SUGAR

Introduction Sugars are soluble carbohydrates of fundamental importance in providing energy for the maintenance of life. Glucose, the most abundant sugar in nature, is a single sugar unit or monosaccharide, as are fructose and galactose. Sucrose, lactose, and maltose are disaccharides. Sucrose, the sugar most widely used as a food in the United Kingdom (1), is composed of glucose and fructose. Disaccharides are broken down in the intestine and absorbed as monosaccharides. The role of dietary sugars in human disease has recently been reviewed by COMA (1). In their Report, sugars were classified on the basis of their availability for metabolism into intrinsic and extrinsic sugars (see 5). Intrinsic sugars are those naturally incorporated into the cellular structure of foods. Extrinsic sugars are those not so incorporated, whether natural and unprocessed, such as honey, or refined, such as table sugar. Extrinsic sugars in milk and milk products were deemed to be a special case, resulting in a sub-group of non-milk extrinsic sugars. The Panel endorsed the conclusions in that Report concluded that non-milk extrinsic sugars were a major cause of dental caries in the UK, and that their consumption by the population should be decreased.


Metabolism of glucose Glucose is distributed to the tissues as a fuel for many chemical processes. If there is insufficient dietary carbohydrate to meet this requirement, the liver releases glucose from stored glycogen or converts certain amino acids, lactate and glycerol into glucose. The brain and nervous system and red blood cells have an obligatory requirement for glucose as an energy source. If the diet is very low in carbohydrate, ketoacids formed in the liver from fatty acids may accumulate. Some dietary carbohydrate is therefore necessary to avoid ketoacidosis, but there is no specific dietary requirement for sugars.


Current sugars consumption Data on supplies of sugars in the UK come from the national food supply statistics of the Ministry of Agriculture, Fisheries and Food (MAFF). In 1987 sucrose, at 104 g/person/d, provided 14 per cent food energy, honey and glucose at 16 g/person/d provided 2 per cent, and lactose, at 23 g/person/d, a further 3 per cent (2) provides data on domestic food purchases. Sucrose purchased as packet sugar was on average 26 g/person/d in 1989. Total sugars, at 95 g/person/d, contributed 18 per cent of food energy3. Surveys of individual food intakes give data on the variation of sugars intakes in individuals. Breast- or bottle-fed infants obtain 40 per cent of their energy from sugars (usually lactose). Pre- school children take 25-30 per cent of food energy as sugars. Older children and adults tend to take less sugars (17-25 per cent) (1). In the recent representative dietary and nutritional survey of British adults, total sugars provided 18 percent of energy. Non-milk extrinsic sugars usually provide at least half of the intake of total sugars (45-73 per cent).


Effects of sugars In addition to chemical differences between sugars, physiological effects depend on the physical presentation of the sugars- whether free in solution, or an integral part of the cellular structure of a food (eg apple juice versus apples). When sugars are consumed as part of the cellular structure of foods, there has been no suggestion of any adverse effects. However, there have been suggestions that "refined", "fibre depleted" or "added" sugars may have adverse effects either indirectly, by reducing the "fibre" in the diet, or by their ability to be taken in quantities greater than in their "natural" form. These issues have recently been discussed by the COMA Panel on Dietary Sugars', whose report the Panel endorsed.


Conclusions The Panel agreed with the following conclusions of the COMA Panel on Dietary Sugars (1).

i. There is no evidence that sugars naturally incorporated in the cellular structure of foods (intrinsic sugars) or lactose in milk or milk products (milk sugars) have adverse effects on health.

ii. Apart from lactose in milk and milk products, extrinsic sugars in the UK, (principally sucrose), contribute to the development of dental caries. In societies where average total sugar supplies are less than 20 kg/person/year (approximately 60 g/person/d or 10 per cent of dietary energy) dental caries is rare. Those particularly at risk of dental caries are children, adolescents and the elderly. There is evidence from laboratory studies for thepotential cariogenicity of fermentable carbohydrates other than sugars, but the epidemiological evidence implicates non-milk extrinsic sugars as the major dietary component contributing to dental caries. Factors other than dietary carbohydrate, in particular fluoridation, are also important in determining the incidence of dental caries (see Fluoride - not yet available).

iii. Non-milk extrinsic sugars may favour the consumption of food energy, and in predisposed individuals may have undesirable metabolic effects, but are not directly related to the development of cardiovascular disease, essential hyper- tension, diabetes mellitus or behavioural abnormalities.

iv. For the obese, consumption of non-milk extrinsic sugars should be restricted as part of a general reduction of dietary energy. For non-obese adults, consumption of non-milk extrinsic sugars up to about 30 per cent of food energy does not carry special metabolic risks.

v. Extreme intakes of sucrose, above about 200 g/day or about 30 per cent of food energy, may be associated in normal adults with elevations of cholesterol, blood glucose and insulin concentrations, all of which may be undesirable.


Dietary Reference Values

The Panel did not recommend that intake of intrinsic or milk sugars be limited. They can usefully contribute, with starch, to energy requirements not met by other restricted dietary components (see Starch DRVs).

Infants who are breastfed receive about 40 per cent of energy from sugars (lactose) and the Panel recommended that infant formulas should contain similar amounts. As well as sugars, international guidelines allow the inclusion of maltodextrins and pre-cooked or gelatinised starch.

The Panel agreed that non-milk extrinsic sugars intake should be limited because of their role in dental caries. However, the Panel recognized that the data in support of any specific quantified targets for non-milk extrinsic sugars intake were scanty. In order to provide guidance for uses as specified in paragraph Energy 4 (not yet available), the Panel agreed that sufficient evidence existed to make proposals for DRVs. The Panel accepted that the dental effects of non-milk extrinsic sugars were most likely to be related to the frequency, and so in practice absolute mass, of sugars consumption rather than the overall dietary composition, but considered that the value of DRVs would be greater if expressed not only as mass, but also as their contribution to dietary energy. This also allows DRVs for starches plus intrinsic sugars to be calculated. The Panel therefore proposed that the population's average intake of non-milk extrinsic sugars should not exceed about 60 g/d or 10 per cent of total dietary energy.


Guidance on high intakes When non-milk extrinsic sugars are con- sumed in excess of about 200 g/day or 30 per cent of dietary energy, undesirable elevations in plasma concentrations of glucose, insulin and lipids may occur'. Such intakes should be avoided, and those who have intakes of this order should replace the excess with starch or intrinsic sugars. For some people with low energy requirements and intakes, relatively high non-milk extrinsic sugars intake may compete with foods which provide other nutrients, and potentially compromise micronutrient intakes. Such individuals, particularly women or the elderly, should exercise special care in making dietary choices.


References

1 Department of Health. Dietary Sugars and Human Disease. London: HMSO, 1989. (Reports on health and social subjects; 37).

2 Central Statistical Office. Annual Abstracts of Statistics. London: HMSO, 1989.

3 Ministry of Agriculture, Fisheries and Food. Household Food Consumption and Expenditure: 1989. London: HMSO, 1990.

4 Gregory J, Foster K, Tyler H, Wiseman M. The Dietary and Nutritional Survey of British Adults. London, HMSO, 1990.