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.
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
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
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.
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
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.
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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 (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
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.
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.
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
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
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.
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.