What do you do when your research reveals that everything you thought you knew about dieting and obesity was wrong? 

If you’re Traci Mann, a psychology professor in the U’s College of Liberal Arts (CLA), you translate those scientific findings into an engaging, accessible book for everyone who’s ever failed at a diet—which, it turns out, is almost everyone.

“People see their weight drop and give the diet credit,” says Mann, founder and director of the Health and Eating Lab in CLA’s Department of Psychology, “but then they blame themselves when they gain it back.”

In her book, Secrets from the Eating Lab: The Science of Weight Loss, the Myth of Willpower, and Why You Should Never Diet Again (Harper-Collins, 2015), Mann shares what she’s learned about eating, dieting, and obesity. Here, she debunks four commonly held beliefs: 

MYTH: DIETING MAKES YOU THINNER.

Almost all of us can lose weight by restricting certain types of food or drastically cutting calories, Mann says. The bad news? Almost everyone gains it back. “The weight coming back is a predictable, expected part of the process,” she explains.

In fact, in a review of dozens of diet studies, Mann found that at the end of the study periods (which ranged from two to 10 years), dieters weighed an average of just 2 pounds less than they had at the beginning. 

That’s partly because when you restrict calories, your metabolism changes to allow you to survive on less. “That means that the number of calories you ate to lose weight eventually becomes too many calories to eat if you want to keep losing weight,” she writes in her book. 

Mann explains that people who diet become preoccupied with food. “You’re more likely to notice food, and once you notice it, you have more trouble taking your attention away from it,” she says. 

MYTH: YOU CAN ACHIEVE ANY WEIGHT YOU WANT.

Mann’s book reviews a number of studies that suggest we each have a “set weight range” that’s genetically determined. Restricting calories to force our bodies below that range is extremely difficult and unlikely to work, as is pushing our bodies above that range. In one study, subjects ate large amounts of food in an effort to gain 20 percent of their starting weight. Some couldn’t gain that much. Of those who did, many found it difficult to keep the weight on.  

“There is somewhere your body wants to be, and it’s not set by you, and your body will defend it biologically and psychologically,” she says.

MYTH: OBESITY IS UNHEALTHY.

The tricky part about testing whether obesity leads to poor health, Mann says, is that in order to do a valid scientific experiment, you’d need to find a group of people and randomly assign part of that group to be obese for long periods of time. Since that’s not possible, the only option is correlational studies—looking at two variables (such as obesity and lifespan, for example) and assessing the relationship between them. 

Unfortunately, when it comes to obesity, there’s no way to narrow down the variables to just two. For example, obesity is correlated with both poverty and a sedentary lifestyle. So if obese people are more likely to get a certain disease, is obesity causing that disease, or is it that they’re living in poverty and less likely to have access to quality health care? Or that they don’t get much exercise ?

Mann cites studies showing that overweight and obese people have the same risk of death as people considered to be a “normal” weight. Only those classified as morbidly obese are likely to die sooner. In addition, people diagnosed with diseases ranging from rheumatoid arthritis to pneumonia are more likely to have a positive prognosis if they’re obese or overweight. Mann says the pattern is so prevalent that it has a name: the obesity paradox.

MYTH: CUTTING BACK SUGAR GRADUALLY IS EFFECTIVE.

Given all the headlines about the negative health effects of sugar, Mann wondered whether the tried-and-true strategy of cutting sugar intake gradually would prove successful for coffee drinkers.

Financial support from the Engdahl Family Research Fund allowed her to compare three groups: One went “cold turkey” eliminating sugar and received mindfulness training in which they focused on aspects like the smell, warmth, and appearance of the coffee before drinking it. This group also learned about five features that professional coffee tasters look for, including viscosity and bitterness. A second group went cold turkey with no mindfulness or tasting training, and a third group cut back sugar gradually. For 12 days, all participants were asked to rate how much they liked their coffee.

The results defied conventional wisdom. The group that used the often-recommended method of gradually cutting back sugar reported that they liked their coffee less and less as they reduced the sugar. The group that received training but went cold turkey on sugar, however, was still drinking coffee without sugar six months after the study ended.

What this and other studies about dieting and eating show, Mann says, is that we should look carefully at the research instead of simply accepting what the media and the diet industry want us to believe. “If you’re exercising and healthy but aren’t as thin as you want to be, you just have to come to terms with your body,” she says.

Amy Sitze is a contributor to Legacy magazine.