- Click here for explanation of classification scheme.

• Current recommendations for fiber intake do not consider total low-digestible carbohydrate (LDC) consumption, nor recommend an upper limit for LDC intake based on potential gastrointestinal effects
• Therefore, a review of published studies reporting gastrointestinal effects of LDCs was conducted.

Listed in Beginning of Study

• Only studies published in refereed journals in English
• Only in studies with a control period, either placebo treatment or no LDC treatment, were included
• Studies must have included an acceptable measure of gastrointestinal effect.

From Table 2: Criteria for Study Selection

• Primary review: Published as complete paper in a journal; English language
• Secondary review: Subjects have complete gastrointestinal tract; free of gastrointestinal disease; no recent use of antibiotics, laxatives, etc.; control (placebo or no LDC treatment)
• Tertiary review: Report of methods for assessing gastrointestinal effects.

• Studies of subjects with incomplete or abnormal functioning gastrointestinal tracts or where antibiotics, stimulant laxatives or other drugs affecting motility were included
• From Table 2:
  • Primary review: Published as abstract only; unpublished internal report; language other than English
  • Secondary review: Subjects have incomplete gastrointestinal tract; have gastrointestinal disease; recent or current use of antibiotics, laxatives, etc.; no control or results compared only to another LDC
  • Tertiary review: No report of methods for assessing gastrointestinal effects.

Recruitment

• Refereed journals in English
• Standard scientific databases for search were used, including PubMed, Medline, Agricola and Web of Science.

Design

• Narrative review
• Qualitative analysis.

Intervention 

Consumption of various LDCs.

 

Timing of Measurements

Not applicable.

Initial N

• 68 studies
• Six review articles.

 

 Key Findings

From Initial Part of Paper

• Low-digestible carbohydrates are carbohydrates that are incompletely or not absorbed in the small intestine but are at least partly fermented by bacteria in the large intestine
• Classifications and definitions of LDCs are given; the two broad categories are fiber and sugar alcohols. Table 1 of the article gives the classifications and descriptions of low-digestible carbohydrates as well as characteristics and sources.
• The consumption of LDCs has been associated with a number of of gastrointestinal effects: Acid reflux and heartburn, belching/burping, borborygmi (flatulence in the bowels) and gas emission, colic (spasmodic abdominal pain), laxation (softer and increased frequency of bowel movements), reduced appetite, meteroism (abdominal distention), nausea, rumbling in the gut, stomachache, watery feces and diarrhea
• Medium characteristics and the chemical structure of the LDCs affect how the gastrointestinal tract responds to the consumption of particular LDCs. The most important medium characteristic is the form of the food, whether it is solid or liquid.
• Acceptability increases when LDCs are consumed as part of a meal. Factors that increase gastrointestinal transit time generally increase gastrointestinal acceptability of LDCs because they increase the time available for LDC digestion and absorption.
• Host factors include personal attributes and lifestyle choices that vary largely between individuals and are significant mediators in gastrointestinal function. Some personal attributes are static (gender, genetics, personality), while others change over time (age, weight, health conditions). Lifestyle choices include the usual consumption pattern of LDCs by consumers, medication and drug use, and the level of physical activity.  
• Health conditions affect gastrointestinal function and may be associated with gastrointestinal effects, regardless of LDC consumption. Enzyme deficiencies, inflammatory bowel disease and celiac disease are among those discussed.
• The total amount of LDCs in the diet affects tolerance. Many foods are natural laxatives because they contain indigestible carbohydrate (whole grains, fruits and vegetables). Therefore, consuming combinations of natural laxatives with or without foods containing added LDCs may increase the occurrence or intensity of gastrointestinal effects.
• Prebiotics, probiotics and antibiotics can alter colonic bacteria, thus affecting fermentation of the LDCs and altering gastrointestinal effects
• Gastrointestinal effects may be measured objectively with methods that quantify gastrointestinal function and subjectively with methods that survey subjects of their bowel movements and gastrointestinal symptoms. In addition, an assessment of other physiological parameters provides information on carbohydrate digestion, absorption or fermentation and may indirectly assist in evaluating the potential gastrointestinal effects of LDC consumption.
• Most studies reporting gastrointestinal responses to LDC consumption rely on subjective questionnaires. The inherent subjectivity of these methods must be taken into account when using results from these assessments to make recommendations for LDC intake to individuals and groups.
• Carbohydrates that are resistant to digestion and absorption in the small intestine may cause gastrointestinal effects, so measuring carbohydrate malabsorption may provide information about potential symptoms that might be associated with particular LDCs. 
• Perfusion and ileostomy studies measure carbohydrate malabsorption directly by analyzing the contents of the ileum or ileostomy bags, respectively, after patients consume a test meal with a polyethylene glycol marker. 
• Hydrogen breath studies measure malabsorption indirectly by measuring hydrogen expiration, which is a product of colonic fermentation
• Oral tolerance tests may also be used, in which after an overnight fast, subjects ingest a bolus of carbohydrate; blood glucose and insulin levels are measured for several hours.

From Results Section

Dietary limitations for studies are summarized in Table 3.

