Topic: Nutrition

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Energy-Providing Nutrients: Carbohydrate, Fat and Protein

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Nutrients are substances the body needs for life, maintenance, growth, repair, maintenance and energy. There are six basic types of nutrients, three of which provide the body with the energy while the other three do not. The three energy-providing nutrients are carbohydrates, fats, and proteins. There will be more information about the non-energy-providing nutrients during week five of the course.

Carbohydrates

Many individuals, when asked to provide examples of carbohydrate-rich foods, may cite bread, cereal, rice and pasta among their lists. Carbohydrates, however, are found in many other foods, including fruits and vegetables. Carbohydrates are the body's main source of energy, so a healthy person's diet should contain enough of the fuel to not only make the body's muscles work properly during activity, but to keep the brain optimally functional. The amounts of energy in carbohydrates, fats, and proteins are measured in calories. There are approximately four (4) calories per gram of carbohydrate (the "kilocalorie" is the actual measure, but the abbreviated term "calorie" is usually what the public sees).

The image to the right is in the public domain, via Wikimedia Commons,

Carbohydrates are most frequently categorized by their structure: simple and complex. Three types of simple carbohydrates include monosaccharides, disaccharides, and oligosaccharides. Monosaccharides are single-unit carbohydrates and include glucose (the body's "main," or usable, form of carbohydrate), fructose (found in fruits and honey), and galactose (not found free in nature). Disaccharides consist of two saccharide units and include sucrose (table sugar, which is one glucose unit and one fructose unit), lactose (one glucose unit and one galactose unit) and maltose (two glucose units). Disaccharides must be broken down into two monosaccharides to be absorbed by the body. Oligosaccharides will contain more than two sugar units, but are still considered simple in structure.

Complex carbohydrates are also known as polysaccharides, which means they consist of numerous sugar units, usually with more complicate structures. Examples of complex carbohydrates include starch, glycogen, and cellulose. Starch is the main form in which plants store energy. When a person consumes starch, the energy is transferred to the person who eats the food. "Starchy" foods include potatoes, rice, wheat, corn, and oats, which can be processed into items such as breads, crackers, cereal, pasta and pancakes. When a person consumes carbohydrates, some of the cells may use it, but much of the carbohydrate is stored as "glycogen" in the liver and muscles. Although cellulose can be considered a complex carbohydrate because it is found in fruits, vegetables and seed coverings, it has no energy value because it cannot be digested by the body. Cellulose is also known as fiber. While most registered dieticians sing the praises of a diet containing adequate amounts of complex carbohydrates, excessive carbohydrate consumption may provide more calories than a person needs, resulting in fat deposition. 

Health-related resources typically recommend a diet in which the carbohydrate content equals 45-65% of the total caloric intake. This is a general number, applied to a healthy individual with an average diet. Different percentages or absolute amounts will change across special populations. One of the main reasons dieticians and other nutrition experts recommend ample carbohydrate consumption is because foods high in complex carbohydrates are also usually higher in vitamins and minerals (two of the three non-energy containing nutrients).

Carbohydrates have received a lot of public attention, with some organizations citing the nutrient as being over-consumed, particularly in America. Many carbohydrate-based foods tend to be considered tasty and subsequently consumed in fairly large quantities. As a result, too many consumed calories and unused glucose from the carbohydrate consumption can result in weight gain and fat deposition. Realistically, then, much of America may have less of a carbohydrate problem than a calorie balance problem. That is, Americans are eating too much food in general while failing to exercise enough.

Low-carbohydrate diets, like other diet plans, incorporate a reduced caloric intake as part of the overall program. When a person consumes fewer calories than usual, over time he or she may lose weight, particularly if the diet program is paired with a regular exercise regimen. Aside from weight loss, these low-carbohydrate diets do seem to help some people improve other cardiovascular disease risk factors, as well, though current evidence is more short-term in nature. Travel to the Harvard School of Public Health to read more information on carbohydrates (R).

