‘Fed Up’ Asks, Are All Calories Equal?

Americans have long been told that the cure for obesity is simple: Eat fewer calories and exercise more.

But a new documentary challenges that notion, making the case that Americans have been misled by the idea that we get fat simply because we consume more calories than we expend. The film explores what it sees as some of the more insidious corporate and political forces behind the rise of childhood obesity, and it examines whether increasing levels of sugar consumption have played an outsized role in the epidemic.

The film, called “Fed Up,” has as executive producers Katie Couric, the former anchor of “The CBS Evening News,” and Laurie David, who was also a producer of the global warming documentary “An Inconvenient Truth.” Ms. Couric, who narrates the film, said she came up with the idea after years of covering the obesity epidemic left her with more questions than answers.

“What struck me was that the more I reported on childhood obesity and the longer I was in this business, the worse the problem seemed to be getting,” Ms. Couric said in an interview. “I felt like we were never really giving people a handle on what was causing this and why the rates were skyrocketing the way they were.”

The film draws on commentary from obesity experts and nutrition scientists, and it tells the stories of several obese children around the country who struggle to lose weight despite strict dieting and in some cases hours of daily exercise. But at the heart of the film is a question that is widely debated among scientists: Are all calories equal?

Dr. David Ludwig, the director of the obesity program at Boston Children’s Hospital, argues in the film that they are not. In recent studies, Dr. Ludwig has shown that high-carbohydrate diets appear to slow metabolic rates compared to diets higher in fat and protein, so that people expend less energy even when consuming the same number of calories. Dr. Ludwig has found that unlike calories from so-called low glycemic foods (like beans, nuts and non-starchy vegetables), those from high glycemic foods (such as sugar, bread and potatoes) spike blood sugar and stimulate hunger and cravings, which can drive people to overeat.

While people can certainly lose weight in the short term by focusing on calories, Dr. Ludwig said, studies show that the majority of people on calorie-restricted diets eventually fail. “The common explanation is that people have difficulty resisting temptation,” he said. “But another possibility is that highly processed foods undermine our metabolism and overwhelm our behavior.”

At Harvard Medical School, Dr. Dariush Mozaffarian, an associate professor of medicine and epidemiology whose research was cited by experts in the film, said that the long-held idea that we get fat solely because we consume more calories than we expend is based on outdated science.

He has studied the effects that different foods have on weight gain and said that it is true that 100 calories of fat, protein and carbohydrates are the same in a thermodynamic sense, in that they release the same amount of energy when exposed to a Bunsen burner in a lab. But in a complex organism like a human being, he said, these foods influence satiety, metabolic rate, brain activity, blood sugar and the hormones that store fat in very different ways.

Studies also show that calories from different foods are not absorbed the same. When people eat high-fiber foods like nuts and some vegetables, for example, only about three-quarters of the calories they contain are absorbed. The rest are excreted from the body unused. So the calories listed on their labels are not what the body is actually getting.

“The implicit suggestion is that there are no bad calories, just bad people eating too much,” Dr. Mozaffarian said. “But the evidence is very clear that not all calories are created equal as far as weight gain and obesity. If you’re focusing on calories, you can easily be misguided.”

Some of the harshest criticism in the film is aimed at a recent food industry initiative – led by companies like Coca-Cola and PepsiCo – to remove calories from their products in an effort to address obesity.

“If somebody is drowning in a swimming pool, you could remove a few gallons of water from the pool, and that person will still likely drown,” Dr. Ludwig said. “Whether there is on average 1,000 calories in the food supply too many per person or 800 is really unlikely to make a meaningful difference. What would make a difference is improvement in the quality of the foods available.”

But Marianne Smith Edge of the International Food Information Council, an industry-financed group that published a review of “Fed Up,” said the film overstates data on how much sugar Americans are consuming and wrongly portrays sugar as a lone dietary villain, much as dietary fat was vilified in decades past. Just as research in the last few years has vindicated some fats and shown them to be beneficial, she said, the science on sugar is evolving as well.

“I think the focus on particular nutrients doesn’t tell you the true story,” she said. “It really is about overall calorie consumption and reduced physical activity.”

Ms. Smith Edge, who is a registered dietitian, cited a 2012 study by Y. Claire Wang of the Mailman School of Public Health at Columbia University, which showed that the average child must eliminate 64 calories a day in order for the childhood obesity rate to fall to 14.6 percent by 2020, a goal set by the federal government.

In an interview, Dr. Wang said that for the most part, “if we’re just talking about body weight and obesity, the evidence seems to point in the direction that calories are calories.”

Dr. Wang said that studies consistently show that sugary beverages, potato chips and other high-glycemic foods are indeed associated with weight gain. But this is because they are rapidly digested and easy to consume in large amounts, “not because they bypass our energy balance.”

Dr. Wang said, however, that reducing calories should not be the sole focus of obesity prevention programs. Studies show, for example, that sugary beverages are linked to an increased risk of diabetes and other chronic diseases, but their impact on body weight explains only half of the increased risk, Dr. Wang said.

“These foods mess up our insulin regulation system and affect other inflammatory pathways,” she said. “And that has nothing to do with how they affect body weight.”

Ms. Couric, who has two children, said that she became involved in making the film “as a mom and a concerned citizen,” and that her goal was to start a national dialogue about the quality of our food supply.

“This film doesn’t purport to have all the answers,” Ms. Couric said. “But this is a wake-up call that I hope will spur some solutions. This is not just about carrying a few extra pounds or looking better in your bathing suit. This is a national epidemic with huge societal ramifications.”