Self & Other · The Things That Actually Help
Food
This does not mean exercise is bad. The opposite. The ordinary amount most people get — not enough — is well below the level where any of these effects matter. The trade-off is real only at the extreme end of the curve. For nearly every reader, the relevant question is whether to move more, and the answer is yes.
The kind of movement matters less than the regularity. Walking counts. Bicycling counts. Dancing counts. Yard work counts. The intervention with the strongest evidence is not any specific exercise program but the habit of moving most days, in ways you will actually keep doing. Compliance beats optimization.
Food
This is the section where the temptation to overclaim is strongest, so we will be brief and conservative.
Here is what the evidence supports. People who eat diets rich in vegetables, fruits, whole grains, legumes, nuts, and fish — the rough pattern called Mediterranean in the medical literature, with analogs in many cuisines — have, at the population level, lower rates of chronic inflammation and most of the diseases associated with it. The evidence is consistent across many studies and many countries. This kind of eating provides the fiber that feeds the gut microbiome we discussed in Chapter 5, the polyphenols and other compounds that seem to dampen excessive inflammation, and the basic nutrients the immune system needs to do its work.
Here is what the evidence does not support. There is no specific food, however heavily marketed, that meaningfully boosts your immune system. There is no single nutrient that, taken in megadose, will protect you from infection. Most popular “immune-boosting” foods (echinacea, elderberry, garlic, certain mushrooms, various powders) have either weak, mixed evidence or essentially none. More on this in the next chapter.
Specific dietary advice that is genuinely supported by evidence. Eat fiber, in plant form, regularly. Your gut microbiome eats it; you do not. The microbiome’s metabolic byproducts — short-chain fatty acids, particularly butyrate — have meaningful effects on the immune cells of the gut wall, and the evidence linking dietary fiber to lower inflammation and better gut barrier function is substantial. Most adults eat far less fiber than the daily recommended amount.
Limit ultra-processed foods. The evidence is still developing, but it is consistently moving in the same direction: diets dominated by foods that have been mechanically and chemically transformed past the point where they resemble their starting ingredients are associated with higher inflammation, worse cardiovascular outcomes, and a long list of other problems. The cautious move is to eat fewer of them.
Drink enough water, eat enough protein, do not skip meals routinely. These are not glamorous recommendations. They are the recommendations.
A note for people with autoimmune disease, allergies, or celiac. Nothing above should be taken to override what your particular condition requires. People with celiac must avoid gluten. People with food allergies must avoid their triggers. People with inflammatory bowel disease often have personal foods that worsen their symptoms. The general dietary pattern is a starting point. Specific medical conditions modify it. Work with the doctors who know your case.
Vaccines
The most evidence-based intervention in the history of human medicine is vaccination.
This is not hyperbole. No other intervention has so dramatically reduced human suffering and death as the systematic vaccination of populations against the diseases that, until recently, killed millions of children every year. The story of smallpox, which we told in Chapter 4, is one of dozens. Polio, once the most feared disease of childhood in many countries, is on the verge of global elimination. Measles, before the vaccine, killed millions annually worldwide; after widespread vaccination, deaths fell to near-historic lows in countries with strong programs. Diphtheria, pertussis, tetanus, hepatitis B, Haemophilus influenzae type b — all of these used to kill or maim children routinely. Most readers of this book have been exposed to none of them, and that is not because the diseases are gone. It is because almost everyone around them has been vaccinated.
The science of vaccines this book has covered, in pieces, since Chapter 4. By now you know what they are doing biologically: triggering the slow, careful, learning machinery of adaptive immunity to produce memory cells against a specific pathogen, without the patient having to actually get the disease. You know the major types: live attenuated, inactivated, subunit, mRNA. You know that adjuvants make them work better, and that the local soreness in your arm afterward is, in most cases, the adjuvant doing its job.
The recommended childhood and adult vaccine schedules in most wealthy countries reflect the considered judgment of large groups of physicians, researchers, and public health officials weighing benefits against risks across millions of people. Vaccines are not free of risk. Some people have side effects. A small number have serious side effects. The math, in every case where a vaccine has been added to a recommended schedule, has been: the risk of the disease, multiplied by the probability of catching it, is meaningfully larger than the risk of the vaccine. The calculation is made openly. It is updated when new evidence comes in.
Some specific vaccines worth knowing about. The annual flu shot is recommended for nearly everyone over six months old; it is reformulated each year to match the strains predicted to circulate, and it reduces both the chance of getting the flu and the severity of the illness if you do. The HPV vaccine, given typically in early adolescence, prevents most cervical cancers and several other cancers — one of the more remarkable cancer-prevention advances of the last quarter century. The shingles vaccine, recommended for adults over fifty, prevents an extraordinarily painful condition that becomes more common with age. The MMR (measles, mumps, rubella) vaccine prevents three diseases that used to disable and kill children regularly. The COVID vaccines have been one of the best-studied medical interventions in human history, and the evidence on them is overwhelming — more in Chapter 17.