1.3.1. Choosing Healthy Carbohydrates and Whole Grains

Glycemic Index

The glycemic responses of various foods have been measured and then ranked in comparison to a reference food, usually a slice of white bread or just straight glucose, to create a numeric value called the glycemic index (GI). Foods that have a low GI do not raise blood-glucose levels neither as much nor as fast as foods that have a higher GI. A diet of low-GI foods has been shown in epidemiological and clinical trial studies to increase weight loss and reduce the risk of obesity, Type 2 diabetes, and cardiovascular disease.[1]

Table The Glycemic Index: Foods in Comparison To Glucose

Foods GI Value
Low GI Foods (< 55)
Apple, raw 36
Orange, raw 43
Banana, raw 51
Mango, raw 51
Carrots, boiled 39
Taro, boiled 53
Corn tortilla 46
Spaghetti (whole wheat) 37
Baked beans 48
Soy milk 34
Skim milk 37
Whole milk 39
Yogurt, fruit 41
Yogurt, plain 14
Icecream 51
Medium GI Foods (56–69)
Pineapple, raw 59
Cantaloupe 65
Mashed potatoes 70
Whole-wheat bread 69
Brown rice 55
Cheese pizza 60
Sweet potato, boiled 63
Macaroni and cheese 64
Popcorn 65
High GI Foods (70 and higher)
Banana (over-ripe) 82
Corn chips 72
Pretzels 83
White bread 70
White rice 72
Bagel 72
Rice milk 86
Cheerios 74
Raisin Bran 73
Fruit roll-up 99
Gatorade 78

Note: Foods can be examined in terms of the glycemic index to determine what their glucose content is. Foods high on the glycemic index are high in glucose whereas foods low on the glycemic index are low in glucose.

For the Glycemic Index on different foods, visit http://www.mendosa.com/gilists.htm.

The type of carbohydrate within a food affects the GI along with its fat and fiber content. Increased fat and fiber in foods increases the time required for digestion and delays the rate of gastric emptying into the small intestine which, ultimately reduces the GI. Processing and cooking also affects a food’s GI by increasing their digestibility. Advancements in the technologies of food processing and the high consumer demand for convenient, precooked foods in the United States has created foods that are digested and absorbed more rapidly, independent of the fiber content. Modern breakfast cereals, breads, pastas, and many prepared foods have a high GI. In contrast, most raw foods have a lower GI. (However, the more ripened a fruit or vegetable is, the higher its GI.)

The GI can be used as a guide for choosing healthier carbohydrate choices but has some limitations:

  1. GI does not take into account the amount of carbohydrates in a portion of food, only the type of carbohydrate.
  2. Combining low- and high-GI foods changes the GI for the meal.
  3. Some nutrient-dense foods have higher GIs than less nutritious food. (For instance, oatmeal has a higher GI than chocolate because the fat content of chocolate is higher.)
  4. Meats and fats do not have a GI since they do not contain carbohydrates.

More Resources

Visit this online database to discover the glycemic indices of foods. Foods are listed by category and also by low, medium, or high glycemic index.

The Functions of Carbohydrates in the Body

There are five primary functions of carbohydrates in the human body:

  • energy production
  • energy storage
  • sparing protein
  • assisting in lipid metabolism

Energy Production

The primary role of carbohydrates is to supply energy to all cells in the body. Many cells prefer glucose as a source of energy versus other compounds like fatty acids. Some cells, such as red blood cells, are only able to produce cellular energy from glucose. The brain is also highly sensitive to low blood-glucose levels because it uses only glucose to produce energy and function (unless under extreme starvation conditions). About 70 percent of the glucose entering the body from digestion is redistributed (by the liver) back into the blood for use by other tissues. Cells that require energy remove the glucose from the blood with a transport protein in their membranes.

Energy Storage

If the body already has enough energy to support its functions, the excess glucose is stored as glycogen (the majority of which is stored in the muscles and liver). A molecule of glycogen may contain in excess of fifty thousand single glucose units and is highly branched, allowing for the rapid dissemination of glucose when it is needed to make cellular energy.

Prolonged muscle use (such as exercise for longer than a few hours) can deplete the glycogen energy reserve. Remember that this is referred to as “hitting the wall” or “bonking” and is characterized by fatigue and a decrease in exercise performance. The weakening of muscles sets in because it takes longer to transform the chemical energy in fatty acids and proteins to usable energy than glucose. After prolonged exercise, glycogen is gone and muscles must rely more on lipids and proteins as an energy source. Athletes can increase their glycogen reserve modestly by reducing training intensity and increasing their carbohydrate intake to between 60 and 70 percent of total calories three to five days prior to an event. People who are not hardcore training and choose to run a 5-kilometer race for fun do not need to consume a big plate of pasta prior to a race since without long-term intense training the adaptation of increased muscle glycogen will not happen.

