Fructose malabsorption | |
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Other names | Dietary fructose intolerance |
Chemical structure of fructose | |
Specialty | Endocrinology |
Fructose malabsorption, formerly named dietary fructose intolerance (DFI), is a digestive disorder [1] in which absorption of fructose is impaired by deficient fructose carriers in the small intestine's enterocytes. This results in an increased concentration of fructose. Intolerance to fructose was first identified and reported in 1956. [2]
Similarity in symptoms means that patients with fructose malabsorption often fit the profile of those with irritable bowel syndrome. [3]
Fructose malabsorption is not to be confused with hereditary fructose intolerance, a potentially fatal condition in which the liver enzymes that break up fructose are deficient. Hereditary fructose intolerance is quite rare, affecting up to 1 in 20,000 to 30,000 people.[ citation needed ]
Fructose malabsorption may cause gastrointestinal symptoms such as abdominal pain, bloating, flatulence or diarrhea. [4] [5]
Fructose is absorbed in the small intestine without help of digestive enzymes. Even in healthy persons, however, only about 25–50 g of fructose per sitting can be properly absorbed. People with fructose malabsorption absorb less than 25 g per sitting. [6] Simultaneous ingestion of fructose and sorbitol seems to increase malabsorption of fructose. [7] Fructose that has not been adequately absorbed is fermented by intestinal bacteria producing hydrogen, carbon dioxide, methane and short-chain fatty acids. [4] [8] This abnormal increase in hydrogen may be detectable with the hydrogen breath test. [7]
The physiological consequences of fructose malabsorption include increased osmotic load, rapid bacterial fermentation, altered gastrointestinal motility, the formation of mucosal biofilm and altered profile of bacteria. These effects are additive with other short-chain poorly absorbed carbohydrates such as sorbitol. The clinical significance of these events depends upon the response of the bowel to such changes. Some effects of fructose malabsorption are decreased tryptophan, [9] folic acid [10] and zinc in the blood. [10]
Restricting dietary intake of free fructose and/or fructans may provide symptom relief in a high proportion of patients with functional gut disorders. [11]
The diagnostic test, when used, is similar to that used to diagnose lactose intolerance. It is called a hydrogen breath test and is the method currently used for a clinical diagnosis. Nevertheless, some authors argue this test is not an appropriate diagnostic tool, because a negative result does not exclude a positive response to fructose restriction, implying a lack of sensitivity. [7]
Sitting down can cause your abdomen to compress, which slows down digestion. This can lead to issues such as bloating, heartburn and constipation. [12] It could thus increase or cause fructose malabsorption. A study show that physical activity between long periods of sitting is not enough: "focusing on acquiring the recommended dose of exercise is not a strong enough of a stimulant to completely protect the body from physical inactivity the other 23+ h/day". [13] "Reducing prolonged overall sitting time may reduce metabolic disturbances" [14]
Xylose isomerase acts to convert fructose sugars into glucose. Dietary supplements of xylose isomerase may improve some symptoms of fructose malabsorption, although there is currently only a single scientific study available. [15]
There is no known cure, but an appropriate diet and the enzyme xylose isomerase can help. [7] The ingestion of glucose simultaneously with fructose improves fructose absorption and may prevent the development of symptoms. For example, people may tolerate fruits such as grapefruits or bananas, which contain similar amounts of fructose and glucose, but apples are not tolerated because they contain high levels of fructose and lower levels of glucose. [4] But a randomised controlled trials in patients with fructose malabsorption (made by the Cochrane institute) found that "Adding glucose to food and solutions to enhance fructose absorption is not effective in preventing fructose-induced functional gastrointestinal symptoms". [16]
Foods that should be avoided by people with fructose malabsorption include:
Foods with a high glucose content ingested with foods containing excess fructose may help patients absorb the excess fructose. [20]
According to the USDA database, [21] foods with more fructose than glucose include:
Food | Fructose (grams / 100 grams) | Glucose (grams / 100 grams) |
---|---|---|
Sucrose (for reference) | 50 | 50 |
Apples | 5.9 | 2.4 |
Pears | 6.2 | 2.8 |
Fruit juice e.g. Apples, Pears | 5–7 | 2–3 |
Watermelon | 3.4 | 1.6 |
Raisins | 29.8 | 27.8 |
Honey | 40.9 | 35.7 |
High fructose corn syrup | 42–55 | 42–53 |
Mango | 4.68 | 2.01 |
Agave nectar | 55.6 | 12.43 |
Ginger | 1.78 | 1.22 |
The USDA food database reveals that many common fruits contain nearly equal amounts of the fructose and glucose, and they do not present problems for those individuals with fructose malabsorption. [22] Some fruits with a greater ratio of fructose than glucose are apples, pears and watermelon, which contain more than twice as much fructose as glucose. Fructose levels in grapes varies depending on ripeness and variety, where unripe grapes contain more glucose.
