Sugars are simple carbohydrates made up of one or two sugar units—monosaccharides or disaccharides, respectively. Complex carbohydrates, such as starch, are made up of multiple sugar units and are broken down in the digestive tract to monosaccharide glucose (blood sugar). Sugar provides no nutrients other than calories for energy.
The cells, tissues, and organs of the body utilize glucose sugar for energy. Extra sugar is stored in the liver and muscles for future use or is converted to fat and stored in fat cells. Naturally occurring sugar is present in fruits, vegetables, milk, and some grains. Sugar is added to foods and beverages for a variety of purposes including:
All sugar, whether obtained directly from food or broken down during digestion from complex carbohydrates such as starch, enters the bloodstream as glucose. Thus, all sugar, regardless of the source, has the same nutritional value. As blood sugar levels rise following a meal, the pancreas releases the hormone insulin to help cells absorb the glucose for fuel or storage. When blood sugar levels fall, the pancreas releases the hormone glucagon, which signals the liver to release stored sugar to maintain blood sugar levels.
A distinction is made between naturally occurring and added sugars. Simple sugars occur naturally in fruits, vegetables, and milk. Starches are complex sugars from foods such as potatoes, beans, peas, corn, and grains and are broken down to glucose during digestion. Added sugar is any sugar or other sweetener that is added to food during refining, processing, preparation, or at the table. Added sugars may be refined, processed, or manufactured. Most sugar names end in the suffix “ose.”
To most people, sugar means table sugar or sucrose. Sucrose is a disaccharide of glucose and fructose that comes from sugar cane or sugar beets. Raw sugar is the brown solid remaining after evaporation of the liquid from sugar cane juice or syrup. Turbinado sugar is a partially refined sugar from cane juice that retains some molasses. Further processing yields solid brown or white cane sugar. Granulated white sugar is processed raw sugar from cane or beets. Brown sugar may be crystallized molasses (the residue from sugar cane processing) or white granulated sugar with molasses added back. Confectioner's or powdered sugar is finely ground white sugar, sometimes with a small amount of cornstarch.
The other common sugars are fructose (levulose), or fruit sugar, a monosaccharide found in all fruits and fruit juices; and lactose, or milk sugar, a disaccharide of glucose and galactose. High-fructose corn syrup (HFCS) is the most common sweetener in processed foods and beverages, such as cereals and sodas, because it is easy and inexpensive to manufacture. HFCS is made from processed corn syrup and is almost the same as sucrose, with about 55% fructose and 45% glucose. The United States is the world's largest manufacturer and consumer of HFCS. In 2010, the Corn Refiners Association proposed relabeling HFCS as “corn sugar” to dodge the unhealthy stigma that has come to be associated with HFCS. The U.S. Food and Drug Administration (FDA) ruled against the change, because corn sugar sometimes refers to dextrose, which is consumed by people who cannot absorb or tolerate fructose.
Other types of sugar include:
Unprocessed foods never have added sugar and do not have nutrition labels and ingredient lists. Ingredient lists on processed food labels indicate whether a product contains added sugar but not the amount. Naturally occurring sugars do not usually appear on ingredient lists. If a product contains no fruit or milk, all of the sugar is added. More than 50 different names are used for added sugar on ingredient lists. The higher that sugar is listed on the ingredient list, the more the food contains. Food labels also may indicate:
The glycemic index (GI) classifies carbohydrates according to how fast and how high they raise blood sugar levels compared with pure glucose. High-GI foods cause rapid spikes in blood sugar. Foods that contain added sugar, as well as highly refined grains, such as white flour and white rice, that are easily broken down to glucose, can cause blood sugar levels to rise very fast. Complex carbohydrates, as in whole grains, are broken down to glucose more slowly, so blood sugar levels rise gradually. Legumes, vegetables, fruits, and low-fat dairy products are also low-GI foods that are digested more slowly, so blood sugar levels do not rise as fast or as high. A GI of 70 or above is considered a high-GI food, and 55 or below is a low GI.
Many factors affect the GI of a food:
The GI can be misleading because it does not depend on the sugar content of a food. For example, watermelon has a very high GI but contains very little sugar per serving, because it is mostly water. The glycemic load of a food is its GI multiplied by the amount of carbohydrate. Generally, a glycemic load of 20 or above is high, 11–19 is medium, and 10 or below is low.
The relevance of the GI is unclear, because some studies have found that it has little effect on weight or health. Other evidence suggests that low-GI foods may help with weight loss and control of Type 2 diabetes. Nevertheless, many low GI foods are considered healthy choices, including fruits, vegetables, whole grains, and beans.