The liver, like muscle, can store glucose energy as a glycogen, but in contrast to muscle tissue it will sacrifice its stored glucose energy to other tissues in the body when blood glucose is low. Approximately one-quarter of total body glycogen content is in the liver (which is equivalent to about a four-hour supply of glucose) but this is highly dependent on activity level. The liver uses this glycogen reserve as a way to keep blood-glucose levels within a narrow range between meal times. When the liver’s glycogen supply is exhausted, glucose is made from amino acids obtained from the destruction of proteins in order to maintain metabolic homeostasis.

Sparing Protein

In a situation where there is not enough glucose to meet the body’s needs, glucose is synthesized from amino acids. Because there is no storage molecule of amino acids, this process requires the destruction of proteins, primarily from muscle tissue. The presence of adequate glucose basically spares the breakdown of proteins from being used to make glucose needed by the body.

Lipid Metabolism

As blood-glucose levels rise, the use of lipids as an energy source is inhibited. Thus, glucose additionally has a “fat-sparing” effect. This is because an increase in blood glucose stimulates release of the hormone insulin, which tells cells to use glucose (instead of lipids) to make energy. Adequate glucose levels in the blood also prevent the development of ketosis. Ketosis is a metabolic condition resulting from an elevation of ketone bodies in the blood. Ketone bodies are an alternative energy source that cells can use when glucose supply is insufficient, such as during fasting.

Carbohydrates are critical to support life’s most basic function—the production of energy. Without energy none of the other life processes are performed. Although our bodies can synthesize glucose it comes at the cost of protein destruction. As with all nutrients though, carbohydrates are to be consumed in moderation as having too much or too little in the diet may lead to health problems.


Health Consequences and Benefits of High-Carbohydrate Diets

The Food and Nutrition Board of the Institute of Medicine (IOM) defines added sugars as “sugars and syrups that are added to foods during processing or preparation.” The IOM goes on to state, “Major sources of added sugars include soft drinks, sports drinks, cakes, cookies, pies, fruitades, fruit punch, dairy desserts, and candy.” Processed foods, even microwaveable dinners, also contain added sugars. Added sugars do not include sugars that occur naturally in whole foods (such as an apple), but do include natural sugars such as brown sugar, corn syrup, dextrose, fructose, fruit juice concentrates, maple syrup, sucrose, and raw sugar that are then added to create other foods (such as cookies).

Do Low-Carbohydrate Diets Affect Health?

Since the early 1990s, marketers of low-carbohydrate diets have bombarded us with the idea that eating fewer carbohydrates promotes weight loss and that these diets are superior to others in their effects on weight loss and overall health. The most famous of these low-carbohydrate diets is the Atkins diet. Others include the “South Beach” diet, the “Zone” diet, and the “Earth” diet. Despite the claims these diets make, there is little scientific evidence to support that low-carbohydrate diets are significantly better than other diets in promoting long-term weight loss. A study in The Nutritional Journal concluded that all diets, (independent of carbohydrate, fat, and protein content) that incorporated an exercise regimen significantly decreased weight and waist circumference in obese women. [2]

Some studies do provide evidence that in comparison to other diets, low-carbohydrate diets improve insulin levels and other risk factors for Type 2 diabetes and cardiovascular disease. The overall scientific consensus is that consuming fewer calories in a balanced diet will promote health and stimulate weight loss, with significantly better results achieved when combined with regular exercise.

Health Benefits of Whole Grains in the Diet

While excessive consumption of simple carbohydrates is potentially bad for your health, consuming more complex carbohydrates is extremely beneficial to health. There is a wealth of scientific evidence supporting that replacing refined grains with whole grains decreases the risk for obesity, Type 2 diabetes, and cardiovascular disease. Whole grains are great dietary sources of fiber, vitamins, minerals, healthy fats, and a vast amount of beneficial plant chemicals, all of which contribute to the effects of whole grains on health. Eating a high-fiber meal as compared to a low-fiber meal (see Figure “Fiber’s Role in Carbohydrate Digestion and Absorption”) can significantly slow down the absorption process therefore affecting blood glucose levels.

Figure Fiber’s Role in Carbohydrate Digestion and Absorption.

Fiber slows the absorption of foods resulting in a lower spike in blood glucose following a meal. Source: image by Allison Calabrese / CC BY 4.0

Fiber slows the absorption of foods resulting in a lower spike in blood glucose following a meal.

