PART B: INTRODUCTION
Since first published in 1980, the Dietary Guidelines
for Americans have provided science-based advice to promote
health and to reduce risk for major chronic diseases through
diet and physical activity. The Dietary Guidelines
is targeted to the general public over age 2 years who are
living in the United States. Because of its focus on health
promotion and risk reduction, the Dietary Guidelines
form the basis of Federal food, nutrition education, and information
programs. By law (Public Law 101-445, Title III, 7U.S.C. 5301
et seq., the most recent edition of the Dietary Guidelines
is reviewed by a committee of experts, updated if necessary,
and published every 5 years. This report presents the recommendations
of the 2005 Dietary Guidelines Advisory Committee (DGAC) to
the Secretaries of the Department of Health and Human Services
(HHS) and the Department of Agriculture (USDA). The legislation
also requires that the Secretaries of HHS and USDA review
all Federal dietary guidance-related publications for the
general public for consistency with the Dietary Guidelines
for Americans.
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THE ROLE OF DIET AND PHYSICAL ACTIVITY IN HEALTH PROMOTION
Poor diet and a sedentary lifestyle contribute to about 400,000
of the 2 million or so annual deaths in the United States.
Specific diseases and conditions linked to poor diet include
cardiovascular disease (CVD), hypertension, dyslipidemia,
type 2 diabetes, overweight and obesity, osteoporosis, constipation,
diverticular disease, iron deficiency anemia, oral disease,
and malnutrition (HHS, 1996; U.S. Preventive Services Task
Force, 1996). Lack of physical activity has been associated
with cardiovascular disease, hypertension, overweight and
obesity, osteoporosis, diabetes, and certain cancers (World
Health Assembly, 2004). Furthermore, muscle strengthening
and balance training can reduce falls and increase functional
status among older adults (World Health Assembly, 2004). Together
with physical activity, a high-quality diet that does not
provide excess calories should enhance the day-to-day health,
vitality, energy, and a sense of well-being among most individuals.
The intent of the Dietary Guidelines Advisory Committee is
to summarize and synthesize knowledge regarding many individual
nutrients and food components into recommendations for an
overall pattern of eating that can be adopted by the public.
Several different indicators of diet quality have been developed
to assess adherence to the Dietary Guidelines for Americans.
Those indicators include the Recommended Foods Score (Kant
et al., 2000), the Healthy Eating Index (Kennedy et al., 1994),
and an Alternate Healthy Eating Index (McCullough et al.,
2002). Although adherence to the Dietary Guidelines for
Americans is low among the U.S. population, evidence
is accumulating that selecting diets that comply with the
guidelines reduces the risk of chronic disease. High scores
on the Alternate Healthy Eating Index were associated with
a 20 percent decrease in the risk of chronic disease in men
and an 11 percent decrease in women (McCullough et al., 2002).
Reductions in risk were particularly strong for CVD. Recently,
Kant and co-workers reported that dietary patterns consistent
with recommended dietary guidance were associated with a lower
risk of mortality among individuals age 45 years and older
in the United States (Kant et al., 2004). The authors estimated
that about 16 percent and 9 percent of mortality from any
cause in men and women, respectively, could be eliminated
by the adoption of desirable dietary behaviors.
Although diet and physical activity influence health both
together and separately, their joint effects have not been
assessed, particularly the extent to which increased physical
activity enhances the ability to meet nutrient guidelines.
Physical activity is a fundamental means of improving the
physical and mental health of individuals. Future studies
of diet quality and health need to include measures of physical
activity.
The Dietary Guidelines for Americans can be used
to prevent the onset of targeted diseases (i.e., primary prevention),
to improve health in individuals who have already developed
risk factors or preclinical disease (i.e., secondary prevention),
and to provide care for individuals with established disease
(i.e., tertiary care) (U.S. Preventative Services Task Force,
1996). Both diet quality and physical activity appear to play
important roles in preventing primary, secondary, and tertiary
prevention.
