Adipose tissue, or body fat, has several roles:
- it provides a concentrated energy source
- it protects internal organs
- it maintains body temperature
Excess dietary carbohydrates and protein are converted to fat and stored in adipose tissue. Fatty acids can be used as an energy source by all cells except red blood cells and central nervous system cells. People have been known to survive total starvation for 30 to 40 days with only water to drink.
Protection of Organs
Fatty tissue surrounds vital organs and provides a cushion, protecting them from traumatic injury and shock.
The subcutaneous layer of fat functions as an insulator that preserves body heat and maintains body temperature. Excessive layers of fat can also deter heat loss during hot weather.
DIETARY FATS AND DENTAL HEALTH
Dietary fats are essential for oral health because they are
incorporated into the tooth structure. There is some evidence
from epidemiological and laboratory studies that fats may
have a cariostatic effect. Eskimos, whose diet may contain
80% fat from animal and seafood sources, have a very low
incidence of dental caries. Another factor that may affect
caries rate in Eskimos is a low carbohydrate intake. Dietary
fats probably have local rather than systemic influence
because fats added to foods protect the teeth more than foods
naturally high in fat. Precisely how fats reduce the caries
rate is unknown; however, several hypotheses have been
explored, as follows:
1. Some fatty acids, specifically oleic acid, are growth
factors for lactic acid bacteria, whereas streptococcal
organisms are inhibited by lauric acid (Lauricidin).
2. Long-chain fatty acids may reduce dissolution of
hydroxyapatite by acids.
3. Oral food retention is reduced by increasing fat intake.
4. Fats may lubricate the tooth surface and prevent penetra-
tion of acid to the enamel (i.e., the “greased” tooth is
impervious to acid, protecting caries-susceptible areas).
5. Fats may produce a film on the food particles and prevent
partial digestion of food particles in the mouth.
6.Dietary fat delays gastric emptying, enhancing fluoride
absorption and increasing tissue fluoride concentration.
Bacterial inflammation and the systemic immune response
are believed to play a central role in the initiation and propa-
gation of atherosclerosis. When bacteria are allowed to
grow rampantly in the mouth, inflammation may occur
throughout the body, including in plaque forming on the
lining of the arteries. This inflammation may serve as a base
for development of arterial atherosclerotic plaques. Research
is ongoing to determine how these conditions are related,
but some researchers believe gingivitis is a risk factor for
coronary artery disease.
A certain amount of fat is needed to provide adequate
amounts of fat-soluble vitamins and EFAs. The acceptable
macronutrient distribution range (AMDR) for fat is esti-
mated to be 20% to 35% of energy intake for adults.
The lower limit for fat intake was established to mini-
mize the increase in blood triglyceride levels and decreases
in HDL cholesterol levels that occur with higher intakes of
carbohydrates. The upper limit of 35% kcal from fat was
based on information indicating higher fat intake is associ-
ated with a greater intake of energy and SFA, which may be
detrimental to health.
Between 1971-2000, the percentage of kilocalories from
total fat decreased to about 33%. This decrease was because
of an increase in total kilocalories consumed; actually, the
total fat consumed increased. The World Health Organiza-
tion (WHO) recommends a range of 15% to 30% of total
kilocalories from fats.
The dietary reference intake (DRI) also recommends SFA
and trans fatty acid be as low as possible while consuming
a diet providing an adequate intake of all essential nutrients.
The percentage of saturated fat in a 2000-kcal diet is cur-
rently about 11%.
The adequate intake (AI) established for linoleic acid is
17 g per day for men and 12 g per day for women 19 to 50
years old, and 14 g per day for men and 11 g per day for
women older than 51 years. When dietary intake is high,
liloleic acid is stored in the tissues.
Of the food groups, animal products contribute the largest pro-
portion of fat, although their share has been declining. The
most important sources of saturated fats are the meat and
milk groups; cocoa butter and coconut and palm oils also
are high in saturated fat. SFAs are found in animal fats,
butter fat, coconut oil, cocoa butter, coffee creamers and
fully hydrogenated vegetable oils.
Animal products and canola and olive oils supply approximately
50% of MUFAs. Oleic acid, the most prevalent MUFA, is
present in most fats, oils, nuts, seeds, and avocados.
PUFAs from the n-6 series are derived from land plants,
especially foods from the grain group, and additional fats
and oils. Linoleic acid is the most prevalent PUFA in the
food supply. Safflower, soybean, and corn oils provide the
most linoleic acid; food sources are nuts and seeds. Approxi-
mately 80% of all vegetable oil consumed in the United
States is soybean oil. CLAs are natural components of
beef, lamb, and dairy products. Linolenic acid is present in
flaxseed, canola, and soybean oils; soybeans; walnuts; flax-
seed; and wheat germ. The long-chain n-3 fatty acids (EPA
and doxosahexaenoic acid [DHA]) are provided from
seafood, including fatty fish such as mackerel, Atlantic
salmon, and albacore tuna (presented in order of highest to
lowest), and fish oils. These foods are also low in saturated
fat. The American Heart Association (AHA) Guidelines rec-
ommend consumption of fish at least two times a week.
Approximately 52% of the soybean oil used in the United
States was partially hydrogenated in 2003-2004. Trans fats
are present in shortening; stick margarine; deep-fried fast
foods such as French fries and commercially baked pastries
and desserts such as doughnuts, cookies, and crackers.
Only animal products contain cholesterol;
it is not found in egg whites or plant foods (i.e., vegetable
oils). It is highest in egg yolks, liver, and other organ