Prebiotics are substances that are not normally digestible, but nourish the bacteria in the colon. Prebiotics are usually carbohydrates (such as oligosaccharides), but they can be non-carbohydrates. The most prevalent forms of prebiotics are nutritionally classed as soluble fiber. To some extent, many forms of dietary fiber exhibit some level of prebiotic effect. A study, published in the Journal of Pediatrics (September 2007, Volume 151, Pages 293-298) looked at 97 healthy adolescents who were not obese. The subjects, averaging 11 ½ years old, were divided into two groups and given either a prebiotic (eight grams of inulin/oligofructose) or a placebo for one year. The BMI (which stands for Body/ Mass Index—it is a measurement of weight as it relates to height; a high BMI is one way to measure if someone is obese)) was lower in the group given the prebiotics. The average difference in BMI for the supplement group was .52 kg/m lower. When the researchers considered subjects whose higher calcium intakes (greater than 700 mg per day), they found that the associated benefits were increased, with an average BMI difference of 0.82 kg per sq. m, compared to the placebo group.
