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Carbohydrate Controversy: "Good" Sugars vs. "Bad" Sugars?
Len Kravitz, PhD

Carbohydrates, which come primarily from plants, are a direct link to the Earth's food chain. Before the industrial revolution, carbohydrates were the major source of nutrients and energy for people throughout the world. In fitness, physiologists regularly extol the importance of carbohydrates as a vital fuel that drives exercise and sport performance. However, the evidence that added sugars in a person's dietary lifestyle presents several health risks is mounting. The purpose of this column is to bring clarity of the important role of carbohydrates for exercise and present the health risks of American's sweet tooth sugar overload.

What are Carbohydrates?
Carbohydrates are biomolecules that contain oxygen, carbon, and hydrogen atoms. They are made up of small building blocks referred to as monosaccharaides (mono=one; saccharide=sugar). When we eat plants and digest them into monosaccharaides, our body converts them to glucose, which the muscle cells used to produce energy. It should be noted that animals can also make carbohydrates, usually for use in their own body. The one meaningful exception is the natural sugar in milk, lactose, which is also a source of dietary carbohydrates. Glucose is the main carbohydrate in our blood, which we store in the form of glycogen in muscle and liver.

Why is Glucose the Preferred Fuel for Challenging Exercise Bouts?
It is important to note that energy that drives life and exercise is released when the chemical bonds in food substrates are broken. The energy in the food's molecular bonds is released in our cells to produce adenosine triphosphate (ATP), which is an immediately available source of energy for practically all bodily functions, particularly muscular contractions during exercises. At rest our body's energy demands are met fairly equally by the breaking of the bonds in fats and carbohydrates. During more intense exercise, glucose and glycogen are the preferred fuel because of their availability (glucose in blood and glycogen in muscle) and our muscle cells' highly developed enzyme system, which can chemically break them down rapidly to synthesize ATP.

Sugar Overload: Too Much Added Sweetness Has Its Perils
Cupcakes, cookies, muffins, doughnuts, chocolate, ice cream, soft drinks, fruit drinks, energy drinks and more. The list of sweet temptations we have developed as a society is quite exhaustive, and now sounding off health alarms. In an invited commentary, Dr. Laura Schmidt (2014) clarifies that this sugar overconsumption to so many products during manufacturing is problematic. It is not due to eating too much fresh fruit, which has naturally occurring sugars, fiber, water, vitamins and antioxidants. Schmidt explains that our health concerns originally were that too much sugar intake would lead to obesity and dental cavities, which has been prodigiously confirmed. The new concerns are these added sugars, predominantly sucrose and high-fructose corn syrup, which may be independent risk factors for cardiovascular disease, type 2 diabetes, abnormal lipids, and hypertension, highlighted in the next few sections.

The Sugar Burden on Cardiovascular Disease
Yang and colleagues analyzed national data (1988 to 2010) on the influence of added sugar consumption on cardiovascular disease (CVD). Their analysis shows that the CVD risk becomes elevated once added sugar intake surpasses 15% of daily calories. The researchers highlight, from their analysis, that regular consumption of sugar-sweetened beverages (&Mac179;7 servings/week) is linked with increased risk of CVD mortality. Woefully, the risk increases with an increase in sugar intake. The researchers summarize that persons who consume approximately 17% to 21% of calories from added sugar have a 38% higher risk of CVD mortality.

Is there a Link with Sugar intake and Type 2 Diabetes
In their systematic review and meta-analysis from 17 studies, Imamura et al. (2015) conclude that habitual consumption of sugar-sweetened beverages is independently linked with a greater incidence of type 2 diabetes. The researchers suggest that the consumption of sugar-sweetened beverages may be linked to 4-13% of type 2 diabetes incidence in the United States. Imamura and colleagues also state that artificially sweetened beverages and fruit juice are not healthy options for the prevention of type 2 diabetes. This data fully supports the recommendations for the healthy consumption of a wide variety of fruits, which have naturally occurring sugars that have not been linked to the incidence of type 2 diabetes.

Does Sugar Overconsumption Influence Blood Pressure and Blood Lipids?
Te Morenga et al. (2014) completed a meta-analysis of randomized controlled trials involving 1699 participants that compared higher intakes of sugar to lower dietary sugar intakes in adults or children (who had no acute illnesses). Study results show that higher intakes of sugar are associated with harmful increased concentrations of triglycerides, total cholesterol, LDL cholesterol, and blood pressure. The researchers continue that the most likely explanation for the effect of higher sugars on blood pressure and lipids is in the fructose component. The researchers explain that overconsumption of dietary fructose, particularly from sugar-sweetened beverages, has been shown to increase liver fat synthesis, which results in increased concentrations of circulating triglycerides and cholesterol. In addition, the elevated liver fructose metabolism may lead to an increase of uric acid (uric acid is a waste product from the digestion of foods containing purines (e.g., dried beans, sardines and certain meats), impairing the function of endothelial cells, resulting in a vasoconstriction of blood vessels and eventual high blood pressure.

