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Your Younger Sister Is the Reason You Are Gaining Weight, Says Research

Your Younger Sister Is the Reason You Are Gaining Weight, Says Research

You love your sister but if she's the reason you're unable to fit into that gorgeous dress, you're going to be mad.

Having a younger sister can be fun... most of the times. From sharing clothes to sharing secrets, growing up with a younger sister you can boss around is exhilarating. Especially when being the older one means that you're in charge. As you grow up, that doesn't really change.

But there's good news and bad news. The good news is, you know you have each other's backs. The bad news... she could also be the reason that you are gaining weight. Not so much fun anymore, right?

Well, a study says that if you have a younger sister, you face a higher risk of becoming obese. So if it wasn't already hard enough to shed fat, especially after having a baby, being the older sister just got harder. Thanks a lot, little sis.

So what does the study really say?

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In a study conducted and published in the Journal of Epidemiology & Community Health on 13,406 pairs of Swedish sisters born between the years 1991 and 2009, it was found that first-borns have a greater body mass index. This means that they were more likely to gain weight and become overweight.

In order to find these results, data was collected from antenatal clinic records from the Swedish National Birth Register over 20 years (1991–2009). The researchers analyzed the information they received about the mothers' pregnancy in the early stages. This helped them come to their conclusion.

However, it also showed that during childhood, older sisters were actually lighter at birth but as they grew up and were close to becoming mothers themselves, they started showing signs of a higher BMI. Not just that, first-born sisters were found to be slightly bigger at birth and taller as an adult. 

The results of the study showed that older sisters had a 2.4% higher BMI than their younger sisters and were also 40% more likely to suffer from obesity. The researchers also made note of the fact that there was a significant increase in average weight over the 18-year period since the study began. They mentioned that the weight was increasing by 4 ounces per year. 

But why is this happening?

The experts hail from the University of Auckland in New Zealand and Uppsala University in Sweden. They too are unclear about why older sisters seem to be heavier than their younger sisters. However, they also said that it may be one of the reasons the figures for obesity are increasing. They explain that since the size of families are reducing with parents choosing to have just one child, there are more first-borns now than there were in the past.

Are there any theories on this?

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There are thankfully some people who can shed some light on this phenomenon by sharing their theories.

The scientific one:

One theory was proposed by Professor Wayne Cutfield from the Liggins Institute at the University of Auckland. He claims that in the case of the first pregnancy, the blood vessels which carry the nutrients from the food to the fetus, are slightly thinner.

So this causes a possible reduction of nutrient supply which can lead to the child's body developing mechanisms to store more fat. It also causes insulin to work less effectively as the child grows into adulthood.  He came up with this idea after co-authoring a study that explored the concept that first-borns have a reduced insulin sensitivity and are at more risk of higher blood pressure.

The cultural one:

Another theory made by Dr. Maria Peña, Director of the Center for Weight Management at Lenox Hill Hospital in New York City leans towards a more cultural explanation. She told CBS News, "In many cultures, moms are more meticulous with their firstborns. With the very first born, everyone's helping out and over-feeding the baby, making sure it's at a 'healthy weight'. But with second children, parents know what to expect and they're not so overprotective so maybe they feed them a little less."

She mentioned that these eating habits could stick with the individuals throughout their lives, which could lead to eating disorders and obesity. "People that develop obesity later on in life forget to listen to the signal in their brain that tells them to stop eating. Early on in life, some kids are taught to override that signal. If a parent tells a child to keep eating even when they're not hungry, then that's a habit they learn," she explained. 

The social one:

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This theory addresses sibling rivalry as a reason for this result. “Maybe the first-born competes with the second-born for food in the household. Maybe more money gets spent on the firstborn,” theorizes Gary Sacks of Deakin University in Melbourne, Australia. 

So if you're an older sister, this study might  explain why you just can't seem to shed the pounds as easily as your younger one. But hey, you have experiences and memories that she doesn't have, so you could consider it a win-win. 

References:

https://jech.bmj.com/content/70/1/78

https://academic.oup.com/jcem/article/98/3/1248/2536805

https://www.cbsnews.com/news/birth-order-may-affect-weight-gain-in-women/

https://www.unilad.co.uk/life/your-sister-is-the-reason-youve-put-on-weight-study-finds/

https://www.dailymail.co.uk/health/article-3212156/Why-firstborn-girls-likely-fat-Oldest-siblings-40-likely-obese-younger-siblings.html

https://www.iflscience.com/health-and-medicine/study-suggests-first-born-women-more-likely-be-overweight/

https://www.newscientist.com/article/dn28101-fatter-than-your-siblings-it-could-be-because-youre-older/

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