Transcript: Treating Asthma With Fruits and Vegetables
In the international study of asthma and allergies in childhood of over a million kids, a consistent inverse relationship (meaning protective relationship) was seen between prevalence rates of asthma, allergies, and eczema, and the intake of plants, starch, grains, and vegetables. If these findings could be generalized, and if the average daily consumption of these foods increased, researchers speculated over a decade ago, an important decrease in symptom prevalence may be achieved. No need to speculate any more, though, plants were finally put to the test.
Researchers had proposed that by eating less and less fruits and vegetables, this had increased the susceptibility of the population as a whole to potentially harmful inhaled substances by reducing the antioxidant defenses of the lung.
That makes sense, the thin lining of fluid that forms the interface between our lung lining and the external environment, is our first line of defense against oxidative damage, which is important in asthma, contributing to airway contraction, mucous, and hypersensitivity. Antioxidants protect against oxidative stress, though, and 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.
In fact you can even quantify the level of oxidative stress in people by measuring their exhaled breath, which drops as they start eating more fruits and vegetables, then drops further when they combine more plants with less animal foods.
So 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 each of the individual phytonutrients they measured: cryptoxanthin, lycopene, lutein, alpha-carotene and beta-carotene compared to healthy controls.
So the accumulating evidence does suggest that diet has an influence in modulating the response of the lung to inhaled allergens and irritants, but wait a second, 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. (Or in cholesterol-free vernacular, which came first, the pea or the pod?)
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, like they did here, take asthmatics and remove fruits and vegetables from their diets and see if they get worse.
This was the first research group to see if altering the intake of antioxidant-rich foods directly affects asthma outcomes. Placing subjects with asthma on a low antioxidant diet for just a matter of days led to a significant worsening of lung function and asthma control. 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.
Interestingly, 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 the study diet or less, it appears likely that this dietary pattern, which must be considered suboptimal for lung health, may be having 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 actually help with asthma? That was the second phase of the study.
Asthmatics on the standard American diet in this study, had about a 40% chance of relapsing into an asthma exacerbation within 3 months. But put them on seven servings of fruits and vegetables instead of three, and you cut their exacerbation rate in half, down to 20%. Just with a few fruits and vegetables.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Ariel Levitsky.
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