Current Knowledge of the Health Effects of Sugar Intake
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Current Knowledge of the Health Effects of Sugar Intake Anne L. Mardis, MD, MPH1 Twenty years ago, the common themselves or from corresponding Center for Nutrition Policy perception was that sugar intake was simple sugars added to foods during and Promotion associated with several chronic processing. Within the body, most diseases: Diabetes, coronary heart dietary sugars are converted to glucose, disease, obesity, and hyperactivity in a major fuel used by all cells and the children. Sugar was also thought to be primary fuel required by brain tissue the sole cause of dental caries. Recent for normal function. Low levels of advances in scientific knowledge, glucose in the blood will impair the however, have shed some light on the brain and cause permanent mental role of sugar in chronic diseases and impairment or worse—coma or death. dental caries. The evidence indicates The body can store a limited amount that sugar is not in itself associated of glucose as glycogen, which it can with the aforementioned chronic draw upon for less than a day. After diseases and is not the sole offender this, other sources such as proteins, in the development of dental caries. from the breakdown of body tissues, This research brief discusses current must be used to synthesize glucose scientific knowledge of the health for the cells (15). effects of sugar. Diabetes Physiology The relationship between dietary Despite having been labeled as “empty carbohydrates and insulin resistance calories,” sugars are truly important (a risk factor for diabetes mellitus, compounds from the perspective of ischemic heart disease, and hyper- the human organism. Humans have tension) is not clear based on available retained the ability to synthesize all research (7). In two studies based on forms of carbohydrates the body needs a large, prospective study of U.S. from simple sugars. This is not the case women, sucrose and carbohydrate with the other dietary macronutrients, intake were not associated with an fats, and proteins. Following ingestion, increased risk of diabetes (6,27). all digestible complex dietary carbohy- However, based on the same popula- drates are broken down in the gut to tion, associations were found between simple sugars before they are absorbed a diet with high glycemic load2 (26) into the body. Because simple sugars and high intake of refined grains (21) are all identical chemically, the and the risk of diabetes. The general absorption process cannot distinguish consensus, based on epidemiological 1 studies, is that sugar intake alone is not Currently at the National Institute for simple sugars resulting from the Occupational Safety and Health, Centers breakdown of complex dietary carbo- for Disease Control and Prevention, hydrates from corresponding simple 2 Morgantown, WV. sugars occurring naturally in the foods Glycemic load is a function of the effect of a carbohydrate meal on glucose levels in the blood (3). 2001 Vol. 13 No. 1 87 associated with the development of study of 32 hypertriglyceridemic Hyperactivity diabetes mellitus. Sugars fed at levels patients provided evidence that an equivalent to those consumed by the “extrinsic sugar-free” diet significantly Many people still believe that sugar U.S. population do not produce adverse lowers abnormally elevated plasma intake in children causes hyperactivity. glycemic effects in non-diabetics (23). triglyceride levels (28). Evidence also A meta-analysis, however, of 16 The effects of sugar intake on glucose suggests that insulin resistance and different reports from 23 separate 5 tolerance, insulin levels, and plasma compensatory hyperinsulinemia have studies with 560 subjects showed lipids are confounded by other dietary major roles in the regulation of blood virtually no effect of sugar intake on components. The American Diabetes pressure in subjects predisposed to the hyperactivity in children (30). In a Association has also acknowledged, hypertension due to hereditary or review of the literature, Krummel et al. in its nutrition recommendations for environmental factors, possibly (19) reported that in 12 double-blind, people with diabetes, that there is no mediated by activity of the sympathetic placebo-controlled studies, no associa- evidence that refined sugars such as nervous system. But there are multiple tion was found between sugar intake sucrose behave any differently from metabolic abnormalities associated and hyperactive behavior. Thus, despite other types of simple carbohydrates (1). with hyperinsulinemia in hypertensive numerous anecdotal perceptions to the patients that increase the risk of contrary, systematic, controlled studies coronary heart disease (24). show that sugars do not cause hyper- Heart Disease activity. The Sugars Task Force of the U.S. Obesity Food and Drug Administration (29) Dental Caries presented a comprehensive review of Despite popular belief that sugar causes epidemiological, clinical, and animal obesity, a number of studies show an Dental caries is a chronic disease that studies dealing with the relationship inverse