New York Mayor Michael Bloomberg told David Letterman that “for the first time in the history of the world, more people will die from overeating than under-eating this year.” After Letterman expressed surprise, Bloomberg added: “It’s all happened in the last 20 years.”

So, is obesity going to lead to more deaths than not getting enough food this year for the “first time” in history? No. Has there been a shift in such risk factors for deaths in the last 20 years? Yes.

Bloomberg, who has attracted national attention for attempting to ban the sale of sugary drinks over 16 ounces, has repeated this talking point several times since last summer.

But the change in mortality risk factors isn’t surprising to public health experts, who have been predicting this shift for a long time. In fact, obesity has been a greater risk factor for death than children being underweight worldwide since as early as 2005, according to the Institute for Health Metrics and Evaluation at the University of Washington. “People in public health, we’ve been talking about this for a long time,” Ali Mokdad, professor of global health at IHME, told us. “I’ve been saying, ‘It’s coming, it’s coming, it’s coming.’ ” (Adults can die from being underweight, too, but not in significant numbers — it’s the vulnerable population, kids, Mokdad said, that is affected.)

When we asked Bloomberg’s office about the mayor’s remarks, spokeswoman Samantha Levine told us that the mayor meant that this year, there would be a continuation of the years-long trend, not that this year would be the first time obesity-related deaths would outnumber underweight-related deaths. “The Mayor was noting that more people are dying from obesity than from hunger and that — over [the] course of human history — this is the only period of time that has occurred. This year that trend will continue,” she said in an email.

That point may be lost on viewers and listeners of Bloomberg’s interviews on this topic, particularly since he uses the future tense and the “first time” stipulation.

It’s unclear exactly when this change occurred for worldwide statistics, but it would be sometime between 1990 and 2005, according to figures provided to us by the Institute for Health Metrics and Evaluation, which publishes the Global Burden of Disease Study with the help of hundreds of coauthors. The study determined that in 1990, childhood underweight was the sixth leading risk factor for premature death worldwide, while having a high body mass index (being overweight or obese) came in ninth. The institute told us that in 2005, childhood underweight had dropped to the 11th leading risk factor while high body mass index moved up to seventh.

In 2010, being overweight or obese moved up one more spot, to the sixth leading risk factor for death globally, and childhood underweight stayed in 11th place. The institute could not provide year-to-year statistics.

Note that these are risk factors for premature death, which would also include behaviors and conditions such as smoking, drinking alcohol or having high blood pressure. They are the factors that lead to death, but the causes that would be listed on death certificates would be heart disease, diabetes, cancer, cholera, pneumonia, malnutrition, and so on. For instance, being overweight could lead to death from heart disease. Being overweight is the risk factor; heart disease is what’s on the death certificate.

The Institute for Health Metrics and Evaluation told us that 2.3 million children worldwide died due to being underweight in 1990; in 2010, the number was 860,000. That’s a 63 percent drop. Similarly, 2 million deaths worldwide in 1990 can be attributed to high body mass index; that shot up to an estimated 3.4 million people in 2010, an increase of 70 percent.

The world’s population, of course, also increased during that time — from 5.3 billion in 1990 to 6.9 billion in 2010, a jump of 30 percent, according to the U.S. Census Bureau.

The shift certainly means that obesity is a global problem, but it also shows that there have been great successes in fighting infectious diseases that affect underweight children. Those children can die from communicable diseases because they’re more susceptible to them.

Bloomberg’s Talking Point

Bloomberg has repeated this talking point several times since last summer. For instance, on July 23, 2012, he said on MSNBC’s “Morning Joe”: “More people — and it’s not just America, more people will die this year of overweight than of starvation in the world. First time in the history of the world.”

A month later, he again said on MSNBC: “And obesity, for the first time in this world — in the history of the world — more people are dying from being overweight than from starvation. This is the first disease that’s gone from being a rich man’s disease to a poor man’s disease, and it will bankrupt the country, and I just want to make sure we get ahead of it.”

On March 1, he added that this has “come about in the last 20 years.” Bloomberg said on “The John Gambling Show with Mayor Mike” on New York radio station WOR 710 AM: “For the first time in the history of the world, more people will die from too much food than from too little food. Think about that. It’s the first time in the history of the world, and it’s all come about in the last 20 years.”

And he again used both the “first time” and “last 20 years” lines in his March 11 interview on the “Late Show with David Letterman”:

Letterman: And what would be the statistics of people who are dying of starvation versus people who are dying from obesity? Bloomberg: For the first time in the history of the world, more people will die from overeating than under-eating this year. Letterman: Isn’t that remarkable. Bloomberg: It’s all happened in the last 20 years.

