Is a calorie is a calorie is a calorie? Or is one kind of calorie more likely to make you gain weight than another?
The question has been hard to answer scientifically since it's unethical to make adults gorge themselves until their body mass index reaches unhealthy ranges. But for mice? Ethics aren't so much of a problem in a lab.
In a diet study published in Cell Metabolism, researchers assigned one of 29 different diets to hundreds of adult male mice, including high-fat, super-high fat, high-carb, high-sugar, low-protein, high-protein. The mice stayed on the same diet for three months — roughly equal to nine human years. At the end of their study, the weight and body compositions of the mice were measured, as well as their brain tissue for altered gene activity.
"Only some of the mice became obese — almost every one of which had been on a high-fat diet," wrote Gretchen Reynolds in The New York Times. "These mice showed signs of changes in the activity of certain genes too, in areas of the brain related to processing rewards; fatty kibble made them happy, apparently."
The bottom line: "Sugar did not make the mice fat, and neither did protein deficits. Only fat made them fat."
Harvard doctors have found similar results in their studies, which revealed five foods strongly associated with weight gain (potato chips; other potatoes; sugar-sweetened beverages; unprocessed red meats; processed meats) and five linked with less than average weight gain (vegetables; whole grains; fruits; nuts; yogurt).
But counter to the study on mice, there was not a strong correlation between fat and weight gain.
"There were huge differences in four-year weight gains based on what people did," researcher Dariush Mozaffarian, MD, DrPH, associate professor of medicine and epidemiology at Harvard School of Public Health, Brigham and Women's Hospital and Harvard Medical School told WebMD. "The quantity of fat in the food didn't seem to be strongly related to weight gain." For instance, no differences were seen for low-fat or skim milk compared to whole-fat milk.
''The message here is that the type and quality of food and beverage one eats are incredibly important," he said.
If you're not looking to pack on the pounds, steer clear of foods and drinks that offer little in the way of nutrition. In addition to the five mentioned above, check out this list of offenders:
Loaded with sugar and refined carbs, which Healthline calls "some of the most fattening ingredients in existence," breakfast cereals set you off on a roller coaster. After your blood sugar and insulin levels spike, they'll crash a few hours later, leaving you longing for another carby quick-hit.
Alcohol increases the release of the hormone cortisol, which breaks down muscle and blocks the body from burning fat by increasing the release of the hormone cortisol that breaks down muscle and retains fat. Muscle loss will put the brakes on your metabolism. Insult to injury? Alcohol causes a drop in testosterone in men, a hormone which helps burn fat.
When you see white, run the other way: white rice, pasta, and white bread rank sky high on the high glycemic index advises Care2. But don't be fooled by brown bread. The grains used to make whole wheat bread have been pulverized into a fine flour that causes blood sugar to spike just as fast as refined grains and whole wheat bread has a glycemic index (a measure of how quickly foods spike blood sugar) that is just as high as regular white bread.
More often than not, pretend to be a woman living on a rocky slope in Greece. Center your diet around leafy greens (they'd grow wild near your door); fresh, in-season fruits; whole grains, and proteins that are neither red nor processed. Or, make like those non-obese mice and eat whatever you want, except a fatty diet.