Why is it that we haven't seen ads for cigarettes on television since the Nixon administration?

Because public health officials said the ads caused people to smoke more and raised their risk of getting cancer. And because Nixon stood up to the tobacco industry to sign legislation banning the ads to protect people from that temptation.

By that same logic, public health advocates argue, food ads should also be tightly regulated: Food companies use them to entreat us to indulge in their products. And we have an obesity epidemic linked to those unhealthy foods we see on TV.

But the burden of proof when it comes to obesity is higher, partly because eating is a lot more complicated than smoking. And so far the public health community's battle against food ads has been mostly a losing one.

Two new meta-analyses may help put the nail in the coffin of doubt about whether food ads are bad for our health and partly to blame for our obesity epidemic. While different in size and scope, both papers show how food advertising influences eating behavior — and can have a major impact on eating and eventual weight gain.

One of the studies is by Hedy Kober, who runs the Clinical & Affective Neuroscience Laboratory at Yale University. Kober and graduate student Rebecca Boswell decided to review the evidence on the effect of exposure to food cues — both real food and visual cues like ads — and craving on both eating behavior and weight gain. They looked at 45 published reports involving about 3,300 participants.

"We found very, very strong relationships between reactivity and cues and weight and eating," Kober tells us. And she says the results, published online in the journal Obesity Reviews, should inspire us to crack down on how food companies advertise to us.

"Why do we still allow food advertising when children can sit in front of TV cartoons, and in between they get exposed to burgers, fries, chocolate — things we know are nutritionally not the best?" she says. "[Those ads] lead them to ask [for] and want to eat those foods, and that's something we need to think about really seriously."

The second meta-analysis appears in the American Journal of Clinical Nutrition and is a bit narrower in scope: It looked only at studies on how exposure to unhealthy food advertising affects food consumption.

While Kober's meta-analysis found no difference in how visual cues affected eating in adults and children, the second paper did. Ads for junk food significantly increased food consumption in children, but not adults, the researchers found in their analysis of 22 different studies.

"We have also shown that the effects are not confined to TV advertising; online marketing by food and beverage brands is now well established and has a similar impact," study leader Emma Boyland said in a statement. She's a lecturer in psychological sciences at the University of Liverpool's Institute of Psychology, Health & Society.

The takeaway? We need more strategies and policy options to reduce children's exposure to food advertising — not just in the U.S., but everywhere.

Policy experts in the U.S. says they're not particularly optimistic about the prospects of legislation restricting food advertising to children here.

"I really don't have a lot of hope for regulating food ads," says Robert Paarlberg, a global food and agricultural policy scholar affiliated with the Harvard Kennedy School and Wellesley College. "They're considered to be commercial protected speech, and the Supreme Court would have to weigh in to overthrow that."

As Paarlberg writes in his 2015 book, The United States of Excess: Gluttony and the Dark Side of American Exceptionalism, the Obama administration had proposed voluntary guidelines for the industry on food advertising. But the White House dropped that proposal in 2012, after Congress passed a bill requiring a cost-benefit analysis of the guidelines and whether it would lead to job losses in the food and beverage sectors.

The industry does have a voluntary Children's Food and Beverage Advertising Initiative.

But as Dale Kunkel, a professor emeritus of communications at the University of Arizona, told my colleague Allison Aubrey last year, these efforts to cut back on marketing unhealthy foods to children "have barely moved the needle in terms of shifting food advertising to children to genuinely healthy products."

American kids see, on average, three to five ads for fast food per day. And about 50 percent of all ads directed at children are for food.

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