In my video Preventing Asthma With Fruits and Vegetables, I highlighted an international study of asthma and allergies involving more than a million kids. The study found a consistent inverse relationship between prevalence rates of asthma, allergies, and eczema and the intake of plants, starch, grains, and vegetables. Researchers speculated “over a decade ago that if these findings could be generalized, and if the average daily consumption of these foods increased, an important decrease in symptom prevalence could be achieved.” No need to speculate any more, though, because plants were finally put to the test.
Researchers have proposed that “by eating fewer fruits and vegetables, the susceptibility to potentially harmful inhaled substances of the population as a whole may be increased because of the reduction in antioxidant defenses of the lungs.” The thin lining of fluid that forms the interface between our respiratory tract and the external environment is our first line of defense against oxidative damage. Oxidative damage is important in asthma, contributing to airway contraction, excessive mucous production, and hypersensitivity. Antioxidants protect against oxidative stress, so our lung lining contains a range of antioxidants our body makes itself, as well as those obtained from our diet, particularly from fruits and vegetables.
We can even quantify the level of oxidative stress in people by measuring the level of oxidation products in their exhaled breath, which drops as we start eating more fruits and vegetables, and drops further as we combine more plants with fewer animal foods.
Do those with asthma really have lower levels of antioxidants than people without asthma? Compared to healthy controls, subjects with asthma had lower whole blood levels of total carotenoids and lower levels of each of the individual phytonutrients they measured: cryptoxanthin, lycopene, lutein, alpha-carotene and beta-carotene compared to healthy controls.
Therefore, they posit, “the accumulating evidence does suggest that diet has an influence in modulating the response of the lung to inhaled allergens and irritants. However, it is possible that the reduced carotenoid levels in asthma are a result of increased utilization in the presence of excess free radicals.” So it’s like a chicken-or-the-egg phenomenon.
We know antioxidant-rich diets have been associated with reduced asthma prevalence. However, direct evidence that altering intake of antioxidant-rich foods actually affects asthma was lacking, until now.
There are two ways to test the effects of fruits and vegetables on asthma. Add fruits and vegetables to people’s diets and see if their asthma improves, or take asthmatics and remove fruits and vegetables from their diets and see if they get worse.
The first such study of its kind, highlighted in my video, Treating Asthma With Fruits and Vegetables, placed subjects with asthma on a low antioxidant diet. After just a matter of days, there was a significant worsening of lung function and asthma control. The researchers conclude that “This finding is highly significant for subjects with asthma, as it indicates that omitting antioxidant-rich foods from the diet, for even a short time frame, will have a detrimental effect on asthma symptoms.”
Ironically, the low antioxidant diet consumed by subjects, where they were restricted to one serving of fruit and up to two servings of vegetables per day, is typical of Western diets. In other words, the low antioxidant diet they used to worsen people’s asthma, crippling their lung function, was just like the standard American diet.
As about “half the population usually consumes a diet with an intake of fruit and vegetables equivalent to that in the study diet or less, it appears likely that this dietary pattern, which must be considered suboptimal for lung health, may have a significant impact on asthma management, indicating the potential for typical Western dietary patterns to contribute to a worsening of lung function and asthma control.”
Within just days, cutting down fruit and vegetable intake can impair lung function, but does adding fruits and vegetables help with asthma? That was the second phase of the study.
Asthmatics on the standard American diet had about a 40% chance of relapsing into an asthma exacerbation within three months. However, put them on seven servings of fruits and vegetables a day instead of three, and we cut their exacerbation rate in half, down to 20%. Imagine if there were a drug that could work as powerfully as a few fruits and vegetables.
If manipulating antioxidant intake by increasing fruit and vegetable intake can so powerfully reduce asthma exacerbation rates, why not just take antioxidant pills instead? I cover that in my video Treating Asthma With Plants vs. Supplements?
And if a few extra servings of fruits and vegetables can make that kind of difference, what about a whole diet composed of plants? Check out Treating Asthma and Eczema With Plant-Based Diets.
What else might antioxidant-rich diets help with? See:
How many antioxidants should we shoot for? See:
- Minimum “Recommended Daily Allowance” of Antioxidants
- How to Reach the Antioxidant “RDA”
- Antioxidant Rich Foods with Every Meal
Where are antioxidants found the most?
-Michael Greger, M.D.
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Image Credit: Pacific Northwest Agricultural Safety and Health Center / Flickr