Definition
Fructose malabsorption, formerly named "dietary fructose intolerance," is a digestive disorder 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 in the entire intestine.
Fructose Malabsorption Prevention
There is no known cure, but an appropriate diet will help.
Foods that should be avoided by people with fructose malabsorption include:
- Foods and beverages containing greater than 0.5g fructose in excess of glucose per 100g, greater than 3g fructose in an average serving quantity regardless of glucose intake and greater than 0.2g of fructans per serving.
- Fructose consumed in large quantities
- Foods with high fructose-to-glucose ratio (NB: Glucose enhances absorption of fructose, so fructose from foods with fructose-to-glucose ratio <1, like bananas, are readily absorbed, while foods with fructose-to-glucose ratio >1, like apples and pears, are often problematic regardless of total amount of fructose in the food
- Foods rich in fructans and other Fermentable Oligo-, Di- and Mono-saccharides and Polyols (FODMAPs)
- Foods rich in sorbitol
- Foods such as high fructose corn syrup (HFCS) or honey
Foods with a high glucose content ingested with foods containing excess fructose may help sufferers absorb the excess fructose.
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. 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.
Natural sources of fructose include fruits, vegetables (including sugar cane), and honey. Fructose is often further concentrated from these sources. Melons, berries, and honey are specially high in fructose. Fructose exists in foods either as a free monosaccharide, or bound to glucose as sucrose, a disaccharide. Fructose, glucose, and sucrose may all be present in a food; however, different foods will have varying levels of each of these three sugars.
Ratio of Glucose to Fructose
The sugar contents of common fruits and vegetables are presented in Table 1. In general, in foods that contain free fructose, the ratio of fructose to glucose is approximately 1:1; that is, foods with fructose usually contain about an equal amount of free glucose. A value that is above 1 indicates a higher proportion of fructose to glucose, and below 1, a lower proportion. Some fruits have larger proportions of fructose to glucose compared to others. For example, apples and pears contain more than twice as much free fructose as glucose, while for apricots the proportion is less than half as much fructose as glucose.
Apple and pear juices are of particular interest to pediatricians because the high concentrations of free fructose in these juices can cause diarrhea in children. The cells (enterocytes) that line children's small intestines have less affinity for fructose absorption than for glucose and sucrose. Unabsorbed fructose creates higher osmolarity in the small intestine, which draws water into the gastrointestinal tract, resulting in osmotic diarrhea. This phenomenon is discussed in greater detail in the Health Effects section.
Table 1 also shows the amount of sucrose found in common fruits and vegetables. Sugar cane and sugar beet have a high concentration of sucrose, and are used for commercial preparation of pure sucrose. Extracted cane or beet juice is clarified, removing impurities; and concentrated by removing excess water. The end product is 99.9% pure sucrose. Sucrose-containing sugars include common table white granulated sugar and powdered sugar, as well as brown sugar.
Table 1. Sugar content of selected common plant foods (g/100g)
| Food Item |
Total
Carbohydrate
|
Total
Sugars |
Free
Fructose |
Free
Glucose |
Sucrose |
Fructose/
Glucose
Ratio |
Sucrose
as a % of
Total Sugars |
| Fruits |
|
|
|
|
|
|
|
| Apple |
13.8 |
10.4 |
5.9 |
2.4 |
2.1 |
2.0 |
19.9 |
| Apricot |
11.1 |
9.2 |
0.9 |
2.4 |
5.9 |
0.7 |
63.5 |
| Banana |
22.8 |
12.2 |
4.9 |
5.0 |
2.4 |
1.0 |
20.0 |
| Grapes |
18.1 |
15.5 |
8.1 |
7.2 |
0.2 |
1.1 |
1.0 |
| Peach |
9.5 |
8.4 |
1.5 |
2.0 |
4.8 |
0.9 |
56.7 |
| Pineapple |
13.1 |
9.9 |
2.1 |
1.7 |
6.0 |
1.1 |
60.8 |
| Pear |
15.5 |
9.8 |
6.2 |
2.8 |
0.8 |
2.1 |
8.0 |
| Vegetables |
|
|
|
|
|
|
|
| Beet, Red |
9.6 |
6.8 |
0.1 |
0.1 |
6.5 |
1.0 |
96.2 |
| Carrot |
9.6 |
4.7 |
0.6 |
0.6 |
3.6 |
1.0 |
70.0 |
| Corn, Sweet |
19.0 |
3.2 |
0.5 |
0.5 |
2.1 |
1.0 |
64.0 |
| Red Pepper, Sweet |
6.0 |
4.2 |
2.3 |
1.9 |
0.0 |
1.2 |
0.0 |
| Onion, Sweet |
7.6 |
5.0 |
2.0 |
2.3 |
0.7 |
0.9 |
14.3 |
| Sweet Potato |
20.1 |
4.2 |
0.7 |
1.0 |
2.5 |
0.9 |
60.3 |
| Yam |
27.9 |
0.5 |
tr |
tr |
tr |
na |
tr |
| Sugar Cane |
|
13 - 18 |
0.2 – 1.0 |
0.2 – 1.0 |
11 - 16 |
1.0 |
100 |
| Sugar Beet |
|
17 - 18 |
0.1 – 0.5 |
0.1 – 0.5 |
16 - 17 |
1.0 |
100 |
Source: USDA
Cane and beet sugars have been used as the major sweetener in food manufacturing for centuries. However, with the development of HFCS, a significant shift occurred in the type of sweetener consumption. As seen in Figure 3, this change happened in the 1970s. Contrary to the popular belief, however, with the increase of HFCS consumption, the total fructose intake has not dramatically changed. Granulated sugar is 99.9% pure sucrose, which means that it has equal ratio of fructose to glucose. The most commonly used HFCS, 42 and 55, have about equal ratio of fructose to glucose, with minor differences. HFCS has simply replaced sucrose as a sweetener. Therefore, despite the changes in the sweetener consumption, the ratio of glucose to fructose intake has remained relatively constant.
The absorption capacity for fructose in monosaccharide form ranges from less than 5 g to 50 g and adapts with changes in dietary fructose intake. Studies show the greatest absorption rate occurs when glucose and fructose are administered in equal quantities. When fructose is ingested as part of the disaccharide sucrose, absorption capacity is much higher because fructose exists in a 1:1 ratio with glucose. It appears that the GLUT5 transfer rate may be saturated at low levels, and absorption is increased through joint absorption with glucose. One proposed mechanism for this phenomenon is a glucose-dependent cotransport of fructose. In addition, fructose transfer activity increases with dietary fructose intake. The presence of fructose in the lumen causes increased mRNA transcription of GLUT5, leading to increased transport proteins. High-fructose diets have been shown to increase abundance of transport proteins within 3 days of intake.
For more information:
https://en.wikipedia.org/wiki/Fructose_malabsorption
https://en.wikipedia.org/wiki/Fructose
Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)
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