It seems so simple: Too much food and too little activity make people fat. But the actual processes that create and perpetuate that imbalance are proving to be astoundingly complex. Biology, physiology, psychology, genetics and environment figure in the obesity equation to varying degrees. Scientists are trying to understand how, in recent decades, the population has bloated to a point that lean people are a minority.
It seems so simple: Too much food and too little activity make people fat.
But the actual processes that create and perpetuate that imbalance are proving to be astoundingly complex.
Biology, physiology, psychology, genetics and environment figure in the obesity equation to varying degrees. Scientists are trying to understand how, in recent decades, the population has bloated to a point that lean people are a minority.
“There is no simple answer,” said Bernard Fuemmeler, a Duke University researcher who is studying the mind-body link in obesity. “People tend to think that it may be willpower or just a lack of control. And these may be reasons, but not explanations for what is driving the epidemic.”
In their quest for explanations, researchers at Duke, UNC-Chapel Hill, Wake Forest and East Carolina universities are discovering or are building upon findings that prove just how intractable a foe fat can be.
Rich foods work much like heroin on the brain, making it hard to stop eating them. A recent study indicates a genetic link between overeating and drug addiction, explaining why obese people have such intense cravings and build up such tolerance.
Depression and obesity can be so tightly linked, it’s hard to tell which comes first. Some of the same hormones and neurotransmitters are active in both, which could explain a tendency to eat when not hungry.
And as people gain weight earlier in life, they not only get chronic diseases sooner, they also set the course for a lifetime of weight battles. Growing evidence points to biological changes in obese people that means they must work harder to keep weight off than those who never gained.
The consequences are huge. Obesity is estimated to directly kill 112,000 people a year in the United States and to contribute to the deaths of many hundreds of thousands more. Health costs associated with the epidemic are tabbed at $147 billion a year, according to an analysis by RTI International.
“We evolved from species that have lived for the last millions and millions of years in environments in which food was hard to come by,” said Wayne Pratt, a behavioral psychologist at Wake Forest University who has explored the connection between food and addiction. “And the food environment has changed in the last 50 years.”
Those changes – cheap, abundant and tasty food that requires almost no physical effort to obtain – have upset an intricate equilibrium within the body that is at the very essence of existence.
Food is life; every system in the body depends on it. But too much of anything, even a basic necessity, can create a poison.
A Food Addiction
Well-educated and motivated, Jennifer Joyner began every day determined to lose weight. By noon, she was off course.
“I used that failure to go ahead and eat (poorly) the rest of the day,” said Joyner, 38, who lives in Fayetteville, N.C., with her husband and two children. At her heaviest, she carried 336 pounds on her 5-foot-5-inch frame.
Joyner firmly believes she was addicted to food.
“Nobody is that heavy because they don’t know how many calories they should limit themselves to,” Joyner said. “That’s absurd.”
There’s growing evidence she might have a case.
High-energy foods hit the same pleasure centers of the brain that heroin and cocaine activate, recent research has found. Wake Forest’s Pratt said that very brain circuitry was once an evolutionary benefit.
Humans were programmed to like sweets and fatty foods so they’d eat more of them during those fleeting moments of abundance – finding a berry bush or a trove of tree nuts.
“It makes sense to eat more than you’d need for that day, so you could put down a layer of fat to survive” during the inevitable periods of scarcity, Pratt said. “The reward system is there to take advantage of things that are beneficial to us.”
Even though people are hard-wired to find rich foods pleasurable, most are not addicted in the sense of becoming increasingly compulsive and self-destructive.
But in an unprecedented environment of food abundance, a steady diet of cheeseburgers, pizzas and doughnuts can trigger in some the same cravings and tolerances that an addict gets from heroin or cocaine. Recent brain studies show that drug addicts and people who are obese have similar neurobiological circuitry.
Studies with rats show why we start craving fat. Rats on high fat and sugar diets begin craving the foods because the reward centers in their brains grow numb to the pleasure signals, much like the addict develops a tolerance to cocaine that fuels more and bigger binges. As a result, the rats eat more and more, growing obese.
Adding to the biological evidence, a team of scientists that included UNC-Chapel Hill researchers reported in 2009 that they had found a gene, NRXN3, associated with obesity in some people. The same gene previously was identified as playing a role in substance abuse.
Keri Monda, an epidemiologist at the UNC Gillings School of Global Public Health and one of the study’s authors, said the finding draws a strong inherited link between overeating and drug addiction – problems characterized by difficulties limiting enjoyable experiences.
“We do know there are common underpinnings,” Monda said, adding that additional studies are needed to make a definitive association.
For Joyner, the science only confirms her experience. In March 2008, she had weight-loss surgery and has since dropped 150 pounds and written a book about her experience, “Designated Fat Girl.” But overcoming her addiction, she said, has taken counseling and work beyond the operation.
“You don’t treat addiction with a diet-and-exercise plan,” she said. “There needs to be intervention, family support, ongoing counseling.”
Depression and Obesity
As anyone who has battled obesity knows, the struggle is as much mental as physical. Sadness, self-loathing, disgust and frustration often accompany weight gain. Bad health begets a bad frame of mind, which begets more bad health.
