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Nutrition Concepts - Part I

Nutrition Basics

 

Nutritional status affects oral health just as it affects overall general health. When evaluating a person’s oral health, nutritional status must be taken into consideration along with oral hygiene practices. Adequate nutritional status is essential for both the proper development of bones, muscles, nerves, and the dentition as well as for maintaining the health of these structures throughout life.

 

Guidelines for Nutrient Intake

The Dietary Reference Intakes (DRI), which were established in 1997 by the Food and Nutrition Board of the Institute of Medicine, are the most recent guidelines for nutritional health. The DRIs replace the older Recommended Dietary Allowances (RDA), which were established during World War II. The RDAs are still used, but they now are a part of the DRIs. The DRIs are a system of guidelines, which includes RDAs as well as Estimated Average Requirements (EAR), Adequate Intakes (AI), and Tolerable Upper Intake Levels (UL).

Recommended Dietary Allowances represent the amount of nutrients – based on research – that would be sufficient for almost all (97 to 98 percent) of the people in a certain age group. Recommended Dietary Allowances differ according to age groups and sometimes differ for males or females. Most nutrients, including macronutrients, vitamins, and minerals have been assigned RDAs. Recommended Dietary Allowances change as new research warrants.

Estimated Average Requirements, also based on research, represent the amount of nutrients that would be sufficient for half of the people of a particular age group. Recommended Dietary Allowances are based on EARs and are usually about 20% higher.

Adequate Intakes are recommendations for nutrients that that do not have sufficient data available to calculate an EAR. Adequate Intakes are believed to represent sufficient intake of certain nutrients, but the research is less certain than for those nutrients that have an RDA.

Tolerable Upper Intake Levels are assigned to those nutrients, such as fat-soluble vitamins, that could produce toxic effects if taken at high doses. The Tolerable Upper Intake Level is the maximum recommended amount of a nutrient that will not produce toxic side effects.

 

Digestion and Absorption

Digestion refers to the breaking down of large molecules into smaller molecules that can be used by the body for energy and to build and repair tissues. Absorption is the transport of those small molecules from the alimentary canal to the blood or liver.

The food that is consumed must be broken down into nutrients by the digestive tract, and then those nutrients must be absorbed from the digestive tract and carried to body tissues. The digestive tract, also referred to as the alimentary canal, is basically a tube from the mouth to the anus. It consists of the mouth, pharynx, esophagus, stomach, and the small and large intestines. The small intestine comprises the duodenum, where most digestion and absorption take place, as well as the jejunum and the ileum.   The small intestine is lined with villi, which are finger-like projections of tissue containing capillaries. The villi themselves are lined with microvilli, which are microscopic projections that further increase the surface area of the lining of the small intestine. By increasing the surface area in the small intestine, these villi and microvilli facilitate the absorption of nutrients. The large intestine includes the cecum, colon, and rectum. In adults, the alimentary canal is about 30 feet long; roughly 15 feet of that length is taken up by the small intestine.

In addition to the alimentary canal, the digestive system includes the liver, pancreas, and gall bladder. The liver secretes bile, which helps with fat metabolism; the liver also plays a large part in processing the nutrients that are absorbed from the small intestine. The pancreas secretes insulin to lower the amount of sugar in the bloodstream; it also secretes enzymes, which aid digestion in the small intestine. Bile is stored in the gall bladder until the body needs it.

 

Energy Balance

Nutrients are obtained by the body through digestion and absorption of the food that is eaten. These nutrients are ultimately broken down into adenosine triphosphate (ATP) by several complicated reactions. The body cells use ATP as their main source of energy for necessary functions.  Adenosine triphosphate is obtained primarily by the breakdown of glucose, which is the end product of carbohydrate metabolism. Digestion of protein and fat, however, also results in the production of ATP. Fats, or lipids, provide more than twice as many calories per gram as do protein and carbohydrates.  Lipids provide nine calories per gram while carbohydrates and protein provide four calories per gram.

Three components make up total energy expenditure: resting or basal metabolic rate (BMR); the thermic effect – also referred to as diet-induced thermogenesis (DIT), which refers to the energy needed to digest and store food; and energy expended in physical activity.

