For decades doctors have agreed that breastfeeding has significant advantages for both mom and baby. Mother's milk helps build baby's budding immune system, establishes emotional bonding and even triggers the release of oxytocin, the so-called "love hormone" that is associated with both hugging and orgasm.
But what about weight loss for the mother? At least one study says this is a myth. But those who work with nursing mothers say the issue is more complex and argue that in the long run, breastfeeding does contribute to overall fitness.
Salma Hayek Weighs In
Just this week sexy actress and new mother Salma Hayek told Oprah in animated tones, "It's a lie! It's not true! I'm going to say something. Except for a couple of exceptions, the only reason people lose weight like that when they're breastfeeding. It's that they're not eating and they're breastfeeding. And that's not good for the baby."
Her reaction is typical of the strong opinions many mothers have about breastfeeding and weight gain.
Like Amanda Socci, who says she tipped in at 210 pounds when she gave birth to her daughter in 2006. One year after delivery, Socci made little progress in getting back to shape.
But now - two years after delivery - the 36-year-old, first-time mother, who is still nursing her daughter Margarita, has lost 40 pounds. She attributes the eventual weight loss to running around after a toddler, not to breastfeeding.
"People say nursing helps you lose weight," said Socci, who works as a volunteer in her hometown of Alexandria, Va. "It doesn't help. Every two hours I was sitting and nursing. I couldn't walk or run. I was eating more. But when my daughter learned how to walk, I started running. I couldn't keep up with her."
The truth probably lies somewhere in the middle. Breastfeeding does have a metabolic effect that encourages the body to return to its natural shape. But nursing alone, especially if mother leads a sedentary life and hits the freezer for ice cream — just won't burn off the pounds.
Most studies show that mothers who "eat to hunger" show a steady, gradual weight loss while nursing, according to Kathleen Huggins, author of the classic "Nursing Mother's Companion," which has sold more than one million copies.
"There may be a wide variation in the loss but most nursing mothers lose most of their weight during the first three to six months post partum," Huggins told ABCNews.com. "A few studies may show little difference in weight loss and this may be because breastfeeding is not clearly defined. Some mothers may only be partially breastfeeding."
Hayek, 41, who won an Academy Award nomination for best actress for the 2002 film, "Frida," said she has struggled with her weight since her daughter Valentina Paloma was born last September. She was also treated for gestational diabetes — a common, but temporary form of the disease that increases the size of the fetus and leads to weight gain, among other medical hazards.
Socci, too, experienced gestational diabetes and was placed on a strict diet during her pregnancy, avoiding sugars and salt. But after delivery, she was able to return to a normal diet and found breastfeeding increased her appetite.
Hayek's story elicited numerous reactions online. Kendra, a mother of four, commented on Huffington Post that exercise and breastfeeding, "will shrink your stomach up. I'm thinner now than I was in high school.
"I applaud Salma and anyone who has the courage to breastfeed in the fishbowl celebrity environment," wrote another commenter who has nursed two children, but found it harder to lose the weight with the third child.
"Your metabolism changes," she said. "My advice: Eat the healthiest diet possible, exercise as much as possible, and not worry about it so much."
Study Disproves Myth
At least one study has shown that despite myriad benefits for mothers and their babies, breastfeeding — contrary to popular belief — does not help shed the pounds faster. In a study published by The American Journal of Clinical Nutrition in 2004, researchers concluded that non-breastfeeding women actually lose body fat faster than nursing mothers.
"Body composition changes occur differently in non-lactating and lactating women during the first six months postpartum and occur at some body sites until 12 months postpartum despite previous lactation status," reported researchers at Children's Hospital Medical Center in Cincinnati. "This data agrees with those from previous reports that trunk fat and thigh fat are the primary energy depots mobilized to support lactation."
The six-month study looked at 326 new mothers and measured their body changes after delivery. What researchers failed to ask was whether non-nursing mothers had intentionally — as Hayek suggested — restricted their diets to lose weight.
The Cincinnati medical team found that body composition can change quickly after delivery. In the first six months after giving birth, 81 of the nonbreastfeeding mothers lost fat from their whole body, arms, and legs faster than the 87 breastfeeding moms. In addition, the lactating women gained fat in their arms.
A change in body composition was determined by imaging the whole body and determining fat and muscle mass. They found both groups lost weight at similar rates and decreases in body weight was not influenced by breastfeeding.
The hormone prolactin stimulates appetite and aids in milk production in breastfeeding mothers, according to the study, which could account for the extra calories. Also, non-nursing mothers reported more physical activity than nursing ones.
Surprisingly, after one year, the body weight and percentage of fat in the two groups of women was equal.
These findings support anecdotal evidence from lactation experts, who say it takes about one year to regain the pre-pregnancy figure. The key is whether a woman is at a normal and healthy weight before getting pregnant. Most doctors recommend a weight gain of 20 to 25 pounds.
Nursing Mothers Are Fitter
Nancy Clark, a certified lactation consultant from Northern Virginia, said that breastfeeding does, indeed, make a difference. She has worked with nursing mothers for 22 years and said nursing women tend to be more conscious of their health — not drinking alcohol or smoking and paying attention to their food choices. But it's more than that.
"It takes calories when you make milk, and with a reasonable diet of unprocessed food, you can lose weight," she said.
Nursing a baby has multiple benefits for overall health, according to Clark. It shortens bleeding time, preventing post-partum anemia; releases oxytocin to make the uterus contract and return to its normal size; and helps the body rid itself of excess fluids carried during pregnancy.
"It gets the tummy back quicker," she said. "People don't gain weight with breastfeeding unless they eat an excessive amount of food," she said.
Still, it takes time to lose the baby fat and lactation experts recommend losing no more than one to two pounds a week.
"A crash diet of 800 calories a week is not normal," said Clark. "People may tease you because you don't look like a movie star. But she had a personal chef, a nanny and trainer every day. Most physicians won't let you go back to the gym right away and it's even longer for a C-section (caesarean section)."
Meanwhile, actress Hayek is looking as beautiful as ever, despite claims of weight gain. In an interview with television's "Extra," she said her daughter's birth had changed her life.
"I don't even remember what my life was like before," she said. "I can tell you that I don't sleep. This is a cliché but it's true. I haven't slept in the last six months."
"The blessing of having a healthy child," said Hayek, "I think is the best thing that can happen to anyone."