• Non-starch polysaccharides:
  • Guar gum: Consumption may contribute to other gastrointestinal effects such as abdominal pain, bloating, flatulence, but in terms of the frequency and intensity of gastrointestinal effects, any differences between the guar gum and control treatments were insignificant in this study. However, the authors reported great variations between individuals. In further studies, higher amounts are needed in order to determine a laxative threshold and amounts at which flatulence and other effects become unacceptable; studies should investigate the effects of single and daily divided intake of guar gum and PHGG in unadapted and adapted individuals.
  • Inulin and Fructo-Oligosaccharides (FOS): Most of the studies were with lower intakes
  • Polydextrose: Adults should tolerate polydextrose at levels of at least 50g per day, even in fasting conditions and dissolved in water. Higher intakes of polydextrose are associated with an increase in gastrointestinal symptoms (75g) and diarrhea (88g). Children may tolerate up to 1g polydextrose per kg body weight, though this amount may cause diarrhea in children ages two to three years.
•   Resistant starch:
  • Data from questionnaires or interviews and, in some studies, fecal collection, indicate RS may have a mild laxative effect
  • As with other fibers, RS increases fecal weight
  • Reports of diarrhea were rare and only with high intakes of RS and increases in gastrointestinal symptoms were associated with high RS consumption (an average of least 30g per day).
• Sugar alcohols:
  • Erythritol: In one study, on a per-kg-body-weight basis, females were shown to have a higher toleration threshold (0.80g per kg body weight, or about 41g) than males (0.66g per kg body or about 43g) [based on development of diarrhea].  Increases in other gastrointestinal effects such as nausea and borborygmi were reported with intakes of about 50g per day. Other reviews of clinical studies with erythritol have concluded single or repeated intakes as high as 1g per kg body weight or even 132g per day, could be well-tolerated. Such high intakes may be perfectly acceptable if intake is increased gradually over days and the daily intake is consumed as divided portions throughout the day.
  • Xylitol: Few studies have been published concerning the gastrointestinal effects of xylitol consumption compared to a placebo or control diet as well as report methods for assessing effects. Based on the limited evidence, most people may tolerate 30g per day and adapt to higher intakes if the daily intake is divided and in the solid rather than the liquid form.
  • Sorbitol: Overall, single intakes of about 10 to 15g sorbitol may have laxative effects and are associated with other gastrointestinal symptoms; however, 20 to 30g per day may be well-tolerated
  • Mannitol: Few studies concerning the gastrointestinal tolerance of mannitol have been published. One study reported a laxation threshold of 10 to 20g; however, 20g per day of mannitol was reported in another study as an intake that would not cause laxation in most adults
  • Lactitol: While 10g does not appear to induce gastrointestinal effects in healthy subjects, intakes of 20g affect bowel movements and may be associated with other gastrointestinal symptoms. As the intake increases, symptoms are likely to increase; however, intakes of 30 to 40 and even 50g could still be considered acceptable, especially if they are divided throughout the day.
  • Isomalt: Threshold amounts for diarrhea or other gastrointestinal effects have not been estimated for isomalt, but based on the published studies, a single intake of up to 30g isomalt should be tolerated by most adults, and adapted individuals may be able to tolerate daily intakes of 50g per day.
  • Maltitol: Maltitol is better tolerated as an ingredient in chocolate or other foods rather than dissolved in water. As the level of a single dose increases, gastrointestinal effects like flatulence and borborygmi become more common, but these effects are generally mild so that even single intakes of 40g maltitol may be generally well-tolerated in unadapted individuals. Higher daily intakes may be tolerated if the total amount is divided throughout the day and gradually increased over time, but intakes above 60g or 70g per day would contribute to diarrhea in most individuals.
  • Polyglycitol: Based on these studies, polyglycitol should be expected to cause few if any gastrointestinal side effects with amounts between 20 to 30g and increased symptoms and possibly diarrhea at amounts of 40g per day and above, though tolerance may be increased over time and with divided daily amounts even as high as 65g per day, though another study reported polyglycitol syrups are generally tolerated up to 30 to 50g per day after adaptation.
• Children and low-digestible carbohydrates:
  • There are relatively few published clinical studies of children and adolescents and LDCs, so the focus of the review was on studies with adults
  • Most of the published studies have concerned sugar alcohols. Some studies concluded the tolerance level of xylitol in children is lower than that of adults (about eight to 10g) and is affected by the rate of ingestion (lozenges or syrups work faster than gum)
  • Based on these studies, daily intakes of eight to 10g sorbitol and xylitol and 25g isomalt or polyglycitol may contribute to a mild laxative effect, yet may be acceptable for school-age children and adolescents, but the consumption of sugar alcohols by younger children should be more limited. 

 

Recommendations stated by authors:

• Despite great variety in study designs, protocol and types of results, some recommendations and generalizations can be made for consuming LDCs (see Figures two and three in paper)
• Guar gum and inulin should be tolerated at daily intakes of 10 to 15g
• Polydextrose may be consumed at 50g without experiencing diarrhea
• The main side effect of resistant starch, excessive flatulence, is significantly greater at intakes above 45g per day
• Daily amounts of 40g erythritol, isomalt, maltitol and polyglycitol and 30g of xylitol, sorbitol and lactitol should be acceptable to most people
• Mannitol intake should be limited to 20g per day
• Gastrointestinal effects tend to increase in a dose-dependent manner
• When compared to similar amounts of a particular LDC in hydrated forms, solid forms have better gastrointestinal acceptability
• Large intakes of LDCs have better gastrointestinal acceptability if the amount is increased gradually over days or weeks and divided into several portions throughout the day.

Given the potential for gastrointestinal side effects, it would be prudent for food manufacturers to consider the amount of LDCs in a single serving of a product, including all categories of LDC. Although some LDCs may be consumed at high amounts without undesirable effects, typical serving sizes of solid foods should limit total LDCs to 10 to 15g; this amount should be less in beverages or foods often consumed on empty stomachs in order to reduce the likelihood that average consumers will experience side effects.

Other:

none listed