The Weight of the Evidence

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.

This isn’t breaking news; doctors know the holy trinity of obesity treatments—diet, exercise, and medication—don’t work. They know yo-yo dieting is linked to heart disease, insulin resistance, higher blood pressure, inflammation, and, ironically, long-term weight gain. Still, they push the same ineffective treatments, insisting they’ll make you not just thinner but healthier.

In reality, 97 percent of dieters regain everything they lost and then some within three years. Obesity research fails to reflect this truth because it rarely follows people for more than 18 months. This makes most weight-loss studies disingenuous at best and downright deceptive at worst.


One of the principles driving the $61 billion weight-loss industries is the notion that fat is inherently unhealthy and that it’s better, health-wise, to be thin, no matter what you have to do to get there. But a growing body of research is beginning to question this paradigm. Does obesity cause ill health, result from it, both, or neither? Does weight loss lead to a longer, healthier life for most people?

Studies from the Centers for Disease Control and Prevention repeatedly find the lowest mortality rates among people whose body mass index puts them in the “overweight” and “mildly obese” categories. And recent research suggests that losing weight doesn’t actually improve health biomarkers such as blood pressure, fasting glucose, or triglyceride levels for most people.

So why, then, are we so deeply invested in treatments that not only fail to do what they’re supposed to—make people thinner and healthier—but often actively makes people fatter, sicker, and more miserable?


Weight inched its way into the American consciousness around the turn of the 20th century. “I would sooner die than be fat,” declared Amelia Summerville, author of the 1916 volume Why Be Fat? Rules for Weight-Reduction and the Preservation of Youth and Health. (She also wrote, with a giddy glee that likely derived from malnutrition, “I possibly eat more lettuce and pineapple than any other woman on earth!”) As scales became more accurate and affordable, doctors began routinely recording patients’ height and weight at every visit.  Weight-loss drugs hit the mainstream in the 1920s, when doctors started prescribing thyroid medications to healthy people to make them slimmer. In the 1930s, 2,4-dinitrophenol came along, sold as DNP, followed by amphetamines, diuretics, laxatives, and diet pills like fen-phen, all of which caused side effects ranging from the annoying to the fatal.

The national obsession with weight got a boost in 1942, when the Metropolitan Life Insurance Company crunched age, weight, and mortality numbers from policy holders to create “desirable” height and weight charts. For the first time, people (and their doctors) could compare themselves to a standardized notion of what they “should” weigh. And compare they did, in language that shifted from words like chubby and plump to the more clinical-sounding adipose, overweight, and obese. The word overweight, for example, suggests you’re over the “right” weight. The word obese, from the Latin obesus, or “having eaten until fat,” conveys both a clinical and a moral judgment.

In 1949, a small group of doctors created the National Obesity Society, the first of many professional associations meant to take obesity treatment from the margins to the mainstream. They believed that “any level of thinness was healthier than being fat, and the thinner a person was, the healthier she or he was,” writes Nita Mary McKinley, a psychologist at the University of Washington-Tacoma. This attitude inspired a number of new and terrible treatments for obesity, including jaw wiring and stereotactic brain surgery that burned lesions into the hypothalamus.

Bariatric surgery is the latest of these. In 2000, about 37,000 bariatric surgeries were performed in the United States; by 2013, the number had risen to 220,000. The best estimates suggest that about half of those who have surgery regain some or all of the weight they lose. While such surgeries are safer now than they were 10 years ago, they still lead to complications for many, including long-term malnutrition, intestinal blockages, disordered eating, and death. “Bariatric surgery is barbaric, but it’s the best we have,” says David B. Allison, a biostatistician at the University of Alabama-Birmingham.


Reading the research on obesity treatments sometimes feels like getting stuck in an M.C. Escher illustration, where walls turn into ceilings and water flows upward. You can find studies that “prove” the merit of high-fat/low-carb diets and low-fat/high-carb diets, and either 30 minutes of daily aerobic exercise or 90 minutes. You’ll read that fen-phen is safe (even though the drug damaged heart valves in a third of those who took it). Studies say that orlistat (which causes liver damage and “uncontrollable” bowel movements) and sibutramine (which ups the risk of heart attacks and strokes) are effective. After reading literally more than a thousand studies, each of them claiming some nucleus of truth, the only thing I know for sure is that we really don’t know weight and health at all.

“We make all these recommendations, with all this apparent scientific precision, but when it comes down to it we don’t know, say, how much fat someone should have in their diet,” says Asheley Skinner, a pediatrician at the University of North Carolina–Chapel Hill School of Medicine. “We argue like we know what we’re talking about, but we don’t.”

Photo illustration by Slate. Photo by Thinkstock

For instance, much of the research assumes that when fat people lose weight, they become “healthy” in the same ways as a thinner person is healthy. The evidence says otherwise. “Even if someone loses weight, they will always need fewer calories and need to exercise more,” says Skinner. “So we’re putting people through something we know will probably not be successful anyway. Who knows what we’re doing to their metabolisms.”

Debra Sapp-Yarwood, a fiftysomething from Kansas City, Missouri, who’s studying to be a hospital chaplain, is one of the three percenters, the select few who have lost a chunk of weight and kept it off. She dropped 55 pounds 11 years ago, and maintains her new weight with a diet and exercise routine most people would find unsustainable: She eats 1,800 calories a day—no more than 200 in carbs—and has learned to put up with what she describes as “intrusive thoughts and food preoccupations.” She used to run for an hour a day, but after foot surgery she switched to her current routine: a 50-minute exercise video performed at twice the speed of the instructor, while wearing ankle weights and a weighted vest that add between 25 or 30 pounds to her small frame.

“Maintaining weight loss is not a lifestyle,” she says. “It’s a job.” It’s 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.

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