relationship between reported has many causes. Sugar is involved in between sugar intake and heart disease sugar consumption and degree of tooth decay, but it is one of many or risk factors for heart disease (14). overweight (10,11,20,25). An increase factors, including oral bacteria, saliva, The report concluded that at current in the percentage of calories from sugar tooth enamel, food substrate, and host levels of consumption, sugar is not is, by definition, associated with a susceptibility. All fermentable carbohy- an adverse risk factor in heart disease. decreased consumption of calories drates are potentially cariogenic. Other The same conclusion was made by the from fat. Obesity is basically a conse- dietary factors such as the retention of National Research Council in its report quence of higher energy intake than food in the mouth affect cariogenic on chronic disease risk (23). There is energy expenditure, where excess potential. Even starches, which may no conclusive evidence that dietary calories are stored as fat (5). The type not taste sweet, are chains of glucose sugar is an independent risk factor for of calories consumed is the subject of and are broken down to glucose in the coronary artery disease in the general much study in obesity research. For mouth. Good oral hygiene, good genes, population. However, hypertrigly- instance, extra calories consumed as fluoridation of water, and restricting 3 4 ceridemia and central fat distribution, sugar cause an appropriate compensa- snacks between meals can prevent consequences of abnormal glucose tory increase in carbohydrate oxidation tooth decay, no matter how high the tolerance and diabetes mellitus, are (metabolism of carbohydrates for sugar consumption (13,18,25). independent risk factors for coronary energy), whereas extra calories heart disease (8). A 1996 randomized consumed as fat do not (17). Simply stated, obesity results from energy intake in excess of energy require- Nutrient Displacement 3 Elevated blood levels of triglycerides: a form of ments. Many factors contribute to fatty acid found in animal and vegetable fats. obesity, but evidence does not single Research on the effects of sugar intake 4 and nutrient displacement in the diet of A type of body fat distribution with a high ratio out dietary sugar as a cause (25). of waist or abdominal circumference to hip or children is inconclusive. In a review of gluteal circumference that is epidemiologically the literature, Ruxton et al. (25) found 5 associated with heart disease and diabetes. An increase in pancreatic secretion of insulin to that higher intake of sugar did not compensate for cellular resistance to insulin. negatively affect micronutrient intake. Gibney et al. (10) found, in an analysis 88 Family Economics and Nutrition Review of the 1987-88 USDA Nationwide But, the nutritional quality of the diet Food Consumption Survey, that high of children with higher sugar intake consumption of sugars was not appeared to be adequate regarding associated with a poorer quality diet. vitamin and mineral intakes and were In a study of 143 children ages 11 and closer to meeting current recommenda- 12 years, a 7-day weighed and recorded tions for dietary fat. Nevertheless, a food inventory revealed that as the relationship between the consumption proportion of energy from sugars of sugars and nutrient displacement has increased, there was no decline in not been observed consistently nor has dietary fiber or micronutrient intake, there been consistency among the with the exception of niacin, which specific nutrients displaced when a exceeded recommended levels (22). relationship has been found. Thus, this However, Linseisen et al. (20) and issue remains unsettled and requires Gibson (12) did demonstrate intake additional data from primary research. of many micronutrients below recom- mended levels in persons in Germany and the United Kingdom who con- Conclusion sumed high (energy-adjusted) amounts of sugar. In addition, high consumption Recent evidence shows that aside of non-diet soft drinks, a significant from dental caries, the intake of added source of added-sugar intake in sugars is not directly related to diabe- children, is associated with lower tes, heart disease, obesity, and hyperac- consumption of milk and fruit juice tivity, as was previously thought. This and lower intake of riboflavin, vitamin conclusion was also reached in a 1997 A, calcium, phosphorus, and the ratio review of the literature on the health of calcium to phosphorus, which may effects of sugar intake (2). Because be considered markers for milk high intake of sugars along with other consumption (16). factors can affect oral health and can displace important foods and nutrients In an analysis of the Continuing Survey in the diets of children when consumed of Food Intakes by Individuals (1994- as soft drinks, it seems prudent to limit 96), Bowman found that compared excessive intake. But the focus on with Americans over 2 years of age sugar as an independent risk factor with lower added sugar consumption for chronic disease and hyperactivity as a percentage of total energy, indi- should be de-emphasized.