Functions of Lipids, Carbohydrates, Nucleic Acids & Proteins

Carbohydrates, proteins and lipids make up the three macronutrients that provide energy for your body. Carbohydrates and proteins provide 4 calories per gram, and lipids provide 9 calories per gram. Nucleic acids carry genetic information within cells that help maintain proper cell division, protein synthesis, and fetal development.

Macronutrients Types
Lipids come in different types, including waxes, steroid hormones, cholesterol, phospholipids and triglycerides. Although they have different structures, all lipids contain either one or more long, fatty acid chains that are made up of strong carbon and hydrogen bonds--except cholesterol.

Simple carbohydrates are made up of one sugar molecule, while complex carbohydrates are made up of more than one sugar molecule. Dietary fiber and starches are two main types of complex carbohydrates that your body uses.

Proteins are made up of 20 different types of amino acids, including eight essential and 12 non-essential amino acids. Your body can synthesize non-essential amino acids, but not the essential ones. Essential amino acids must be obtained from food.

Your body uses carbohydrates as the main source of energy for all cellular functions, particularly in your brain and central nervous system. These include simple and complex sugars derived from fruits, grains and starchy vegetables. Although your body cannot process dietary fibers for energy, they provide bulk in your feces to avoid constipation and satiety without additional calories. Fibers also absorb cholesterol and slow glucose absorption.

Dietitian Ellen Coleman recommends that 50 to 60 percent of your diet should be based on carbohydrates. Ninety percent of the carbohydrates should be complex carbohydrates.

Proteins provide the basic structures for every organ system in your body, including muscles, bones, hair, skin, cartilages and circulatory systems. They also provide structures for enzymes which are organic compounds that serve as catalysts for many chemical reactions in your body, including converting food into energy. According to former nutrition professor Gordon Wardlaw of Ohio State University, some proteins, such as antibodies and insulin, perform cell signaling that allows cells in different parts of your body to communicate with each other. This is important for releasing hormones and fighting infections.

Triglycerides provide you with energy during aerobic metabolism and are stored in your adipose (fat) tissues beneath your skin, within skeletal muscles and around your organs. Cholesterol provides structure for steroid hormones, such as estrogen and androgen, cell membranes, and bile acids. Within cells, it regulates fluid balance within the cell and its external fluid environment. Fats in your body cushion your organs from shock and blunt trauma and stores energy for future use.

Nucleic Acids
Deoxyribonucleic acid (DNA) contains genetic instructions that your cells use to develop and carry out biological functions. It stores information to construct proteins and other organic molecules to develop an organism. Ribonucleic acid (RNA) regulates what types of genes are expressed in you. It carries information from DNA to your cells' ribosomes which are the sites for protein synthesis.

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Nucleic Acids In Foods
Most commonly found as deoxyribonucleic acid or DNA, and ribonucleic acid or RNA, nucleic acids are found in all foods derived from living things. RNA consumption has been found beneficial to human health by the Gordon Research Institute, as RNA may help to slow the aging process or the progression of degenerative diseases. Increased consumption of nucleic acids is helpful in repairing liver damage. However, high intake of nucleic acid has been implicated as a possible cause of gout. Nucleic acids can be found in vegetarian and non-vegetarian foodstuffs.

Protein sources including meat and nuts have a relatively high concentration of nucleic acids. Red meats typically have a nucleic acid content of 0.5 percent, with beef being considered a good source of nucleic acid. Sardines have the highest RNA concentration, with approximately 1.5 percent of a sardine's weight being made up of RNA. Beans are a good source of nucleic acid for those who do not eat meat.

Certain carbohydrate-rich foods are also good sources of nucleic acids. Cereals and pulses have a high RNA component while being rich in carbohydrates. Other carbohydrate-containing sources of nucleic acid include mushrooms of the button, oyster and flat varieties, cauliflower, leek, spinach, broccoli and Chinese cabbage. Yeast--which in hydrolysed or autolysed forms is often found as an additive in instant vegetarian meals--increases a food's nucleic acid content.

All dairy products contain nucleic acid; RNA is found in milk, yogurt and eggs. However, the concentration of nucleic acid is relatively less in dairy products than in meat and fish-based proteins. Eggs have about twice the nucleic acid content of cottage cheese or yogurt, when like weights of food are compared.

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Functions of Lipids in Organisms

Fats, triglycerides, waxes, cholesterol and fat-soluble vitamins comprise a broad class of compounds called lipids. Lipids perform many essential functions in the body. The Institute of Medicine recommends a daily intake of lipids between 25 and 30 percent of total caloric intake.

Energy Storage
Excess lipids are stored as triglycerides in fat tissue, also called adipose. The breakdown of triglycerides provides twice as much energy as the breakdown of carbohydrates or proteins. The Virtual Chembook notes that the energy stored in fat in an average person can supply enough energy without food for greater than 30 days when water intake is sufficient.

Biological Membranes
Biological membranes are composed of two layers of lipids (phospholipid bilayers) which surround all cells in the body and are especially important for central nervous system function. Lipids in membranes play a role in regulating the transport of molecules between cells and their environment.

The Virtual Chembook notes that lipids provide structural support and acts as a cushion to protect vital organs such as the heart, liver and kidneys. Fat tissue also insulates the body, preventing heat loss and extreme changes in body temperature in different environments.

Hormone Synthesis
Many hormones are synthesized from lipids, incuding estrogen, progesterone, testosterone, cortisol, aldosterone and calcitriol.

