What we eat, or don’t eat, can affect our immune system. This study was conducted to determine the effect of the consumption of brightly colored vegetables on the immune system: the first two weeks basically no fruits and veggies, then two weeks drinking a cup-and-a-half of tomato juice every day, then carrot juice, then spinach powder. This is a graph of a marker of immune function over those eight weeks. Within just two weeks of a fruit and veggie deficient diet, immune function plummets. But just a cup-and-a-half of tomato juice can bring us back from the ashes. Not five servings a day, just that tall glass of tomato juice. But the carrot juice alone didn’t seem to work as well, nor did the powder equivalent of about one serving of spinach. This says to me two things—how remarkably we can affect our immune function with simple dietary decisions, and not all veggies are alike. Though this study was repeated looking at other immune markers and the tomato versus carrot appeared more evenly matched, there is one family of vegetables we definitely don’t want to miss out on. Inflammation, leaky gut, all because of an absence of AHR ligands; in other words an absence of cruciferous vegetables: cabbage, collards, cauliflower, kale, Brussels sprouts, and broccoli.

So, do people who eat healthier actually get sick less? Those who eat more fruits and vegetables appear to have a lower risk of getting an upper respiratory tract infection, like the common cold, whether they’re vegetarian or not. Even just one added apple a day may help keep the doctor away. The common cold is so innocuous, though, why not test against something stronger?

One can also look at more serious respiratory infections like influenza. Looking at the relationship between various risk factors and influenza-related hospitalizations in the United States, researchers found that a 5% increase in the prevalence of obesity was bad, associated with a 6% increased hospitalization rate. But physical inactivity was worse: 7%. But just tiny bump in the rates of low fruit and vegetable consumption may increase flu-related hospitalization rates even more.

And the common cold isn’t always innocuous. A common cold during the first trimester of pregnancy is associated with a number of birth defects, including one of the worst, anencephaly, a fatal malformation of the brain. More recent data suggest it’s the fever, as anti-fever drugs appear able to prevent the possible birth defects causing effect of the common cold, but even better, not to get sick in the first place.

A thousand women and their diets were followed before and during pregnancy, and women who consumed more fruits and vegetables had a moderate reduction in risk of upper respiratory tract infection during pregnancy, and this benefit appears to be derived from both fruits and vegetables instead of either alone.

Whole fruits and vegetables provide a natural balance of all sorts of things that may improve our immune function in a complementary, combined, or synergistic manner that could account for the protective effect observed from high consumption of both fruits and vegetables. Or maybe that’s the only way they got enough. The women who appeared protected in this study were eating nearly nine servings of fruits and vegetables a day, compared with only five servings of fruits, or four of veggies. That may fulfill some arbitrary five or six a day minimum, but may be insufficient for effective immunity.

For example, in that famous study I profiled previously, elderly individuals randomized into a five-a-day group had an improved antibody response to their pneumonia vaccination, compared to just two servings of fruits and vegetables a day; an 80% increase. But only about 30% reached their target levels: 12 out of 40. Six times better than the two-a-day group, but maybe eight-, nine-, or ten-a-day would have worked better.

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 Katie Schloer.

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