food
plans based on these guidelines, they may well breathe more easily
and will surely improve their general health and reduce their risk
for other chronic diseases such as cancer, heart disease, and diabetes.
At the same time, cautions Harsch, it’s important for dietitians
to emphasize the effectiveness and irreplaceability of traditional
medical therapy.
The foremost role of the dietitian, says Moores,
is to meet the client with an open mind. If they believe a food
has an impact upon their symptoms, she suggests, listen and learn.
A good practitioner, she says, is willing to work with a client
if they want to explore safe adjunctive approaches, and a dietitian
is in the position to do so in the safest possible way. “Some
of these dietary interventions might be important enough at least
to try. And dietitians can lend their trained eyes to help clients
avoid pitfalls, concerns, and red flags. It’s not something
people should go into blindly,” Moores says, adding that dietitians
must keep up with the rapidly changing medical literature concerning
nutrition. In light of conflicting evidence, she says, “it
pays for RDs to look at all the data and use their skills to come
up with the best plan for each patient.”
Dietitians may also assist clients with asthma in
three other ways. Educating individuals with food allergies about
food labels and helping them shop carefully may improve their ability
to avoid food allergens that may trigger asthma. Second, eating
may be challenging for people with breathing problems, and dietitians
can help by advising them to eat smaller, more frequent meals that
will place less stress upon the diaphragm to avoid worsening shortness
of breath. Finally, although most asthma patients use oral steroid
medications rather than oral steroids that can impair their ability
to metabolize calcium, dietitians can help those few in the latter
category eat better and can recommend calcium and vitamin D supplements
if appropriate to counter loss of bone density. Use of systemic
steroids may also cause appetite increase and weight gain as well
as fluid retention—problems RDs can address through counseling.
Until science points toward more specific benefits
of dietary intervention, the simple guidelines described above,
say experts, may not necessarily help, but they’re still sound
diet recommendations. Says Moores, “They’re not radical.
When you talk about eating more fish, fruits, and vegetables, for
example, that’s just a good habit that may have a ripple effect
on many health fronts. It won’t hurt anyone, and it might
do some wonderful things in all sorts of other areas.”
— Kate Jackson is a staff writer for Today’s
Dietitian.
An Asthma Diet?
Fred Pescatore, MD, head of the Centers for Integrative and Complementary
Medicine in Dallas and New York and author of The Allergy and Asthma
Cure: A Complete 8-Step Nutritional Program, doesn’t claim
that diet causes asthma but believes it may arouse symptoms and
cause flare-ups in someone who’s genetically predisposed to
develop the disease. He came upon his nutritional approach to the
tackling of asthma through personal experience. As an overweight
youth, he suffered greatly from spring and fall allergies. In college,
he went on a diet, lost weight, and, he recalls, his asthma and
allergies disappeared. It was eye-opening, he says, to think there
might be a connection, and he was spurred to study nutrition and
explore the link he suspected.
Allergies and asthma, he realized, were highly inflammatory
conditions, and it became clear to him that if you decrease the
internal inflammation, you’re less likely to suffer from external
sources. He explored the connections between inflammation and asthma.
His research led him to study in particular the role of sugar on
the immune system, its impact on internal candidiasis, and the role
of fats in inflammation. Based on that research, he devised a diet
that eliminates those three inflammatory factors and, according
to his clinical study, brings about improvement in asthma. He put
20 of his patients on a low-yeast, low-sugar diet. Eighteen patients,
he says, were able to reduce their medication use by half, and three
were able to stop their medications entirely.
He recommends that patients experiencing severe
symptoms use a low-yeast, low-sugar cleansing diet described in
his book. Among the foods that are prohibited are yeast breads,
vinegar, and other fermented products, alcohol, dairy, white rice,
and pasta other than whole grain. Also forbidden are trans fats
and “partially hydrogenated anything.” It sounds difficult,
but Pescatore comments that it’s not necessary to stay on
the diet forever—just for several months until one gets rid
of the inflammation in the body. Meanwhile, patients can fill up
on whole grains, lean proteins, fruits and vegetables, and cook
and serve with healthful monounsaturated oils, so there’s
no danger of being undernourished. Asthma experts and dietitians
suggest that while the diet may seem unorthodox, it’s not
unhealthy and might help reduce inflammation associated with asthma.
— KJ
Breast-feeding
Reduces Risk of Asthma in First Four Years of Life
Exclusive breast-feeding from birth to 4 months of age reduces the
risk of asthma during the first four years of life, according to
a study in the October 2004 issue of the Journal of Allergy &
Clinical Immunology. Inger Kull, RN, and colleagues from the Department
of Occupational and Environmental Health in Stockholm, Sweden, evaluated
the relationship between breast-feeding and asthma in 4,089 newborns.
Data was collected from the parents on symptoms related to wheezing
and other allergic disease in their child at 1, 2, and 4 months
of age. Data on breast-feeding was collected after 2 years of age.
Exclusive breast-feeding was defined as the period when the infants
were given only breast milk and no cow’s milk or solid foods
had been introduced.
Researchers found the following:
• Four-year-olds who had been exclusively
breast-fed for the first four months showed a lower risk of asthma
• 9.1% of children exclusively breast-fed
for less than four months had asthma, compared with 6.4% among children
breast-fed four months or more.
• Continued partial breast-feeding after exclusive
breast-feeding also had a protective effect.
• The protective effects of breast-feeding
were greatest among children whose parent(s) did not have asthma
or allergies.
The researchers had previously shown the same results
in children at 2 years of age. This study expands on those findings,
showing that more prolonged period of breast-feeding not only reduces
the risk of asthma during the first four years of life, but it also
appears to reduce the severity of the disease.
— Source: The American Academy of Allergy,
Asthma & Immunology
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