Effect of Soluble Corn Fiber supplementation for 1 year on bone metabolism in children, the MetA-Bone Trial: Rationale and Design

Abstract

Calcium intake is critical for adequate bone mineralization in adolescence, but it is usually inadequate in US adolescents. A strategy to maximize bone mineralization is to increase calcium absorption, which could be achieved by soluble corn fiber (SCF). There are no studies determining the long-term effects of SCF on bone mass in children.

Objectives:

To determine the effect of one-year SCF supplementation compared to placebo on bone mass and bone biomarkers in children with low habitual calcium intake. We hypothesize that SCF supplementation will result in a higher bone mineral content and higher levels of bone formation and lower bone resorption biomarkers.

Methods:

240 healthy children (10-13 years), with usual low calcium intake, will be randomized to four experimental groups for 1 year: (1) SCF (12 g/d); (2) SCF (12 g/d) + 600 mg/d of calcium; (3) Placebo (maltodextrin); and (4) Placebo + 600 mg/d of calcium. The supplements have been pre-mixed with a flavored powder beverage and participants will only need to dilute it in water and drink this twice per day. Bone will be measured using dual energy x-ray absorptiometry (DXA) at baseline, 6 and 12 months. Serum bone biomarkers will be measured at baseline and at 12 months.

Conclusions:

If supplementing diets with SCF lead to higher bone mass during adolescence, this could help achieve the genetic potential for PBM and to start adult life with stronger bones. If successful, SCF can be incorporated into diets for promoting bone health in adolescents.

INTRODUCTION

The adolescent period is crucial for optimizing future bone health because bone accumulates rapidly during these years and accounts for up to half of adult peak bone mass (PBM). In addition, PBM is a strong predictor of bone fragility later in life [1]. Calcium intake during this period is critical for adequate bone mineralization. A high calcium intake during adolescence is associated with a high PBM, which would predict a low risk of osteoporotic bone fracture later in life [2]. In fact, in the 2016 National Osteoporosis Foundation position paper, calcium intake was the only dietary factor receiving an A grade for building PBM.

More than 1.5 million fractures occur yearly in the US with an estimated cost of osteoporosis fractures expected to be $25.3 billion by 2025 [3]. Therefore, maximizing bone calcium retention within the genetic potential during growth is key for preventing osteoporosis.

Calcium intake is inadequate in the diets of US children, with only 30% meeting the Institute of Medicine (IOM) recommendation [4]. Use of dietary supplements contributes significantly to intake in the US, but even with supplements, there is a large proportion not reaching the recommendation [5]. Low calcium intakes could lead to low bone mineral content (BMC) and density (BMD), which are associated with an increased risk of fractures in girls 3-15 year old [6] while adequate calcium intakes increases BMD in adolescence [7] and prevents bone loss and fractures later in life [8].

A strategy to maximize bone mineralization during this critical period is to increase absorption of the calcium being consumed. This could be achieved by certain non-digestible carbohydrates, such as inulin [9], galacto-oligosaccharides [10] and soluble corn fiber (SCF) [11]. These are fermented by bacteria in the lower intestine producing short-chain fatty acids (SCFA), which solubilize minerals in the gut, improving mineral absorption and resulting in higher bone mass in rats [12]. SCFA also increase cecal weight and beneficial gut bacteria [10,11,13], increasing calcium absorption. In animal studies (rats), the most effective fiber for increasing bone mass and resistance to fractures was SCF [12]. In adolescents, a randomized, double-blind, placebo-controlled crossover study that tested SCF supplementation (12 g/d) for 3 weeks in 24 adolescents found that calcium absorption increased by 12% compared to controls while consuming diets low in calcium (600 mg/d) [11]. Another study among free-living adolescents on a self-selected diet, SCF (12 g/d) had similar results on calcium absorption and distinct differences in gut microbial communities [14]. However, to our knowledge, there are no published studies determining the long-term effects of SCF on bone mass or biomarkers in humans. It is necessary to test if this short-term increase in calcium absorption translates into an increase in bone mass over time in humans, particularly during adolescent growth spurt.

The MetA-Bone Trial was designed to test the effects of SCF supplementation on bone mass in children. This report details the study design, rationale, and procedures used to assess the effects of SCF on bone mass.