Researchers at Monash University in Australia developed dietary guidelines [19] for managing fructose malabsorption, particularly for individuals with IBS.
The following list of favorable foods was cited in the paper: "Fructose malabsorption and symptoms of Irritable Bowel Syndrome Guidelines for effective dietary management". [19] The fructose and glucose contents of foods listed on the Australian food standards [23] would appear to indicate that most of the listed foods have higher fructose levels.
Producers of processed food in most or all countries, including the US, are not currently required by law to mark foods containing "fructose in excess of glucose". This can cause some surprises and pitfalls for fructose malabsorbers.[ citation needed ]
Foods (such as bread) marked "gluten-free" are usually suitable for fructose malabsorbers, though they need to be careful of gluten-free foods that contain dried fruit or high fructose corn syrup or fructose itself in sugar form. However, fructose malabsorbers do not need to avoid gluten, as those with celiac disease must.[ citation needed ]
Many fructose malabsorbers can eat breads made from rye and corn flour. However, these may contain wheat unless marked "wheat-free" (or "gluten-free") (Note: Rye bread is not gluten-free.) Although often assumed to be an acceptable alternative to wheat, spelt flour is not suitable for people with fructose malabsorption[ citation needed ], just as it is not appropriate for those with wheat allergies or celiac disease. However, some fructose malabsorbers do not have difficulty with fructans from wheat products while they may have problems with foods that contain excess free fructose.[ citation needed ]
There are many breads on the market that boast having no high fructose corn syrup. In lieu of high fructose corn syrup, however, one may find the production of special breads with a high inulin content, where inulin is a replacement in the baking process for the following: high fructose corn syrup, flour and fat. Because of the caloric reduction, lower fat content, dramatic fiber increase and prebiotic tendencies of the replacement inulin, these breads are considered a healthier alternative to traditionally prepared leavening breads. Though the touted health benefits may exist, people with fructose malabsorption will likely find no difference between these new breads and traditionally prepared breads in alleviating their symptoms because inulin is a fructan, and, again, consumption of fructans should be reduced dramatically in those with fructose malabsorption in an effort to appease symptoms.[ citation needed ]
Fructose and fructans are FODMAPs (fermentable oligo-, di- and mono-saccharides and polyols) known to cause gastrointestinal discomfort in susceptible individuals. FODMAPs are not the cause of these disorders, [24] but FODMAPs restriction (a low-FODMAP diet) might help to improve short-term digestive symptoms in adults with irritable bowel syndrome (IBS) and other functional gastrointestinal disorders (FGID). [24] [25] [26] [27] Nevertheless, its long-term follow-up can have negative effects because it causes a detrimental impact on the gut microbiota and metabolome. [26] [27] [28] [29]
Fructose, or fruit sugar, is a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed by the gut directly into the blood of the portal vein during digestion. The liver then converts both fructose and galactose into glucose, so that dissolved glucose, known as blood sugar, is the only monosaccharide present in circulating blood.
