In 1978, it was first experimentally confirmed by a Swedish medical scientist. Fructose is a kind of monosaccharide, food in the monosaccharide does not need to be digested, can be absorbed by the small intestine directly into the blood. If you eat too much fructose, not absorbed fructose remains in the intestinal tract, making the osmotic pressure of the intestinal fluid to be higher than that of the plasma, plasma water loss to the intestinal tract, the intestinal tract more water than usual. When fructose reaches the colon, it becomes food for the bacteria living there, and the fermentation produces short-chain fatty acids and a lot of gas, which stimulates intestinal peristalsis, so that the water in the intestines, which is already abundant, is not fully absorbed, leading to diarrhea. The result of the experiment is that a normal person can absorb 25 to 50 grams of fructose at one time. This amount is actually quite a lot, to consume 25 grams of fructose need to eat about 430 grams of apple.　

Dietary fructose intolerant patients are not what fruits can not eat, some fruits eat will have diarrhea, some will not, this is how it is? Originally, in the small intestine there is a carrier called GLUT2, which can transport both glucose and fructose. Its efficiency in transporting fructose is originally very low, but glucose can greatly improve its transport efficiency. So glucose can help the absorption of fructose. The ability of a fruit to cause fructose intolerance depends not only on the amount of fructose, but also on the ratio of fructose to glucose.

Fruits that contain more glucose than fructose, such as bananas, oranges, grapefruit, pineapples, kiwis, and strawberries, are less likely to be fructose intolerant, while fruits that contain more fructose than glucose, such as apples, pears, watermelon, cantaloupe, dates, poppies, mangoes, cherries, lychees, papayas, and grapes, are more likely to be fructose intolerant. In addition, honey and "artificial honey" (fructose syrup) added to processed foods can also lead to fructose intolerance due to the higher fructose content than glucose. Some people feel that drinking honey is a "laxative", which, in addition to psychological factors, may be related to fructose intolerance.　Contrary to glucose, sugar alcohols can reduce the activity of fructose carriers, not conducive to the absorption of fructose. So those fruits containing sugar alcohols, such as peaches, plums, apricots, although the glucose content is higher than fructose, may also cause fructose intolerance. Fructose intolerance has no cure, the best way to prevent fructose intolerance is to avoid foods with high fructose content and sugar alcohols. Eating foods high in fructose along with foods high in glucose can sometimes prevent fructose intolerance, but it doesn't work for everyone.

Bananas are much higher in glucose than fructose and do not contain sugar alcohols, which do not cause fructose intolerance. In fact, in foreign countries, bananas are not only not considered to be able to laxative, on the contrary, is considered to be able to stop diarrhea, is one of the first choice of food for diarrhea patients. Bananas contain anti-amylase starch, can protect the intestinal mucosa, double-blind controlled trials show that eating bananas can reduce diarrhea in children. The misconception that bananas are a "laxative" may be due to the shape and consistency of the banana, and is not empirical.