STUDY DESIGN AND METHODS

Study rationale and overall design

The overall MetA-Bone trial study aim is to determine the effects of SCF supplementation for one year on bone metabolism in children using a randomized double-blinded placebo controlled clinical trial. Bone mass will be assessed at baseline, 6 months, and 12 months. Bone related biomarkers will be assessed at baseline and 12 months.

The primary outcome measures are change in total BMC and spine BMC between baseline and 6 months and between baseline and 12 months. The secondary outcomes are changes in BMD between baseline and 6 months and between baseline and 12 months and changes in bone biomarkers in blood and urine between baseline and 12 months. Additionally, we will explore 1-year changes with the intervention in gut microbial communities.

The Institutional Review Board at Florida International University (FIU) approved the study.

Study population

The trial plans to recruit 240 healthy children, 10-13 years of age. We anticipate recruiting an equal number of healthy boys and girls living in the Miami Metropolitan Area. This includes a diverse racial and ethnic group, with about 72% Hispanics, 19% Non-Hispanic Black, 7% Non-Hispanic Whites and 2% other races, following the census data in this county.

Eligibility criteria:

Age 10-13 years:

We will be aiming for a Tanner stage 2-4 to match the previous study on SCF supplementation for three-week in adolescents conducted by Dr. Weaver [15]. This developmental stage, the most important for bone mineralization, will be assessed with a validated self-reported picture instrument [16]. Because Hispanics have an earlier age of menarche [17], we will start recruitment at age 10.

Healthy weight:

This will be assessed by calculating body mass index (BMI) from current weight and height as self-reported in the pre-screening form. To be eligible, BMI must be between the 5^th and 85^th percentiles for age and sex based on the Centers for Disease Control Growth Charts.

Healthy adolescents:

Subjects with any chronic illness requiring regular medication, such as antiepileptics or anticonvulsants, corticosteroids, thyroid hormone, antacids, laxatives, and immunosuppressive therapy, will be excluded from the study. Health status will be assessed with a short screening form at the pre-screening visit.

Low habitual calcium intake:

we will include only those children consuming 2 or fewer servings of dairy products per day, which translates into about 600 mg/d of calcium (half of the recommendation for this age group [18]). In a previous study with boys and girls this age, we found mean calcium intake to be 657±359 mg/d in boys and 585±322 mg/d in girls, which is about half of the Estimated Average Requirements (EAR) [19]. Therefore, we expect that most adolescents screened will have low habitual calcium intake. Those consuming calcium supplements (>200 mg/d) will be excluded, this will be assessed using a short form at the pre-screening visit. Multivitamin/Multimineral supplements usually contain little (100-200 mg) or no calcium.

Adequate vitamin D status:

Only participants with adequate vitamin D levels (25OHD ≥20 ng/ml, as established by the Institute of Medicine for bone health¹⁶) will be included in the study. Although previous studies have not found that vitamin D supplementation increases calcium absorption in adolescents [20], an adequate vitamin D status is generally important for calcium absorption [21]. Although we do not have data on vitamin D deficiency in children in South Florida, based on a study among healthy weight children in Puerto Rico, a place with ample sun, only 3% had deficient levels [22]. We expect a somewhat similar prevalence in Miami, which is also a place with ample sun, but because we lack data, we assumed a more conservative approach to address the proportion of healthy weight adolescents with vitamin D deficiency in South Florida (10%). Our sample size was adjusted for this. Vitamin D status will be evaluated in the baseline visit from the serum sample collected.

Recruitment

Participants will be recruited on a rolling basis for 2-3 years or until total sample is achieved. Siblings will be recruited if eligible. We will use a combination of recruitment efforts, as detailed below [23]:

(1). Clinics:

we will recruit from the Citrus Health Network (CHN) Inc., a not-for-profit health care organization and a Federally Qualified Health Center funded by section 330 from the HHS Health Resources and Services Administration. It serves over 30,000 persons per year through primary care services and it also has school-based health services in 20 schools serving over 2,600 children.

(2). Community:

we have partnered with the FIU Office of Engagement and the Office of Academic Affairs in our recruitment efforts. These offices have close communication with the Miami Dade County Public Schools (more than 200 elementary and middle schools), with other private schools in the area (more than 50 elementary and middle schools) and with more than 30 community organizations, including youth groups and after care programs. We already have IRB approval from Miami Dade County Public Schools to recruit in their schools. We will also recruit from summer camps and summer programs at FIU and near FIU.