Bloomberg is wrong to say that this “will” happen for the “first time” “this year.” He would be correct to say that this shift has occurred sometime in about the last 20 years.

Obesity has become more of an issue around the world at the same time that progress has been made in fighting childhood underweight deaths. “Deaths due to overweight/obesity are increasing, and deaths due to child underweight are decreasing rapidly,” Tarik Jasarevic, a spokesman for the World Health Organization, told us in an email. “The trends on child underweight are partly a result of successful efforts to combat childhood diseases that used to kill underweight children — now these children are more likely to receive proper treatment and survive.”

Mokdad at the Institute for Health Metrics and Evaluation said that the statistics show “a success story” for the fight against communicable diseases. “People who have been working on infectious diseases should be acknowledged that they have done a good job,” he said, explaining that much has been done to immunize children and make sure they are well nourished. But that means, naturally, another risk factor has popped up and needs that same kind of attention. “As a result, we’re paying for it with more chronic diseases.”

People are also living longer — another success story, Mokdad said. But as we’re living longer, chronic diseases become more of a problem, too.

We would note that groups that work on child hunger issues use much higher statistics than 860,000 underweight deaths, the Institute for Health Metrics and Evaluation’s 2010 figure. UNICEF’s child mortality report, for instance, says that 7.6 million kids under the age of 5 died in 2010 (down from 12 million in 1990), and the underlying cause was undernutrition in “more than a third” of them — or about 2.6 million kids. But “undernutrition” is not always the same thing as “underweight.” Plus, Mokdad said that in his group’s analysis, “total mortality has to add to 100 percent. We don’t have double-counting.” Advocacy groups use different numbers. “We’re neutral,” he said, “and people do it differently.”

Bloomberg’s office referred us to the WHO to back up his claim. A WHO fact sheet attributes at least 2.8 million adult deaths each year to obesity or being overweight and attributes certain percentages of health problems to high body mass, saying that “44% of the diabetes burden, 23% of the ischaemic heart disease burden and between 7% and 41% of certain cancer burdens are attributable to overweight and obesity.” But the WHO couldn’t provide more detailed data on overweight versus underweight deaths. It referred us to the institute at the University of Washington for the most up-to-date statistics.

The university’s Institute for Health Metrics and Evaluation coordinated and published the Global Burden of Disease reports. The 2010 report, which was released in December 2012, found a “rapid transformation” in global health. People were living longer and countries made strides in preventing childhood deaths and infectious disease. “The leading causes of death and disability have changed from communicable diseases in children,” the report says, “to non-communicable diseases in adults. Eating too much has overtaken undernutrition as a leading risk factor for illness.”

The report looks not only at death but also ill health, using a measurement it calls disability-adjusted life years, or DALYs, which are years of life lost to premature death and disability. High body mass index, or BMI, was a major contributor to DALYs in 2010, as it was in 1990. But it increased dramatically and surpassed childhood underweight, which was a more significant risk factor in 1990.

The report notes, however, that such global rankings “mask important differences across countries and regions.” Childhood underweight in 2010 was still the leading risk factor for premature death and disability in most countries in sub-Saharan Africa. It was the No. 1 risk factor in 14 African nations and the second or third leading risk factor in six other countries.

However, Mokdad said it was correct for Bloomberg to say that obesity “has gone from a rich person’s disease to a poor person’s disease.” He said the problem, with the exception of some African nations, has spread throughout the world to both rich and poor communities. “It’s not the composition of your diet, how expensive it is,” he said. It’s how many calories one consumes.

Public health experts have been predicting for some time that unhealthy lifestyles would surpass infectious diseases as a major killer in the developing world. An April 6, 1993, United Press International report said that the WHO estimated that 45 percent of deaths in developing countries were due to unhealthy living, but that would increase to 60 percent by 2015. Unhealthy living would account for 75 percent of deaths in industrialized countries, the WHO said.

A few years later, in 1997, the WHO again said this shift in global health was occurring: “Indeed, overweight and obesity are now so common that they are replacing the more traditional public health concerns such as undernutrition and infectious diseases as some of the most significant contributors to ill health,” it said in a report on a 1997 meeting on obesity in Geneva. In a 2004 report, the organization said that “a profound shift” had happened in the causes of death and illness in developed countries and was under way in developing nations, as noncommunicable diseases increased.

That’s the shift the Global Burden of Disease Study noted in its 2010 report. And the one Bloomberg could accurately describe as having occurred “over the past 20 years,” not “for the first time … this year,” as he has repeatedly said.

— Lori Robertson