Sugars are categorized into two groups namely simple and complex sugars (carbohydrates). The simple sugars are further subdivided into mono- and disaccharides and include fructose, galactose and glucose; and sucrose, maltose and lactose respectively. On the other hand, complex sugars are polysaccharides like starches. Naturally occurring monosaccharides include fructose in milk products, vegetables and fruits. Naturally occurring sugars are sometimes referred to as intrinsic sugars while added sugars are also known as extrinsic sugars (Howard & Wylie-Rosett, 2012). This paper though, will focus on the added sugars and their impact on the health status of individuals. Extrinsic or Added sugars are normally used to sweeten food and are different from the naturally occurring sugars in foods such as milk and fruits. The recommended intakes for energy from carbohydrate is 45- 65%, 10- 35% for protein and 20-25% for fat. Maintenance of these consumption benchmarks has been linked to reduced risks of conditions like coronary heart diseases, diabetes and obesity.
However, majority of people lack information on the deleterious health ramifications brought by consumption of added sugars (Canadian Sugar Institute, 2004). According to Continuing Survey of Food Intakes by Individuals (CFSII) conducted in 1994- 1996 by USDA, an average of 20.5 teaspoons (approximately 3 ounces) of added sugars are consumed each day in the U.S. This figure is thought to be low due to underreporting; Shanty Bowman of the USDA-ARS Community Nutrition Research Group says that, “about one-third of our added sugars come from no diet soft drinks…Next are bakery products—cakes, cookies, pies, and other pastries—which contribute about 13 percent” (McBride, 2000). The high quantities of added sugar consumption is not confined to the U.S. alone but is a problem that many on the global front grapple with as can be noticed in the skyrocketing prevalence of non-communicable diseases like diabetes, obesity and heart diseases. In addition, globalization has paved way for international trading resulting into exportation and importation of products with added sugar to other nations.
Sources, Examples and Uses of Added Sugars
Added sugars are instrumental in several avenues and this perhaps could be one of the factors attributable to its high and widespread consumption. Added sugars enhances the flavor and texture of foods, prevents spoilage in jellies and jams, retains moisture in baked foods thus lengthening the duration of freshness and browning of the crust in baked products, and provides food for yeast during leavening. Added sugar can be subtly obtained from an array of sources including tabletop sugars, candy, fruit drinks, baked foods, sweetened milk, dairy desserts like ice-cream and soft drinks which is highly culpable for the supply of extrinsic sugar. Generally, foods that contain a large quaintly of added sugar have few nutrients to show for relative to the amount of kilocalories they provide (Drummond & Brefere, 2010).
High- Fructose corn syrup (HFCS) is one of the common added sugars industrially used. It is manufacture through the conversion of some glucose present in corn syrup to fructose and is used mostly in regular sodas, fruit drinks, sweet pickles, jams and jellies, and sweetened teas. Glucose is converted to fructose because it is sweeter. Therefore, this paper will focus much on the health implications of high consumption of fructose since most of the studies surround the ramification of its use. This paper will also use the term “added sugar” to loosely mean the other category of sugars that include sucrose, molasses, honey, corn sweeteners, maple sugar and corn syrup.
Health Impacts of Added Sugar
Much as added sugar is beneficial, too much consumption leads to very dire health consequences. It is notable from the aforementioned that a large quantity of added sugar is consumed through food stuffs and beverages since it forms part of the main ingredients during processing. Some of the health problems attributable to frequent or high consumption of added sugars are discussed hereafter.
Metabolic Syndrome and Coronary Heart Disease (CHD)
Added sugars may contribute to a conglomeration of biochemical and clinical features like insulin resistance, abdominal obesity and dyslipidemia. For instance, in one ten week trial covering 32 overweight or obese persons between ages 42 and 70 years, it was observed that concentration of lipoproteins and plasma lipids spiked up and maintained the status quo even in subjects who consumed glucose. Besides, those who consumed fructose developed insulin resistance and visceral obesity (Schwarz et al., 2009). In the trial, the level of fasting plasma glucose and insulin levels were raised as insulin sensitivity reduced in subjects who consumed beverages sweetened with fructose as opposed to those consuming glucose.