Sugar Re-Start Suggestions
The evidence clearly shows that added sugars are not just empty calories, they are very hurtful calories. Health implications clearly indicate we should eat more whole foods as opposed to processed foods. Curbing the intake of sugar-sweetened beverages and sugar-laden yogurt would be a most healthful lifestyle change. In addition, choosing breakfast cereals with little or no sugar is a positive strategy. Interesting, added sweeteners to foods, which began as a way to combat high fat intake (and obesity) is now becoming an even bigger health problem. The bottom line message for fitness pros to clients is that healthy, unprocessed (or minimally processed) carbohydrates fuel our workouts and deliver beneficial vitamins, minerals, fiber and phytonutrients. It's time to be mindful about all of the added sugars in foods, including foods not commonly thought of as sweet such as sauces, salad dressings, crackers and breads. Perhaps the first step for many clients in their sugar re-start is not to avoid all sugar-sweetened products, just start 'limiting' them in the daily diet.

Side Bar 1: Sugar Intake vs. Sugar Recommendations
White (2018) summarizes estimates that the average American currently consumes about 19.5 teaspoons daily, which is approximately 66 lbs of added sugar over the course of a year. In contrast, White notes that in 1790 that data suggest that the average yearly intake of sugar was 8 lbs annually. As a reminder, the average dose of sugar in one 16-ounce soda is about 16 teaspoons. White recaps that the American Heart Association recommends that adult females consume less then or equal to 6 teaspoons (about 25 grams) and that adult males consume less then or equal to 9 teaspoons (about 38 grams) of added sugar daily. Presently, Americans consume approximately 3 to 6 times more sugar that what is currently recommended.

Side Bar 2: Are There Unique Health Risks to High-Fructose Corn Syrup?
High-fructose corn syrup (HFCS), which was first introduced in the 1970's, is produced by a process that converts glucose to fructose. HFCS makes up a very large proportion of added sweeteners in beverages and many packaged foods (i.e., cereals, baked goods, desserts, flavored dairy products, and canned foods). Dornas et al. (2015) note that fructose is advantageous in processing because it is 1.5 times sweeter than sugar and inexpensive to produce. The researchers conclude, from their review, that HFCS definitely contributes to the development of several adverse health effects (i.e., insulin resistance, high blood fats, intra-abdominal fat accumulation, high blood pressure and elevated uric acid). However, more research is needed to determine how excess HFCS causes these diseases, and the doses of HFCS that produce these negative health outcomes. With reliable data, evidence-based guidelines for HFCS intake may be proposed and recommended.

Len Kravitz, PhD, CSCS, is the program coordinator of exercise science at the University of New Mexico, where he received the Outstanding Teacher of the Year and Presidential Award of Distinction. He just released his third book, HIIT Your Limit (Amazon).

Dornas, W.C., de Lima, W.G., Pedrosa, M.L. et al. (2015). Health implications of high-fructose intake and current research. Advanced Nutrition, 6, 729-737.
Imamura, F., O'Connor, L., Ye, Z. et al. (2015). Consumption of sugar sweetened beverages, artificially sweetened beverages, and fruit juice and incidence of type 2 diabetes: systematic review, meta-analysis, and estimation of population attributable fraction, British Medical Journal, 2015; doi:10.1136/bmj.h576
Schmidt, L.A. (2014). New unsweetened truths about sugar. JAMA Internal Medicine, 174(4), 525-526
Te Morenga, L.A., Howatson, A.J., Jones, R.M. et al. (2014). Dietary sugars and cardiometabolic risk: systematic review and meta-analyses of randomized controlled trials of the effects on blood pressure and lipids. American Journal of Clinical Nutrition, 100:65-79.
White, J.R. (2018). Sugar. Clinical Diabetes, 36(1), 74-76.
Retrieved January 9, 2019
Yang, Q., Zhang, Z., Gregg, E.W., et al. (2014). Added sugar intake and cardiovascular diseases mortality among U.S. Adults. JAMA Internal Medicine, 174(4):516-524.