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As I have been writing reviews about fructose for a number of years, I would like to set the record straight.

What is fructose?
Fructose is a sugar or a so-called monosaccharide, which, together with glucose, occurs naturally in fruit and honey. Fructose is sometimes referred to as 'fruit sugar'.

Besides occurring in fruit and honey, fructose is increasingly entering the food supply, particularly in countries such as the USA, in the form of high-fructose corn syrup. The latter is manufactured by enzymatically changing the glucose in cornstarch (derived from maize) into fructose.

High-fructose corn syrup is very sweet and also inexpensive, which is why it is being added to foods such as canned and frozen fruit and sweetened cold drinks. This trend is particularly evident in the USA. It is estimated that more than 9% of the energy in the US diet is obtained from high-fructose corn syrup.

If we consider that the use of fructose has increased in the USA from 64 g per day to 81 g per person per day in the period between 1970 and 1997, it is perfectly feasible that such a dramatic change in food intake could have an effect on many aspects of metabolism.

This trend has not yet occurred in South Africa, where most of our canned fruit and sweetened cold drinks are still sweetened with sucrose or table sugar.

Fructose and obesity
Most people are aware of the obesity epidemic that is swamping the world. New research is concentrating on fructose as a possible factor that contributes to this epidemic.

Ludwig and his co-workers (2001) first identified the staggering energy contribution that cold drinks make to the diets of American children. In the USA, drinking two 400 ml cold drinks a day can provide up to 50 g of fructose to the daily diet or 10% of the energy requirement of a woman of average weight.

Additional research will hopefully clarify the role that fructose may play in exacerbating obesity.

In South Africa – where our cold drinks are sweetened with sucrose – the scenario may be different, but it is a good idea to limit the number of sweetened cold drinks you consume on a daily basis. Some research also indicates that the intake of liquid energy in the form of sugars may contribute more to overweight than the intake of solid sugars.

Fructose and diabetes
A research team led by Elliott (2002) published a review on existing information about the metabolic effects of fructose. The researchers noted that small to moderate amounts of dietary fructose promote better blood glucose control. This is because fructose has a lower glycaemic index (GI) compared to many other carbohydrates (white bread has a GI of 100 and sucrose has a GI of 92, while fructose has a GI of 32).

Foods with a lower GI do not make blood glucose levels rise as high as those with a high GI, thus improving the so-called glycaemic control.

Small quantities of fructose also promote glycogen synthesis (glycogen is the form in which glucose is stored in the liver and muscles for use as an energy source for physical activity).

In 2002, the American Diabetes Association issued a warning to diabetics to avoid fructose that does not occur naturally in fruit. This warning was based on the findings that fructose from sucrose (sucrose is broken down in the human body to glucose and fructose) and high-fructose corn syrup (as used in sweetened drinks in the USA) increase blood fat levels.

Both the total blood cholesterol and the LDL or 'bad' cholesterol levels are increased when the diet contains high levels of fructose.

Another type of blood fat, called triglyceride, also rises sharply (particularly in people with insulin problems) if fructose is eaten. However, no scientific evidence has proved that using small quantities of sugar to make low-fat diets more palatable (prescribed to patients with increased blood fat levels) will have a harmful effect.

Moderation is key
Once again, it is evident that moderation is the key. Diabetics can use small quantities of about 25 g of fructose for purposes such as baking, because this sugar helps to improve the colour of baked products.

And if you believe that patients with diabetes may never eat a single slice of sucrose-free cake or have a teaspoon of sugar on their high-fibre breakfast cereal, then you are being unrealistic.

Diabetics may use sucrose and small quantities of fructose if these are part of the diet that has been worked out specifically for their circumstances by their dietician. No one is saying that diabetics should eat heaps of sugar or that they may take 3 t of fructose in every cup of coffee or tea they drink during the day.

In any case, fructose is known to cause gastric upsets such as diarrhoea and cramps, so most people would not be able to eat large quantities of fructose anyway.

I agree that people in the USA should limit their intake of cold drinks that are sweetened with high-fructose corn syrup and that people in South Africa should cut down on their sweetened cold drink intake too.

What about honey, fruit and fruit juices?
Honey, fruit and fruit juices also contain fructose, but it is generally believed that the benefits associated with eating fruit (dietary fibre, vitamins, bioflavonoids, minerals, antioxidants) are so important that fruit should continue to form a significant part of the diet.

It has also been determined that the intake of naturally occurring fructose from honey and fruit is relatively low (only about 15 g per day).

However, fruit juices should not be ingested in excess – especially not by children. This is due to their relatively high energy value, the problem that liquid sugars may be more inclined to cause obesity than solid sugars, and the fact that fruit juice may contribute to tooth decay (both the sugars and the acids in fruit juice can corrode tooth enamel). It is best to dilute fruit juice for children and to teach them to rinse their mouths or brush their teeth after drinking fruit juice.

So while I agree that people in general, and diabetics in particular, should limit their intake of fructose, sugars and sweetened cold drinks, I do believe that even diabetics and individuals on slimming diets may use small quantities of sugar and fructose to make their diets more palatable and acceptable. But always in moderation. – (Dr Ingrid van Heerden, DietDoc)

(Reference: Elliott SS et al, (2002). Fructose, weight gain, and the insulin resistance syndrome. American Journal of Clinical Nutrition, Vol 76, pp 911-922; Ludwig DS et al (2001). Relation between consumption of sugar-sweetened drinks and childhood obesity: a prospective, observational analysis. The Lancet, Vol 357, pp 505-508; Proudfoot, K (2004). Fructose: www.centre4activeliving.ca/ Research/ResearchUpdate/ 2004.June.htm )
 

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