Dietary Sources of Carbohydrates

Carbohydrates are contained in all five food groups: grains, fruits, vegetables, meats, beans (only in some processed meats and beans), and dairy products. Fast-releasing carbohydrates are more prevalent in fruits, fruit juices, and dairy products, while slow-releasing carbohydrates are more plentiful in starchy vegetables, beans, and whole grains. Fast-releasing carbohydrates are also found in large amounts in processed foods, soft drinks, and sweets. On average, a serving of fruits, whole grains, or starches contains 15 grams of carbohydrates. A serving of dairy contains about 12 grams of carbohydrates, and a serving of vegetables contains about 5 grams of carbohydrates. Table “Carbohydrates in Foods (Grams/Serving)” gives the specific amounts of carbohydrates, fiber, and added sugar of various foods.

Table Carbohydrates in Foods (Grams/Serving)

Foods Total Carbohydrates Sugars Fiber Added Sugars
Banana 27 (1 medium) 14.40 3.1 0
Lentils 40 (1 c.) 3.50 16.0 0
Snap beans 8.7 (1 c.) 1.60 4.0 0
Green pepper 5.5 (1 medium) 2.90 2.0 0
Corn tortilla 10.7 (1) 0.20 1.5 0
Bread, wheat bran 17.2 (1 slice) 3.50 1.4 3.4
Bread, rye 15.5 (1 slice) 1.20 1.9 1.0
Bagel (plain) 53 (1 medium) 5.30 2.3 4.8
Brownie 36 (1 square) 20.50 1.2 20.0
Oatmeal cookie 22.3 (1 oz.) 12.00 2.0 7.7
Cornflakes 23 (1 c.) 1.50 0.3 1.5
Pretzels 47 (10 twists) 1.30 1.7 0
Popcorn (homemade) 58 (100 g) 0.50 10.0 0
Skim milk 12 (1 c.) 12.00 0 0
Cream (half and half) 0.65 (1 Tbs.) 0.02 0 0
Cream substitute 1.0 (1 tsp.) 1.00 0 1.0
Cheddar cheese 1.3 (1 slice) 0.50 0 0
Yogurt (with fruit) 32.3 (6 oz.) 32.30 0 19.4
Caesar dressing 2.8 (1 Tbs.) 2.80 0 2.4

Source: (1) National Nutrient Database for Standard Reference. US Department of Agriculture. http://www.nal.usda.gov/fnic/foodcomp/search/. Updated December 7, 2011. Accessed September 17, 2017. (2) Database for the Added Sugars Content of Selected Foods. US Department of Agriculture. http://www.nal.usda.gov/fnic/foodcomp/search/. Published February 2006. Accessed September 27, 2017.

It’s the Whole Nutrient Package

In choosing dietary sources of carbohydrates the best ones are those that are nutrient dense, meaning they contain more essential nutrients per calorie of energy. In general, nutrient-dense carbohydrates are minimally processed and include whole-grain breads and cereals, low-fat dairy products, fruits, vegetables, and beans. In contrast, empty-calorie carbohydrate foods are highly processed and often contain added sugars and fats. Soft drinks, cakes, cookies, and candy are examples of empty-calorie carbohydrates. They are sometimes referred to as ‘bad carbohydrates,’ as they are known to cause health problems when consumed in excess.

There is limited scientific evidence that consuming products with artificial sweeteners decreases weight. In fact, some studies suggest the intense sweetness of these products increases appetite for sweet foods and may lead to increased weight gain. Also, there is very limited evidence that suggests artificial sweeteners lower blood-glucose levels. Additionally, many foods and beverages containing artificial sweeteners and sugar alcohols are still empty-calorie foods (i.e. chewing sugarless gum or drinking diet soda pop) are not going to better your blood-glucose levels or your health.

Health Concerns

The most common side effect of consuming products containing sugar substitutes is gastrointestinal upset, a result of their incomplete digestion.

Since the introduction of sugar substitutes to the food and beverage markets, the public has expressed concern about their safety. The health concerns of sugar substitutes originally stemmed from scientific studies, which were misinterpreted by both scientists and the public.

