Health Maintenance And Disease Prevention

Although the amount of carbohydrate required to avoid ke-tosis is relatively small (about 50 g/day), carbohydrate provides the majority of the energy in the diets of most people (1). This is desirable not only for providing easily available energy for oxidative metabolism, but also carbohydrate-containing foods are good vehicles for micronutrients and phytochemicals. Carbohydrates are important in maintaining glycemic homeostasis and for gastrointestinal integrity and function. Diets high in carbohydrates, as compared with diets high in fat, reduce the likelihood of developing obesity and related conditions. An optimum diet should consist of at least 55% of the total energy coming from carbohydrates obtained from a variety of food sources. However, carbohydrates intakes at or above 75% of total energy could have significant adverse effects on nutritional status by the exclusion of adequate quantities of protein, fat, and other essential nutrients.

Energy Balance and Weight Maintenance

In adults, it is very important that the energy ingested be matched to the amount of energy expended (1,11). Main tenance of energy balance is necessary to avoid obesity and associated chronic diseases such as diabetes and cardiovascular disease. Positive energy balance (weight gain) occurs when total energy intake exceeds total energy expenditure, regardless of the composition of the excess energy. However, composition of the diet may affect to what extent positive energy balance occurs.

The composition of the diet may affect the body's ability to maintain energy (1,11). Especially, diets containing at least 55% of energy from a variety of carbohydrate sources, as compared with high-fat diets, reduce the probability of body fat accumulation. Substantial data suggest those diets high in fat tend to promote consumption of more total energy than diets high in carbohydrates. This effect may be due to the low energy density of high-carbohydrate diets, because total volume of food consumed appears to provide an important satiety cue. Although there are no data to suggest that different types of carbohydrates affect total energy differently, the composition of the diet may affect the proportion of excess energy stored as body fat. The body has a large fat storage capacity, and excess dietary fat is stored very efficiently in adipose tissue. Alternatively the body's capacity to store carbohydrates is very limited, and excess dietary carbohydrates are not efficiently stored as body fat. Instead, excess carbohydrate tends to be oxidized readily, resulting in indirect fat accumulation by reductions in fat oxidation. Although the overall contribution of de novo lipogenesis from carbohydrates is small, it may increase with appreciable carbohydrates overfeeding, insulin resistance, and with extremely high intakes of sucrose or fructose.

There is considerable controversy surrounding the extent to which sugars and starch promote obesity (1,11). There is no direct evidence to implicate either form of carbohydrate in the etiology of obesity, based on data derived from studies in Western countries. In spite of that, it is important to state that excess energy in any form promotes body fat accumulation. Excess consumption of low-fat foods, although not as obesity producing as excess consumption of high-fat foods, leads to obesity if energy expenditure (such as physical activity) is not increased.

Physical Activity

Maintaining regular physical activity reduces the likelihood of creating positive energy balance or weight gain, regardless of diet composition (1,12). There is general agreement that the combination of high-carbohydrate diets and regular physical activity is the best way to avoid positive energy balance. The increased energy needs of people with high physical activity can be efficiently met by dietary carbohydrates. In many developing countries, the major challenge is to meet the daily energy needs of high physical labor. The importance of carbohydrates in the diet becomes more critical as the amount of and the intensity of physical activity increases.

There is substantial evidence that supplemental carbohydrates can improve performance for elite, endurance-trained athletes (1,12,13). A high-carbohydrate diet including meals and snacks such as energy bars have been shown to enhance performance during long-distance cy cling and running. There is, however, no clear evidence that carbohydrate supplements and snacks would improve the performance for the majority of people who engage in recreational physical activity of lower intensity and duration. On the other hand, carbohydrate intake after exercise can help to quickly replenish depleted glycogen stores.

Dental Caries

The incidence of dental caries is influenced by a number of factors (1). Foods containing sugars and starch may be easily hydrolyzed by «-amylase and bacteria in the mouth, which can increase the risk of caries as a result of excess production of organic acids. Starches with a high glycemic index produce more pronounced changes in plaque pH than low glycemic index starch, especially when combined with sugars. However, the impact of carbohydrates on caries is dependent on the food, frequency of consumption, degree of oral hygiene performed, availability of fluoride, salivary function, and genetic factors.

