After long days discussing America's obesity problem, Melinda Sothern has had enough of windowless conference rooms.
"I need to exercise," she says, pausing to review her plans in the San Diego Convention Center lobby. She plans to rent a bicycle in Coronado and ride, fast and far.
Sothern, 55, is a woman who practices what she preaches. And one of her messages about obesity is aimed at women like herself: mothers.
Fat mothers. Thin mothers. And especially mothers-to-be.
A leading fitness and nutrition expert at Louisiana State University, she has a theory that the tide of obesity that has swept the nation in the last two decades had its roots in what young mothers did, or didn't do, in the postwar, suburban-sprouting 1950s.
If she's right — and evidence is stacking up on her side — reproductive-age women may become the central focus of efforts to reverse America's fat problem.
The obesity epidemic has multiple causes, Sothern acknowledges. Food has changed in the last five decades. Americans have become much more sedentary. But she thinks that obesity rates soared just when they did — in the 1980s — because a generation of young women decades earlier smoked, spurned breast-feeding and restricted their weight during numerous, closely spaced pregnancies.
"It was the evil '50s. A perfect recipe for obesity," she says.
Sothern calls her theory "the obesity trinity." And she thinks the key to getting Americans to slim down lies in studying those lessons from the past. Among her prescriptions for change: Women who are significantly overweight should be discouraged from having babies until they shed some pounds.
A central part of Sothern's theory — that obesity starts in the womb — is gaining currency with a growing number of doctors and researchers who say that reversing the epidemic, with its attendant cases of weight-related illnesses such as diabetes, should begin by addressing nutrition in pregnancy and early-life feeding practices.
"We don't completely understand how people become obese, when people become obese and why children become obese," says Michael L. Power, a senior research associate at the American College of Obstetricians and Gynecologists and a coauthor of the book "The Evolution of Obesity."
"But children of parents in the '50s and '60s may have started this off."
Sothern points to her own family as an example of the obesity trinity in action.
Her mother was told by the obstetrician in the 1950s to gain less than 20 pounds during pregnancy. Smoking a pack of cigarettes a day was a good way to keep the weight down, the doctor said.
Breast-feeding was not in vogue, so Sothern and her two siblings were bottle-fed formula. The kids were born within a span of four years.
All three children — Sothern thinks it's no coincidence — battled with their weight as adults: Her brother is diabetic and her sister is obese.
Sothern, at a healthy-looking 5 feet 3 and 129 pounds, has spent her adult life beating down a tendency to pack on weight by sticking to a diet rich in fruit, vegetables and fish and a regimen of dancing, biking, housework, gardening, sailing and strength training.
Her story, she says, is nothing unusual.
Women in the 1950s and 1960s — think Betty Draper on the hit TV show "Mad Men" — were generally advised to restrict weight gain in pregnancy to as little as 10 pounds. Inadequate nutrition in some of these women could easily have programmed their babies to catch up on growth during infancy — and studies suggest such growth spurts increase the risk of later obesity.
Women smoked with abandon, unaware of the health risks. Smoking during pregnancy is thought to contribute to obesity risk in offspring because nicotine disrupts mechanisms in the body that control appetite, metabolic rate and fat storage.
By the mid-1970s, breast-feeding in the U.S. had hit an all-time low of 25%. Studies show that formula-fed babies have a higher risk for obesity than breast-fed babies, perhaps because of metabolic changes or because drinking formula from a bottle is passive and easy and generally done till a bottle is empty.
And since breast-feeding can prevent ovulation, women using formulas were more apt to experience multiple pregnancies over a shorter period of time. Babies born close together can have inferior nutrition during gestation, which can permanently program their metabolism toward becoming overweight.
Things only worsened with subsequent generations, according to Sothern's theory.
Over-nourished kids grew up to be over-nourished women, producing large babies. Large babies, just like too-small babies, are at heightened risk of obesity, says Sebastien Bouret, an assistant professor of pediatrics at the USC Keck School of Medicine. They are less sensitive to hunger cues and less sensitive to insulin.
Overweight women are more likely to have diabetes — and in a study in mice published last month, Bouret found that diabetes during pregnancy triggers obesity in the offspring.
Today, about one-third of women are overweight when they enter pregnancy. And almost one-third of U.S. babies are too fat by nine months.
Statistics tell the tale.
In 1960, middle-aged men were, on average, about 27 pounds lighter than middle-aged men in 2002, and women were more than 25 pounds lighter.
In 1963, the average 10-year-old boy weighed 74 pounds and the average 10-year-old girl 77 pounds — compared with 85 pounds and 88 pounds, respectively, in 2002.
"It is stunning, looking at pictures of kids in the '50s," says Dr. Matthew Gillman, a professor in the department of nutrition at Harvard School of Public Health. "They look scrawny."
Other changes were afoot in the mid-20th century, of course: the growth of suburbs, a car culture and modern conveniences. The fast-food craze was launched with the first McDonald's in 1961.
Nonetheless, Sothern thinks there must be more to the story for the changes to have happened the way they did, at warp speed: "There had to be physiological and metabolic changes in our bodies."
Indeed, scientists are coming to realize that subtle changes in our genetic material — technically known as epigenetic changes — can alter the way that genes are turned on and off, in ways that affect the body's functioning.
Sothern thinks the obesity trinity tweaked our genetic material to make us prone to pack on pounds.
If yesterday's young women may have gotten us into the obesity epidemic, today's must be counted on to help us get out, Sothern said. She doesn't mince words when describing the necessary changes.
"Significantly overweight women should not have babies. Women should be physically active and have a healthy diet for at least a year before pregnancy," she says. "I do think we can de-program, but you have to be very aggressive."
Women should breast-feed for at least six months after childbirth or — better yet — take one year off from work and breast-feed. They should not smoke.
And after those babies become toddlers and enter preschool, they should have 60 minutes a day of recess plus a 40-minute physical education class.
Reproductive-age women are, in fact, becoming attractive targets for change.
In 2009, the Institute of Medicine introduced limits on how much weight an obese woman should gain during pregnancy; critics felt the board should have gone further.
In January, U.S. Surgeon General Regina M. Benjamin launched a plan to increase the number of babies that are breast-fed for at least six months.
A strategic plan to tackle obesity released in March by the National Institutes of Health highlights the period of before and during pregnancy as "a critical period to intervene."
"The epidemic is partially reversible if we intervene at the right time," Bouret says. "If we can convince women to have a better diet during pregnancy for the health of their babies, most women will do that."
It can take as little as two generations for our genes to be programmed in ways that tip us toward obesity. It may take more generations than that to reverse the damage done. But after all, Sothern says, we have to start somewhere.
"We can reverse it," she says. "I think the next generation knows what is good for their babies."