Copyright! Reproduction and dissemination – also partial – applicable to all media only with written permission of Umschau Zeitschriftenverlag GmbH, Wiesbaden. Science & Research | Original Contribution Peer-reviewed | Manuscript received: March 23, 2017 | Revision accepted: November 28, 2017 Fructose in different apple varieties Implications for apple consumption in persons affected by fructose intolerance Katharina Hermann, Ursula Bordewick-Dell Fructose malabsorption is often er- Abstract roneously referred to in the media as Fructose malabsorption (FM) and hereditary fructose intolerance (HFI) are path- fructose intolerance, which means ological diseases that should be clearly distinguished from one another, but for that it can be easily confused with both of which fructose is a relevant substrate. The treatment for both diseases the metabolic disease hereditary consists of fructose restriction, but with a completely different focus for each. In fructose intolerance [2]. The diffe- the case of HFI, consumption of fructose must be avoided completely, but in the rent forms of fructose intolerance case of FM, a desensitization strategy can be adopted. This strategy exploits the should be clearly distinguished mechanism of glucose-induced fructose transport. Thus, for FM (unlike for HFI) from one another [3]. • Table 1 pro- it is not necessary to abstain from consuming foods containing fructose comple- vides a comparison of HFI and FM tely. with regard to their pathomecha- Apples have a high fructose content, and also have an unfavorable fructose/glu- nisms, symptoms, diagnosis, and cose ratio of > 1, which means that at first glance, they appear unsuitable for treatment. In both of these diseases, patients with FM. treatment is based on nutritional therapy with fructose restriction Our investigations have shown that depending on the variety, the fructose con- playing a key role, but the focus of tent of apples can vary considerably. Although in every variety of apple, the fruc- the treat ment is completely different tose content is higher than the glucose content, it is still not necessary to abstain for each. from the consumption of apples completely in the case of FM. In addition to The main reason for the current selecting an apple variety with the lowest possible fructose content, other re- trend of increasing fructose intake commendations that can help to improve fructose absorption can also be taken is (in addition to general nutritional into account. The extent to which glucose promotes the absorption of fructose or recommendations promoting a high improves the symptoms of FM by doing so requires further investigation. fruit and vegetable intake), the wide Keywords: Food intolerances, fructose malabsorption, hereditary fructose intol- range of foods available [2]. How­ erance, fructose/glucose ratio, fructose content, apples, fruit ever, the increasing use of high fruc- tose corn syrup (HFCS) in the food industry has had a particular impact in terms of increased intake of fruc- tose from non­natural sources [1]. This sweet syrup made of maize Introduction consists of up to 90% fructose. It is a cheap alternative to sucrose that Fructose intake has increased signi- is used for sweetening [4]. HFCS ficantly in recent years [1] and this is often used to make soft drinks, Citation: trend is partly responsible for the in- bread products, confectionery, and Hermann K, Bordewick-Dell U creasing prevalence of fructose mal- ketchup [5]. Fructose naturally oc- (2018) Fructose in different apple absorption (FM) [2]. Fructose is also curs mainly in fruit, vegetables, and varieties. Implications for apple the substrate involved in diseases of honey [3]. consumption in persons affected fructose metabolism, such as here- Foods with added HFCS, as well as by fructose intolerance. Ernah- ditary fructose intolerance (HFI). fructose­rich fruits are key concerns rungs Umschau 65(3): 48–52 Therefore, fructose content in food for patients with diseases of fructose This article is available online: is an important issue for patients metabolism and impaired fructose DOI: 10.4455/eu.2018.010 who have diseases in which fructose absorption. While HFI treatment fo- is a key factor. cuses solely on strict abstinence from 48 Ernaehrungs Umschau international | 3/2018 Copyright! Reproduction and dissemination – also partial – applicable to all media only with written permission of Umschau Zeitschriftenverlag GmbH, Wiesbaden. fructose malabsorption (FM) hereditary fructose intolerance (HFI) general description impairment of intestinal disease of fructose metabolism [11] fructose absorption [10] genetic defect unknown [3] mutation of the ALDOB gene [12] heredity unknown [13] autosomal recessive [14] prevalence approx. 