Given the caloric intake challenge many Americans share, some people may find their bodies react differently to various carbohydrate forms. The Glycemic Index (GI) scale is a numerical scale used to rank carbohydrates based on how quickly they can raise blood sugar. Foods with high glycemic index values (70+) are thought to result in greater, more rapid increases in blood sugar than foods with lower glycemic index values (55 or less). Since some people may be sensitive to marked blood sugar fluctuations typical of high GI foods, they may wish to consume more foods with lower GI values. The concept is especially interesting because GI values of complex carbohydrates--considered to be generally preferred over simple carbohydrates--can vary considerably. A potato, for example, has a very high GI value while brown rice has a low GI value, even though both foods are considered complex carbohydrates. To read more about the GI, travel to the Glycemic Index website (O).

The GI scale is used to compare the same amount of carbohydrate across different foods. Of course, foods contain differing amounts of carbohydrate. For example, a food may have a high GI value, but there may not be much actual carbohydrate in the food, which could make a difference in a person's reaction. The Glycemic Load (GL) is a numerical tool used to account for the amount of carbohydrate in a food. Higher GL values (20+) means a food has more carbohydrate than  a food with a lower GL value (10 or below). Freelance medical writer David Mendosa received permission from Professor Jennie Brand-Miller, University of Sydney, to publish a list of 750 foods with their respective GI and GL values on his website (O). He also provides a much shorter list on his website (O).

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Educational Enrichment

Wheat Foods Council

Ethnic Vegetables (pdf, University of Kentucky)

Carbohydrates: The Bottom Line (Harvard School of Public Health)

U.S. Per Capita Food Supply Trends (pdf file)

Food & Nutrition - Health Canada

Complex Carbohydrate Research Center

Whistler Center for Carbohydrate Research

National Agricultural Library Catalog (AGRICOLA)

USDA Healthy Meals Resource System

USDA National Nutrient Database

USDA Dietary Reference Intakes: Macronutrients

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Proteins

The above image of chickpeas is in the public domain, obtained via Wikimedia Commons

Protein is the second most abundant source in the body next to water. Protein contains four calories per gram and is found in meat, fish, eggs, milk, cheese, beans, and whole grains. The basic unit of a protein is the amino acid. There are approximately 20 different amino acids in the body required for human function. Of these 20, 11 of them are already produced by the body and hence termed nonessential amino acids. Nine of these 20 must be obtained from food and hence called "essential" amino acids. Foods containing all nine required amino acids in them are termed complete proteins, such as meat, fish, poultry, eggs, and milk. Some plant foods are complete protein sources, but many are incomplete proteins, lacking one or more of the required nine amino acids. This fact becomes important when considering a vegetarian diet.

 

All vegetarians refrain from eating meat and fish products. Some of them, however consume milk and egg products (ovolactovegetarians), some of them only consume milk products (lactovegetarians), while others consume only plant products (vegans). While all vegetarians can easily meet their protein needs, vegans should vary their diets to ensure adequate protein intake. For more information, travel to the American Dietetic Association's stance on vegetarianism. (O)

Although some individuals need to be concerned about inadequate protein intake, excessive protein intake is not a good idea, either. The body can either store the excess protein as fat or excrete it. When protein is broken down for excretion, one of the bi-products is ammonia. When the body processes the ammonia into a less-toxic substance, one of the products is water, also excreted with the protein. In chronic and extreme circumstances, this can lead to dehydration and kidney complications. Excessive animal protein intake also may be related to bone loss. Enerex Botanicals provides information on Soy Protein Products (O-pdf file).

There are approximately four (4) calories per gram of protein. Many health-related sources will recommend a diet in which the protein content equals 10-15% of the total caloric intake. Again, this number will change across populations.

Many like to obtain their protein through fish consumption. In 2004 the FDA and EPA released advisories on fish consumption, linking specific conditions with methylmercury poisoning (O). There are advisories against consuming high-mercury content fish (shark, swordfish), recommendations to limit intake of other fish containing mercury, and a third recommendation about fish caught by friends and family in local waters. Travel to the FDA website to see a list of mercury levels present in a variety of fish and shellfish (O).

The Harvard School of Public offers information on protein and weight control (O).