To maintain weight, the amount of energy taken in (food) should be balanced with the amount of energy expended through activity. This is expressed by “energy in = energy out” (neutral energy balance). Positive energy balance occurs when more energy is taken in than expended and results in weight gain. Negative energy balance is just the opposite; more energy is expended than is taken in, resulting in weight loss.

(Continued from page 1 )

Macronutrients

Macronutrients are those nutrients that the body requires in larger amounts. Carbohydrates, fats (lipids), and protein are macronutrients, as well as water. The three main macronutrients – carbohydrates, protein, and lipids – all contain carbon, hydrogen, and oxygen in their molecules. Protein additionally contains nitrogen, which is one of the characteristics that distinguishes it from the other two nutrients.

 

Carbohydrates

Carbohydrates (also called “saccharides”) include simple carbohydrates or sugars (mono- and disaccharides) and complex carbohydrates or starches (polysaccharides). A disaccharide is formed by the linkage of two monosaccharides. Some common monosaccharides include glucose, fructose, and galactose. Common disaccharides include sucrose (glucose plus fructose), lactose (glucose plus galactose), and maltose (glucose plus glucose). Polysaccharides contain three or more monosaccharides.

Carbohydrates should ideally be the basis of a nutritionally sound diet. It is recommended that 45% to 65% of one’s daily caloric intake be from carbohydrates. Complex carbohydrates are starchy foods such as whole grain breads and cereals, potatoes, rice, quinoa, bulgur wheat, and couscous. Simple carbohydrates are generally those foods that contain simple sugars or added sugars: white bread, cakes, pies, and other sweets. 

Complex carbohydrates are generally more nutritionally sound (popularly referred to as “good carbs”) than simple carbohydrates (“bad carbs”). Complex carbohydrate foods tend to contain vitamins, minerals, and fiber that are lacking in some of the foods that are made up of simple sugars. Some fruits, vegetables, milk and other dairy products contain naturally occurring simple sugars; however, they  contain vitamins and minerals as well.

Digestion of carbohydrates begins in the mouth with the salivary enzyme amylase (also called ptyalin). Digestion continues in the stomach and small intestine. During digestion, polysaccharides are broken down into disaccharides and then monosaccharides. Glucose, a monosaccharide and the form of sugar that the body uses for energy, is the principal end product of carbohydrate digestion. Glucose enters the bloodstream and the glucose that is not needed immediately is stored in the liver as glycogen until it is needed by the body. When the body cells need energy, the stored glycogen is converted back to glucose.

 

Protein

As protein is digested, it is broken down into peptides and then into amino acids, which are the end products of protein digestion. Digestion of protein begins in the stomach with hydrochloric acid and the enzyme pepsin, which break the protein molecules down into peptides. The enzymes trypsin and chymotrypsin continue the digestive process in the small intestine. Trypsin and chymotrypsin, which are produced in the pancreas, break the peptide bonds to produce amino acids and complete the process of digestion.

Amino acids, which are categorized as essential or nonessential, are considered the “building blocks” of proteins and could be thought of as the building blocks of the body. Amino acids are used by the body to repair and replace tissues. Essential amino acids are those amino acids that the body cannot synthesize and, therefore, must be obtained in the diet. Nonessential amino acids can be synthesized by the body and are necessary for the body, but since the body can make these amino acids, they are considered “nonessential.”  A third categorization of amino acids is conditionally essential; these are amino acids that are normally nonessential but, in times of illness or stress, become essential because the body cannot synthesize them at those times. Unlike carbohydrates and fats, the body cannot store proteins or amino acids, so proteins must be taken in regularly to supply the body’s needs.

There are a total of twenty amino acids in nature. Nine of those are considered essential amino acids for adults. These essential amino acids are: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. A healthy diet includes these nine essential amino acids. Foods that are good sources of protein include meats, eggs, dairy products, soy products, dried beans, and nuts and seeds. Whole grain foods are good sources of protein also. Quinoa, a grain that contains all the essential amino acids, is an excellent source.

The terms “complete protein” and “incomplete protein” are older terms that used to refer to whether foods contained all nine essential amino acids (complete proteins) or lacked one or more essential amino acids (incomplete proteins). These terms are no longer used in describing protein foods. “Complete protein” foods were mostly meats and eggs, while “incomplete protein” foods described beans, nuts, and seeds. It used to be thought that people who didn’t eat meat needed to be very careful about combining the right kinds of non-meat protein foods to get the proper amount of protein (a process called “mutual supplementation”). Recent research shows, however, that a varied, well-rounded vegetarian diet will supply the proper amount and kinds of protein for good health. In reality, most Americans get more than enough protein in their diets.

