Fiber for bones? Prebiotic soluble corn fiber boosts bone mass in teen girls, trial finds

Early adolescent girls adding a prebiotic soluble corn fiber to their usual diets built more bone than those taking a placebo, according to findings from a new double-blind, randomized clinical trial. 

The 12-month study led by Florida International University (FIU), US, found that bone mineral content in 9- to 14-year-old girls supplementing with 12 g per day of the prebiotic increased by 18.8% (a gain of 216.3 g), compared to 12.9% (139.9 g) in the placebo group receiving 12 g of maltodextrin daily.

However, the researchers did not observe this outcome in boys or when 600 mg per day of calcium supplementation was added.

“That 6% may sound like a small difference, but this is a significant, clinically relevant number for just adding this powder to the diet,” stresses lead study author Cristina Palacios, professor and chair of the department of dietetics and nutrition at FIU’s Robert Stempel College of Public Health & Social Work.

These results were adjusted for age, Tanner stage (a method of tracking puberty), height velocity, weight velocity, lean mass velocity, fat mass velocity, and compliance.

The team caution that the study was not designed to detect differences between the boys and girls, so the finding needs to be confirmed in larger trials. At baseline, girls had a significantly higher Tanner score and higher body fat percentage than boys, which led the researchers to stratify the results by sex.

While more research is still required, Palacios believes these early results are promising. She points to the potential of fortifying child-friendly foods with soluble corn fiber to help children absorb more of the calcium they already consume.

Early bone building for life

Findings from the National Institutes of Health-funded “MetA-Bone” clinical trial are published in The American Journal of Clinical Nutrition.

The trial evaluated whether the fiber could help children build more bone mass and bone mineral density during a critical period of childhood growth. The research team notes that adolescence accounts for up to half of adult peak bone mass.

Researchers referenced previous short-term studies showing that 12 g per day of soluble corn fiber increases calcium absorption by 12% in adolescents on low-calcium diets.

Early adolescence, which is around the beginning of puberty, is when the body builds most of the bone mass carried for life, they explain. Children require more calcium during these years as the amount of deposited calcium during childhood influences peak bone mass, which is a strong predictor of bone fragility later in life.

One possible explanation for why boys didn’t have the same benefit is that they were at a different stage of puberty and skeletal development, note the authors.

Calcium absorption

Palacios and her colleagues ran a year-long trial that randomized 177 children aged 9–14 who consumed too little calcium. The trial included White (41.3%) and Hispanic (69.5%) participants, and 74% had a healthy weight. Participants retained their regular diets while adding either a twice-daily soluble corn fiber powder or the maltodextrin placebo.

Around half of the participants were assigned the prebiotic while the rest received the placebo, with secondary groups exploring the effect of adding 600 mg/d calcium gluconate.

The research team checked participants’ whole-body bone mineral content and bone mineral density three times — at the start of the study, six months in, and again at 12 months, analyzing 151 completers — using dual-energy X-ray absorptiometry (DEXA) scans.

Girls taking soluble corn fiber achieved around 5% greater bone density growth than those in the placebo group.

Current US national guidelines recommend adolescents get 1,300 mg of calcium daily. However, dietary surveys cited in the paper indicate that only 14–32% of girls and 38–44% of boys meet the recommended dietary allowance for calcium, while only 6–21% of girls and 21–24% of boys reach the recommended three daily servings of dairy products.

Prebiotic potential

According to the researchers, an estimated 90% of girls and 70% of boys don’t receive enough calcium, while many also swap calcium-rich milk for sodas that may take calcium out of bones.

Calcium gets into the body through the walls of the small intestine, explain the researchers. The efficiency of this process partially depends on the bacteria living in the gut.

The researchers pinpoint certain prebiotics known to feed beneficial microbes, which can boost calcium absorption in the colon. These prebiotics include soluble fiber, chitin-glucan, chitosan, inulin, galacto-oligosaccharides, fructo-oligosaccharides, and xylooligosaccharides.

Those “good” bacteria break down the fiber, resulting in the production of short-chain fatty acids) that help more calcium get absorbed by solubilizing minerals, increasing cecal weight, and prompting colonic cell proliferation.

“My message is the same for everyone. For kids growing bone and for adults maintaining bone. This can be a small, easy addition to your diet,” says Palacios. “Whether it’s through your diet or popular over-the-counter fiber supplements, just find a way to increase your intake of soluble fiber.”

Earlier this year, researchers in a separate trial found that fiber-derived butyrate promotes the development of dendritic cells, which they call the “sentinels” of the immune system. Butyrate is a short-chain fatty acid, a secondary metabolite produced by gut bacteria through the fermentation of dietary fibers such as inulin and pectin.