Response to Commentary

Abstract

Thank you to the Editors for the opportunity to respond to Dr. Geoffrey Livesey’s comments regarding the methodology used in the publication (1). At the outset, the authors agree that the field of dietary fibers is quite vast and encompasses a variety of carbohydrates, each with different human health benefits and unique properties such as structure, solubility, and fermentability. The diversity in the types of fibers supports the need to continue conducting robust, high quality scientific research to understand the relationship between biological effects and health benefits. We would like to address key points raised by Dr. Livesey. Use of breath hydrogen as a measure for carbohydrate fermentation and an estimate of caloric value is established in the scientific literature. Other resistant maltodextrins have utilized this methodology (2) as have low and no calorie sweeteners (3). It is also typical to have this study last until the ten-hour time point. We acknowledge Dr. Livesey’s point that there is a possibility of additional fermentation, and therefore breath hydrogen, which could have been produced over the next fourteen hours. To minimize undue burden to the clinical subjects, we decided against this length of study design. It is also important to note that our decision was validated as we saw the breath hydrogen curves returned to baseline at the ten-hour time point. The authors wish to clarify that they did not claim that no breath hydrogen was produced as a result of SCF70 or SCF85B consumption, as can be seen in the original publication figure 2. The authors would also like to highlight that mixtures of different fermentable carbohydrates were not provided to the clinical subjects, as each individual fiber was provided in a beverage on separate occasions. Dr. Livesey did mention that in our study there was not a time for adaptation of colonic microflora to the presence of SCF70 or SCF85B. He is correct in this interpretation of the study design and this aspect of the protocol design was intentional. We did not provide either SCF70 or SCF85B to the participants for a longer duration, in advance of the breath hydrogen collection, to best simulate real world consumption pattern of consumers. In order to address the likelihood of instability of the baseline hydrogen excretion, a low-fiber diet was provided to the subjects the day before the testing as well as the meal provided during the collection of breath hydrogen samples. In Dr. Livesey’s commentary, he references three conventional energy balance studies in animals. It is important to note that one of the studies referenced did not use PROMITORR SCF, but another soluble fiber (4). For the remaining two studies, Dr. Livesey provided values of 1.8 kcal/g SCF70 in pigs (5) and 1.5 kcal/g SCF70 in roosters (5). It must be noted that these values are the kcals per gram of ingredient and not kcal per gram of fiber. Table 3 of Canene-Adams et al presents caloric values for both, per gram fiber level and for per gram ingredient. The total energy per gram of ingredient included the energy obtained from breath hydrogen (representing the fiber portion) and energy from digestible carbohydrate at 4 kcal/g. Energy per g ingredient (kcal/g ingredient) was significantly greater for SCF70 (1.1 kcal per gram of ingredient) compared to SCF85B (0.46 kcal per gram of ingredient) as expected due to the greater portion of non-fiber carbohydrate in SCF70 compared to SCF85B. At the time of these animal studies being performed, the SCF85B ingredient was not yet developed by Tate & Lyle. In Table 3, the average caloric value for SCF70 on an ingredient basis, is 1.1 kcal per gram of ingredient. This value is not dissimilar from the porcine (1.8 kcal per gram of ingredient) and rooster (1.5 kcal per gram of ingredient) studies performed prior and could be due to physiological differences in species, microbiota strain and amounts present, and/or methodology differences. Ultimately, the values determined in humans are the ones most relevant to the caloric calculations performed for Nutrition Facts panels. Authors acknowledge Dr. Livesey’s comment that the human clinical trial to quantify the amount of PROMITORR Soluble Corn Fiber in stool samples has not been performed and would be useful information to obtain and analyze in due course. Nevertheless, the lack of this data does not negate the breath hydrogen results currently presented, nor does it refute the beneficial physiologic health effects seen in multiple human studies. The International Association for Probiotics and Prebiotics (ISAPP) defines a prebiotic as “a substrate that is selectively utilized by host microorganisms conferring a health benefit” (6). This definition states that the prebiotic must be utilized, not limited to fermentation, as in the case of some polyphenolics which have prebiotic related health benefits despite not being fermented (7). The definition of prebiotic also does not state to what extent the fiber must be utilized or fermented. In fact, there are many slightly fermented fibers consumed by humans with established