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THE ROLE OF FOOD SAFETY IN DISEASE PREVENTION
Food will promote health only if it is safe to eat. Foodborne
diseases cause approximately 76 million illnesses, 325,000 hospitalizations,
and 5,000 deaths in the United States each year. Three pathogens
(Salmonella, Listeria, and Toxoplasma)
are responsible for more than 75 percent of these deaths. Actions
by consumers can reduce the occurrence of foodborne illness
substantially.
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THE ROLE OF DIET AND PHYSICAL ACTIVITY IN REDUCING HEALTH
DISPARITIES
Of substantial concern are disparities in health among
racial and ethnic minorities and among different socioeconomic
groups. For example, blacks tend to have a higher prevalence
of elevated blood pressure and a greater incidence of blood
pressure-related diseases, such as stroke and kidney failure,
than non-blacks. Also, several subgroups of the population
(e.g., Hispanics, American Indians, and blacks) have a
strikingly high prevalence of overweight and obesity—even
higher than the already high prevalence rates observed in the
general population (see "Overweight
and Obesity" below).
Dietary patterns differ among different groups. For example,
individuals of lower education and income levels tend to eat
fewer servings of vegetables and fruit than do those with
more education and higher income. According to national surveys,
blacks tend to have the lowest intakes of fruits and vegetables
among ethnic and racial groups. (USDA 2004; USDHHS 2004)
While the reasons for these differences are complex and multifactorial,
this report addresses research indicating that certain dietary
changes provide a means to reduce disparities. Part D, Section
7 "Fluid and Electrolytes" provides evidence that blacks tend
to be more salt sensitive than non-blacks. Likewise, blacks
tend to be more sensitive to the blood pressure lowering effects
of increased potassium intake. Ironically, the average potassium
intake of blacks is less than that of non-blacks. A healthful
low sodium, high potassium dietary pattern, termed the DASH
diet (described in Part D, Section 1), has been shown to lower
blood pressure to a greater extent in blacks than in non-blacks.
The effects on blood pressure of a reduced salt intake, increased
potassium intake and an overall healthy dietary pattern provide
an example of how dietary changes could reduce health disparities.
Such evidence exemplifies important, yet under-appreciated,
opportunities to reduce health disparities in minorities through
dietary changes.
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THE ROLE OF THE ENVIRONMENT IN IMPLEMENTING THE GUIDELINES
Ultimately, individuals choose the types and amount of food
they eat and the amount of physical activity they perform.
In conducting the research on which this report is based,
the Committee was struck by the critical and likely predominant
role of environment in determining whether or not individuals
consume excess calories, eat a healthful diet, and are physically
active. By environment we mean the constellation of cultural
forces, societal norms, family influences (e.g., mealtime
structure and parental feeding styles), changes in meal patterns,
and commercial advertising that potentially influence individual
behavior.
In brief, the Committee believes that the current environment
tends to encourage the over-consumption of calories and discourage
the expenditure of energy. Changes in the environment and
changes in individual behavior (but not changes in genes)
are the driving forces that account for the obesity epidemic.
Environmental factors that may contribute to excess calorie
intake include, but are not limited to, the increased availability
of energy dense, nutrient-poor foods and beverages, expanding
portion sizes, and increased consumption of meals outside
the home. Environmental factors that discourage physical activity
lead to reduced energy expenditures at school, work, and home.
Among these factors are limited time for physical education,
labor-saving devices, long work hours or commutes, and increased
time in sedentary activities such as watching television,
using computers, and playing video games.
In this report, we assess the impact of several of these
environmental factors as well as the effects of individual
food components and food groups on overweight and obesity
(e.g., the roles of added sugars, fats, alcohol, fruits and
vegetables, and dairy products). Not surprisingly, no single
factor appeared to be responsible for the epidemic. Such findings
reinforce the belief that multiple factors, rather than any
one factor, are responsible for the obesity epidemic and that
the optimal strategy to arrest the epidemic will be multi-factorial.
Teasing apart the relative importance of each factor is inherently
difficult given the challenges of estimating calorie intake
and energy expenditure on a population basis. Because many
of these factors often are beyond the control of individuals
(e.g., the size of portions served in food establishments
and lack of information on calorie content at point of purchase),
substantial changes to the environment are required to achieve
a milieu that supports healthy behaviors.
