On its face, it all seems so easy: Calories are calories, no matter the food. And if you want to lose weight, all you have to do is simply "spend" more calories than you consume, either by exercising more or eating less.
But anyone who has ever attempted to lose weight this way knows that it's not easy at all. And long-term weight management seems downright impossible for most, given the dismal number of those who do manage to keep the pounds off over the years.
The problem, says cardiovascular research scientist James DiNicolantonio of St. Luke's Hospital, is the idea of calories themselves as a weight loss tool.
"Every country around the world is having a problem with obesity, and so far nothing has worked," said DiNicolantonio. "But it's important to note that we're not dying of obesity, we're dying of chronic metabolic disease."
Things like heart disease, diabetes and stroke contribute to about 800,00 annual deaths in the U.S. alone -- and now researchers are hoping to isolate foods that are metabolically disruptive, rather than high in calories, in the hope of lowering the rates of such illnesses.
In a study review published in the journal Public Health Nutrition, DiNicolantonio argues that thinking about the human body as a balance sheet of calories -- keeping a ledger of calories in and calories out -- ignores the very real and negative metabolic effects that certain ingredients, like simple carbohydrates (pastas and white bread, for example) and added sugars, have on the body.
In the review, DiNicolantonio argues that rapidly absorbable carbohydrates -- things like sugar, high-fructose corn syrup, potatoes, white rice, cereal and anything made with white flour -- result in weight gain because they spike blood sugar, which causes insulin levels to rise. This leads to a sudden drop in blood sugar, prompting the person to crave still more carbohydrates. He calls this a "reinforcing loop for overconsumption" that, in the long term, could disable leptin (the hormone that makes us feel full), resulting in even more overeating.
This pathway has been investigated and described in previous studies by scientists like University of California, San Francisco sugar researcher Dr. Robert Lustig, who described sugar as a "poison," and Dr. Peter Havel of University of California, Davis, who is investigating the link between fructose and metabolic syndrome.
"Just as we wouldn't blame a child for growing taller if they're going through puberty -- because their hormones are causing that to happen -- hormones also can cause fat storage, and they can promote hunger," DiNicolantonio explained in a phone interview with The Huffington Post.
"Once you know the biochemistry, you realize that it's not your fault, and it's not about willpower. These foods have altered your biochemistry to make you literally feel starved."
Focusing on calories can also create a bias against many healthful foods, particularly high-fat foods. Dietary fat is more caloric than carbohydrates or protein, so low-calorie foods are often low in fat. This leads people to replace healthy fatty foods like nuts with lower-calorie foods like low-fat baked potato chips that aren't as nutritious or filling.
Moreover, accurately estimating calorie intake and expenditure is extremely difficult, even for the most well-informed and dedicated person with the latest gadgets.
More crucially, our bodies will simply not be fooled. If you exercise more, your body responds by prompting you to eat more food. If you eat less, your body will respond by holding back energy that you might otherwise use. And unless you like going to bed hungry, something -- either exercise or eating less -- is going to give. DiNicolantonio described this as the biological coupling of calorie intake and calorie expenditure, and researchers theorize that it may be one reason why people struggle to maintain weight loss over the long term.
DiNicolantonio doesn't endorse any particular diet, but the message from the review was straight-forward: If you want to lose weight, "don't focus on calories," advised DiNicolantonio. "A higher-fat, higher calorie food is generally going to promote more satiety, and you're going to eat less of it."
Earlier this year in an unrelated but influential study, Tulane University nutrition professor Lydia Bazzano conducted a year-long randomized controlled trial of two groups of dieters: those who cut down on carbs and those who cut down on fat. She found that low-carb dieters lost eight pounds more than the low-fat group. The low-carb dieters also significantly decreased their estimated 10-year risk for coronary heart disease, while the low-fat group did not. Her study participants didn't count calories, and her results are corroborated by much of DiNicolantonio's work.
Bazzano praised the new review for pointing out that different foods affect the body differently, in more profound ways than the calories they contribute.
"Acknowledging that not all calorie sources have equivalent effects in the body is crucial, and the 'calorie is a calorie' theory actually prevents this," Bazzano wrote in an email to HuffPost. "These macro-nutrients, carbohydrates, fats and protein, go down different metabolic pathways in our bodies and produce different feelings, trigger different hormones and cellular messengers, producing different outcomes in terms of weight and disease risk."
A decades-long obsession with lower calories (and consequently lower fat) has benefited companies that make low-fat foods but add sugar and salt to make their products tastier, Bazzano continued.
"Food items that are 100 percent rapidly absorbable carbohydrate could add 'low fat' to their labeling and thereby be perceived as 'healthy' and potentially assisting with weight loss, because these items didn't contain that concentrated source of calories: fat," said Bazzano.
According to the World Health Organization's global figures for 2008, the latest available, more than 1.4 billion adults were overweight. In 2013, 42 million preschoolers worldwide were overweight, and overweight children are more likely than normal-weight children to be obese as adults.