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Educational Enrichment

The Journal of Renal Nutrition

List of the 20 amino acids, Institute of Chemistry, Berlin

Protein in the Vegan Diet, Vegetarian Resource Group

European Food Information Council

Dietary Reference Intakes: Macronutrients

Protein in the Vegan Diet (Reed Mangels, PhD, RD, via Vegetarian Resource Group)

Protein: The Bottom Line (Harvard School of Public Health)

Nutrition for Everyone: Protein (Centers for Disease Control)

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Fats

 

Everyone needs at least a little fat, as evident in every cell membrane, which contains a layer of fat. Fat is used to insulate, to protect the body's organs, to carry the fat-soluble vitamins A, D, E, and K, and to provide an extra energy source. Examples of food sources containing fat include meat products, milk, cheese, nuts, avocados, and processed foods. There are approximately nine calories per gram of fat. Triglycerides and cholesterol are examples of fats. Triglycerides are the form of fat most commonly consumed. Triglycerides consist of a glycerol molecule and three fatty acids. The fatty acids will vary in their chemical length as well as their saturation.

The above image is in the public domain, retrieved from Wikimedia Commons, originally available through USDA


The saturation of a fatty acid refers to its chemical structure. A saturated fat has no double bonds between carbon atoms, but instead features hydrogen saturation around each carbon atom. Examples of saturated fatty acids include those fats that are solid at room temperature, such as lard and butter, and also tropical oils, such as coconut and palm oils. Saturated fats tend to increase the liver's production of cholesterol, and diets high in saturated fats tend to increase one's risk for cardiovascular disease. To see the chemical structures of fatty acids at different levels of saturation, travel to a University of California biology class web page (O).

Polyunsaturated fatty acids feature one or more multiple bonds between carbon atoms. There are two general types of unsaturated fatty acids: monounsaturated, containing one multiple bond and polyunsaturated, containing more than one multiple bond. Unsaturated fats are generally liquid at room temperature and are considered a more healthful choice than saturated fats. Some unsaturated fats, however, are hydrogenated (hydrogen atoms are added) to improve texture or spreadability, which decreases their benefits over saturated fats. Good sources of monounsaturated fats include some nuts and avocadoes, as well as olive, canola and tea seed oil. Omega-3 and omega-6 fatty acids are two examples of polyunsaturated fats. The BBC has an online article, Omega Wave, regarding the unexpected "brainpower" benefits provided by omega fatty acids (O).

There are approximately nine (9) calories per gram of fat. Most health-related sources will recommend a diet in which the fat content equals 25-30% of the total caloric intake. This number will vary for individuals with special needs, such as people with cardiovascular disease.

In 2001, the National Heart, Lung and Blood Institute's National Cholesterol Education Program (NCEP) issued new guidelines for fat and cholesterol consumption. An historical conference in June 2001, Advances in Cholesterol Management, was held in Washington, DC in part to publicly announce these guidelines. If you have Real Player, there are selected webcasts available from the conference (O). In 2004 there was a follow-up to the 2001 report (O-NHLBI), a summary of which can be read at JournalWatch (O). The National Heart, Lung and Blood Institute, along with the National Institutes of Health, issued the third report of Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (O)

Interestingly, while many physicians and dieticians recommend a low-fat diet for weight loss and general health, there are also many professionals who believe a low-fat diet does not assist in weight control. There is research backing up both sides, so consumers need to educate themselves, thinking critically when reading nutrition information and news.

Students interested in supplementing knowledge with more information on fat and cholesterol, should travel to the Harvard School of Public Health, scrolling down the screen to read about "Cholesterol in Food," "Dietary Fats and Heart Disease: Beyond the 30% Recommendation," "Dietary Fats and Cancer," "Dietary Fat and Obesity," and "The Bottom Line: Recommendations for Fat Intake" (O).

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Fat Substitutes

Many Americans recognize too much fat can be harmful to one's health. Fat, containing over double the calories per gram as either carbohydrate or protein, can increase risk for obesity. A high-fat diet can also set a person up for high levels of low density lipoproteins (LDL's), tagged in the media as "the 'bad' cholesterol." Because fats have been an area of concern within the public, foods containing fat substitutes have been widely researched, marketed and used. 