(3). Informatics:

We will recruit from social media (Facebook, Twitter, Instagram), through our webpage metabone.fiu.edu, and within FIU via intranet emails. Although these strategies are less effective than in-person contact [24], as more young individuals are using them, it may become an important strategy.

(4). Others:

we have partnered with different on campus active projects with children to help disseminate the study. We will also use word of mouth among screened and recruited participants.

Study events and timeline (Figure 1)

Figure 1.

Study flowchart

1. Pre-screening session. We will explain the study to interested children and their parents. Parents and their children will complete a short pre-screening form to assess eligibility criteria. Those who qualify and wish to participate will be asked to sign the parental consent and participant’s assent forms. We will ask parents and children to complete general health, nutrition and physical activity questionnaires.

2. Baseline visit: this visit will take place at the FIU Child and Family Center. Participants will undergo anthropometric measurements (these results will not be used for eligibility), provide a fasting blood sample, and undergo a bone scan using the HOLOGIC DXA. A separate blood tube will be collected to evaluate vitamin D status through the measurement of serum 25(OH)D; this tube will be sent immediately to a local laboratory. If vitamin D status is adequate, then we will inform the participant about their randomized group (see next section). Before completing the visit, we will provide participants with instructions and materials to collect 24-h urine and a fecal sample at home; we will gather these samples during the next home visit.

3. Randomization: The study statistician created a block randomization scheme to assure approximately equal numbers per intervention group through enrollment. Block size are variable and masked to all other investigators and study personnel so that they cannot anticipate or influence future group assignments, as this may bias the allocation. Randomization was conducted a priori by the statistician who will have no participant contact. Throughout the study, our study statistician will monitor the baseline demographic equality by group to ensure randomization is performing as expected.

4. Study supplement delivery visit (within 1-2 weeks of the baseline visit): We will deliver the participants ‘randomly assigned study supplement to their home, collect the 24-h urine and fecal samples and provide detailed written instructions on how to take the study supplements. At this visit we will also show participants how to download the compliance mobile app that was specifically designed for the study (more details in the Compliance section).

5. Follow-up home visits (3 and 9 months): home visits will be conducted by the study staff to collect the supplements not consumed and to provide study supplements for the next 3 months. We will review with the participants their compliance during the last 3 months with a questionnaire and also as recorded in the database (or the study compliance calendar among those without a smartphone) and if compliance is low, discuss ways to improve it. Participants will also complete short questionnaires to record changes in their diet and in physical activity during the last 3 months. We will also inquire about newly prescribed medications and dietary supplements during the last 3 months and assess if there are new safety alerts and adverse events. At the 9 months visit, we will provide the materials and instructions to collect the 24-h urine sample and a fecal sample at home. Participants will be asked to bring these samples to the last visit (12 months visit).

6. Assessment visit (6 and 12 months): participants will undergo anthropometric measurements and a bone scan (DXA). We will collect study supplements not consumed, provide more study supplements (only during the 6-month visit), and review compliance. Participants will also complete diet and physical activity questionnaires. For the 12-month visit, participants will also provide a fasting blood sample and provide the urine and fecal samples that were collected at home.

Supplements

The four supplement groups are:

• SCF (12 g/d)

• SCF + calcium (12 g/d of SCF + 600 mg/d of elemental calcium)

• Placebo (12 g/d of maltodextrin, which is a polysaccharide with no effect on calcium or bone; it is often used as a food thickener, filler or preservative in many foods)

• Placebo + calcium (12 g/d of maltodextrin + 600 mg/d of elemental calcium)