Moreover, a cross-sectional study done during a National Health and Nutrition Survey among U.S. adults (> 6000) revealed that the correlation between blood lipid levels and caloric sweeteners (High- Fructose Corn Syrup- 55) was statistically significant. Another clinical study conducted among youthful and healthy male volunteers who consumed 3 grams of 20% fructose solution per Kilogram body weight per day for 6 days, revealed a substantial rise in plasma triglycerides coupled with suppression of adipose tissue lipolysis (Faeh et al., 2005). Even though studies show the detrimental aspects of added sugars like fructose, the mechanism of its operation is still under scrutiny. For instance, experimental evidence has revealed that the production of tumor necrosis factor (TNF) which is a pro-inflammatory cytokine that induces lipoprotein production and insulin resistance is exacerbated by the consumption of fructose (Welsh et al., 2010; Kanuri et al., 2011).
The dynamics of lipoprotein and triglycerides levels brought about by increased intake of added sugar contribute to heart diseases. Dyslipidemia, an elevated level of triglycerides and reduced level of high density lipoprotein (“good” cholesterol), has been linked to high sugar intake; consequently, this imbalance in blood fat levels results into CHDs as they lead to plaque development along the blood vessels or deposition of fat in the heart.
That added sugars like fructose is linked to hypertension is thought to be the consequence of its ability to raise the levels of uric acid. Epidemiological studies have linked the consumption of fructose to hypertension. An NHANES survey done from 1999 to 2004 in adolescents showed a strong link between drinks containing added sugar sweeteners with the levels of uric acid and hypertension. In the same vein, another survey by NHANES conducted from 2003 to 2006 still showed that there was a correlation between fructose and elevated levels of blood pressure (Nguyen, Choi, Lustig & Hsu, 2009; Jalal, Smits, Johnson & Chonchol, 2010). In addition, a study conducted with the administration of low-fructose diets showed a reduced level of blood pressure. The study involving 810 adults whose consumption of a sugar-sweetened beverage was reduced every day for 18 months. A reduction of 1.1 mmHg and 1.8 mmHg diastolic and systolic pressures respectively was observed. Surprisingly, in this study, the observed effect was independent of levels of serum uric acid. However, since the vascular effects are pegged on the intracellular uric acid, the observed effect may still be attributable to the levels of uric acid.
On the flip side, a study done by Forman, Choi and Curhan (2009) failed to find a correlation between intake of fructose and development of hypertension. The study was based on health professional and nurses who received large quantities of fructose derived from natural fruits. This inconsistency with the other studies was contributed by the high quantities of flavenols and antioxidants that curb the hypertensive effects of the fructose; furthermore, ascorbic acid present in fruits stimulates renal excretion thereby lowering the levels of uric acid. The fructose hypothesis has been further challenged by laboratory tests on rats that have observed no association between fructose and blood pressure. However, this observation is probably due to the presence of the enzyme uricase in rats that lowers the levels of uric acid and hence countering the expected observation- a higher level of serum uric acid.
Studies highlighted under the metabolic syndrome and hypertension sections (2.2.1) above have shown that added sugars like fructose are contributors to these lethal conditions (metabolic syndrome and hypertension). The occurrence of the aforementioned conditions establishes a domino effect that results into chronic kidney disease. Hitherto, there is only one human study that links consumption of sweetened beverages with chronic kidney disease. Particularly, between 1999 and 2004, the NHANES noticed that the risk of having albuminuria was enhanced by the intake of two or more beverages with added sugar as an ingredient (Shoham et al., 2008). Experimental studies on the other hand show that the consumption of fructose is contributory factor rather than causative. For instance, an administration of a 60% diet of fructose to rats worsened renal function, quickened glomerulosclerosis and enhanced proteinuria. On the contrary, administration of glucose never produced these dire consequences. In addition, micro puncture studies have recorded that reduced renal blood flow and glomerula hypertension is linked to intake of sucrose (Gersch et al., 2007; Sanchez-Lozada et al., 2008).