As the American Heart Association (O) describes, fat substitutes are agents placed in food to mimic the texture and flavor of fat. These fat substitutes may be carbohydrate-based, protein-based or even fat-based, but their general commonality is a lower calorie value.

The first fat replacer, a protein-based agent, was developed by the Nutrasweet Company and approved by the Food and Drug Administration in 1990. Simplesse, made from proteins found in egg white and milk, is typically used in dairy-based foods such as ice cream or sour cream.  In the 1990's, the FDA approved the use of olestra, a fat-based fat substitute present in some snack foods. Olestra, also known as Olean, is not digested well by the body. Because the body prevents olestra absorption, consumers can "enjoy" eating snack chips without the fat. Unfortunately, because olestra is indigestible, it passes through the body and, as a result, can cause stomach cramping and loose stools among some individuals. Furthermore, olestra can prevent the body's absorption of Vitamins A, D, E and K (fat-soluble vitamins). As an answer to this issue, olestra makers have infused some of their products with added fat-soluble vitamins, though skeptics may wonder whether there are long-term effects of olestra's blockage of fat absorption. Learn about what the Center for Science in the Public Interest (O) and the Nutrition Committee of the American Heart Association (O) have to say about olestra. Kennesaw State University posts some easy-to-read information about olestra and its interaction with fat-soluble vitamins and medications (O).

Another substance which can be used as a fat substitute is Z-Trim (O). Made from hulls or bran from oats, corn and other insoluble fiber sources, Z-Trim is marketed as a more natural, less disruptive fat substitute. Another fat-substitute is Oatrim, developed by Agricultural Research Service (O).

What About Trans Fats? Is Butter Better?

For years butter has been marketed as a generally unhealthy food due to its high content of saturated fat. Foods containing higher levels of saturated fat are linked to higher LDL levels in the blood than foods containing higher levels of unsaturated fat, particularly monounsaturated fat. As explained in Week 4, "saturation" of a fat refers to the fat's chemical structure. Within the saturated fat, a carbon atom will be surrounded--or saturated--with hydrogen atoms. In an unsaturated fat, the carbon atom is not surrounded by hydrogen atoms. Many margarines are put through a hydrogenation process in order to improve spreadability and enhance shelf life, but in the process this hydrogenation creates a trans fat. The man-made hydrogenation process makes the unsaturated fat more saturated in nature, perhaps increasing the risk for higher blood LDL levels and concomitant cardiovascular disease risk.  Since many resources cite a link between cancer and trans fat consumption, many health advocates are currently recommending consumers choose butter over a trans fat-laden margarine.

 Softer, tub-based margarines tend to have less hydrogenation--and therefore fewer trans fatty acids--than harder cube-based margarines. A canola margarine, for example, typically is low in saturated and trans fat contents. Ultimately, maintaining a diet low in overall fat and high in vitamins and minerals can decrease the need to worry about making such a choice. To assist the general public in making healthier fat consumption decisions, the American Heart Association provides some "smart substitutions (O)," including recipe and snacking substitutions.

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Educational Enrichment

Dr. Nick Hibbeln, National Institutes of Health, describes omega-3 and omega-6 fatty acid consumption in the United States in this vimeo video clip

Omega-3 Learning for Health & Medicine (University of Connecticut)

Dietary Guidelines for Americans 2005 (USDA)

American Journal of Clinical Nutrition's position stand on trans fatty acids.

A Prospective Study on Trans Fatty Acids in Erythrocytes and Risk for Coronary Heart Disease (AHA, April, 2007)

American Heart Association weighs in on fat substitutes

Did olestra make you sick? You can report your story to the Center for Science in the Public Interest

Center for Food Safety and Applied Nutrition information on trans fat labeling

Know Your Fats (American Heart Association)

Background on Dietary Fats and Fat Replacers (Food Insight)

Fats and Cholesterol: The Bottom Line (Harvard School of Public Health)

Omega-3 and Omega-6 Fatty Acids (Franzen-Castle and Ritter-Gooder via University of Nebraska's NebGuide, pdf)

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