SCF and the placebo (maltodextrin) were provided by Tate & Lyle PLC (Hoffman Estates, IL) and the calcium (in the form of calcium lactate gluconate) was purchased from Stauber Fullerton, CA. These ingredients are being pre-mixed with a beverage powder (flavor matrix) to increase acceptance over the 12 months period. We did several pilot panel testing of ingredients mix with popular children’s beverage matrix among our staff and among a group of children 11-13 years old for solubility and flavor. Based on the flavors most accepted by these children and based on the solubility and masking of flavors, we chose Kool-Aid. This was provided by Kraft in several different flavors. The pre-mixing of ingredients is currently being done at the FIU pharmacy following a standardized protocol and specialized equipment for commercial blending of powders. The pre-mix supplement is transferred into 128-ounce canisters for a 3-month supply for each participant for each flavor (every participant will receive 2 canisters, one with a different flavor, every 3 months). Standard scoops are included inside each canister, which is specific to each supplement group, to deliver the amount of specified ingredients (25-30 grams of product). The FIU pharmacy is also responsible for labeling the products based on the “a priori” randomized list for maintaining blinding.

We will allow participants to choose flavors every 3 months to maintain compliance over time. Each participant will be instructed to consume 1 scoop of product diluted in 8-10 ounces of water twice per day. All containers are of the same color, with the name of the trial (MetA-Bone), blinded code (A, B, C or D), flavor of the powder beverage and production date. They all look very similar, with little difference in weight, solubility when mixed with water and flavor. We will also provide a study water bottle that has a bottom storage compartment which holds a scoop of supplement; this will facilitate taking the supplement to school, travel, or during extracurricular activities. The study supplements will be tested yearly for microbiology integrity (aerobic plate count, coliforms, E. coli, Salmonella, yeast, and mold) by an independent external laboratory.

Compliance

Subjects will be provided with detailed instructions, counseling, and assessment to ensure supplement adherence and compliance. This will be evaluated in different ways:

• Compliance app: We will ask parents to download the compliance app specifically designed for the study; this is a very popular way of communicating and engaging with participants in clinical trials. The app will send a daily automatic notification to ask if the participant took the 2 study supplements, only 1, or none during that day; depending on the answer, it will automatically either congratulate them and motivate them to continue or encourage them to improve their supplement intake for the following day. Answers will be automatically stored in a database; this will be reviewed periodically by our research staff. In case of non-compliant or non-response, we will call the parents to discuss with them barriers for supplement consumption and to suggest ways to improve compliance, such as offering a different flavor. If parents do not own a smartphone, we will provide them with a paper calendar to record daily consumption of study supplements. However, we expect this to be minimal, as 92% of adults 30-49 years (which will probably be the range in which most of the parents of our study will be) reported to own a smartphone in 2019 [25] and this is expected to increase every year [26].

• Phone calls: We will call families regularly, particularly during the first few weeks of the study and during school breaks, to remind their child to consume the supplement and to assess compliance.

• Leftover supplement: We will also monitor compliance when we meet with them every 3 months by recording the amount of supplement not consumed. All canisters are pre-weighed before delivery so using this as the initial weight, we will subtract the amount left to calculate the amount consumed.

• Questionnaire: We will ask participants a few questions about the study supplement intake at every visit (3, 6, 9 and 12 months).

To promote compliance, we will send periodic text messages with ideas on how to take the supplement, offer recipes to vary the supplement, such as smoothies and ice pops, and what to do in case of a trip or vacation away from home to both parents/caregivers and children using an automated one-way text message provider. To avoid incomplete intake due to children occasionally sharing the study supplements with family members, we will provide additional supplement mix for siblings and other family members. Because we will be recruiting from many different sites (>200), we expect that children randomized into the 4 supplements will not know each other so the exchanging of supplements will be minimal. However, if they do, it is unlikely that they can detect differences between supplements as the Kool-Aid masks very well any difference in flavor between ingredients (fiber, maltodextrin and calcium).

Therefore, we will have regular contact with participants to establish rapport with them, either face to face (every 3 months) or by email/text/calls every 2-4 weeks.

Blinding

All assessments will be performed by blinded study staff. Study supplements will be packed in the same containers, identically identified with the name of the trial (MetA-Bone), unique coded for each supplement (A, B, C or D) and will display the production date. The weight and the appearance are similar between supplements. The compounding team, which are not involved in any other study related activity, will be the team with access to the corresponding group by randomization code; therefore, adolescents, parents and study staff will be blinded to the assigned intervention. The volume difference between the supplements with and without calcium (and the measuring scoops) is very subtle and will not be perceived by participants or study staff.