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CHRONIC DISEASE RISKS AFFECTED BY DIET
The reduction of chronic disease risk merits strong emphasis
in our Nation for many reasons. Among the leading causes of
death in the United States in 2000 were poor diet and physical
inactivity (400,000 deaths; 16.6 percent of total U.S. deaths)
and alcohol consumption (85,000 deaths; 3.5 percent of total
U.S. deaths) (Mokdad et al., 2004). Only tobacco accounted
for a greater percentage of total U.S. deaths (18.1 percent).
Poor diet and physical activity could overtake tobacco as
a cause of death if the trend continues. Together, cancer,
cardiovascular disease, and diabetes account for about two-thirds
of all deaths in the United States and about $700 billion
in direct and indirect costs annually (Eyre, 2004). An overview
of specific diet-related causes of death and morbidity and
of selected risk factors for some of these conditions is presented
in the following sections.
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Cardiovascular Disease
CVD1 comprises coronary heart
disease (CHD), the leading cause of death in the United States),
cerebrovascular disease (also termed stroke, the third leading
cause of death), and other conditions. In 2001, CVD accounted
for 38.5 percent of all deaths or 1 of every 2.6 deaths in the
United States. To put this in context, CVD accounts for more
deaths than the next five leading causes of death combined,
which are cancer, chronic lower respiratory diseases, accidents,
diabetes mellitus, and influenza and pneumonia. While the occurrence
of CVD typically occurs earlier in men than women, CVD is also
the leading cause of death in women. In 2001, 32 percent of
CVD deaths occurred before age 75 years.
The healthcare costs associated with CVD are staggering.
The estimated direct and indirect costs in 2004 are projected
to be $368.4 billion. Direct costs account for about $226.7
billion and include the cost of physicians and other professionals,
hospital and nursing home services, medications, home health
care, and other medical durables. Indirect costs account for
the remainder and include lost productivity caused by CVD-related
morbidity and mortality.
A substantial body of research has documented the importance
of traditional CVD risk factors, which are extraordinarily
common in the United States. Modifiable risk factors include
elevated blood pressure, dyslipidemia, diabetes, and smoking.
As documented in this report, several dietary factors and
physical activity directly influence these risk factors or
have independent effects on CVD. Hence, changes in diet and
physical activity provide an important opportunity to delay,
if not prevent, the occurrence of CVD.
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Overweight and Obesity
Overweight and obesity in the United States among children
and adults (Flegal et al., 2002) have increased at an alarming
rate. The prevalence of obesity among adults has doubled in
the past two decades (31 percent have a BMI > 30) (Flegal
et al., 2002; Hedley et al., 2004). Overweight among children
has doubled (7 percent in 1980 to 16.5 percent in 1999–2002),
whereas overweight among adolescents has tripled (5 percent
in 1980 to 16 percent in 1999–2002) (Hedley et al., 2004).
There is no significant difference in the prevalence of obesity
among men across racial/ethnic categories for all age groups
(Hedley et al., 2004). Among women at least age 20 years,
the prevalence of obesity in 1999–2000 differed significantly
between racial/ethnic groups, with non-Hispanic white women
having the lowest prevalence (30.7 percent) and non-Hispanic
black women having the highest (49.0 percent) (Hedley et al.,
2004). The prevalence of obesity in non-Hispanic black men
and women has increased from 21.1 to 28.1 percent and from
38.2 to 49.7 percent, respectively, in the past two decades,
whereas, during the same time, obesity in Mexican American
men and women increased from 23.9 to 28.9 percent and from
35.3 to 39.7 percent, respectively (Flegal et al., 2002).
The prevalence of overweight among non-Hispanic black and
Mexican American adolescents increased more than 10 percent
between 1988–1994 and 1999–2000 (Ogden et al., 2002). Data
suggest that obesity is more prevalent among persons living
in lower income households, especially among women (Healthy
People 2010, 2000).
A high prevalence of overweight and obesity is of great public
health concern because excess body fat leads to a much higher
risk for premature death and for many serious disorders, including
diabetes mellitus, hypertension, dyslipidemia, cardiovascular
disease, stroke, gall bladder disease, respiratory dysfunction,
gout, osteoarthritis, and certain kinds of cancers (NHLBI,
1998; Pi-Sunyer, 1993).
