Teens who lost weight after bariatric surgery had weaker bones afterward, study says

By Sandee LaMotte, CNN

(CNN) — The bones of teens and young adults who lost significant weight after bariatric surgery were weaker than those of youth with similar levels of obesity who did not have surgery, a new study found.

But that doesn’t mean bariatric surgery should be avoided for youth with severe obesity, said lead study author Dr. Miriam Bredella, professor at Harvard Medical School and vice chair for faculty affairs and clinical operations of radiology at Massachusetts General Hospital in Boston.

“Totally get the surgery — diabetes and heart disease cause much more morbidity and mortality than osteoporosis, and type 2 diabetes is also bad for your bones,” Bredella said.

“Our study was not to say, ‘Don’t get bariatric surgery,’ but to say ‘Hey, if you get the surgery, just make sure you have a healthy diet, you do weight-bearing exercise, and you get enough vitamin D and calcium,” she said.

Significant weight loss for any reason causes bones to weaken as the body adjusts to the new reality of not carrying extra weight, said Dr. Thomas Inge, surgeon-in-chief and director of the adolescent bariatric surgery program at Ann & Robert H. Lurie Children’s Hospital of Chicago.

“NASA scientists are very worried about this issue with sending human beings into space,” said Inge, who was not involved with the study. “Bone mass and density can decline within weeks, and that’s why they have astronauts trying to mitigate the bone loss that happens when they’re weightless with physical activity.”

A two-year study

The study, published Wednesday in the journal Radiology, compared the bone health of 25 youth between the ages of 13 and 25 years who underwent bariatric weight loss surgery with that of 29 youth of the same age group who did not. All received dietary and exercise counseling and were reevaluated after two years.

Despite counseling, teens and young adults who did not undergo weight loss surgery continued to gain weight over those two years, the study found. Those who had surgery, however, lost around 20 BMI points, which is astonishing, Bredella said. BMI is short for body mass index, an approximate measurement of a patient’s body fat based on height and weight.

“Some of these kids had a BMI of 50 or 60 and lost so much weight they got down to a BMI of 30 or 35, which is huge,” she said. “Unfortunately, a BMI of 30 and 35 is still obese.”

Stronger bones are necessary to support the 100 or more extra pounds of weight that teenagers have when they’re severely obese, so it’s not surprising that the bones of teens who lost that much weight would weaken, said Dr. Justin Ryder, associate professor of surgery and pediatrics at Northwestern University’s Feinberg School of Medicine in Chicago.

“If you think about it, they basically taken a big, heavy backpack off of themselves,” said Ryder, who was not involved in the study. “So, they need to find a way to put some of that weight back on the bones through strength and resistance training.”

What was surprising, Bredella said, is that the bones of the children who did not undergo surgery and continued to gain weight also weakened, although the change was not statistically significant.

“Why would their bones not get stronger?” she asked. “Because obesity itself is bad for bones. Obesity is an inflammatory state and we have done studies that show the inflammation negatively influences bone health.”

In addition, the type of visceral fat that comes with severe obesity also slows secretion of growth factor hormones, which are crucial for healthy bones, according to Bredella.

However, it’s difficult to accurately study bone loss in adolescents and young adults. “Kids in this age range haven’t reached full maturity of their bones yet. You don’t hit peak bone formation until your late 20s or early 30s,” Ryder said.

“So, it’s really challenging to study the impact of weight loss surgery on bone health in this variable period where they’re still building bone and the density of those bones,” said Ryder, who is vice chair of research for the department of surgery at Ann & Robert H. Lurie Children’s Hospital of Chicago.

A study would need to follow teens who underwent surgery for at least 10 years to determine if the bone loss seen in the new study lasts, Inge said.

“With just two years of follow-up, this study unfortunately doesn’t really shed light on whether the drop that we’re seeing is pathologic or to be expected as the bones get back to normal density,” Inge said.

An odd finding

In youth who underwent sleeve surgery, by far the most common kind of bariatric surgery used today, there was an odd development — the marrow of their bones contained more fat.

“Despite the fact those children had a significant loss of weight and BMI, which reduced their overall body fat, they had more fatty yellow marrow within their bones,” Bredella said.

There are two types of bone marrow, she explained — red marrow, where our stem cells make white and red blood cells to replenish the body, and fatty marrow that is quite yellow in color.

“We used to think fatty marrow within bones was just filler with no function,” Bredella said. “But we know now that it’s an endocrine organ — it secretes hormones of different kinds and is associated with making bones weaker.

“Why did fatty marrow increase inside the bones of children who had sleeve surgery? That’s the million-dollar question we have to answer,” she said.

Gastric bypass surgery, which was popular in years past, bypassed a section of the small intestine called the duodenum that is critical for uptake of micronutrients such as vitamins and minerals. The newer sleeve surgery removes a section of the stomach without affecting the duodenum, thus allowing more food nutrients to be absorbed, according to Inge.  

In addition, parts of the stomach that send some hunger signals to the brain are removed during sleeve surgery, reducing appetite and food cravings. However, the surgery is associated with deficiencies in some nutrients, such as calcium and vitamins D and B12, which need to be supplemented.

“We do worry long term about adequacy of micronutrients in general, and calcium and vitamin D in particular,” Inge said. “That’s why we insist that people undergoing weight loss surgery take their multivitamin with calcium and vitamin D every day, just like medicine.”

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