Outcomes

1. Bone mass: Change in total and spine BMC z scores are our primary outcomes. BMC was chosen as the primary outcome as in children, dietary intervention can augment bone size rather than the mass of the bone per unit volume. Therefore, because BMD is calculated to adjust for size, one can miss the actual change in bone mass during growth [27]. Bone mass will be assessed using a Hologic DXA bone scan at the FIU Child and Family Center. Body fat, total BMD, total BMD-z score and spine BMC will also be obtained from DXA.

2. Bone biomarkers: changes in bone and other metabolic biomarkers are the study secondary outcomes. Blood and urine will be collected at baseline and 12-months follow-up visits for determination of biochemical markers reflecting vitamin D status and calcium homeostasis. Fasting blood samples (15 ml each) will be collected by venipuncture by research trained phlebotomists. Samples will immediately be centrifuged at 12,000 x g for 10 minutes, and the obtained serum will be stored at −80°C until analysis, except for 25(OH)D, which will be sent to a local laboratory for analysis, as this is the final screening measure to assess vitamin D status. Stored samples will be measured for serum calcium, phosphorus, glucose, lipid profile, creatinine, osteocalcin, serum I collagen N-terminal peptide (P1NP), carboxy-terminal collagen crosslinks (CTX), N-telopeptide cross-links, parathyroid hormone (PTH), bone specific alkaline phosphatase, 1,25(OH)₂D, and insulin growth factor 1 (IGF-I). Urine will be collected for 24-h using ice-chilled containers and analyzed for calcium, phosphorus, creatinine, and measure specific gravity, which is a measure of hydration, a potential confounder.

1. Fecal microbiome: Fecal samples will be collected at baseline and at the end of the intervention for exploring long-term changes in gut microbial communities with the intervention. Procedures will be as previously described for SCF studies [11,14]. DNA will be extracted using the Fast DNA® SPIN kit (MP Biochemicals, Irvine, CA). DNA quality will be checked using a 0.7% agarose gel and Nanodrop One spectrophotometer (Thermo Scientific, Wilmington, DE) and then quantified using a Nanodrop 3300 fluorospectrometer (Thermo Scientific). The phylogenetic diversity of bacterial communities will be determined using 16S rRNA gene sequences (primers targeting the V3-V4 region) obtained from high throughput paired end MiSeq technology (Illumina). Multiple samples will be run and differentiated using a combination of 8-bp tagged forward primer and 8-bp tagged reverse primers using a step out protocol according to manufacturer’s instructions (Illumina). The reads will be pre-processed to remove primer tags, low quality sequences then paired end reads will be merged. Sequences will be analyzed using the QIIME2 pipeline [28] that includes software from many sources that allows Amplicon Sequence Variants (ASV) and taxonomic assignment as well as a number software programs for different beta and alpha community diversity measures and statistical comparisons. Additional statistical analysis of microbial taxa, such as correlations with polyphenol metabolites and calcium retention will be performed as previously described [11,29].

Other variables

1. General health: this will be collected using a structured questionnaire used previously among adolescents [30]. Data collected in this questionnaire includes: socio-demographics, medical history, including fracture(s) history, use of medications, use of alcohol and tobacco, sleep and stress, self-report on pubertal maturity using Tanner staging [31] and menarche date, if applicable. In addition, parents will complete a socio-demographic and medical history questionnaire. For those that have not reached menarche at baseline, we will re-evaluate this at 6 and 12 months.

2. Anthropometric measurements: we will measure weight, height, seated height, leg length and waist and neck circumferences by trained study staff at baseline, 6-month and 12-month follow-up visits following standardized protocols.

3. Dietary evaluation: Dietary intake will be assessed (by a Nutritionist) throughout the study by 24-h recalls using the Nutrition Data System for Research (NDSR) software. Three recalls will be conducted before the screening/baseline visit (at pre-screening and/or by phone) and one recall at each follow-up and assessment visits. Recalls are entered directly in the computer using the multi-pass method of the NDSR. This software analyzes food groups and nutrients. We will assess the intake of the following food groups intake: dairy products, fruits, vegetables and carbonated beverages and the following nutrient intakes: protein, calcium, vitamin D and K, which are all important dietary factors in bone health. We will also assess dietary factors affecting absorption and retention, such as oxalates and caffeine, among others. We will also evaluate calcium intake using a short food frequency questionnaire (FFQ) of foods rich in calcium, that also includes dietary supplement use; this FFQ has been previously validated to assess calcium intake among adolescents [32]. These diet variables will be used as covariates in the statistical analyses.