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Elevated Blood Pressure
Elevated blood pressure is causally associated with several
forms of CVD, including CHD (the leading single cause of death
in the United States), stroke (the third leading cause of
death in the United States), and congestive heart failure
(the leading cause of hospitalizations among Medicare beneficiaries),
and with kidney failure.
The contemporary classification of blood pressure has three
major categories:
Normal (systolic BP < 120 mmHg and diastolic
BP < 80 mmHg) Pre-hypertension (systolic BP 120–139 mmHg or diastolic
BP 80–89 mmHg) -
Hypertension (systolic BP > 140, diastolic
BP > 90 mmHg, or use of anti-hypertensive medication)
Pre-hypertension affects approximately 22 percent of adults
(or about 45 million people), whereas hypertension affects
more than 25 percent of adults (approximately 50 million Americans)
(Chobanian, 2003).
The prevalence of hypertension is increasing. According to
U.S. survey data from the National Health and Nutrition Examination
Survey (NHANES), the prevalence of hypertension in adults
age 18 and older increased from 25 percent in 1988–1991 to
28.7 percent in 1999–2000 (Hajjar and Kotchen, 2003). The
concomitant increase in weight between these periods only
partially explained this trend. Hypertension prevalence was
highest in blacks (33.5 percent), women (30.1 percent), and
older persons (65.4 percent of persons age > 60
years). It is estimated that approximately 90 percent of non-hypertensive
adults will develop hypertension during their lifetime (Vasan
et al., 2002). In a recent report, average blood pressure
levels in children and adolescents age 8 to 17 years increased
between NHANES surveys conducted in 1988–1994 and 1999–2000
(Muntner et al., 2004). In aggregate, these data indicate
that elevated blood pressure is an extraordinarily common
problem, one that is increasing in magnitude in the United
States.
Evidence from numerous observational studies has documented
a direct, progressive relationship between blood pressure
and mortality from CHD and stroke (Lewington et al., 2002).
The relationship between blood pressure and kidney disease
also is direct and progressive (Klag et al., 1996). Strong
support for efforts to reduce blood pressure comes from a
combination of information: (1) the direct relationship of
blood pressure with blood pressure-related cardiovascular-renal
diseases and (2) the well-documented benefits of anti-hypertensive
drug therapy. Efforts to reduce blood pressure are warranted
in both non-hypertensive and hypertensive individuals.
Reduction in blood pressure and the prevention of hypertension
in non-hypertensive individuals are vital and complementary
components of public health strategies to prevent blood pressure-related
chronic disease. A number of lifestyle modifications that
help to control blood pressure are covered in this report.
In non-hypertensive individuals, including those with pre-hypertension,
lifestyle modifications have the potential to blunt the age-related
rise in blood pressure and to lower the risk of blood pressure-related
clinical complications. Indeed, even an apparently small reduction
in blood pressure, if applied to an entire population, could
have an enormous, beneficial impact on cardiovascular events.
Stamler et al. (1989) estimated that a 3-mmHg reduction in
systolic blood pressure could lead to an 8 percent reduction
in stroke mortality and a 5 percent reduction in mortality
from CHD.
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Dyslipidemias
Dyslipidemias are abnormalities in the types and/or amount
of cholesterol and triglycerides in the blood. Of the various
lipid abnormalities, an elevated concentration of low-density
lipoprotein (LDL) cholesterol is especially important. Elevated
LDL cholesterol is causally associated with CHD, the leading
cause of death in the United States, and is considered to
be a major risk factor for the disease. In addition, LDL cholesterol
is the primary target for cholesterol-lowering therapies.
The Third Report of the National Cholesterol Education Program
(NCEP) Expert Panel on Detection, Evaluation, and Treatment
of High Blood Cholesterol in Adults (Adult Treatment Panel
III) has defined the following categories for LDL cholesterol
values (NCEP, 2002):
These recommendations were recently revised (Grundy et al.,
2004). The major modifications follow:
In high-risk persons, the recommended LDL cholesterol
goal is less than 100 mg/dl. When risk is very high, the LDL cholesterol goal
is less than 70 mg/dl (considered a therapeutic option). For more moderately high-risk persons, the recommended
LDL cholesterol goal is less than 130 mg/dl, but an LDL cholesterol
goal of less than 100 mg/dl is a therapeutic option.
