Fructose – 10 things you need to know
1. Fructose is a monosaccharide or single sugar unit. It’s abundant in nature. It’s the main sugar in fruit, berries, honey and there are even small amounts in vegetables and grains. It has provided energy for humans, birds, and mammals for millions of years and usually comes with a bonus – nutritional goodies like vitamins, minerals, fibre and antioxidants.
2. It’s abundant in the supermarket, too. When you throw normal soft drinks and sweetened foods such as yoghurt, dairy and frozen desserts, breads, cookies (biscuits), cake mixes, salad dressings and mayonnaise, sauces (tomato for example) and some soups (tomato again) into your trolley, chances are you will be adding fructose to your diet in the form of sucrose (50% fructose and 50% glucose from sugar cane) or high-fructose corn syrup (regular corn syrup does not contain fructose).
3. Fructose has a low GI (19) because it is absorbed and taken directly to the liver where it is immediately metabolised and only a small proportion is converted to glucose. Remember, the GI is a measure of the effect of the available carbohydrate on your blood glucose levels.
4. Adding fructose to foods and drinks has been a controversial topic in nutrition for many years. There are concerns it is doing something else in our bodies besides adding kilojoules (calories). A 2008 study in the American Journal of Clinical Nutrition reported that consuming more than 50g of pure fructose in a single hit raised post-meal triglycerides (blood fats) – a known risk factor for cardiovascular disease.
5. It’s worth keeping in mind that studies where people (or rats) are given high doses of fructose don’t actually reflect what happens out here in the real world. People rarely consume pure crystalline fructose just for fun, let alone 10 teaspoons (50g) of it in single sitting.
6. Corn syrups are often found on the labels of American foods and beverages. They are the most common form of sweetener in North America because they are cheaper than cane sugar. Some of them contain fructose. The two main types are:
- HFCS 55 – mostly used in beverages like soft drinks. It contains on average 55% fructose and 45% glucose.
- HFCS 42 – used in many solid foods and baked goods. It contains on average 42% fructose and 58% glucose.
Small quantities of HFCS-90 (90% fructose) and crystalline fructose (+99.5%) are also produced for ‘specialty applications’.
7. Fructose malabsorption can occur when fructose is eaten in the absence of glucose but we rarely eat it this way. The small intestine is impaired in its ability to absorb fructose alone, although we don’t yet fully understand the actual mechanism. When fructose is not absorbed properly in the small intestine, it can travel through to the large intestine where bacterial fermentation can cause symptoms such as bloating, wind, pain, nausea, diarrhoea and/or constipation. Dietitian Dr Sue Shepherd has a handy fact sheet on fructose malabsorption HERE.
8. Fructose and obesity. Consumption of HFCS has increased significantly in the US since the 1970s and this increase has run parallel to the increase in obesity in the US. However, while fructose may be one factor associated with the US obesity epidemic (think of all those extra calories for starters), it is unlikely that it is a major factor in the obesity epidemics elsewhere. For example Australians and Brits are getting fatter too while total and added fructose intakes have actually decreased in both those countries.
9. One theory why fructose may be less satiating than other carbohydrates, potentially increasing the risk of weight gain is that it stimulates insulin secretion much less than other sugars like glucose. Because insulin increases leptin release, consuming fructose may inhibit appetite less than consumption of other carbohydrates and therefore may lead to increased energy (kilojoule/calorie) intake. Another possible theory why it may be less satiating is that unlike glucose, fructose bypasses the rate-limiting step of glycolysis and uses a rapid energy-requiring reaction that abruptly depletes our cells energy stores – potentially stimulating appetite.
10. However, despite numerous plausible theories, in our opinion, there is no convincing experimental evidence in humans that dietary fructose actually does increase food consumption in the long-term. We need more studies with realistic amounts of fructose to determine if it truly is a unique and dangerous form of energy. In nutrition, just about everything (including all the fat soluble vitamins and many minerals) are toxic when consumed to excess. That shouldn’t be the basis of excluding them from the diet.
For more information about the GI Symbol Program
Dr Alan W Barclay, PhD
Chief Scientific Officer
Glycemic Index Foundation (Ltd)
Phone: +61 (0)2 9785 1037
Mob: +61 (0)416 111 046
Fax: +61 (0)2 9785 1037