Breath easy, fruits and vegetables can prevent and improve asthma!
The Doctor's Office
Reactive Airway Disease, or Asthma, occurs when airways in the lungs become inflamed and narrowed, making it more difficult to move air (breath). It is largely an allergic response when the body's immune system gets out of balance. The severity of asthma can vary from an occasional nuisance to a lethal condition. Asthma is the most common chronic condition afflicting kids and it is increasing rapidly in the United States.
Recently researchers from England published a study of 1.2 million children from around the world in which they noted a huge variation in asthma rates in different places: as much as 20 to 60 fold differences! As expected, they found that air pollution was associated with higher rates of asthma, but surprisingly the strongest association with asthma rates was the diet. Fruit and vegetable intake was protective against asthma, while diets high in fat, sodium and sugar were associated with increased rates of asthma.
This isn't the first time diet has been found to play a major role in asthma, a small study found that removing eggs and dairy from asthmatic children's diet improved lung function measurably after eight weeks. Another study found that adults with the lowest intake of vitamin C from plants had a 7 fold increased risk of asthma. The lowest intake of saturated fat provided a 10 fold protection from asthma. Researchers from Australia also found saturated fat increases airway inflammation and makes bronchodilator medications less effective. They ranked 46 foods on a scale ranging from inflammatory on one end to anti-inflammatory on the other. Pro-inflammation foods were high in saturated fat, sugar and preservatives. Anti-inflammatory foods were fruits, vegetables, and foods high in fiber. The higher the inflammation index, the higher the chance of asthma. 70% of the asthmatics in the study were found in the highest consumers of pro-inflammatory foods.
It is important to understand that "associations" of variables with disease does not prove cause or cure of disease. For example researchers from the woman's health study found that patients who had the most vitamin E in their blood from diet had half the rate of asthma as those with the least amount of vitamin E. But the vitamin E had to come from food. People with high levels of vitamin E in their blood from supplements weren't protected. So at first we might jump to the conclusion that vitamin E supplements might be a good treatment for asthma, but we see that is not the case. The most likely reason is that high vitamin E levels are a marker for overall healthy diet, so it likely is a combination of many phytonutrients found in food that are acting together to protect whole food plant eaters from asthma, not just high levels of vitamin E. This is supported by other observations made by researchers including men who eat apples were found to have superior lung function, and kids with the highest fruit, salad, vegetable intakes had better pulmonary function testing.
Despite all of this exciting research on asthma, no one had yet tried to treat it with diet, until now. Practitioners in Sweden were making claims that they could treat asthma with a vegan diet, so a group of skeptical physicians at a major teaching institution took a small group of severe asthmatics and subjected them to a vegan diet for a year. 35 asthmatics started, but only 24 patients were able to stick to the vegan diet. Of these 24 patients, 71% ere improved at 4 months and 92% were improved at 1 year as measured by their ratings of their life as well as pulmonary function tests and blood markers of inflammation. Four patients were able to completely stop taking medications and the number of medications dropped from an average of 4.5 per patient to 1.2 per patient. Granted, there was no placebo arm of the study, but neither were there any negative side effects. Patients did however lose weight, improve their cholesterol and blood pressure.
One class of phytonutrients that is responsible for better asthma outcomes is the polyphenols. These phytonutrients bind allergens so our immune system doesn't react to them. They also act in a secondary way by inhibiting activation of the allergic response if the immune system does recognize the allergen.
Another way plant food is thought to protect against asthma is through it's effects on the intestinal flora. (see the previous blog Primer on Prebiotics, Probiotics, and Produce). Intestinal flora is thought to be important in developing and priming our immune systems in childhood. It has been observed that lactobacillus is less likely to be found in kids with allergies and asthma, and probiotics containing lactobacillus may help with childhood asthma. However we couldn't be sure it was the plant strong diet that led to better intestinal flora and less asthma as these children were also more likely to have been born vaginally, more likely to have been breastfed and less likely to have been exposed to antibiotics. So which factor made these kids less likely to have asthma? We are fortunate that researchers set out to answer just that question. They hypothesized that less fruit and vegetable intake led to less anti-oxidant protection in the lungs leaving a person more susceptible to toxic inhaled substances. This makes sense because our lungs and airways are coated with a thin fluid layer that is our first line of defense. This layer contains a range of anti-oxidants. We can actually measure a person's oxidative stress level through the breath exhaled, and oxidative stress does decrease with higher intake of fruit and vegetables. Oxidative stress further decreases by decreasing animal foods. This is consistent with the observation that child asthmatics have lower levels of phyotnutrients and antioxidants in their blood.
These observations are interesting, but what really matters is will changing the children's diet help their asthma? Researchers set out to answer this question first by depriving asthmatic children of fruits and vegetables to examine the effect on their asthma. When fruits and vegetables were removed from their diet, symptoms became much worse in a matter of days. Interestingly, the restrictive diet used in the study was 1 serving of fruit and 2 servings of vegetables a day, which is what the average american diet consists of! 50% of the US population today consumes 3 or less servings of fruits and vegetables daily. Researchers then sought to evaluate the treatment effect of fruits and vegetables for asthma. They compared the 3 serving/day group to a group who ate 7 servings of fruit and vegetables a day and observed the number of asthmatic exacerbations was reduced by half over the next three months in the group that ate more fruit and vegetables. And the side effects of the treatment? Less cancer, less heart disease, longer more productive lives!