Elevated serum LDL cholesterol levels are widely prevalent
in the United States. Based on data collected from 1988 to
1994, at least 25 percent of all adult men and women over
the age of 20 have LDL cholesterol levels above 130 mg/dl.
More than 50 percent of men age 35 to 74 and women over age
55 had LDL cholesterol levels above 130 mg/dl (NCEP, 2002).
According to NHANES data collected from 1988 to 1994 and then
from 1999 to 2000, serum total cholesterol in the U.S. population
decreased from 205 mg/dl to 203 mg/dl (Ford et al., 2003).
Changes in LDL cholesterol would be expected to parallel serum
total cholesterol changes observed in the population during
this time span. This very modest decrease in mean total (and
LDL) cholesterol values reinforces the importance of public
health interventions to reduce this major coronary disease
risk factor.
Epidemiologic studies have shown a progressive, dose-response
relationship of serum total and LDL cholesterol levels with
CHD risk (Stamler et al, 1986). Numerous clinical trials have
shown that a reduction in LDL cholesterol concentration translates
into a reduction in CHD incidence. For every 1 percent decrease
in LDL cholesterol there is a corresponding 1 to 2 percent
decrease in CHD risk (NCEP, 2002). The relationship between
elevated LDL-cholesterol and the progression and development
of CHD is a multistep process that begins early in life. LDL
cholesterol lowering at all ages has beneficial effects on
the risk of CHD. In early life, LDL cholesterol lowering delays,
and even prevents, atherogenesis and subsequent plaque development.
In later life, reductions in LDL cholesterol can slow atheroprogression,
and marked reductions can, in fact, even reverse atherosclerosis.
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Diabetes
Diabetes mellitus is increasing in the United States. At present,
some 18.2 million people, or 6.3 percent of the population,
have diabetes. However, of these, only about 13 million are
aware that they have the disease (National Diabetes Information
Clearinghouse, 2003). There are three primary types of diabetes.
Type 1 diabetes, present in 5 to 10 percent of persons with
diabetes, is an autoimmune disease in which the body makes
antibodies to the beta cells of the pancreas, thereby causing
destruction of these cells and leading to a failure of secretion
of insulin. Type 2 diabetes results from a combination of
insulin resistance (an inability of insulin to carry out its
function appropriately) and insulin deficiency (an inability
of the beta cells to produce enough insulin). Some 90 to 95
percent of persons with diabetes suffer from this type of
diabetes, and 80 to 85 percent of them are obese. Gestational
diabetes affects about 4 percent of pregnant women (about
135,000 cases per year) (American Diabetes Association Web
site, 2004).
Diabetes leads to a number of serious complications. Diabetes
is the leading cause of blindness in the United States today.
It also is a leading cause of kidney failure and the leading
diagnosis of patients requiring kidney dialysis. Compared
with persons without diabetes, persons with diabetes are more
than twice as likely to suffer from heart attacks and have
a 2 to 4 times greater risk for stroke. More than 60 percent
of nontraumatic amputations are related to complications from
diabetes. Diabetes is the sixth leading cause of death in
this country, and more than half of these deaths are due to
heart disease. According to 2002 estimates, the health costs
of diabetes in the United States were calculated at $132 billion
($91.8 billion direct and $40.2 billion indirect) (Brandle
et al., 2003).
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Metabolic Syndrome
The metabolic syndrome is defined by the presence of a collection
of metabolic risk factors in an individual. The root causes
of metabolic syndrome are overweight/obesity, physical inactivity,
and genetic factors. Various risk factors have been included
in metabolic syndrome. Factors generally accepted as being
characteristic of this syndrome include abdominal obesity,
atherogenic dyslipidemia, elevated blood pressure, insulin
resistance with or without glucose intolerance, prothrombotic
state, and proinflammatory state.
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Cancer
Cancer is a general term for diseases in which abnormal cells
divide uncontrollably in various organ systems of our body.