Sorbitol, less commonly known as glucitol, is a sugar alcohol with a sweet taste which the human body metabolizes slowly. It can be obtained by reduction of glucose, which changes the converted aldehyde group (−CHO) to a primary alcohol group (−CH2OH). Most sorbitol is made from potato starch, but it is also found in nature, for example in apples, pears, peaches, and prunes. It is converted to fructose by sorbitol-6-phosphate 2-dehydrogenase. Sorbitol is an isomer of mannitol, another sugar alcohol; the two differ only in the orientation of the hydroxyl group on carbon 2. While similar, the two sugar alcohols have very different sources in nature, melting points, and uses.
Dietary fiber or roughage is the portion of plant-derived food that cannot be completely broken down by human digestive enzymes. Dietary fibers are diverse in chemical composition and can be grouped generally by their solubility, viscosity and fermentability which affect how fibers are processed in the body. Dietary fiber has two main subtypes: soluble fiber and insoluble fiber which are components of plant-based foods such as legumes, whole grains, cereals, vegetables, fruits, and nuts or seeds. A diet high in regular fiber consumption is generally associated with supporting health and lowering the risk of several diseases. Dietary fiber consists of non-starch polysaccharides and other plant components such as cellulose, resistant starch, resistant dextrins, inulin, lignins, chitins, pectins, beta-glucans, and oligosaccharides.
Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating and changes in the consistency of bowel movements. These symptoms may occur over a long time, sometimes for years. IBS can negatively affect quality of life and may result in missed school or work or reduced productivity at work. Disorders such as anxiety, major depression, and chronic fatigue syndrome are common among people with IBS.
Inulins are a group of naturally occurring polysaccharides produced by many types of plants, industrially most often extracted from chicory. The inulins belong to a class of dietary fibers known as fructans. Inulin is used by some plants as a means of storing energy and is typically found in roots or rhizomes. Most plants that synthesize and store inulin do not store other forms of carbohydrate such as starch. In the United States in 2018, the Food and Drug Administration approved inulin as a dietary fiber ingredient used to improve the nutritional value of manufactured food products. Using inulin to measure kidney function is the "gold standard" for comparison with other means of estimating glomerular filtration rate.
A gluten-free diet (GFD) is a nutritional plan that strictly excludes gluten, which is a mixture of prolamin proteins found in wheat, as well as barley, rye, and oats. The inclusion of oats in a gluten-free diet remains controversial, and may depend on the oat cultivar and the frequent cross-contamination with other gluten-containing cereals.
Hereditary fructose intolerance (HFI) is an inborn error of fructose metabolism caused by a deficiency of the enzyme aldolase B. Individuals affected with HFI are asymptomatic until they ingest fructose, sucrose, or sorbitol. If fructose is ingested, the enzymatic block at aldolase B causes an accumulation of fructose-1-phosphate which, over time, results in the death of liver cells. This accumulation has downstream effects on gluconeogenesis and regeneration of adenosine triphosphate (ATP). Symptoms of HFI include vomiting, convulsions, irritability, poor feeding as a baby, hypoglycemia, jaundice, hemorrhage, hepatomegaly, hyperuricemia and potentially kidney failure. While HFI is not clinically a devastating condition, there are reported deaths in infants and children as a result of the metabolic consequences of HFI. Death in HFI is always associated with problems in diagnosis.
Functional gastrointestinal disorders (FGID), also known as disorders of gut–brain interaction, include a number of separate idiopathic disorders which affect different parts of the gastrointestinal tract and involve visceral hypersensitivity and motility disturbances.
Small intestinal bacterial overgrowth (SIBO), also termed bacterial overgrowth, or small bowel bacterial overgrowth syndrome (SBBOS), is a disorder of excessive bacterial growth in the small intestine. Unlike the colon, which is rich with bacteria, the small bowel usually has fewer than 100,000 organisms per millilitre. Patients with bacterial overgrowth typically develop symptoms which may include nausea, bloating, vomiting, diarrhea, malnutrition, weight loss, and malabsorption by various mechanisms.
Prebiotics are compounds in food that foster growth or activity of beneficial microorganisms such as bacteria and fungi. The most common environment concerning their effects on human health is the gastrointestinal tract, where prebiotics can alter the composition of organisms in the gut microbiome.
