In view of the increasing prevalence of overweight and obesity in Europe, the role of certain carbohydrates, like sugar, is often controversially discussed. Here are some facts about the role of carbohydrates, sugars and sugar in our diet.
Carbohydrates, sugars and sugar
The two main types of carbohydrates are sugars and starch. Sugars and starch provide the same energy per gram (4kcal). Carbohydrates provide less energy than fat (9kcal per gram) or alcohol (7kcal per gram). Fibre is a type of carbohydrate. Unlike other carbohydrates, it is not absorbed in the small intestine to provide energy, although some metabolism occurs in the large bowel. At least half the energy in our diets should come from carbohydrates, mostly as starchy carbohydrates.
Starch is found in cereals (rice, maize, wheat, etc) and their derived products (bread, pasta, etc), potatoes and legumes. Sugars include sucrose (or table sugar, that we will call ‘sugar’), glucose, fructose, lactose and maltose and are naturally found in foods such as fruits, vegetables and milk products. Manufacturers also add many of these sugars to foods during processing to perform important functions. Sugars provide sweet taste, texture, structure and consistency to foods. The texture has an important influence on palatability and thus on the acceptance of foods. Other functions of sugars include preserving jams and jellies, aiding in the fermentation of yeast and playing a role in the browning and flavouring of baked goods.
Sucrose (table sugar, a disaccharide consisting of the building blocks glucose and fructose) is a sweet tasting carbohydrate. It is produced by plants from carbon dioxide (CO2) and water with the help of light energy via the photosynthesis process. Large quantities are formed in sugar beet and sugar cane. Sucrose extracted from sugar cane or sugar beet is a natural product, which does not differ in its properties from the sugar present in fruits and vegetables.
Energy for brain and muscles
Carbohydrates are important for the functioning of our body. The brain is almost exclusively dependent on a constant supply of glucose from the blood stream. An adult brain uses about 140 g of glucose per day, and this can represent up to half of the total dietary carbohydrate consumed.
There are a few studies in adults, which have shown that the consumption of a carbohydrate meal or a sugar-sweetened drink is associated with improved mental efficiency, including improved memory, reaction times, attention span and arithmetic ability. Eating carbohydrate rich meals or having a snack or a sugar-sweetened beverage has been found to induce beneficial cognitive effects, and to contribute to reducing feelings of fatigue.1,2 Adults under the conditions of a driving performance test in an automobile simulator over a long-term distance of 120 km had significantly lower error rates while consuming sugar-sweetened beverages before and during the test compared to persons who had only consumed water.3 As studies differ in relation to the type of sugar, amount and total food composition, results are not totally consistent.
As the body’s glycogen stores (short-term energy storage made from glucose) in liver and muscle are limited, the glycogen depletion of muscle is the main cause of fatigue during anaerobic, intensive and long-duration physical activity (60-90 minutes). Sports drinks, containing sugars and electrolytes, as well as water, can prevent dehydration, delay fatigue and protect body’s glycogen stores from depletion, as the sugars ingested and released into the blood stream are preferentially used up by the muscles. In the case of high intensity activity, the glycogen can be mobilised at a later stage if physical demands continue.
With respect to replenishment of depleted glycogen stores, which is particularly important for elite athletes, carbohydrates that are quickly digested and absorbed by our body are stored much faster as glycogen than carbohydrates that have a low glycaemic index (GI). The GI effectively reflects the extent to which foods raise blood sugar levels after eating.
Sugar and body weight
A substantial number of epidemiological studies (looking at factors affecting the health of populations) in adults, adolescents and children repeatedly found a clear inverse relationship between sucrose intake and body weight or BMI as well as sucrose intake and total fat intake.4,5 In other words, individuals who consume a higher percentage of their energy needs (calories) as sugar are generally less overweight than individuals consuming a lower percentage of calories as sugar. Often there is an inverse relationship between the level of sugar intake and the level of fat intake (high sugar consumers tend to eat less fat). However, some individuals may exceed their energy needs by over consuming calories from both fat and sugar, which may result over time in weight gain. In addition, carbohydrates, including sugars, are recognised by the body’s appetite regulatory system and help promote satiety.6
The Health Behaviour in School-Aged Children Study (HBSC-Study) of WHO Europe, conducted during the years 2001-2002 with about 140 000 adolescents in the age range 10-16 years from 34 (mostly European) countries, compared overweight and obesity prevalence and their relationships with physical activity and dietary patterns.5 A significant negative correlation between the consumption of sweets and chocolate, and the BMI of adolescents from 31 out of 34 countries was reported. A higher intake of sweets was associated with a lower odds ratio for overweight and there was also no association between the consumption of soft drinks and overweight.5 These findings could be partially due to confounding factors; overweight and obese children may have already reduced their intake of sweets and chocolate because of weight concerns; they tend to underreport their consumption and may actually consume more of those foods. In a more recent UK study, based on data from 3-day dietary records for over 1000 children aged 5 and 7 years, sugar-sweetened beverages accounted for 3% of total energy intake, and no association was noted between their consumption and adiposity at the age of 9.7 Other studies, mainly from the US, have shown that a higher intake of sweetened soft drinks and fruit juice is linked to higher BMI or weight gain.8 The equivocal evidence on this topic makes it difficult to draw firm conclusions about a direct link between the consumption of sugar-sweetened soft drinks and an increase in body weight.