4. Physical activity: We will estimate physical activity, an important covariate for bone mass, using the International Physical Activity Questionnaire (IPAQ), which has been validated for its use in adolescents [33]. We will record changes in the levels of sedentary, moderate or vigorous activity during the study. This will be done at each visit, every 3 months. We will also ask about changes in structured physical activities during the study.

Data and Participant Safety

The intervention and measurement protocols pose minimal risk to participants. Study design, recruitment strategies, and participant and data safety will be monitored by the Data and Safety Monitoring Board (DSMB) established for this purpose together with the funding agency, Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) at NIH. The DSMB approved the study protocol and will review progress, including recruitment, compliance, and adverse events on a yearly basis. Because the intervention is short and the risks are minimal, there is no stopping rule in this trial. Safety alerts include skin bruising and infections associated with blood drawing, disclosure of personal information, and gastrointestinal discomfort with consumption of the supplement, such as stomach pain, bloating, nausea, diarrhea or transient loss of appetite. A physician will oversee study implementation and safety.

Statistical plan

1. Power Calculations: The primary outcome for which we powered this study is the change in whole-body BMC between baseline and the one-year endpoint for SFC versus control. The power calculations were centered on detecting a conservative clinically meaningful standardized effect size [34], given no prior knowledge is available about the difference in post-intervention whole-body BMC after one-year supplementation with SFC. For an alpha level of 0.05, a total drop-out inflated sample size of 240 participants (60 in each of the three active treatment groups and 60 for the placebo group) provides 80% power to detect a medium effect size of 0.5 units of standard deviation [34] in BMC between any of the active treatment groups compared to placebo. The proposed sample accommodates a 10% non-eligible rate due to vitamin D deficiency plus 20% drop-out rate, similar to rates in our previous trials among adolescents [35-39]. All power calculations were performed with PASS2019 [40].

2. Statistical analysis: Main analyses will be performed on an intention-to-treat basis that will include all randomized participants regardless of the completion status. Data will be examined for outliers and normality. Transformations will be performed where deemed to be the best analytical strategy. Descriptive statistics including means, medians, standard deviations, and ranges, as well as frequencies and proportions will be generated overall and by treatment group, for continuous and categorical variables, respectively. Univariate comparisons of means and proportions by treatment group will consist of ANOVA and chi-square test, respectively, or their non-parametric equivalents, Kruskal-Wallis test and permutation based exact chi-square test. We will use same analytical methods to examine potential differential attrition by treatment group. To compare the characteristics and determine missing data mechanism between study completers and those with missing outcome data, we will apply two-sample t-test and chi-square test for continuous and categorical demographics and other covariates. For the primary analysis, the change from baseline in whole-body BMC to six months and after one year of supplement will be analyzed using linear repeated measures mixed effects regression model. The model will include treatment effects for supplement groups, time, treatment by time interaction, baseline whole-body BMC, baseline age, sex, Tanner stage (puberty status), dietary intake, and physical activity categories during the study as covariates. Least-squares treatment means, differences between the least squares treatment means, and their corresponding 95% confidence intervals at 6 and 12 months for the supplement treatment differences will be computed with Bonferroni adjustments for multiple comparisons. A similar statistical approach will be used for the other aims and secondary outcomes. Following the same procedures as in the intent-to-treat analyses, the supplement treatment effect will be assessed in the per-protocol population taking into consideration participants with complete baseline and 12-month data and at least 70% adherence throughout the intervention. Sensitivity analysis will be performed using model-based multiple imputations of the missing outcome data. First, we will impute enough missing outcomes to create a monotone missing data pattern. Assuming data is missing at random (which will be assessed at the very beginning of the analytical process) we will create sequential predictive regression models to perform 25 imputations for outcomes missing at 6 and 12 months by incorporating all available outcome data at baseline along with other covariates. Finally, results will be combined across all imputations to produce unbiased supplement treatment effect estimates and their standard errors. All data will be analyzed using SAS/STATv14.2. Associations will be considered significant at the alpha level of 0.05.

