To correctly understand "fructose", you must know these six points!

Many people with weak gastrointestinal function have experienced this: after eating too much fruit, they feel uncomfortable in the stomach, are very prone to diarrhea, and even suffer from acute intestinal inflammation. In addition to the fact that dietary fiber in fruits promotes excessive intestinal movement, it is likely related to excessive fructose intake leading to intestinal inflammation. The damaged intestinal barrier and decreased digestion and absorption function are entangled with intestinal flora disorders, causing the human body to become weak and have intolerance to a variety of foods.

A large amount of fructose also causes fat deposition in the liver, resulting in fatty liver, as well as metabolic disorders, reduced insulin sensitivity, and increased risk of diabetes. Excessive intake of fructose can also lead to an increase in endogenous purines (indicating enhanced body catabolism), increased uric acid, and an increased risk of gout. These are previously confirmed research results. In short, a large amount of fructose is harmful to health, and this is absolutely true.

So why do people say that fruits are good for health? Here are six pieces of knowledge to share with you.

Knowledge point 1: Does fructose refer to “sugar in fruits”?

The sugar in fruits is composed of three parts: glucose, fructose and sucrose, of which fructose is only one. Fructose is called fructose in English. It is not the vague concept of "sugar in fruits", but a monosaccharide with a certain structure, which is different from glucose, sucrose and maltose.

Knowledge point 2: Which fruits have a high proportion of fructose in their sugar content?

Some fruits have a higher proportion of sucrose, such as dates and peaches; some fruits have a higher proportion of glucose and fructose, such as watermelons and grapes. Generally speaking, the amount of glucose and fructose in fruits is basically the same.

Fructose gives people a refreshing sweet taste and has the property of becoming sweeter at low temperatures. Sucrose does not have this property and its sweetness is about the same at any temperature. Fruits that feel sweeter when chilled and fruits that taste particularly sweet are almost all fruits with a high fructose content.

Knowledge point 3: Eating white sugar and honey will also increase the fructose in the body

From the perspective of plant metabolism, photosynthesis first synthesizes glucose, and then glucose can isomerize into fructose. One molecule of glucose and one molecule of fructose combine to produce one molecule of sucrose, which is the white sugar we eat every day. After one molecule of sucrose is hydrolyzed by sucrase in the intestine, it will produce one molecule of glucose and one molecule of fructose.

The sugar we eat at home every day, including soft sugar, white sugar, brown sugar, rock sugar, brown sugar, etc., is mainly composed of sucrose. Therefore, after sugar-added sweets are digested and absorbed in the intestines, they bring both glucose and fructose.

Honey also contains three kinds of sugars: sucrose, fructose and glucose. Generally speaking, the easier it is for honey to crystallize, the greater the proportion of glucose in it; the less likely it is for honey to crystallize in winter, the greater the proportion of fructose in it. This is because fructose has the highest solubility, followed by sucrose, and glucose has the lowest solubility.

Knowledge point 4: Where does “industrially produced fructose” come from?

In the modern starch sugar industry, corn is first processed to extract starch; corn starch is then hydrolyzed to produce glucose, and glucose-fructose isomerase is used to convert part of the glucose into fructose to obtain high fructose corn syrup. The fructose content of industrially produced high fructose corn syrup can reach up to 90%.

Fructose corn syrup tastes sweet and is even more refreshing when iced, so it is the main source of sweetness in various sweet drinks such as cola and Sprite. Many dessert shops also use it to prepare drinks. Therefore, among people who like to drink sweet drinks, sweet drinks are the largest source of fructose.

A 500ml bottle of sweetened beverage contains about 50g of added sugar (sucrose or fructose syrup). If we calculate it as half fructose, it will contain about 25g of fructose. Therefore, drinking sweetened beverages will inevitably make the body get too much sugar, and a lot of fructose.

The fructose obtained from drinking beverages, the small amount of sugar obtained from drinking yogurt, the small amount of sugar added when cooking, plus the fructose obtained from eating fruit normally, the combined fructose intake is inevitably excessive.

Knowledge point 5: How much sugar is there in fruit?

Traditionally, it is said that certain fruits have less sugar, but this is not necessarily accurate. This is because the data in the food composition table are the results of measurements from a long time ago, and do not cover all new fruit varieties. They often do not represent the sugar content of fruits on the market. Some fruits are naturally high in sugar. For example, the sugar content of sweet grapes can reach 16%~20%, of which 40%~50% is fructose. According to this calculation, eating 500 grams of grapes with a sugar content of 18% can produce 90 grams of sugar, of which 36~45 grams are fructose.

There are also tropical fruits that Chinese people love to eat, which also have considerable sugar content. Take a look at the sugar content of local fruits measured by Thai scholars: mangosteen 17.5%, rambutan 18.5%, mango 13.9%, lychee 17.9%, jackfruit 19.2%, and sugar apple 17.2%.

However, fruits that originally had low sugar content are now gradually being replaced by high-sugar varieties, so the sugar intake from fruits is getting higher and higher. Rock sugar oranges, sugar oranges, rock sugar heart apples, etc., all use "high sugar content and sweet taste" as their selling point. Since fructose tastes sweet and delicious, fruit varieties with high fructose content will also be more popular, which means that more fructose is consumed from fruits.

For example, our research last year found that a certain type of Fuji apple contains 8.3% fructose and 6.7% glucose. With such a sugar content, apples cannot really be called low-sugar fruits. At this point, everyone must have understood: eating a small amount of fruit is beneficial, but eating a large amount of fruit is not the same as eating a large amount of fruit is beneficial. Eating a large amount of fruit or drinking fruit juice will also lead to excessive fructose!

Knowledge point 6: Eating too much fructose is harmful, but will eating less fructose be harmful?

A small amount of fructose intake may be beneficial to health, for example, it is beneficial to glucose metabolism in the liver. When combined with starchy foods, a small amount of fructose intake without increasing the total amount of carbohydrates can help lower the level of glycated hemoglobin. However, a large amount of intake is counterproductive.

Studies have suggested that too much or too little fruit is not good for preventing diabetes, and two to three hundred grams is the appropriate amount.

Several ways to reduce the harm of fructose

1. Avoid drinking any sweet drinks.

2. Add less sugar to daily family meals, and try not to add sugar to porridge or soup, including honey, which should also be strictly limited.

3. Choose foods such as yogurt that have lower sugar content.

4. The amount of fruit you should eat per day should be 200 to 350 grams (after peeling and removing the core). Do not eat more than 1 kilogram on a regular basis.

5. When eating fruits, don’t be overly obsessed with strong sweetness. For fruits with high sweetness, you should reduce the amount as appropriate.

6. Don’t drink a lot of juice, even if it’s 100% juice. The same applies to homemade juice.

7. Fruit can be used to replace sweets, or replace some cold dishes, and should be eaten in small amounts during meals. This can not only avoid overeating, but also enable a small amount of fructose to promote glucose metabolism.

8. Don’t buy household fructose products on the market just because fructose has a low blood sugar metabolism.

Text/Fan Zhihong

(Director of the Chinese Nutrition Society, Chief Expert in Science Communication appointed by the China Association for Science and Technology)