Nutrition

Do people who eat properly stay healthy? Those who eat more fruits and vegetables have a lower risk of coming down with an upper respiratory tract infection, such as a common cold. Even the famous extra apple a day really can keep the doctor away. At the community level, for more severe respiratory infections such as the flu, a 5-percent share of people with overweight is associated with a 6-percent increase in flu-related hospital admissions. 5 percent less physical activity meant 7 percent more hospitalizations, and low fruit and vegetable consumption can increase flu-related hospitalizations by 8 percent. But those who eat fruits and vegetables also live healthier in other ways. The only way to find out whether fruits and vegetables strengthen the immune system is a study.

To test the theory that poor diet contributes to the loss of immune function in old age, researchers divided 83 volunteers aged 65 and older into two groups. The intervention group ate at least five servings of fruits and vegetables per day; the control group ate fewer than three. Everyone was then vaccinated against pneumonia, which is generally recommended for people over 65. The goal of vaccination is to prepare our immune system to produce antibodies against the pathogen in question in case we ever become infected. Compared with the control group, study participants who had eaten five or more servings of fruits and vegetables had an 82 percent stronger antibody response to the vaccine. And that after just one month with a few extra daily servings of fruits and vegetables. That’s how powerfully our eating habits can affect the immune system.

Kiwis, echinacea, and elderberries

Certain fruits and vegetables can give immune function an extra boost. One fruit that has been tested in this regard is the kiwi. Preschool children were to be randomized to eat either bananas or yellow kiwis every day. Compared with the banana group, the kiwi kids’ risk of getting an influenza-like illness or cold fell by almost half. (Why yellow kiwis? The study was funded by the company that holds the patent on yellow kiwis.) However, approximately every 130th child has an allergic reaction to kiwis, making them the third most common food allergen (after milk and eggs), so they are not suitable for everyone.

A similar experiment was carried out with another high-risk group, older adults. Those in the control group who ate bananas and got an upper respiratory tract infection suffered from nasal congestion and a sore throat for about five days; the kiwi eaters felt better after just one to two days. In contrast, flu drugs such as oseltamivir (Tamiflu) can shorten the duration of symptoms in adults by only an average of about 17 hours. A 2020 review titled “Foods or Medicines? The Therapeutic Effects of Foods on the Duration and Frequency of Upper Respiratory Tract Infections” identified another advantage: kiwis cost “much less.”

Kiwis are actually berries. (They were originally called Chinese gooseberries before a few clever New Zealand exporters named the fuzzy brown fruit after their fuzzy brown national bird.) What about other berries? I cover all the studies on elderberries at see.nf/elderberries. In short, four studies came to positive conclusions, but they were all funded by companies that make elder products. Then in 2020 an independent (philanthropically funded) study was finally published—a randomized placebo-controlled double-blind trial of an elder extract for flu treatment. Unlike the industry-funded studies, participants in this study seemed to do worse when they took elder, and they had more severe pain. Among participants not taking Tamiflu, those randomized to receive the elder placebo were sick for five days, whereas those who received the real elder were sick for seven days. An article about the study summarized the result: “We can confidently advise patients against elder.” As I show in the video, the echinacea herb had similarly disappointing results.

Elder supplements may not even be safe. There is a case report of a man who took elder extract and developed acute pancreatitis (a sudden, painful inflammation of the pancreas). Interestingly, the symptoms disappeared when he stopped the supplement and reappeared years later when he took it again, suggesting cause and effect. But why take elder extract when you can just eat elderberries? Because raw elderberries can make you vomit your guts out, as I found out the hard way when I raided a bush in the garden for breakfast. It turned out that raw elderberries form cyanide. Only after I recovered did I come across reports from the Center of Disease and Control Prevention such as “Poisoning from Elderberry Juice—California” about eight people who had to be airlifted to the hospital after someone served freshly pressed elderberry juice at a gathering. All I can say is I’m glad my body rejected the berries. What would they have written on my headstone? “Author of How Not to Die, killed by a smoothie.”

Other berries

What other berries might help us? At see.nf/immuneberries I go through the whole list. Intervention studies show, for example, that blueberries can increase the number of natural killer cells, that the aromatic spice cardamom can increase their activity, and that black raspberries seem able to do both, but does that also mean fewer infections? Sea buckthorn increases the activity of another type of “first responder” immune cells, but it cannot prevent respiratory tract, digestive tract, or urinary tract infections any better than a placebo.

Goji berries do seem to have real, positive effects on the immune system. Men and women between 65 and 70 were randomized to consume either four teaspoons of goji berry powder daily for 90 days or a deceptively real placebo powder. On day 30, everyone received a flu shot. By day 60, the goji group already had a significantly better antibody response, so that by day 90 three times as many subjects in the goji group achieved seroconversion (a sufficiently protective antibody level): 28 percent compared with only 9 percent in the placebo group.

Does it have to be organic?

A review summarizing the latest findings on the effects of pesticides on human health states that the evidence for a connection between pesticide exposure and cancer is “so extensive that the role of pesticides in causing cancer can no longer be questioned.” However, most of the data demonstrating DNA damage from pesticides come from occupational exposure: from farmers, field workers, and people in the pesticide industry itself, or from areas with heavy pesticide use. But residues still remain on conventionally grown fruits and vegetables, right? I discuss the literature on this in the video see.nf/pesticides. In short, those who choose organic products appear to have lower cancer rates after adjusting for confounders, but even if this is a causal relationship, the benefits of eating conventional fruits and vegetables outweigh the risks from pesticide exposure. Fear of pesticides therefore shouldn’t keep us from eating as much fresh food as possible. Damage from pesticides in food shortens a person’s life, on average, by only a few minutes, which is nothing compared with the health benefits we get from eating fruits and vegetables.