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Health conditions in the United States are heavily bifurcated, with certain segments of the population seeing great progress while others see their health eroding.

The backdrop to the progress is the revolution in health that’s unfolding, with much of it happening in and around Silicon Valley. It’s clear that we’re living in a time of unprecedented possibilities, with new knowledge and technologies accelerating the pace of biomedical discovery. In the area of biomedicine, there’s a convergence of different fields and ideas and approaches underway.

One small but revealing symbol of the potential for progress is the research being conducted by Stanford faculty. Approximately two‐thirds of the professors in the chemistry department are doing biologically focused research. So are about 30 percent of those in Stanford’s engineering school. Several factors account for this shift in focus to research questions and opportunities in biomedicine by experts in other disciplines. The fields of biology and medicine have become quantitative endeavors. Gone are the days when the scientific inquiry in biomedicine was driven principally by qualitative description. The same analytical methods and approaches that have fueled advances in the physical sciences and technology for many decades are now being applied with enormous success in biomedicine. The questions being addressed and the discoveries being made, thanks to these quantitative approaches, are having a tremendous impact.

There are many examples of the transformation in biomedicine that is occurring because of the adoption of quantitative approaches. Mapping of the human genome and the subsequent advances in sequencing technology have changed the landscape of genetics. These advances—exciting as they are—increasingly seem modest compared with the impact of more sophisticated algorithms focused on identification of the relationships between the genome and diseases as well as the interactions between the genome and other nongenetic risk factors for disease. These same transformations are having an impact on fundamental, discovery‐focused science.

The cell atlas initiative of the Chan Zuckerberg Biohub focuses on building a repository of all the different cell types in the human body—something that is currently unknown. Understanding all the different cell types is crucial, points out Steve Quake, a Stanford professor and co‐president of the Chan Zuckerberg Biohub: “Having this knowledge will lead to greater understanding of the basic biology of human beings as well as what goes wrong and causes disease” [1]. It will be enabled by exciting new technologies such as CRISPR (“Clustered Regularly Interspaced Short Palindromic Repeats”), a gene‐editing tool that will be used for experiments exploring whether certain combinations of genes can halt the progression of a disease—or even reverse it. The findings can be the basis for new medicines and new tests that are focused on combating specific diseases.

As breakthroughs like these are pursued, we are seeing the adoption of various technology‐based products that are enabling people to become more engaged with their health and, ultimately, to live longer, healthier lives.

But set against this hopeful environment is an altogether different reality: certain segments of the U.S. population are experiencing a decline in basic indicators of good health. There are many ways to illustrate this decline, but life expectancy is perhaps the easiest to understand.

At the beginning of the 20^th century, U.S. life expectancy was just 47.3 years. That figure rose steadily in the decades that followed, thanks in large part to medical advances, and by the start of the 21^st century U.S. life expectancy was 76.8 years [2]. For the next 14 years, the incremental gains continued. But then something happened.

In 2015, life expectancy declined. Then it happened again in 2016, and again in 2017. This was the first decline in U.S. life expectancy over three consecutive years since the period coinciding with the end of World War I and the Spanish influenza. While the declines were quite modest, they did help illuminate the U.S. health challenges. The declines were also a reminder that the United States fares poorly in international comparisons. U.S. life expectancy is now only the 43^rd highest in the world [3]—in 1960, the U.S. ranked 13^th [4].

The U.S. average masks wide disparities. For example, there is a six‐year difference in life expectancy between the residents of Hawaii and Mississippi, according to a study published in the Journal of the American Medical Association in 2017. There is a 20‐year difference between one county in Colorado and one in South Dakota [5].

There is also a large life expectancy gap based on income. Men with earnings in the top 1 percent of the population live 14.6 years longer than men in the bottom 1 percent (among women, the gap is 10.1 years), according to a 2016 study coauthored by economist Raj Chetty [6]. While men in the top 5 percent of the income distribution saw their life expectancy increase by 2.3 years between 2001 and 2014, it only grew 0.32 years for those in the bottom 5 percent. The gap was even larger among women—2.91 years and 0.04 years, respectively [7].

The gap is not just between the very rich and the very poor. In recent years, the mortality rate for men ages 65–79 in the top 1 percent of wealth distribution has been 40 percent lower than the average mortality rates for all tax filers in that age bracket, according to UC Berkeley economists Emmanuel Saez and Gabriel Zucman. From 1979 to 1983, the difference between the top 1 percent and everyone else was just 10 percent [8].

A study conducted by seven professors at the Stanford School of Medicine, led by Latha Palaniappan, documented the persistence of U.S. health disparities from 2003 to 2015. The study, which was published in November 2018, showed that while the age‐ and sex‐adjusted mortality rates decreased by 12 percent in the total population, high‐income counties experienced a 15 percent decline, while in low‐income counties the decline was only 7 percent. Similarly, adjusted mortality rates for heart disease declined 30 percent in high‐income counties, but 22 percent in low‐income counties. The study also showed that African Americans have a higher mortality rate than other groups (Asian Americans, Hispanics, non‐Hispanic whites, and American Indians/Alaska Natives) [9].

These disparities highlight the need for remedies that will help those who are falling behind. One of the most disturbing facts about U.S. health is the number of people who die prematurely each year and the causes of those deaths. The authors of a 2013 report sponsored by the National Institutes of Health wrote that “Americans are dying and suffering from illness and injury at rates that are demonstrably unnecessary” [10].

The causes of those deaths were spelled out in another comprehensive study, which was published in 2013 in the Journal of the American Medical Association. The researchers found that the primary causes of U.S. morbidity and mortality were poor diet, obesity, smoking, and high blood pressure [11]. The study has continued to be updated, and there is extensive data comparing current trends with those that existed in 1990. Some of the news is encouraging: the number of people dying from ischemic heart disease declined by nearly 100,000. On the other hand, heart disease was still responsible for nearly 545,000 deaths—well more than twice the number of deaths from any other condition. (The second‐biggest killer in 2016 was Alzheimer’s and other dementias, which were responsible for close to 239,000 deaths [12].)

When deaths were broken out by causes, and not specific diseases, one factor stood out from the rest: diet. The researchers found that “dietary risks” accounted for close to 530,000 deaths in 2016. Nearly 84 percent of the deaths stemmed from cardiovascular diseases, and the rest stemmed from a combination of neoplasms and diabetes, as well as urogenital, blood, and endocrine diseases [13].

The dietary risks are reflected in the expanding waistlines of the American people. Today, nearly 40 percent of American adults qualify as obese (meaning a body mass index of 30 or higher), as do 18.5 percent of children 19 and under [14]. The only countries with higher obesity rates (not counting a number of tiny Pacific and Caribbean islands) are Kuwait, Belize, Qatar, and Egypt.

What’s striking is how quickly the profile of the American population changed. As recently as 1980, just 10 percent of the U.S. population was obese. Although obesity rates have been rising globally—there’s been a tenfold increase in childhood obesity over the past 40 years [15]—the percentage point increase in American obesity since 1980 has been greater than in any other country in the world, according to a study published in 2017 in the New England Journal of Medicine [16].

The reasons for this decline in health are varied, and they speak to the need for new approaches to health—particularly focused on prediction and prevention. In later chapters, I highlight how select initiatives can not only treat obesity but try to prevent it (particularly in children) by emphasizing the value of both a healthy diet and regular physical activity.