Diet in the Prevention and Control of Obesity,
Insulin Resistance, and Type II Diabetes
American College of Preventive Medicine Position
Statement
American College of Preventive Medicine
Writing Group: Ginie Chan, MD, MPH (University
of South Carolina Department of Family & Preventive Medicine,
Columbia, SC); David L. Katz, MD, MPH, FACPM (Yale
University School of Medicine, New Haven, CT) and the ACPM
Policy Committee
Corresponding author:
David L. Katz, MD, MPH, FACPM
C/o Jennifer K. Bretsch, MS
American College of Preventive Medicine
1307 New York Avenue, NW
Suite 200
Washington, DC 20005
Tel: 202-466-2044
Fax: 202-466-2662
Email: jkb@acpm.org
with copy to: katzdl@pol.net
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Purpose
- The American College of Preventive Medicine (ACPM) presents
this position statement on the use of diet to prevent and
control obesity, insulin resistance, and type II diabetes.
ACPM recognizes that factors other than diet, including but
not limited to physical activity, genetics, environmental
exposures, and public policies influence these conditions.
This statement is limited to consideration of dietary pattern,
specifically in response to the promotion and popularity of
unconventional dietary regimens for weight control. The
College position is intended to lend guidance and clarity to
practitioners and the public alike. The position espoused is
subject to change as new scientific evidence accrues.
Introduction
Obesity, insulin resistance, and type II
diabetes mellitus are epidemic in the United States. Over 97
million adults are overweight (BMI>25), 1 and
the associated morbidity, mortality, and economic costs are
enormous. Over 300,000 deaths each year are attributable to
obesity.1 The direct and indirect cost of medical
treatment for obesity and its sequelae was $117 billion in 2000.
Overweight and obesity (particularly excess abdominal fat) are
closely associated with insulin resistance and the metabolic
syndrome (i.e., the insulin resistance syndrome), an important
risk factor for type 2 diabetes and cardiovascular disease;2,3
the risk of type 2 diabetes attributable to obesity is estimated
to be as high as 75%. As the prevalence of obesity continues to
increase, it is expected that the prevalence of diabetes will rise
concomitantly.4 Epidemic overweight has already shifted
the age distribution of type 2 diabetes mellitus downward, so that
it, too, is considered an epidemic of children.5 High
rates of insulin resistance in adults6 and children5
have recently been documented.
Against this backdrop, various diets
stipulating alternative distributions of macronutrient classes
(carbohydrate, protein, fat) have been promoted to the general
public for weight control. The competing and largely
unsubstantiated claims of such diets threaten to confuse and
distract the large population affected by these epidemics. The American
College of Preventive Medicine issues its official position on
diet in the prevention and control of obesity, type II diabetes,
and insulin resistance in response to this hazard.
Background
Whether weight gain causes insulin resistance, insulin
resistance contributes to weight gain propensity, or both, remains
controversial.7 Abdominal obesity is an integral
feature of the insulin resistance syndrome, 2 and
weight gain over time is considered a strong predictor of diabetes
risk. 8 The role of insulin in the pathogenesis of both
obesity and diabetes is well established. 9
A variety of competing dietary patterns have been promoted to
the general public as potential means of controlling weight. Among
the more popular are those advocating restriction of carbohydrate
to levels well below prevailing guidelines, in conjunction with
liberal intake of total fat, protein, or both.10,11
Such diets typically invoke the role of insulin in weight gain as
a rationale for restricting carbohydrate, citing the glycemic
index as the link between carbohydrate and insulin levels. 12
Popular, or "fad" diets often imply
that insulin is involved in the metabolism of only carbohydrate.
