The author of a new obesity book says we shouldn't try to lose weight. She's wrong.

There are few things I'd more love to report than the idea that you no longer need to worry about your weight.

"This whole obesity thing has been an industry-fueled charade!" I'd say, and then we'd all throw away our salads and sink our teeth into cheeseburgers and cupcakes.

Body of Truth. (Amazon)

This is just what Harriet Brown, author of a new book, Body of Truth, suggests (she has also written a Slate article on the subject, which I have extracted below). Brown builds on the "obesity paradox" studies, which have found that some people who classify as overweight appear to have better health and mortality rates than their normal weight counterparts.

She also raises a recurring argument: that the multibillion-dollar fitness and weight-loss industries perpetuate an "obesity myth," and that the current concern over body size isn't rooted in science. She then takes the scientific uncertainties one step further, suggesting that most people can't keep weight off anyway, so they shouldn't even bother to try. It all sounds so appealing and counterintuitive. But unfortunately her argument has a number of flaws.

Obesity is very complex, and diet manufacturers do sell insane weight-loss claims that no one should ever waste money on. But at the same time, those scientific uncertainties and industry perversion in no way outweigh the overwhelming body of evidence we now have that excess fat is still very, very bad for health.

Insane fad diets may fail — but that shouldn't indict all weight loss attempts

Alexander Prokopenko/Shutterstock

(alexpro9500/Shutterstock)

"If you’re one of the 45 million Americans who plan to go on a diet this year, I’ve got one word of advice for you: Don’t. You’ll likely lose weight in the short term, but your chance of keeping if off for five years or more is about the same as your chance of surviving metastatic lung cancer: 5 percent. And when you do gain back the weight, everyone will blame you. Including you."

A lot of weight loss fails because most people try unsustainable diets or buy into insane fads that have no chance of working in the long term. But this doesn't indict all diets.

I've talked to leading weight loss and obesity researchers and experts across North America, and they've consistently had one clear message: weight loss can work when you cut calories in a way you like and can sustain, and focus on eating more healthfully.

Some of the best research on what works for weight loss comes from the National Weight Control Registry, a study that has parsed the traits, habits, and behaviors of adults who have lost at least 30 pounds and kept it off for a minimum of one year. There are currently more than 10,000 members enrolled in the study, who respond to annual questionnaires about how they've managed to keep their weight down.

What makes maintaining weight loss seem impossible are the goal posts society has generally set

The researchers behind the registry found that people who have had success losing weight share a few habits: they weigh themselves at least once a week. They exercise regularly at varying degrees of intensity, with the most common exercise being walking. They restrict their calorie intake, stay away from high-fat foods, and watch their portion sizes. They also tend to eat breakfast. But there's a ton of diversity as to what makes up their meals (meaning there was no "best" diet or fad diet that did the trick.) And they count calories.

"What makes maintaining weight loss seem 'almost impossible,'" writes obesity doctor Yoni Freedhoff, "are the goal posts society has generally set to measure success." So no to quick diets, yes to long-term lifestyle changes. They can help.

Managing your weight is work — but the alternative is not a stress-free option

"[Maintaining weight loss is] a job that requires not just time, self-discipline, and energy—it also takes up a lot of mental real estate. People who maintain weight loss over the long term typically make it their top priority in life. Which is not always possible. Or desirable."

Keeping your weight down requires daily consideration. It requires planning and thought to chose foods carefully and make time for exercise. This indeed takes up "mental real estate."

But I would ask Brown: does being obese require any less mental energy?

Is it really more mentally freeing to feel tired when you walk up a flight of stairs, to have to buy two seats on an airplane because one won't do, to not be able to play with your children because you're too unfit, to continually worry about whether your clothes are going to fit in the morning ... the list goes on.

(BSIP Universal Images Group)

In North America, we have gone to the extreme in our obsession with health and wellness. But that doesn't mean throwing up our hands is the appropriate alternative. "There needs to be a balance and a recognition that lifestyle change needs to happen in a way that’s healthy and sustainable," says Andrew Stokes, a professor who has researched obesity at Boston University. "We can’t just drink protein shakes for the rest of our lives."

So yes: maintaining weight loss is difficult and requires mental energy. But so does obesity, and giving up on maintaining a healthy weight is no alternative.

Uncertainties about the health effects of obesity doesn't mean they're not real

"While concerns over appearance motivate a lot of would-be dieters, concerns about health fuel the national conversation about the 'obesity epidemic.' So how bad is it, health-wise, to be overweight or obese?... Right now, we know obesity is linked with certain diseases, most strongly type 2 diabetes, but as scientists are fond of saying, correlation does not equal causation."