1:3 [13] 1:20 000 [14] pathophysiology altered activity of the relevant transporters in deficiency of the enzyme fructose-1-phosphate- the intestinal wall [15], incomplete absorption aldolase (aldolase B) of genetic origin [14] of fructose with subsequent fermentation in the toxic accumulation of fructose-1-phosphate, colon [3] especially in the cells of the liver, the intestines, and the proximal tubule [16], and disorder of fructose metabolism with blocking of glycolysis and glucogenesis [14] symptoms gastrointestinal symptoms [3, 10] symptoms of persistent hypoglycemia, liver and kidney damage, failure to thrive, reduced blood coagulation, edema, and ascites [14] diagnosis hydrogen breath test after oral intake of fructose [3] genetic analysis using DNA sequencing [14] treatment three-step model [17]: strict restriction of fructose, sucrose, - significantly reduced fructose intake on a tem- and FODMAPs [3] porary basis, especially free fructose (abstinence phase) [3], - followed by gradual reintroduction of fructose in order to increase fructose tolerance and to determine individual fructose tolerance (testing phase), - then, transition to long-term nutrition that is adapted to the patient’s needs and require- ments [17] prognosis can be treated successfully through changes to if the dietary recommendations are adhered to the diet; taking account of individual preferences in a consistent manner, there is no reduction in and avoiding nutrient deficiencies ensures preser- life expectancy; if hereditary fructose intoler- vation of quality of life [17] ance is present but not detected, this can lead to death [3] Tab. 1: Comparison of fructose malabsorption with hereditary fructose intolerance FODMAPs = fermentable oligo-, di-, monosaccharides and polyols [1] fructose as a treatment method, die- high fructose content and an imba- the individual variety is taken into tetic modification of FM aims to in- lance between fructose and glucose account, the free fructose content crease fructose tolerance. If glucose [7]. Therefore, at first glance, it ap- and free glucose content of the apple intake is increased at the same time pears that people with FM should varieties Elstar, Braeburn, and Jo- as fructose intake, fructose can also be advised against eating this fruit. nagored was determined and com- be transported to the enterocytes via However, usually, little distinction pared to the respective contents of the GLUT2 transporters, which are is made between the sugar content mandarins and bananas. expressed more strongly this case. of different varieties of apple, even This relieves some of the strain on though initial results show that GLUT5 transporters, which are the there are indeed differences between Method transporters that are primarily res- the varieties [8, 9]. Mandarins and ponsible for fructose absorption [3]. bananas are better tolerated alter- For each variety of apple, five Therefore, tolerance of sucrose, as natives to apples due to their more samples from various shopping well as foods that have at least a bal­ favorable fructose/glucose ratios outlets were investigated. The anced fructose/glucose ratio (≤ 1) is [3]. same procedure was followed for far better than tolerance of fructose mandarins and bananas. Each of the alone [3]. This glucose­induced fruc- measurements was done as a double Objectives tose transport is particularly useful determination. during the abstinence phase. In order to better evaluate whether The fruit was first peeled and ho- Apples are the most popular fruit in consumption of apples is feasible in mogenized. In order to perform the Germany [6]. However, they have a the case of fructose intolerance if measurements, in each case, 1 g Ernaehrungs Umschau international | 3/2018 49 Copyright! Reproduction and dissemination – also partial – applicable to all media only with written permission of Umschau Zeitschriftenverlag GmbH, Wiesbaden. Science & Research | Original Contribution strate fructose, but their pathome- chanisms are completely different. glucose fructose In the case of HFI, apples and other foods containing fructose must be ATP ATP strictly banned from the diet, where­ HK HK as in the case of FM, fructose intake ADP ADP only needs to be restricted and re- moved from the diet in a more mod­ PGI G-6-P F-6-P erate fashion. Since the literature only provides NAD insufficient data on fructose and G-6P-DH glucose content of various varieties of apple, these measurements were NADH carried out using the three most commonly consumed varieties of gluconate-6-phosphate apple in Germany in the years 2014 and 2015 [19]. Fig. 1: Diagram of reaction for the enzymatic determination The measurements show that the of glucose and fructose [18] different varieties of apple differ in ADP = adenosine diphosphate;