Fructose

Fructose is the sweetest of the natural sugars, found in fruit, honey and some vegetables. In whole fruit it comes with fibre and is not a concern. In large amounts from sweetened drinks and syrups, it is linked to fatty liver and high triglycerides.

What is it?

Fructose is a monosaccharide, also called fruit sugar. It is sweeter than sucrose and glucose. Table sugar (sucrose) is half fructose and half glucose, and some sweeteners (such as high-fructose corn syrup, agave syrup and honey) contain a lot of free fructose.

Unlike glucose, fructose does not trigger much insulin release and is handled mainly by the liver, which turns some into glucose, some into glycogen and, when there is too much, some into fat.

What it does

1. Provides energy at about 4 kilocalories per gram
2. Adds sweetness with a low glycaemic index (about 15 to 25)
3. Is converted mostly in the liver

Food sources

Fruit (apples, pears, mangoes, watermelon, grapes, dates, dried fruit), honey, agave and fruit syrups, fruit juice, some vegetables (onion, asparagus), and sweetened foods and drinks made with sugar or fructose syrups. Table sugar provides fructose too, because it is half fructose.

Singapore food examples

1. Mango, papaya, watermelon, apple, pear, longan and lychee
2. Dates and dried fruit
3. Honey and sweetened fruit juices
4. Sweet drinks — bubble tea, canned drinks and sugarcane juice
5. Eat whole fruit rather than juice, and limit dried fruit portions

How much do I need?

There is no recommended intake for this sugar on its own, and Singapore's RDA table does not list it. Singapore's dietary guidelines advise that added sugar provide no more than 10 percent of daily energy — about 10 teaspoons (around 50 g) on a 2,000-kilocalorie diet, with about 5 teaspoons (25 g) even better — see Singapore's dietary guidelines for adults (HealthHub). Whole fruit is encouraged — Singapore's guidelines recommend at least two servings of fruit a day.

Low intake and deficiency

There is no deficiency; the body does not need fructose.

Too much and safety

Large intakes of free fructose, mainly from sweetened drinks and syrups, can raise liver fat and blood triglycerides, and are linked to fatty liver disease, weight gain and insulin resistance. Whole fruit contains fibre and water that slow absorption, and fruit intake is linked with better health.

Some people malabsorb fructose, especially in larger amounts or when a food has more fructose than glucose (apples, pears, mango, honey, juice). It reaches the colon and causes gas, bloating, cramps and loose stools; people with irritable bowel syndrome are often sensitive. Reduce portion size or swap for lower-fructose fruit such as banana, orange, pineapple and berries, and ask a dietitian.

Absorption and bioavailability

Fructose is absorbed more slowly and less completely than glucose, through the GLUT5 transporter. Eating glucose with fructose (as in table sugar and most fruit) improves its absorption; fructose in excess of glucose is absorbed less well, which is why some foods trigger symptoms.

Connection to daily life

1. Liver health: cutting sweet drinks lowers fructose load and helps reduce liver fat
2. Digestive comfort: if fruit or honey bothers your gut, try smaller portions
3. Healthy eating: whole fruit, with fibre, is a healthy choice for most people
4. Related: see Sugars and Fibre

Sources: 1. HealthHub Singapore — Dietary guidelines for adults: https://www.healthhub.sg/well-being-and-lifestyle/food-diet-and-nutrition/dietary_guidelines_adults 2. HealthHub Singapore — Recommended Dietary Allowances: https://www.healthhub.sg/well-being-and-lifestyle/food-diet-and-nutrition/recommended_dietary_allowances 3. Health Promotion Board — Singapore Food Insights Database (SG FoodID): https://www.hpb.gov.sg/healthy-living/food-and-beverage/sgfoodid/ 4. FAO/INFOODS — Food composition tables and databases: https://www.fao.org/food-composition/tables-and-databases/en/ 5. National Academies of Sciences, Engineering, and Medicine — Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005)