Maureen Leslie of Raleigh, N.C., started that spiral six years ago, when she was diagnosed with pre-diabetes, a condition of early metabolic failure characterized by a growing inability to clear sugar from the bloodstream. It can often be reversed with diet and exercise, or it can bloom into full-blown diabetes.
Leslie then lost her job, her marriage fell apart and she sank into despair. Sweets offered a poisonous escape, turbocharging the tailspin.
“The stress of all that stuff was overwhelming,” said Leslie, now 45.
The connection between depression and obesity, long linked by the anecdotal experiences of people who suffer from both, is only recently becoming better understood. Some of the same hormones and neurotransmitters are active in both diseases.
Fuemmeler, the Duke researcher, was the lead author of a 2009 study that investigated the intersection of depression and obesity.
It’s a confounding area of research.
“There is some controversy about the relationship between obesity and depression,” Fuemmeler said, noting that many factors cause depression and that an equal number cause obesity. Often, the two overlap, and it’s hard to determine whether one causes the other.
Fuemmeler said his colleagues are studying brain chemicals that regulate reward and mood.
“These biobehavioral mechanisms might be driving both depression and/or a tendency to eat when not hungry,” he said.
For Leslie, the two problems had to be addressed as one. A year ago, she carried 209 pounds on a 5-foot-4-inch frame and was well on her way to full-blown diabetes. She had blurred vision, and her feet and hands tingled from nerve damage caused by the high glucose levels in her blood. Every night, she cried herself to sleep.
Finally, through a free clinic in Raleigh and a diabetes intervention called Project DIRECT that provided free education and resources, Leslie began addressing her sadness and learned that, with proper attention and management, diabetes isn’t a death sentence.
She has lost more than 30 pounds, eats more vegetables and fewer sweets and works out by mowing neighbors’ yards – which also boosts her mood.
“It’s a mental thing,” she said. “You know you need to eat right, you know you have something to accomplish, but you may not be fully prepared to commit to it. Finally, I realized I couldn’t keep doing this to myself. I was slowly killing myself.”
The Yo-Yo Diet
Most people gain their greatest amount of excess weight between ages 18 and 35.
There are lots of reasons – people go to school or work and don’t exercise as much, eat convenience foods, party more, keep odd hours, have children. The weight inches up by an average of 30 pounds over that 17-year period of young adulthood.
It can be a dangerous accumulation, giving a head start to diabetes, cardio-vascular disease, hypertension and other diseases once associated with old age.
Courtney Ward actually wanted to gain a little weight after high school. At 6 feet 5 inches and 170 pounds, he thought he was too skinny. But he hit his desired weight of 200 pounds and kept gaining.
A year ago at age 43, the office manager at RDU International Airport weighed 269 pounds, putting him at 31.9 on the height-weight calculus known as the body mass index. A BMI over 30 is called obese.
Suffering high blood pressure and other signs of poor health, Ward was committed to shedding the weight. He has lost about 45 pounds, primarily by cutting out junk food and exercising daily at the Institute of Diet & Weight Management, a doctor-guided program in West Raleigh.
“I had to realize it was a lifestyle change,” he said. “The dieting thing was never me – it had to be a total lifestyle change.”
But Ward has a difficult task ahead. By gaining that weight, he might have created a monster because his body will challenge his willpower and try to drive his weight back up.
The yo-yo effect is one dieters know all too well. Most people gain all their weight back within five years, and 33 percent have some weight return in the first year after a successful diet.
Scientists attribute this to basic physiology. For the same survivalist reasons the brain is hard-wired to favor rich foods, the body’s cells are programmed to sock away extra fuel as a hedge against famine.
That extra fuel is stored as fat. And once the body has created a fat bank, it fights to protect it, perceiving a successful diet as a heist.
To restock, the body sets into motion a complex cascade of hormones and brain signals that trigger hunger, while it simultaneously downshifts energy. The food cravings and a lack of energy often get worse the longer a dieter tries to stay compliant.
And in a diabolical irony, the body’s pepped-up metabolism appears to store fat more efficiently. This makes it difficult for even the most committed to maintain their hard-won weight loss.
Heba Salama and Ed Brantley are a Raleigh couple who appeared on NBC’s “The Biggest Loser” reality show two years ago and dropped more than 130 pounds each. They still fight to keep the weight from returning. Each has put back on about 30 pounds.
“It’s hard,” Heba said, noting that her body seems comfortable maintaining a weight that’s about 10 pounds heavier than she’d like.
But the couple took the show’s boot-camp mentality to heart and now work to promote healthy eating and exercise. They work out regularly, running or attending hot yoga and other workouts at a gym. They’re also training to climb Mount Kilimanjaro in February.
Exercise may be the secret to success.
Deborah Tate, an associate professor of nutrition at UNC-Chapel Hill, said she worked on a study while at Brown University that showed the benefits of exercise outlast a diet, even when people return to unhealthy eating.
Tate noted that 90 percent of the people on the National Weight Control Registry, a research compendium of more than 5,000 dieters who have kept off significant amounts of weight, exercise on average an hour a day.
At the same time, Tate said, her research has reinforced a difficult truth: “People who successfully kept it off had to work a little harder than those who never gained in the first place.”