Why Today's Moms Need Fewer Calories Than 50 Years Ago

The housewife workout (photo by: Getty Images)There was no Zumba in 1965, no hot yoga, CrossFit, spin nor many other faddish exercises that  modern-day moms plunk down their money for to stay trim and healthy. But, there was a lot more housework, like cooking, cleaning, and childcare — and a lot less passive entertainment, like watching television, which may explain weight differences between moms about 50 years ago and mothers today.

According to a new study published in the medical journal Mayo Clinic Proceedings, over the last 50 years, mothers have become significantly less active overall and require about 1,200-1,500 fewer calories per week to stay at a healthy weight compared to their 1965 counterparts. The authors say that this energy imbalance — calories consumed versus calories burned — is contributing to the obesity epidemic for both women and their children.

More on Yahoo: Can You Be Obese and 'Healthy'?

"I'm not saying that women should do more housework, but they need to add physical activity back into the day," lead author Edward Archer of the University of South Carolina tells Yahoo Shine. "Why did the obesity epidemic come about as it did? We've engineered physical activity out of all domains of our lives." The study is a follow-up to research done on occupational activity levels that found that there was a strong correlation between obesity and the decrease in manual labor for men over the decades. This new study was devised to take into account the fact that women traditionally have burned more calories engaged in activities like housework and child care. "The reason we focused on mothers is that the vast majority of caregivers in the world are women," says Archer, and, he adds, mothers have the most influence on the health of future generations. (There are plans for another study on fathers.)

More on Yahoo: Our Titanic Obesity Problem

According to the study, the impact of maternal inactivity on children begins in the womb. Research suggests that body-fat composition and metabolism is, to a certain extent, programmed in utero. Children are also highly influenced by the activity level of their mothers. "With each passing generation, mothers have become increasingly physically inactive, sedentary, and obese, thereby potentially predisposing children to an increased risk of inactivity, adiposity, and chronic non-communicable diseases," Archer said in a release. "Given that physical activity is an absolute prerequisite for health and wellness, it is not surprising that inactivity is now a leading cause of death and disease in developed nations."

The researchers looked at activity logs gathered for over 45 years from 50,000 daily diaries compiled by the American Heritage Time Use Study. They found that women with kids under 5 reported a decline in physical activity (defined as childcare, cleaning, cooking, and other housework, as well as sports and exercise) from 44 hours per week in 1965 to less than 30 hours per week in 2010 — more than two hours per day. This means that women in 1965 could eat about 225 calories per day more, or the equivalent of two eggs and a piece of toast, without gaining weight. Mothers with older children reported a decline in activity of about 11 hours a week, which comes out to 177 calories per day. In addition to being less active, mothers reported an increase in sedentary behavior — such as watching television, looking at the computer, and driving. Moms of young children increased their sedentary behavior from 18 to 25 hours per week, and moms of older children from 17 to 23 hours. "While [200] may not seem like that many calories," says Archer, "it's equal to about 10 percent of your daily energy requirements." What's more, physical activity rates drive changes in appetite and metabolism. When you get below a certain activity level, your hunger no longer corresponds to your energy output and your metabolism slows, so you tend to gain even more weight, he explains.

"We aren't what we eat, we are what we do with what we eat," says Archer. "That's where the activity comes in." He adds that you don't need to sign up for a gym; instead, think about small daily changes, such as taking a walk after every meal, standing up when possible, and pacing while on the phone. He also recommends cutting recreational screen time in half. The average American watches about four hours of television a day. As Archer says, "The second-greatest correlate for obesity after having an obese mom is having a TV in your bedroom."

More on Yahoo Shine:

4 Ways Exercise Equals More Pay

8 Surprising Foods with Trans Fats

Early Puberty: Another Scary Side Effect of Obesity