One tsp. (4 g) of granulated sugar has about 16 calories. The 2015–2020 Dietary Guidelines for Americans, as well as the World Health Organization, recommend that no more than 10% of total daily calories come from added sugar—no more than 200 calories (about 12 tsp. or 48 g) in a 2,000-calorie daily diet. Research has shown that it is difficult to meet nutrient needs within daily calorie limits when consuming more than 10% of calories as added sugar. The American Heart Association recommends even less added sugar—a maximum of 100 calories (about 6 tsp. or 25 g) per day for children, teens, and women, and 150 calories (about 9 tsp. or 36 g) for men. This is about one-half of daily discretionary calories. Most U.S. adults get about 13% of their total daily calories from added sugars. For example, a 12-oz. (355-mL) can of regular soda has about 12 tsp. (192 calories) of added sugar. Snack foods with high sugar content are called “empty calories,” because they usually contain few other nutrients. No daily recommendations have been established for naturally occurring sugars in milk and fruit, but calories from total sugars in a food (naturally occurring plus added sugars) can be calculated from nutrition labels by multiplying the total grams of sugar by 4, because sugar has 4 calories per gram.
The FDA classifies sugar as a safe food, but some experts argue that it is an addictive substance or even a toxin. Diets high in sugar, especially added sugar, are associated with obesity, as well as cavities and tooth decay. U.S. consumption of added sugar increased steadily over the last decades of the twentieth century, significantly contributing to the obesity epidemic. Consumption of added sugar has fallen somewhat since 2003, but it remains above recommended levels. In addition to weight gain, added sugar can raise blood triglyceride levels, which can increase the risk of heart disease. Furthermore, high-sugar diets may lack other important nutrients, including vitamins and minerals. Sugary soft drinks are a particular culprit, because it is easy to fill up on soda instead of nutritious beverages and water. Portion sizes of sugary drinks also have increased dramatically over past decades: from 6.5-oz (192-mL) soft-drink bottles before the 1950s, to 12-oz. (355-mL) cans in 1960, to 20-oz.(591-mL) plastic bottles in the early 1990s, to 42-oz. (1.25-L) bottles in 2011. Sugary drinks went from 4% of daily American calories in the 1970s to about 9% by the turn of the century. This increase was even higher among children and teens. Diets rich in naturally occurring sugars and other healthy carbohydrates do not appear to lead to weight gain or obesity.
Diets high in added sugar, and possibly other high-GI foods, may increase the risk of developing conditions such as insulin resistance, type 2 diabetes, and heart disease, as well as excess weight and obesity. Insulin resistance is a condition in which the cells of the body no longer respond efficiently to insulin, so both blood sugar and insulin levels remain high. Under these conditions, the pancreas may slow or even halt insulin production. Insulin resistance is linked to other problems, such as high blood pressure, high blood triglyceride levels, low levels of “good” (HDL) cholesterol, and excess weight. These symptoms are sometimes collectively referred to as metabolic syndrome. Insulin resistance and metabolic syndrome can lead to type 2 diabetes, heart disease, stroke, and possibly some cancers. It is estimated that up to 25% of adult Americans have metabolic syndrome, as it can affect even lean and fit people who consume large quantities of added sugar.
The health effects of naturally occurring sugars are less clear than those of added sugar. For example, fructose in fruit is about 70% sweeter than glucose but has a low GI, because it raises blood sugar only slightly. Fructose in juice and processed foods goes to the liver, where it is thought to contribute to metabolic syndrome. This is due to the fiber content in fruits that dampens the rise of sugar. Hence, eating the whole fruits rather than drinking juices is better for blood sugar control.
Some experts believe that high-sugar diets can lead to sugar addiction, because sugar overload turns off hormones that signal satiety and affects brain neurotransmitters to cause sugar cravings. Therefore, it has been argued that sugar should be regulated as a toxic, addictive substance that is creating a public health crisis. Studies have found a strong association between sugary soda consumption and weight gain, obesity, and type 2 diabetes in children and adults. In adults, consumption of one can of a sugary beverage per day increases the risk of a heart attack or dying from a heart attack by 20% and increases the risk of gout by 75%. Overweight children and adults who reduce their consumption of sugary beverages have been shown to have better weight control. New taxes on added sugar and sodas and age limits for purchasing sugary snacks have been enacted in some locales.
See also Adult nutrition ; Alcohol consumption ; Calories ; Carbohydrates ; Childhood nutrition ; Cravings ; Insulin ; Low-sugar diets ; Metabolic syndrome ; Obesity ; Oral health and nutrition ; School lunches ; Sugar sweetened beverages ; Sugar tax .
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Margaret Alic, PhD