Food ‘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.

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