Chemical Messenger Synthesis
In addition to hormones, lipids synthesize other molecules like eicosanoids and prostaglandins that act as chemical messengers in the body. These molecules have several functions including regulating muscle contraction, hormone synthesis, inflammatory responses, cell growth and central nervous system function.

Bile Acid Synthesis
Bile acids are synthesized in the liver from cholesterol and are stored in the gall bladder. Bile acids aid in the digestion of dietary fats.

Fat-Soluble Vitamins
Fat-soluble vitamins, including A, D, E and K aid in many essential functions in the body including vision, blood coagulation, ameliorating oxidative stress, immune system function and bone metabolism.

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Carbohydrates and Maintaining Good Health

Carbohydrates are necessary for life and make up the base of a healthy diet. However, choosing nutritious carbs instead of refined products with little nutritional value is essential to maintaining good health. Too many unhealthy carbs can actually damage health and may lead to diseases instead of providing the benefits that healthy carbohydrates do.

The healthiest carbs can be found in whole grain products, legumes, fruits and vegetables. Milk and other dairy products also contain carbs. Refined grain products, sugars and products containing added sugars are other sources of carbs, but these are generally unhealthier options. The best carb choices contain high levels of fiber, nutrients and antioxidants.

In the body, carbs fuel all physical activity and energy expenditure. After consuming carbs, the body breaks down most of their components into sugars, which can then cross into the bloodstream. Blood carries these sugars throughout the body to the cells, and insulin produced by the pancreas helps shuttle the sugars to where they are needed. Without carbs, the body begins to break down muscle mass and fat stores to get the energy it needs.

Fiber is the only carb that does not get broken down into sugars. Instead, fiber passes through the digestive tract intact. One type of fiber, called soluble fiber, dissolves in water in the intestines and lowers LDL cholesterol by carrying fatty substances out of the body. Insoluble fiber, which doesn't dissolve in water, promotes healthy digestion, prevents constipation and may lower the risk of colorectal cancer.

Consuming too many refined or simple carbohydrates, such as white bread, sugary sodas and white rice, can lead to health problems. These kinds of carbs raise blood sugar rapidly, which increases the risk of diabetes and causes problems for individuals who already have diabetes or prediabetes. Sugars and refined carbs can also contribute to weight gain and may raise the risk of cardiovascular disease and cancer.

The Dietary Guidelines for Americans 2005 recommends consuming six or more servings of grain-based carbs, with at least half of these chosen from whole grain sources. Another five servings of carbs should come from fruits and vegetables. Between 40 to 60 percent of your total caloric intake should be from carbs. According to the CDC, you should aim for about 14 g of fiber for every 1,000 calories you consume.

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Protein in Foods

A protein-enriched diet can help increase satiation and assist with weight loss and weight management. Increasing your intake of lean proteins while still maintaining an adequate intake of carbohydrates and monounsaturated fats is a sound way to approach a healthy diet. Although organizations like the American Heart Association still warn against high-protein diets because of the potential over-consumption of saturated fat, studies continue to suggest that protein enriched diets do not adversely affect health, according to an article in the July, 2005 issue of "The American Journal of Clinical Nutrition."

A protein-enriched diet involves increasing the amount of the macronutrient, protein, in your daily diet. The United States Department of Agriculture recommends a person make anywhere from 15 to 25 percent of your daily calories come from protein sources. The Institute of Medicine has raised its protein recommendation range to as much as 35 percent of daily calories, noting that the higher amount yields no negative health effects. A person following a protein-enriched diet strives to include extra amounts of complete proteins--those that contain all the amino acids that the human body must consume from outside sources--like soy, meat, fish, poultry, eggs and dairy. Protein enhancement might be sought to bring protein intake levels up to USDA guidelines, or to exceed those guidelines in an effort to lose weight or enhance muscle growth.

Protein is an essential macronutrient that helps with the development of lean muscle mass and is an important component in the skin, hair, nails and internal organs. Ensuring adequate protein intake is essential for good health, growth and development. The elderly and children often benefit from protein-enriched diets as they tend to eat less balanced diets and are vulnerable to the effects of nutritional deficiencies. Vegetarians may also need to seek out specific complete protein sources because, without proper food combining, they may fail to consume adequate complete proteins. Athletes--especially bodybuilders--seek protein-enriched diets to support their strength-training regimens. Many dieters also follow high protein, low carbohydrate plans to help them drop weight quickly.

Arne Astrup of the Department of Human Nutrition at the Royal Veterinary and Agricultural University in Denmark indicated in an editorial in a 2005 edition of the "American Journal of Clinical Nutrition" that protein has great potential as a weight loss tool. People who follow high protein diets report higher levels of fullness and lower levels of hunger, even while restricting their caloric intake. Protein-enriched diets provide for more even insulin levels, reducing spikes in blood sugar and extreme cravings. The Harvard School of Public Health acknowledges that a greater intake of protein also slightly raises the metabolism.

No studies have confirmed the safety of following a high-protein diet in the long term. Many sources of protein contain saturated fat, especially meats and full-fat dairy. Limiting your consumption of saturated fat to less than 7 percent of total daily fat calories is recommended by the American Heart Association and the USDA to protect yourself from cardiovascular disease and some cancers. Be wary of protein drinks and bars that contain extra carbohydrates, sugars and unregulated supplements. Seek out natural protein sources to enrich your diet--such as pure whey or soy powders.

A protein-enriched diet should not push out other important macronutrients. Healthy carbohydrates, like fruits, vegetables and whole grains provide antioxidants and vitamins as well as energy for the body. Choose low-fat sources of protein, but augment them with heart healthy monounsaturated fats.

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Molecule Fact Table