Food intolerance is a detrimental reaction, often delayed, to a food, beverage, food additive, or compound found in foods that produces symptoms in one or more body organs and systems, but generally refers to reactions other than food allergy. Food hypersensitivity is used to refer broadly to both food intolerances and food allergies.
Abdominal bloating is a short-term disease that affects the gastrointestinal tract. Bloating is generally characterized by an excess buildup of gas, air or fluids in the stomach. A person may have feelings of tightness, pressure or fullness in the stomach; it may or may not be accompanied by a visibly distended abdomen. Bloating can affect anyone of any age range and is usually self-diagnosed, in most cases does not require serious medical attention or treatment. Although this term is usually used interchangeably with abdominal distension, these symptoms probably have different pathophysiological processes, which are not fully understood.
A hydrogen breath test is used as a diagnostic tool for small intestine bacterial overgrowth and carbohydrate malabsorption, such as lactose, fructose, and sorbitol malabsorption.
A fructan is a polymer of fructose molecules. Fructans with a short chain length are known as fructooligosaccharides. Fructans can be found in over 12% of the angiosperms including both monocots and dicots such as agave, artichokes, asparagus, leeks, garlic, onions, yacón, jícama, barley and wheat.
Agave syrup, also known as maguey syrup or agave nectar, is a sweetener commercially produced from several species of agave, including Agave tequilana and Agave salmiana. Blue-agave syrup contains 56% fructose as a sugar providing sweetening properties.
Sucrose intolerance or genetic sucrase-isomaltase deficiency (GSID) is the condition in which sucrase-isomaltase, an enzyme needed for proper metabolism of sucrose (sugar) and starch, is not produced or the enzyme produced is either partially functional or non-functional in the small intestine. All GSID patients lack fully functional sucrase, while the isomaltase activity can vary from minimal functionality to almost normal activity. The presence of residual isomaltase activity may explain why some GSID patients are better able to tolerate starch in their diet than others with GSID.
Gluten-related disorders is the term for the diseases triggered by gluten, including celiac disease (CD), non-celiac gluten sensitivity (NCGS), gluten ataxia, dermatitis herpetiformis (DH) and wheat allergy. The umbrella category has also been referred to as gluten intolerance, though a multi-disciplinary physician-led study, based in part on the 2011 International Coeliac Disease Symposium, concluded that the use of this term should be avoided due to a lack of specificity.
FODMAPs or fermentable oligosaccharides, disaccharides, monosaccharides, and polyols are short-chain carbohydrates that are poorly absorbed in the small intestine and ferment in the colon. They include short-chain oligosaccharide polymers of fructose (fructans) and galactooligosaccharides, disaccharides (lactose), monosaccharides (fructose), and sugar alcohols (polyols), such as sorbitol, mannitol, xylitol, and maltitol. Most FODMAPs are naturally present in food and the human diet, but the polyols may be added artificially in commercially prepared foods and beverages.
Non-celiac gluten sensitivity (NCGS) or gluten sensitivity is a controversial disorder which can cause both gastrointestinal and other problems.
A low-FODMAP diet is a person's global restriction of consumption of all fermentable carbohydrates (FODMAPs), recommended only for a short time. A low-FODMAP diet is recommended for managing patients with irritable bowel syndrome (IBS) and can reduce digestive symptoms of IBS including bloating and flatulence.
An emerging body of research now demonstrates the efficacy of fermentable carbohydrate restriction in IBS. [...] However, further work is urgently needed both to confirm clinical efficacy of fermentable carbohydrate restriction in a variety of clinical subgroups and to fully characterize the effect on the gut microbiota and the colonic environ¬ment. Whether the effect on luminal bifidobacteria is clinically relevant, preventable, or long lasting, needs to be investigated. The influence on nutrient intake, dietary diversity, which might also affect the gut microbiota,137 and quality of life also requires further exploration as does the possible economic effects due to reduced physician contact and need for medication. Although further work is required to confirm its place in IBS and functional bowel disorder clinical pathways, fermentable carbohydrate restriction is an important consideration for future national and international IBS guidelines.