Britain has a new approach to fighting COVID-19: It is encouraging citizens to lose weight, because obesity makes the new coronavirus more dangerous. Among other steps, the U.K. government is requiring restaurants to post calorie information on menus. It’s not clear, however, that either of the assumptions underlying this new rule — that obesity exacerbates COVID-19 and that calorie labeling fights obesity — is correct.

The evidence is stronger for the first idea: Obesity does seem to contribute to mortality and other severe outcomes from COVID-19. The effect appears to vary substantially across groups of people, however. And as with most things related to the virus, ambiguities exist. A new analysis of almost 7,000 Kaiser Permanente COVID-19 patients in Southern California found that “obesity was strongly associated with risk for death.” However, the elevated risk applied only to men under the age of 60; there was no association between obesity and coronavirus mortality among women, and very little for anyone over 60, male or female. And the effect for men under 60 applied only to the severely obese (those with body mass index measures above 40).

In the United Kingdom, almost 29 percent of the population is obese. But most of those people — more than 85 percent — are not severely obese. Less than 4 percent of the overall population has a body mass index above 40. And many of these severely obese people are over 60 or female. So if the Kaiser analysis reflects COVID-19’s broader effects, the U.K. strategy stands to protect only a tiny share of the British population. (It should be noted that a U.K. government review of the link between obesity and COVID-19 found a stronger and more universal connection than the Kaiser study did.)

My point here is that, while encouraging people to become healthier and lose weight is a great thing to do, it probably won’t turn out to be important in combating the new coronavirus. And that’s before we even get to difficulties of getting the message across. Which brings us to calorie posting.

Under the new U.K. rules, large restaurants and take-out chains with more than 250 employees will need to provide information about the calorie content of their food. I have some personal experience with this idea: In the administration of U.S. President Barack Obama, we pushed hard to include a similar requirement in the Affordable Care Act. That law requires retail food establishments with 20 or more locations to list calories on the menu. After multiple delays, the rule was finally implemented in 2018.

Calorie labels seem like a good idea. Unfortunately, though, the evidence on their effectiveness has turned out to be remarkably unimpressive. One study of New York City’s labeling requirements, focused on low-income residents, found the rules had no effect on calorie consumption. Studies that have found effects have detected only small ones — a 30-calorie decline per meal in one, for instance, although one analysis discovered large effects for obese men (which would include the severely obese that the Kaiser study indicates are at heightened risk from COVID-19). A recent meta-analysis of the studies concluded:

“Nutritional labeling on restaurant menus reduced the amount of energy (i.e. calories) purchased, but the quality of the three studies that contributed to this finding was low, so our confidence in the effect estimate is limited and may change with further studies. Eight studies assessed this same type of intervention in laboratory settings, but instead of evaluating how much energy participants purchased, these studies evaluated how much energy participants consumed. These studies did not conclusively demonstrate a reduction in energy consumed when menus or foods were labeled, and they were also of low quality.”

The U.K. government is also taking other steps to cut obesity beyond calorie-posting rules. That’s all good. The question, however, is how much to expect from these measures, especially over the coming year or so when the pandemic’s effects will remain the most significant. Losing weight is difficult, and we shouldn’t expect wonders.

After recovering from COVID-19 himself, British Prime Minister Boris Johnson said he was “too fat.” Becoming healthier is a great goal, but government programs to encourage healthy eating will likely be a relatively small element in reducing COVID-19 risks during the time that’s most needed.

Peter R. Orszag is a Bloomberg Opinion columnist. He is the chief executive officer of financial advisory at Lazard. He was director of the Office of Management and Budget from 2009 to 2010, and director of the Congressional Budget Office from 2007 to 2008.

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