Plant-Based Diet

Weighing fertility against longevity may be one reason our pets live longer when they are neutered or spayed. A study of millions of dogs and cats showed that sterilized male and female dogs live about 20 percent longer than “intact” animals, sterilized cats live 40 percent longer, and neutered male cats an impressive 60 percent longer.

And castrated men? Eunuchs appear to live about 25 percent longer than non-castrated men. In the United States, the government forcibly sterilized tens of thousands of people labeled “feebleminded” up into the 1950s, a practice affirmed by none other than the famous Supreme Court Justice Oliver Wendell Holmes. In the context of the 8-to-1 majority in Buck v. Bell—that is, the decision to keep this eugenics practice—he wrote: “The principle that sustains compulsory vaccination is broad enough to cover cutting the Fallopian tubes.” The abhorrent procedure of forced sterilization did, however, enable a natural experiment, and at a psychiatric institution it was found that castrated men lived, on average, 14 years longer than non-castrated men in the same facility.

An analysis of a genealogical database with information on nearly 200 000 men and women over 300 years from 16 countries found that those who had fewer children lived longer. For example, it turned out that people who lived to 100 had fewer children and had become parents at an older age. This is not to say that you live longer if you have fewer children, but rather that the factors that lead to extending human lifespan may come at the cost of reproductive potential—another example of the theory of antagonistic pleiotropy. For example, selection for lifespan extension in model organisms can produce animals that live longer but are less fertile. That makes intuitive sense when you consider the context of food scarcity.

In lean times, it makes sense to put reproduction on hold until conditions are again favorable for long-term survival. Calorie restriction can extend animals’ lives, but can also lead to a lower number of offspring. A similar pattern can be seen in humans. In the Minnesota Starvation Study, subjects quickly lost their libido after their caloric intake was cut in half. Remember the nutrient-sensing pathways of aging—AMPK, IGF-1, and mTOR? There can be a back-and-forth between tissue growth and reproduction on the one hand and tissue maintenance and rejuvenation on the other. Fortunately, we can shift the emphasis through diet so that a better balance results.

The later girls get their first period, the longer they tend to live. Each year that bleeding does not begin is associated with a significantly lower risk of dying from heart disease, cancer, or stroke, and this levels out at the lowest overall mortality among those who do not get their first period until after their 15th birthday. Earlier breast development (before age ten compared with twelve or thirteen) is associated with up to a 23 percent higher risk of breast cancer later in life, and each year that the first bleeding occurs earlier significantly increases the cancer risk of the bladder, breast, colon, liver, lung, skin, and uterus.

A hundred years ago, girls were on average nearly 17 when they got their first period; today they are younger than twelve. Accordingly, worldwide the age at which breast development begins has also declined over the last 50 years by an average of about three months every ten years. In the United States, it is now nine or ten, so one would really have to adjust the term “precocious puberty” in the professional literature. But we have some control over this.

Higher IGF-1 levels mean earlier sexual maturation, so it is no wonder that children who eat more animal protein go through puberty significantly earlier. This effect is not seen with plant proteins. A meta-analysis of 16 studies on diet and development found that with each additional gram of animal protein consumed daily in childhood, the first period occurs up to two months earlier. This means that seven-year-old girls who eat more than twelve servings of meat per week have a 75 percent higher likelihood that their menstruation will begin within the next five years than seven-year-old girls who eat fewer than four servings of meat per week—a calculation that applies to both red meat and poultry. IGF-1 and other aging pathways may not be solely responsible for this development, because persistent pollutants such as DDT, which accumulate in meat, are also associated with precocious puberty.

Plant-Based Diet

The core component thought to underlie the extraordinary longevity of the Adventists in California’s Blue Zone is their plant-based diet. Among Adventists, vegetarians not only live longer than nonvegetarians, who consume relatively little meat, but they also have less cancer and are less likely to have high blood pressure and diabetes. Overall, a comprehensive meta-analysis and a systematic review of the largest observational studies investigating plant-based diets and chronic diseases found that vegetarian diets significantly protect against developing heart disease or dying from it, and that vegan diets cut cancer risk in half.

What about those who abandoned a vegetarian diet and started eating meat? The Adventist Health Study found that, compared with those who remained vegetarian, they had a 230 percent higher risk of gaining weight, as well as a 170 percent higher risk of developing diabetes, and a 150 percent higher risk of stroke or heart disease. If they continued to eat meat, they might also shorten their lifespan by as much as 3.6 years. Conversely, long-term vegetarians showed a longevity benefit. Those who had eaten no meat for at least 17 years had an estimated life expectancy of 86.5 years; for less than 17 years it was 82.9 years. Those who ate meat (including poultry and fish) had a threefold higher risk of dementia than long-term vegetarians.