Added sugars can exacerbate the risk of developing type 2 diabetes since as mentioned under metabolic syndrome, it induces insulin resistance. Though a link between added sugars and development of diabetes is still elusive, some studies do prove otherwise. In a study conducted by Schulze et al (2004), it was observed that consumption of soft drinks as opposed to fruit juices was strongly linked to a high risk of diabetes, even after adjusting the BMI. The mechanism in operation is that HFCS is highly absorbable and produces an effect similar to that of sucrose. Intake of large quantities of beverages sweetened with added sugars leads to high glycemic load which results into a poor glycemic control in diabetics due to the spikes in blood sugar levels (Foster-Powell & Brand-Miller, 2002; Willet, Manson & Liu, 2002).
Moreover, a current study conduct to investigate the impact of drinks and foods sweetened artificially or with sucrose on inflammatory biomarkers like haptoglobin and C-reactive protein among overweight subjects concluded that intake of products sweetened with sucrose significantly raised the plasma transferrin and haptoglobin levels. No significant effect was observed on the C-reactive protein. Thus, it is reasonable to conclude that a high consumption of rapidly digested carbohydrates like added sugars enhances the proinflamatory process which is a risk factor for diabetes (Sorensen, Raben, Stender & Astrup, 2005).
Dental Caries, Overweight and Obesity.
Intake of large quantities of added sugar feeds naturally occurring bacteria in the mouth; after feeding on the sugars, the bacteria produce tooth-decaying acid. This erosion of the enamel is exacerbated by other factors in play namely the duration added sugars take in the mouth, dental hygiene and fluoridation. It has been noted that this risk of dental caries is enhanced by an intake of nutritive sweeteners (The British Dietetics Association, 2010).
Overweight and Obesity are intertwined in their occurrence since more often than not obesity is a consequent of overweight. Some longitudinal studies have tried to link added sugar with obesity through the promotion of weight gain. The Detroit Dental Health Project in 2002-2003 did a two-year study among African-American children hailing from low income families recruited at ages 3-5 years. It was observed that the prevalence of obesity skyrocketed by doubling from 10.3 % to 20.4 % due to increased consumption of Sugar-Sweetened Beverages (fruit drinks and regular soda) from averagely 19.2 ounces to 21.6 ounces per day. At the beginning of the study, the odds of gaining weight and developing obesity rose by 4 % for every ounce of fruit drink or soda that was additionally consumed (Kumanyika, Grier, Lancaster, Lassiter, 2011, p. 8).
Sugars supply empty calories in bulk relative to other essential nutrients which are available only in aliquots amounts. Honey for instance contains some mineral and vitamins but in limited quantities. Therefore, an elevated intake of added sugars simply displaces the much needed macro and micro-nutrients necessary for the overall growth and development of the body. However, some studies have shown that vitamins and minerals are not necessarily affected by the intakes of diets with added sugar. This is attributable to the supplementation of such diets with vitamins and minerals. In a heart study done among children in Bogalusa, though, a linear reduction in the consumption of a variety of essential nutrients was linked to elevated levels of total sugar consumption. Nutritionally speaking, sugars are not “bad” if consumed in appropriate quantities but can be detrimental if their intake levels are not checked (Herman, 2012).
The various studies that have been conducted to support these negative health effects of high intake of added sugar provides credible evidence that added sugars, even though they may not directly cause these and other conditions, significantly add to their occurrence. Added sugar is one key contributor to the serious health conditions discussed herein and many others. Further, since it has been noted from the various studies covered that an increased intake of sucrose results into renal disease, there should be a restriction of added sugars such as fructose along with protein restrictions in patients suffering from chronic kidney disease. It is also necessary that more human studies that look into the correlation between dietary fructose and uric acid on renal disease occurrence be conducted. Moreover, in a summary by Carbohydrate News of Canadian Sugar Institute (2004), there is no enough evidence that can be used for setting the upper limits for total or added sugars and that can be used to hold added sugars culpable in contributing to lifestyle diseases. Therefore, it is necessary for more cross-national studies to be done to clarify on the association of added sugars with non-communicable diseases like overweight and obesity, diabetes, dental caries, hyperlipidemia among others.