 

Lipids

Lipids, or fats, are very necessary and essential for life, but most Americans’ diets are too high in fat. It is recommended that 20% to no more than 35% of calories should come from fat, and that no more than 10% of calories should be from saturated fat. Fats are broken down during digestion to form fatty acids, which help control inflammation, are part of the membranes of cells, and are necessary for brain development. Fatty acids can be saturated or unsaturated. The presence or absence of double bonds in the fatty acid molecule determines its saturation status. 

A saturated fatty acid molecule contains all single bonds; each bond of each carbon atom is joined to a hydrogen atom. An unsaturated fatty acid molecule contains one or more double bonds because one or more of the hydrogen atoms are missing from the molecule. A monounsaturated fatty acid molecule contains one double bond; a polyunsaturated fatty acid molecule contains more than one double bond. Generally, saturated fats are solids at room temperature, while unsaturated fats tend to be oils and are liquids at room temperature.

Unsaturated fats have more health benefits than saturated fats. It is recommended that saturated fats be limited and emphasis placed on including unsaturated fats in the diet. There are two essential fatty acids that the human body can’t synthesize itself. They are alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid). Both are polyunsaturated fatty acids that must be acquired in the diet. 

There is some digestion of fats in the stomach by the gastric enzyme lipase, but fats are digested mainly in the small intestine by pancreatic lipase. Fats are not soluble in water, so the bile produced by the liver acts as an emulsifier to break up the fat molecules in the small intestine and make them easier to digest. 

Once lipids are digested, they are transported as triglycerides and cholesterol through the blood by lipoproteins. Lipoproteins, as their name suggests, contain both lipids and proteins. The protein in lipoproteins is water-soluble, unlike lipids, and this solubility in water allows lipids to be transported through the blood by the lipoproteins. 

Two well-known lipoproteins are high-density lipoproteins (HDL – “good cholesterol”) and low-density lipoproteins (LDL – “bad cholesterol”). It’s believed that LDLs carry cholesterol and triglycerides to the cells, where they can cause damage by contributing to plaque build-up in blood vessels. On the other hand, HDLs are believed to transport cholesterol and triglycerides from the cells and blood vessels back to the liver, where they leave the body. Dietary intake of saturated fat appears to be a risk factor for high levels of LDLs in the blood.

 

Water and Electrolytes

Water has been called the most important nutrient. It is estimated that the human body is about 60% water. Water lubricates the body’s joints, regulates body temperature, helps with carrying nutrients and oxygen to cells, and protects the organs. It’s important to get enough water and fluids, and it’s also important to have the correct balance between water or fluids and electrolytes.

Electrolytes are ions or charged minerals; the most important electrolytes in the body are sodium, potassium, and calcium. Electrolytes within and between body cells keep cells and muscles functioning properly and maintain the chemistry of the blood. Too much or too little intracellular or extracellular fluid can affect electrolyte balance with serious consequences.

The body keeps the electrolytes and water in balance through osmosis. Osmosis is the movement of water (the solvent) through a semi-permeable membrane (the cell wall) from an area with less concentration of electrolytes (the solute) to an area of higher concentration of electrolytes. This movement of water tends to keep the solute/solvent concentrations equal on both sides of the membrane.  

 

Micronutrients

The micronutrients include vitamins and minerals that are needed in smaller amounts than the macronutrients. Although needed in much smaller amounts, micronutrients are essential for proper body functions, growth, and development. Their deficiencies can produce severe effects. Deficiency of iron, a micronutrient, is the most common deficiency and a widespread public health problem in both developing and developed countries. Sufficient micronutrients can be obtained with a well-balanced diet rich in vegetables and fruits.

 

Related Reading:

  1. http://www.ncbi.nlm.nih.gov/books/NBK26882/
  2. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Carbohydrates.html
  3. http://digestive.niddk.nih.gov/ddiseases/pubs/yrdd/
  4. http://fnic.nal.usda.gov/dietary-guidance/dietary-reference-intakes
  5. http://www.nutrition.gov/
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