Weight gain occurs when energy intake from food and beverages is greater than the energy burnt through metabolism or activity. It is thus difficult to establish links between obesity and the consumption of a single food, nutrient or ingredient. Eating too many calories, no matter what the source is, can lead to overweight if they are not expended through activity. This is true for all types of foods and drinks: if they contribute to an excessive energy intake relative to energy needs, then they contribute to weight gain.
Vitamin and mineral supply
There is a popular belief that adding sugar would displace other foods from the diet and would lead to reduced intakes of vitamin and minerals. However, research has shown that added sugar intake can be compatible with a healthy diet, and there is no evidence to support a displacement of micronutrients caused by sugar.9 The nutritional quality of the diet of children even with the highest sugar intake was adequate with respect to vitamin and mineral intakes.
Dental health
People frequently point to sucrose as the only cause of cavities (dental caries). However, all food carbohydrates are capable of being involved in tooth decay. Research has shown that not only sugar, sweets or honey but also fruits, as well as non sweet-tasting carbohydrate-rich foods, like wholegrain bread, potatoes, and crisps, are potentially caries-promoting. Cavities occur when bacteria in dental plaque ferment starches and sugars to produce acids that destroy the teeth. Good oral hygiene and the use of fluoride containing tooth paste are now considered the main factors responsible for preventing dental caries and promoting good oral health. Caries prevalence has declined substantially in children and adolescents since the 1970’s despite unchanged sugar consumption and increasing between-meal snacking. Nowadays, the majority of 12 year olds have caries-free dentition.10 Caries can be prevented if the teeth are cleaned twice a day with fluoride toothpaste, and if drinking or eating occasions are limited to 6 times per day avoiding continuous sipping and nibbling.11
Diabetes
Type 2 diabetes has a strong genetic base and the onset of symptoms is linked to age, obesity and lack of physical activity. There are no causal links between sugar intake
and diabetes. Nowadays, moderate amounts of sugars, as a part of a balanced diet, are approved in the diets of well-controlled diabetics.12
References
1. Westenhoefer J. (2006) Carbohydrates and cognitive performance. Aktuelle Ernaehrungsmedizin 31 Supplement 1: S 96-S 102
2. Sunram-Lea SI, Foster JK, Durlach P, Perez C (2001): Glucose facilitation of cognitive performance in healthy young adults: examination of the influence of fast-duration, time of day and pre-consumption plasma glucose levels. Psychopharmacology 157: 46-54
3. Keul J and Jakob E (1990) Zur Wirkung von Saccharose auf Fahrverhalten, Kreislauf und Stoffwechsel. Oesterreichisches Journal fuer Sportmedizin 20: 102-110
4. Bolton-Smith C and Woodward M (1994): Dietary composition and fat to sugar ratios in relation to obesity. International Journal of Obesity 18: 820-828
5. Janssen I et al. (2005) Comparison of overweight and obesity prevalence in school-aged youth from 34 countries and their relationships with physical activity and dietary patterns. Obesity Reviews 6: 123-132
6. Anderson GH and Woodend D. (2003) Consumption of sugars and the regulation of short-term satiety and food intake. American Journal of Clinical Nutrition; 78:(suppl):843S-849S
7. Johnson L et al. (2007) Is sugar-sweetened beverage consumption associated with increased fatness in children? Nutrition 23 (7-8): 557-563
8. Malik VS et al (2006) Intake of sugar-sweetened beverages and weight gain: a systematic review. American Journal of Clinical Nutrition, Vol. 84, No. 2, 274-288
9. Rennie KL and Livingstone MBE (2007): Associations between dietary added sugar intake and micronutrient intake: a systematic review. British Journal of Nutrition 97: 832-841
10. WHO Global Oral health data base http://www.whocollab.od.mah.se/index.html http://www.whocollab.od.mah.se/euro.html
11. Touger-Decker R and van Loveren C (2003) Sugars and dental health. American Journal of Clinical Nutrition. 78 (Suppl): 881 S-892 S
12. Franz MJ., et al. (2002) Evidence-based nutrition principles and recommendations for the treatment and prevention of diabetes and related complications. Diabetes Care, 25(1): p. 148-198.
