Chapter 105
Vegetables
A series of experiments involving fruit and vegetable deprivation showed dramatically how important healthy foods are for our immune system. The scientists assumed that carotenoid pigments were responsible for the immune-boosting effect, so volunteers in the study were supposed to eliminate all colorful fruits and vegetables. After just two weeks, their immune function measurably declined. When their immune systems were activated, their white blood cells multiplied only sluggishly. To find out how quickly their activity could be restored, they pursued three possible rescue routes: one and a half cups of tomato juice every day, one and a half cups of carrot juice, or a serving of spinach powder. After a week of tomato juice, the activity of the white blood cells began to recover noticeably, but neither the carrot juice nor the spinach seemed able to get the immune system back in order. This tells us two things: We can influence our immune function with diet, and not all vegetables are the same.
When this study was repeated to examine other immune markers, tomato and carrot had more similar effects. (Spinach was left out this time.) After the end of the deprivation, both tomato juice and carrot juice, for example, brought about a significant increase in the activity of natural killer cells. In contrast, dietary supplements with tomato extract (Lycomato) did not strengthen immune defenses. Could something as simple as tomato juice improve immune protection even in those who had not been kept from eating carotenoid-rich fruits and vegetables? Healthy-eating older men and women were randomized for eight weeks to receive either one and a half cups of tomato juice or mineral water, but no differences in immune function were found. So if you habitually eat mostly colorless foods like potatoes, you can very easily restore at least some of your lost immune defenses, but if you regularly eat a minimum amount of healthy fruits and vegetables, it takes more than a glass of tomato juice for further strengthening. Either increase your daily fruit and vegetable intake by several servings, as in the influenza vaccination study, or expand your menu to include top vegetables like broccoli.
Cruciferous vegetables
Cruciferous vegetables are important for the immune defenses of the gut. Broccoli also strengthens our natural killer cells. Researchers drew blood from study participants before and after they ate broccoli sprouts for a few days and found that their natural killer cells’ ability to produce granzyme B had increased. This is an enzyme that activates so-called effector caspases in virus-infected and cancer cells and causes them to destroy the diseased cells. Does that help us actually ward off infections? To find out, researchers dripped influenza viruses into the noses of volunteer subjects.
In a randomized study of smokers, consuming about 120 grams of broccoli sprouts the day before and on the day of infection, compared to a placebo (alfalfa sprouts), significantly reduced viral load and viral inflammation in the nose. From this, the researchers concluded that cruciferous vegetables like broccoli can be a “low-cost and low-risk intervention to reduce the effects of influenza.” The same thing happened with respiratory syncytial virus in mice and with Epstein–Barr virus in vitro. Sulforaphane, presumably the active compound in broccoli and other cruciferous vegetables, also restores the recognition and digestion of bacteria by macrophages obtained from the lungs of patients with lung diseases such as emphysema (COPD). However, the concentration used can be reached in the bloodstream only if one eats about five cups of broccoli in a single meal, so we will learn something about the clinical relevance only once it has been studied at lower doses.
No news is good news
Nitric monoxide, or nitric oxide, is known as the “open sesame” molecule that the arterial lining produces so that artery walls can dilate, but it also has a broad spectrum of antiviral, antibacterial, and antifungal properties. It is released in the airways as a first line of defense against infections, where it shoots up to 500 percent above baseline. Nitrate-rich vegetables can improve athletic performance—can they do the same for immune performance? Infusions of leaf spinach have been used since antiquity to treat respiratory complaints, but as I explain in see.nf/noimmune, the evidence that this leads to lower infection rates is only suggestive.
Seaweed
How about underwater vegetables? Every year, billions of tons of it are harvested from the sea. Japan is among the countries with the highest per-capita consumption of seaweed, and this has been associated with lower rates of disease and even lower overall mortality—though that may simply be a marker that people are eating a more traditional Japanese diet. The wakame seaweed used in seaweed salad strengthens an important part of our immune defenses against viruses such as herpes because it doubles or even quadruples the replication potential of T cells. In the video see.nf/wakame, you can see what consuming just two grams of wakame per day can do for various herpes infections and how wakame can significantly boost the protective antibody response to an influenza vaccination.
Soy products strengthen antibody-producing B cells. In those randomized to drink three cups of soy milk daily, the population of B cells in the blood increased by about 35 percent more than in those who received cow’s milk. Japan also has a very high per-capita consumption of soy, so the suspicion that eating seaweed explains the relatively low rates of HIV and Covid-19 in that country could also be extended to other traditional Japanese foods.
What about nori, probably the most readily available seaweed? These are the sheets that hold sushi together, but you can also make quick and easy snacks with them—my absolute favorites. The nutrient density is hard to beat, and each sheet has only one calorie. In study participants randomized to receive a nori extract for eight weeks, an increase in natural killer cell activity was found. The amount they received corresponded to about seven nori sheets per day, so it is not clear how smaller doses would work.
Chlorella
About 95 percent of all infections begin in our mucous membranes, the moist layer in the eyes, nostrils, and mouth. To protect these surfaces, the body coats them with a special antibody called immunoglobulin A (IgA) on the order of 10 000 million billion (1019) per day. This creates an immunologic barrier that neutralizes viruses and prevents them from entering the body. IgA in saliva, for example, is the first line of defense against pneumonia, influenza, and other respiratory infections.
In Japan, researchers found that the IgA concentration in breast milk can be increased when mothers eat chlorella, a single-celled green freshwater algae sold as a powder or tablets. And in the rest of the body? Chlorella did not convincingly enhance the immune response to the influenza vaccine, but it did increase IgA secretion in the mouth. Unfortunately, as I explain in see.nf/chlorella, it is not clear whether this also makes you get sick less often.
Chlorella can also significantly increase natural killer cell activity. This may play a role in reducing liver damage from chronic hepatitis C virus infections, with additional benefits for cholesterol levels, blood pressure, and blood sugar, but as I report in the video see.nf/chlorella, there was also a concerning case report of a psychosis presumably triggered by chlorella, which makes me cautious.