DISCUSSION

The MetA-Bone trial study will determine the independent and combined effects of SCF and calcium on bone mass in growing children. Studies have shown that supplementation with SCF in healthy adolescents increases calcium absorption by 12% compared to the placebo group using stable isotopes [11,14]. This increase in calcium absorption was also related to an increase in Bacteroides, Alistipes, Butyricicoccus, Oscillibacter, and Dialisterin the gut. But these were short-term studies and the long-term effect of SCF on the gut microbiota associated with calcium absorption is still not known. These positive effect of SCF on calcium absorption may translate into a greater bone mass, which will be determined in the present study. In 14 post-menopausal women, a study comparing 0, 10, and 20 g of SCF/d for 50 days found improvements in bone calcium retention of 4.8% with 10 g of SCF/d and 7% with 20 g of SCF/d [41]. Also, a significant 8% increase in bone-specific alkaline phosphatase, which is a bone-formation marker, was found in women consuming the 20 g of SCF/d compared to the 0 g of SCF/d. However, there are very limited studies testing the effects of SCF on bone. A study in rats found that SCF, significantly increased whole body BMC and femoral BMD, cortical area and thickness, and resistance to fractures by >8% [12]. To our knowledge, there is no published study testing the effects of SCF on bone.

Any positive change in bone mass may have significant impact in bone health later in life. This is particularly important in adolescence, as bone accumulates rapidly during this period and accounts for up to half of adult PBM and is a strong predictor of bone fragility later in life [1]. Currently, musculoskeletal disorders account for the second cause of disability worldwide [3]. In particular, osteoporosis, one of the musculoskeletal disorders, leads to bone fragility and increases the risk of fractures [42]. Osteoporosis affects 1 in 2 women over age 50 (more than breast cancer) and 1 in of 4 men over age 50 (more than prostate cancer) [3]. Moreover, osteoporotic fractures have almost doubled in the last 10 years and they are expected to rise by almost 50% in the future [3]. In addition, more than 1.5 million fractures occur each year in the US, and the estimated cost of an osteoporotic fractures is expected to be $25.3 billion by 2025 [3].

Within diet, calcium is the mineral with the greatest impact in bone mass, as it is the largest component of BMC. A high calcium intake during adolescence is associated with a high PBM, which would predict a lower risk of osteoporotic bone fracture later in life [2]. Therefore, maximizing calcium retention by the skeleton within the genetic potential during growth is a key strategy to prevent osteoporosis. However, calcium is precisely the nutrient with the greatest inadequacy in the diets of US adolescents, with only 30% meeting the recommended intake level [4]. If SCF can maximize the efficiency of the little calcium intake in adolescents, that could have beneficial long-term benefits on bone mass. This type of intervention may prove to be a practical way to safely and effectively address the problem of suboptimal calcium intake in US adolescents. Changing behaviors to improve diet quality in adolescents, such as increasing the intake of dairy products, takes time to overcome with many barriers and challenges in adolescents [43]. We have shown from a previous study in adolescents that diet quality, assessed using the Healthy Eating Index, is poor in most individuals, with no adolescents falling into the good diet quality category [44]. Therefore, increasing calcium intake using behavioral strategies may take time. It can be estimated that the increase in calcium absorption from consuming a fiber such as SCF would be comparable to increasing daily calcium intake by at least 250 mg in adolescents [45]. This is about 1 serving of dairy product intake (1 serving is 1 cup of milk, 1 slice of cheese, ¾ of cup of yogurt). Therefore, the use of SCF supplementation to improve calcium absorption may decrease the calcium requirement in this group, by improving calcium absorption efficiency. This could potentially help adolescents reach PBM during this crucial stage, which could translate in a decrease in the risk of osteoporosis later in life. SCF could be added to different food matrices or to dietary supplements. Fortification of foods highly consumed by adolescents could be a strategy at population level.

In conclusion, SCF supplementation has been shown to improve calcium absorption and improve bone formation biomarkers in adolescents and in adults. The evidence for a benefit of SCF on calcium absorption is expected to be translated into bone, particularly during the most important age for PBM. However, no published trial has tested the effects of SCF on bone mass. This type of intervention may significantly improve bone mass and reduce the risk of osteoporotic fractures in the future.