These cells can invade nearby tissues and spread through the
bloodstream and lymphatic system to other areas of the body
(NCI, 2004). It has been estimated that more than 1.3 million
people will be diagnosed with cancer and more than one-half
million will die from cancer in 2004 (ACS, 2004).
Among Americans, the risk of developing and dying from cancer
declined from 1975 to 2001 (ACS, 2004). The overall observed
cancer incidence rate dropped 0.5 percent per year from 1991
to 2001, and the overall death rate from all cancers combined
decreased 1.1 percent per year from 1993 to 2001. Death rates
decreased for 11 of the top 15 cancers in men and 8 of the
top 15 cancers in women. The incidence declined in men for
lung, colon, oral cavity, leukemia, stomach, pancreas, and
larynx cancers but increased for melanoma, prostate, kidney,
and esophagus cancers. A decline in lung cancer incidence
was noted for the first time in women. Incidence rates in
women also declined for colon, cervix, pancreas, ovary, and
oral cavity cancers but increased for breast, thyroid, bladder,
kidney, and melanoma cancers (NCI, 2004).
This progress can be attributed to prevention, earlier detection,
and better treatment; however, health disparities and wide
variations in survival are observed among different ethnic
and racial populations (Jemal et al., 2004). Many cancers
are preventable, especially since nutrition and dietary practices,
as well as adherence to healthy lifestyles, appear to be important
in reducing the risk and mortality of cancer (Cerhan et al.,
2004; Forman et al., 2004).
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Osteoporosis
According to a World Health Organization definition (WHO,
1994), osteoporosis is characterized by reduced bone mass,
increased bone fragility, and increased risk of fracture.
Osteoporosis is a major health risk for Americans, with 10
million individuals already having osteoporosis and 18 million
more having low bone mass, placing them at increased risk
for this disease (NIH, 2000). The prevalence of osteoporosis
among postmenopausal women in the United States is 21 percent
in Caucasian and Asian, 16 percent in Hispanic, and 10 percent
in African American women (Looker et al., 1995).
In the United States each year approximately 1.5 million
fractures are associated with osteoporosis, including 300,000
hip fractures, 700,000 vertebral fractures, 250,000 distal
forearm fractures, and 250,000 fractures of other sites (Riggs
and Melton, 1995). Among individuals at age 50, the risk of
having a hip fracture at some point in the future is estimated
at 17 percent for Caucasian women, 6 percent for African American
women, 6 percent for Caucasian men, and 3 percent for African
American men (Cummings et al., 1993; Melton et al., 1992).
Osteoporosis may be attributed to three factors: (1) accelerated
bone loss at menopause in women or as men and women age; (2)
suboptimal bone growth during childhood and adolescence, resulting
in failure to reach peak bone mass; and (3) bone loss secondary
to disease conditions, eating disorders, or certain medications
and medical treatments (NIAMS, 2000).
Osteoporotic fractures, particularly vertebral fractures,
can be associated with chronic disabling pain. Nearly one-third
of patients with hip fractures are moved to nursing homes
within the year following a fracture. Notably, one in five
patients is no longer living 1 year after sustaining an osteoporotic
hip fracture. Hip and vertebral fractures are a problem for
women in their late 70s and 80s, wrist fractures are a problem
in the late 50s to early 70s, and all other fractures (e.g.,
pelvic and rib) are a problem throughout postmenopausal years
(NIH, 2000).
Direct financial expenditures for treatment of osteoporotic
fracture are estimated at $10 billion to $15 billion annually.
A majority of these estimated costs are due to inpatient care
but do not include the costs of treatment for individuals
without a history of fractures, nor do they include the indirect
costs of lost wages or productivity of either the individual
or the caregiver. Consequently, these figures substantially
underestimate the true costs of osteoporosis (NIH, 2000).
With the expected increase in the average age of the population,
the incidence of hip fractures in the United States may triple
by the year 2040 (Schneider and Guralnik, 1990).