Table Sweeteners

Sweeteners with trade name Calories Source/origin Consumer recommendations Controversial issues Product uses
  • NutraSweet
  • Equal
4 kcal/g Composed of two amino acids (phenylalanine + aspartic acid) + methanol. Two hundred times sweeter than sucrose. FDA set maximum Acceptable Daily Intakes (ADI):50 mg/kg body weight = 16 12 oz. diet soft drinks for adults. *Cannot be used in products requiring cooking. People with PKU should not consume aspartame. Children have potential to reach ADI if consuming many beverages, desserts, frozen desserts, and gums containing aspartame routinely. Beverages, gelatin desserts, gums, fruit spreads.
  • Sweet ‘n’ Low
0 kcal/g Discovered in 1878. The basic substance is benzoic sulfinide. Three hundred times sweeter than sucrose. ADI: 5 mg/kg body weight.*Can be used in cooking. 1970s, high doses of saccharin associated with bladder cancer in laboratory animals. In 1977, FDA proposed banning saccharin from use in food
  • protest launched by consumer & interest groups
  • warning label listed on products about saccharin and cancer risk in animals until 2001 when studies concluded that it did not cause cancer in humans
General purpose sweetener in all foods and beverages. Sold as Sweet ‘n’ Low in United States; also found in cosmetics and pharmaceutical products.
Acesulfame K
  • Sunnette
  • Sweet One
0 kcal/g Discovered in 1967. Composed of an organic salt, potassium (K). Structure is very similar to saccharin’s. It passes through the body unchanged which means it does not provide energy. Two hundred times sweeter than sucrose. ADI: 15 mg/kg body weight. Body cannot digest it.* Can be used in cooking. Chewing gum, powdered beverage mixes, nondairy creamers, gelatins, puddings, instant teas and coffees.
  • Sugar Twin
0 kcal/g Thirty times sweeter than sucrose. Discovered in 1937. No ADI available. 1949, cyclamate approved by FDA for use. Cyclamate was classified as GRAS (Generally Recognized As Safe) until 1970 when it was removed from GRAS status and banned from use in all food and beverage products within the United States on the basis of one study that indicated it caused bladder cancer in rats. Approval still pending for use in the United States since the ban. Canada and other countries use this type of sweetener. Recommended as a substitute for table sugar for diabetics in 1950s, baked goods.
  • Splenda
1 Splenda packet contains 3.31 calories = 1g First discovered in 1976. Approved for use in 1998 in the United States and in 1991 in Canada. Derived from sucrose in which three of its hydroxyl (OH) groups are replaced by chlorine (Cl−).Six hundred times sweeter than sugar. ADI: 5 mg/kg body weight.*Can be used in cooking. General purpose sweetener, baked goods, beverages, gelatin desserts, frozen dairy desserts, canned fruits, salad dressings, dietary supplements; currently recommended as a replacement for table sugar and additive for diabetics.
  • Stevia
  • Sweet Leaf
N/A Derived from stevia plant found in South America. Stevia rebaudiana leaves. Classified as GRAS. Considered to be a dietary supplement and approved not as an additive, but as a dietary supplement. Used sparingly, stevia may do little harm, but FDA could not approve extensive use of this sweetener due to concerns regarding its effect on reproduction, cancer development, and energy metabolism. Sold in health food stores as a dietary supplement.
  • Sugar
~4 kcal/g Extracted from either sugar beets or sugar cane, which is then purified and crystallized. It is illegal to sell true raw sugar in the United States because when raw it contains dirt and insect parts, as well as other byproducts. Raw sugar products sold in the United States have actually gone through more than half of the same steps in the refining process as table sugar. Over-consumption has been linked to several health effects such as tooth decay or dental caries and contributes to increased risk for chronic diseases. Biscuits, cookies, cakes, pies, candy canes, ice cream, sorbets, and as a food preservative.
Honey 3 kcal/g Made from sucrose. Contains nectar of flowering plants. Made by bees. Sucrose is fructose + glucose; however, honey contains more calories than sucrose because honey is denser. *Considered safe for baking and cooking. Infants under twelve months old should not be given honey because their digestive tracts cannot handle the bacteria found in honey. Older children and adults are immune to these effects. Honey contains some harmful bacteria that can cause fatal food poisoning in infants. Sweeteners in various foods and beverages such as sodas, teas, alcoholic beverages, and baked goods.
  • high fructose corn syrup
Dry form: 4 kcal/g; Liquid form: 3 kcal/g Corn is milled to produce corn starch, then the cornstarch is further processed to yield corn syrup. Controversial because it is found ubiquitously in processed food products, which could lead to overconsumption. Study results are varied regarding its role in chronic disease. Soft drinks, desserts, candies, jellies.
Sugar Alcohols
  • Sorbitol
  • Xylitol
  • Mannitol
2–4 kcal/g. Not calorie free Sugar alcohols. Sorbitol is derived from glucose. Less likely to cause tooth decay than sucrose. Sugar alcohols have a laxative effect. May cause diarrhea and gastrointestinal distress if consumed in large amounts. Provide bulk and sweetness in the following sugar-free items: cookies, jams, jellies, chewing gum, candies, mints, pharmaceutical and oral health products.

Source: Carbohydrates and Personal Diet Choices

  1. Brand-Miller J, et al. Dietary Glycemic Index: Health Implications. J Am Coll Nutr. 2009; 28(4), 446S–49S. https://www.ncbi.nlm.nih.gov/pubmed/20234031. Accessed September 27, 2017.
  2. Kerksick CM, et al. Changes in Weight Loss, Body Composition, and Cardiovascular Disease Risk after Altering Macronutrient Distributions During a Regular Exercise Program in Obese Women. J Nutr. 2010; 9(59). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3000832/. Accessed September 27, 2017.


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Fundamentals of Health and Physical Activity by Kerri Z. Delaney and Leslie Barker is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.