Obese teens are at risk of iron, protein and vitamin D deficiency, a new research shows.

The nutritional problems are faced by teens who undergo weight loss surgery and even those who don't, the study found.

Researchers at the Cincinnati Children's Hospital Medical Center studied 79 obese teens who either received weight loss surgery or were assessed but did not undergo treatment. The patients were evaluated between 2001 and 2007 and were told to participate in the study between 2011 and 2014.

Dr Stavra Xanthakos, lead researcher of the study found that the patients had experienced "durable and significant" weight loss, about 28 percent, after an average 8 years of surgery. Those who did not receive surgery did not lose weight.

"We knew there were nutritional difficulties in teens who had undergone bariatric surgery, but everyone thought it was primarily the surgery that caused these problems since gastric bypass excludes the portion of the small intestine where many nutrients, especially iron, are most absorbed," said Xanthakos, MD, medical director the Surgical Weight Loss Program for Teens at Cincinnati Children's and a co-author of the study. "What this shows us is that nutritional deficiencies occur even in teens who don't undergo surgery. Severely obese patients should be screened for nutritional deficiencies, regardless of whether they've undergone weight loss surgery."

Researchers stated that at least five years after undergoing gastric bypass surgery, teens and young adults had significant weight loss. However, they were at risk of nutritional deficiencies, particularly low iron, mild anemia and low vitamin D. The study also found low iron and low vitamin D in the teens who were severely obese teens and those who did not receive weight loss surgery.

The Cincinnati Children's Hospital Medical Center study was presented at the annual meeting of the Pediatric Academic Societies in Vancouver, Canada, Sunday.