Behavior

There is emerging evidence that food intake may have important effects on behavior (1,14). Although providing breakfast to children who do not typically eat breakfast can increase cognitive performance, it is less clear that overall composition of the diet can affect behavior. Although it is often suggested that sugar consumption may lead to hyperactivity in children, there is no evidence to support the claim that refined sugars have a significant influence on child hyperactivity and related behaviors. Because glucose is an essential energy source for the central nervous system, carbohydrate has been suggested to play a role in memory and cognitive function. Although there appears to be a relationship between glucose levels and memory processing, the clinical significance of this effect has yet to be determined.

Blood Glucose and Diabetes Management

The rise of blood glucose in normal and diabetic people after meals varies markedly and depends on many factors, including the source of the carbohydrate, its method of preparation, and composition of the total meal (1,15). Classification of carbohydrates as simple or complex does not predict their effects on blood glucose or insulin. Rapidly absorbed carbohydrates, which promote large blood glucose responses, may be in the form of both sugars and starches. Sugars added to foods have no different effects on blood glucose from those of sugars alone. The natural sugars from fruits dhd fruit juices raise blood glucose approximately as much as does sucrose and less than do most refined starchy carbohydrate foods.

Consuming a wide range of carbohydrate foods is now regarded as acceptable in the nutrition management of people who already have non-insulin-dependent diabetes (1). It is suggested that between 60 and 70% of total energy should be derived from a mix of carbohydrates and mono-unsaturated fats. Carbohydrates should mainly come from a wide range of appropriately processed cereals, vegetables, and fruit. Sucrose and other sugars have not been directly implicated in the etiology of diabetes, and recommendations concerning intake relate primarily to the avoidance of all energy-dense foods in order to reduce obesity. Most recommendations for the management of diabetes permit modest (30-50 g/day) intakes of sucrose and other added sugars in the diabetic dietary plan.

Blood Lipids and Cardiovascular Disease Risk

The cornerstone of dietary advice aimed at reducing coronary heart disease risk is to increase the intake of carbohydrate-rich foods, especially cereals, vegetables, and fruits rich in nonstarch polysaccharides, at the expense of fat (1). There is increasing evidence that antioxidants have a protective effect against coronary heart disease, and complex carbohydrates such as fruits and vegetables tend to be rich sources of antioxidant nutrients and food components. Cereal foods rich in nonstarch polysaccharides tend to have a protective effect, and there is not evidence that sucrose consumption increases risk. Certain nonstarch polysaccharides such as /?-glucan have been shown to have an appreciable effect on lowering plasma cholesterol when consumed in naturally occurring foods, enriched foods, or dietary supplements. Many carbohydrate-rich plant foods are rich in potassium, which may help to reduce the risk of hypertension.

Gastrointestinal Illnesses and Cancer Risk Management

Minimally refined carbohydrate staple foods may be a good source of dietary fiber or oligosaccharides and phytochem-icals, which might mitigate the risk of colorectal and other cancers (1). The process of complex carbohydrate (eg, dietary fiber, resistant starch, oligosaccharides) fermentation in the large intestine may protect the colorectal area against the genetic damage that may lead to cancer through a range of mechanisms that include (2) the dilution of potential carcinogens; (2) the reduction of products of protein fermentation through the stimulation of bacterial growth; (3) pH effects through the production of butyric acid; (4) maintenance of the gut mucosal barrier; and (5) effects of bile degradation. High intake of prebiotics such as fructo-oligosaccharides may facilitate the colonization of bifidobacteria and lactobacilli in the large gut, this may reduce the risk of acute infective gastrointestinal illnesses.

Inherited Conditions

There are a number of inherited conditions having significant implications for restricting dietary intake in infants and children (1). These include rare conditions such as fructose intolerance, galactosemia, and sucrase deficiencies. Though rare diseases, their early detection and careful dietary management is important in avoiding severe handicap or pathology.

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