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AUDIENCE FOR DIETARY GUIDELINES
The Dietary Guidelines is intended for the general
public over age 2 years. Since the general public now comprises
large numbers of individuals with chronic health problems
such as obesity, high blood pressure, and dyslipidemias, the
Committee considered topics beyond the dietary concerns of
persons who meet strict definitions for good health. The populations
addressed in the following sections posed special challenges
regarding dietary guidance.
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Children
Relatively few studies addressing the role of diet quality
and physical activity in promoting health focus on children.
Nevertheless, a high-quality diet, sufficient but not excessive
in calories, and physical activity are integral in promoting
the health, growth, and development of children. The rapid
rates of growth occurring during adolescence increase the
need for iron and calcium during that period to higher amounts
per 1,000 calories than required at any other stage of life.
In other words, the additional need for iron and calcium for
growth is greater than the additional need for energy. Failure
to achieve the recommended calcium intakes may reduce the
peak bone mineral content and predispose the individual to
osteoporosis later in life. Inadequate iron intakes increase
the risk of iron-deficiency anemia, particularly among women.
A nutrient-dense diet rich in milk and milk products, lean
meats, poultry, fish, and legumes is needed to meet the calcium
and iron recommendations during adolescence.
Moreover, it is important to address the needs of children
when developing dietary guidance because development, extending
from the fetal period through childhood and adolescence, can
have a substantial influence on the risk of chronic disease.
Furthermore, eating patterns established during childhood
often are carried into adulthood (Aggett et al., 1994; Baranowski
et al., 2000).
Recent research suggests that adult diseases may have their
roots very early in life, even as early as the fetal period,
as a result of inadequate nutrient intakes during pregnancy.
According to the Barker hypothesis, low birth-weight infants
may have increased risk of heart disease, obesity, and type
2 diabetes as a result of conditions in the womb, or in the
first few weeks of infancy (Barker, 2003). Childhood and adolescence
also are critical periods for developing the antecedents of
chronic disease. It is well recognized that peak bone development
occurs during the pubertal period. Blood pressure rises through
childhood and tracks into adult years. Evidence from autopsy
studies of young soldiers has documented early evidence of
atherosclerosis in persons under the age of 20. The high and
increasing prevalence of overweight has markedly increased
the prevalence of type 2 diabetes in children. As recently
as 20 years ago, only 2 percent of all newly diagnosed cases
of diabetes among youths age 9 to 19 were type 2 diabetes.
Today, type 2 diabetes accounts for up to 50 percent of new
cases of diabetes among youths. One in 400 youths, by the
time they are 20, will have type 2 diabetes mellitus. Excess
weight, particularly around the abdomen, as well as too little
physical activity, appears to be the basis for developing
this disease early in life. At least 2 percent of children
have an inherited tendency toward high cholesterol levels
known as familial hyperlipidemia, predisposing them to heart
disease as an adult if not treated. In addition, children
may adopt health behaviors that have a major influence on
chronic disease, including dietary habits, physical activity,
and smoking. In fact, 4.1 million children age 12 to 17 are
already smokers, and nearly half of the children age 12 to
21 do not exercise on a daily basis.
Thus, children, as well as adults, are at risk for developing
chronic disease because of a poor intrauterine environment,
inherited tendencies toward the diseases, or an unhealthy
lifestyle. Healthy lifestyles started at an early age (e.g.,
sensible eating and regular exercise) have the potential to
diminish these health problems greatly. Childhood represents
a sensitive time for developing healthful eating patterns.
Studies have documented that patterns of food and nutrient
intake track from childhood into later years, including adulthood.
When 5 to 6 year olds were followed for 2 years, the correlations
between initial and subsequent distribution of energy from
macronutrients were statistically significant, ranging between
0.46 and 0.65 (Kemper et al., 1999; Nader et al., 1995; Singer
et al., 1995; Stein et al., 1991). Other studies suggest that
the intake of micronutrients also tracks from childhood to
later years of life (Kelder et al., 1994; Moilanen et al.,
1987; Nicklas et al., 1991; Singer et al., 1995). For example,
fruit and vegetable consumption (Resnicow et al., 1998) and
dairy food intake in childhood both show a moderate degree
of tracking with age (Dwyer et al., 1989; Teegarden et al.,
1999; Skinner et al., 2003; Welton et al., 1997). In other
words, those who consume fruits and vegetables or milk regularly
as children are more likely to do so as adults.