We are only beginning to understand the causes and impact of this relatively new condition called obesity, and there are big uncertainties at the center of the science.

A lot of the data can only demonstrate correlations, because it's observational and not experimental. In other words, researchers can't randomly assign people to obesity in an experiment and make them gain weight; they must observe health outcomes in people who are already overweight or obese. (Read more about the limitations of different types of scientific evidence here.)

Still, overall, studies have found that excess weight — especially obesity and morbid obesity — is a major risk factor for death and many, many diseases.

There's no question that it's healthier to have a normal body mass index"Excess weight, especially obesity, diminishes almost every aspect of health," according to the Harvard School of Public Health, "from reproductive and respiratory function to memory and mood." Being obese raises one’s risk of death from a range of diseases including diabetes, high blood pressure, stroke, heart disease, asthma, sleep apnea, kidney stones, and several types of cancer. One study estimated that in 2012, 3.6 percent of all new cancers worldwide were attributable to high body mass index.

While there are some questions about why these links exist, that doesn't make them any less real or troubling.

"There's no question that it's healthier to have a normal body mass index that's below 25," said Dr. Frank Sacks, who has conducted several pivotal studies on diet at the Harvard School of Public Health, summed up. Losing weight improves cardiac risk factors, reduces blood pressure, and prevents diabetes and several forms of cancer. "You can debate whether it should be a BMI of 20, 21, 22, 23. But if Americans were below 25, we'd be a lot healthier."

There are big problems with the science of the "obesity paradox"

"We don’t fully understand the relationship between weight and overall mortality. Many of us assume it’s a linear relationship, meaning the higher your BMI, the higher your risk of early death. But Katherine Flegal, an epidemiologist with the CDC, has consistently found a J-shaped curve, with the highest death rates among those at either end of the BMI spectrum and the lowest rates in the 'overweight' and 'mildly obese' categories."

Throughout her piece in Slate, Brown refers to an "obesity paradox" some researchers have observed: that being overweight is associated with some protective health effect, and even mild obesity confers no excess health risk.

This is a paradox because it's inconsistent with all the data I mentioned above, which suggests excess fat is associated with all kinds of diseases.

When you start unpicking the "obesity paradox" science, the J-shaped curve isn't all that surprising, explained Harvard's Sacks. Some thin people do have a higher risk of death than their heavier counterparts — but it's not necessarily because of their waistlines. "People who have a low body mass index may be at a higher risk of death because they have other co-morbidities, other problems, and bad habits," he said.

Many smokers would fall into this category, for example, and there have been studies showing the paradox in the elderly, and in heart failure patients. "But they have lost weight because they're sick," said Sacks. "The weight loss is the result of the disease." In other words, yes, they are thinner, yes, they have a higher morbidity rate, but it's not their low weight that is putting them at a higher risk of death — it's their illness.

In addition to health costs, obesity has also been associated with financial costs. (Atlantic)

There's also a big flaw with all the studies on the obesity paradox, said BU's Stokes: they only look at people's weight at one point in time. This is like asking someone who has smoked for her entire life but quit last week about her health, and then classifying her as a nonsmoker without incorporating any data about her long affair with cigarettes.

Stokes actually looked at more than 10 years of data from the Centers for Disease Control and Prevention and death records of American adults between the ages of 50 and 84, and went back in time, accounting for people's weight histories. This made it possible to break up the normal weight category into two separate groups that are usually lumped together: those who had maintained a normal weight throughout their lives, and those who were normal weight at the time of the study but had experienced weight loss.

The obesity paradox boils down to reverse causation

Stokes  found that people who were always normal weight had an extremely low risk of death, but that the other normal weight group — with people who were formerly obese — had a much higher mortality rate. After redefining the normal weight category to only include the stable weight individuals, he found much stronger associations between excess weight and mortality.

"It all boils down to reverse causation," Stokes told me. "The obesity paradox has been found in a lot of different populations: in the general population, in older and sick people, people with heart failure and other conditions." But when you start picking apart the science, looking at people over time, the paradox disappears.

Could the science behind obesity be more rigorous? Yes, Stokes said. But when I asked him, based on the current, best-available evidence, how dangerous obesity is, he added, "Maybe much worse than we appreciate, and that definitely has implications for the intensity with which we should be pursuing lifestyle and behavioral modification."

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