Insulin is actually integral to the metabolism of all
macronutrient classes. 12 Limits to the glycemic index
as a basis for food selection in either diabetes management4or
weight control have been noted. Perhaps most important,
carbohydrate is a highly heterogeneous category, a fact obscured
by fad diet claims. Highly processed carbohydrate tends to have a
high glycemic index, low satiety index, low fiber content, and
limited nutritional value; grains, vegetables, and fruits,
however, are carbohydrate sources that tend to have exactly the
opposite characteristics. 13,14 There is evidence that
high-fiber carbohydrate sources evoke modest insulin release, can
help reduce post-prandial glucose and insulin levels, and can even
attenuate glycemic responses to high-glycemic index foods. 15
Cereal grain intake is inversely associated with diabetes risk.14
High dietary fiber intake, 15 and high intake of
monounsaturated fat, 16 have been shown to ameliorate
metabolic control in diabetes; there is no such evidence for
saturated or trans fat, or protein. The best available
data regarding sustainable weight loss come from the National
Weight Control Registry, and indicate that a diet abundant in
grains, vegetables, and fruit, and restricted in fat, together
with regular physical activity, is most useful.17
Clinical trial data pertaining to blood pressure control, 18
cardiovascular disease prevention, 19,20 and diabetes
prevention21 all support a diet rich in grains and
plant foods, along with either restriction of fat intake, or a
shift from saturated and trans fat to monounsaturated and
polyunsaturated fat. There is widespread consensus that abundant
intake of fruits and vegetables is inversely associated with
cancer risk.22
On the basis of its review of evidence linking dietary pattern
to health outcomes, The United States Preventive Services Task
Force advises clinicians to endorse to all patients over the
age of 2 a diet restricted in fat, particularly saturated fat, and
abundant in fruits, vegetables, and grains.23 The USDA
recommendations, depicted in the food guide pyramid, emphasize
abundant intake of grains, vegetables, and fruits, with restricted
intake of both simple sugars and total fat.24 The National
Cancer Institute sponsors the "5-a-day" program
encouraging fruit and vegetable intake, and endorses dietary
guidelines that include 20-35 grams of fiber per day, with 30% or
less of calories from fat.25 The American Heart
Association offers dietary guidelines that call for 55% or
more of calories from carbohydrate, 30% or less from fat ( 7-10%
saturated/trans fat, 10% polyunsaturated and 15% monounsaturated
fats), and 15-20% from protein.26 The American
Dietetic Association supports the USDA Dietary Guidelines for
Americans 2000 and recommends a variety of grains, at least 5
servings of fruits and vegetables daily, restriction of saturated
fat and cholesterol, and limited sugar and sweet consumption.27
The American Diabetes Association advocates 55% of
calories from carbohydrate, up to 30% from fat (10%
saturated/trans fat, 10% polyunsaturated fat), and 15-20% from
protein.4
Finally, in 2002, The National Academy of Sciences’ Institute
of Medicine (IOM) released dietary guidelines calling for 45-65%
of calories from carbohydrate, 20-35% from fat, and 10-35% from
protein, in conjunction with 60 minutes each day of moderately
intense physical activity.28 The IOM guidelines further
emphasize the restriction of saturated and trans fat, linked to
cardiovascular disease risk, and their replacement with
monounsaturated and polyunsaturated fat.
Statement
On the basis of available evidence, the
American College of Preventive Medicine takes the position that a
diet rich in complex carbohydrate from unrefined cereal grains,
vegetables, and fruits; moderate in total fat and restricted in
saturated and trans fat; and moderate in protein is advisable for
weight control, diabetes prevention, and health promotion. The
College specifically recommends a macronutrient distribution
within the newly released IOM ranges, with approximately 55% of
calories from carbohydrate, approximately 25% of calories from
fat, and approximately 20% of calories from protein. Saturated and
trans fat intake should be restricted, with the bulk of fat
calories derived from monounsaturated and polyunsaturated fat. The
College further recommends a fiber intake of at least 24 grams per
day, with additional benefit likely from levels up to 50 grams per
day in adults with diabetes.
The College notes that there is currently a
lack of evidence for the claims of popular diets that unrestricted
intake of all varieties of dietary fat, or of protein, are
conducive to weight control.
Further, the College advises against such
diets, and all diets advocating restricted intake of grains,
vegetables, or fruits, as they are incompatible with the aggregate
evidence linking dietary pattern to human health. Given the large
population with, or at risk for, obesity, insulin resistance, and
diabetes, dietary intake recommended for the control or prevention
of these conditions must be consistent with recommendations for
health promotion in the public at large. Fad diets generally
emphasize short-term weight loss while neglecting considerations
of long-term health, and are to be discouraged.
Rationale
Available evidence indicates that diets
abundant in grains, vegetables, and fruit; restricted in highly
processed foods; moderate in fat and restricted in saturated and
trans fat; and moderate in protein are associated with a wide
range of health benefits. This same basic dietary pattern is
linked with weight control and sustainable weight loss; with
regulation of serum insulin levels; and with the prevention and
amelioration of diabetes mellitus. The College invokes this
evidence, and the importance of considering the overall influence
of diet on health, to justify its position.
_______________________________________________________________________
Writing Group: Ginie Chan, MD, MPH (University of South
Carolina Department of Family & Preventive Medicine, Columbia,
SC); David L. Katz, MD, MPH, FACPM (Yale University School
of Medicine, New Haven, CT) and the ACPM Policy Committee
_______________________________________________________________________
"This is an official Position Statement of the American
College of Preventive Medicine and does not reflect the position
of the American Journal of Preventive Medicine. This statement has
been edited for clarity and consistency of style but has not
otherwise been subjected to the Journal's editorial or peer-review
process"
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