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Pregnant and Lactating Women
Both pregnancy and lactation are critical periods during
which maternal nutrition is a key factor influencing the health
of both child and mother. Since physiologic adaptations to
increased nutrient demand occur during both of these periods,
the dietary need for nutrients is similar to that of nonpregnant
women of comparable age (IOM, 1991). However, diet quality
during pregnancy may influence fetal growth (see the section
on children presented earlier). Certain dietary factors, including
folic acid intake, may be especially important for normal
development of the embryo and fetus during the first 3 months
of pregnancy. Dietary factors may contribute to impaired glucose
tolerance, a common disorder of pregnancy (Clapp, 1998; Saldana
et al., 2004). Dietary contaminants, such as methylmercury,
may adversely affect fetal growth. Maternal diet also may
influence breastmilk composition somewhat, especially the
milk's content of certain vitamins and alcohol (IOM, 1991).
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Older Persons
The 2000 U.S. Census Report showed that about 13 percent of
the U.S. population, or about 1 in 7, are over age 65. In
2011, the "baby boom" generation will begin to turn 65, and
by 2030, it is projected that one in five people will be over
age 65. Individuals age 85 and older are the fastest growing
segment of the older population.
As the number of older Americans increases, the role of diet
quality and physical activity in reducing the progression
of chronic disease needs to be addressed in this population
group. Furthermore, the process of aging can influence how
nutrients are used and can exacerbate the effect of poor diet
quality on health. For example, aging may reduce nutrient
adsorption, increase urinary nutrient loss, and alter normal
pathways of nutrient metabolism. These changes associated
with aging need to be compensated by dietary changes, which
are discussed later in the report.
Most important, modifications of diet and increases in physical
activity have tremendous potential as a means to prevent or
delay chronic disease in older persons. First, the high absolute
risk of chronic disease (e.g., high risk of stroke) is modifiable,
not fixed. Second, older individuals achieve, in many instances,
greater benefit from a given improvement in diet (e.g., older
individuals tend to be more responsive to the blood pressure
lowering effects of salt) or from an increase in physical
activity. Third, it is well-documented that older individuals
can make and sustain behavior changes, including weight loss
(DPP, 2002; Whelton et al., 1997).
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USES OF DIETARY GUIDELINES FOR AMERICANS
A major goal of the 2005 Dietary Guidelines Advisory Committee
was to use the available scientific base to characterize elements
of guidance for a healthful diet—dietary guidelines that,
if followed, will reduce the risk of chronic disease while
meeting nutrient requirements.
The U.S. Government takes steps to promote health and reduce
risk in its food assistance programs, nutrition education
efforts, and decisions about national health objectives. For
example, the National School Lunch Program and the Elderly
Nutrition Program incorporate the Dietary Guidelines
in menu planning; the Special Supplemental Nutrition Program
for Women, Infants, and Children (WIC) applies the Dietary
Guidelines in its educational materials; and the Healthy
People 2010 objectives for the Nation include objectives
based on the Dietary Guidelines. Using the Dietary
Guidelines helps policymakers, educators, clinicians,
and others to speak with one voice on nutrition and health
and to reduce the confusion caused by mixed messages in the
media.
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SUMMARY
In this report, the Dietary Guidelines Advisory Committee
integrates scientific evidence on diet, physical activity,
and health into a set of conclusions and recommendations to
be used as the basis for a revision of the Dietary Guidelines
for Americans. The guidelines will provide steps that
individuals can take toward achieving good health and well-being—both
in the present and well into the future. Since the nutrient
needs and risks of developing disease differ from person to
person, the response to selecting a diet consistent with the
Dietary Guidelines will vary among individuals. Some
may enjoy a substantial health response to the dietary changes,
whereas others may still develop elevated blood lipids, high
blood pressure, or high blood glucose values. Differences
in genetic backgrounds likely contribute to the divergent
responses. However, irrespective of diverse biochemical and
disease response to the dietary changes, improving diet quality
and physical activity can substantially improve public health
by reducing the risk of chronic disease.
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