VEG Diet:A Convergence of Science & Philosophy

08-31-2003, 02:35 AM

Monday, March 24, 1997
# 01
Vegetarian Diets: The Convergence of Philosophy and Science -- Walter Willett
KEYNOTE ADDRESS
Populations of vegetarians living in affluent countries appear to enjoy
unusually good health, characterized by low rates of cancer, cardiovascular
disease, and total mortality. This important observation has provided fuel for
many lines of research and has raised at least three general questions. Are
these unusual health statistics due to better nondietary lifestyle factors,
such as low prevalence of smoking and higher levels of physical activity? Are
these statistics due to low intake of harmful dietary factors, in particular
meat? Are these observations due to higher intake of beneficial dietary factors
that tend to replace meat in the diets?
Due to the complex intercorrelations of dietary factors and other lifestyle
variables, these questions have posed challenges to epidemiologists. However,
there is now sufficient evidence to indicate that the answers to all three
questions are likely to be "yes". Certainly, low smoking rates contribute
importantly to the low rates of coronary heart disease and many cancers,
probably including colon cancer, in the Seventh-day Adventist and other
vegetarian populations. Also, avoidance of red meat is likely to account in
part for low rates of coronary heart disease and colon cancer, but this does
not appear to be the primary reason for general good health in these
populations. Very generally, evidence accumulated in the past decade has
emphasized the importance of adequate consumption of beneficial dietary
factors, rather than just the avoidance of harmful factors. This includes
abundant intake of fruits and vegetables, the regular consumption of vegetable
oils including those in nuts, and the importance of consuming grains in a
minimally refined state. The notion that fat per se is a major cause of ill
health has not been supported by recent data. Many critical questions will
require additional research. Further knowledge about the types of fruits and
vegetables that are beneficial and their biologically important constituents
would make possible more specific advice and more focused interventions. Also,
observations that intakes of fish and poultry seem to be beneficial for some
health outcomes raises the possibility that some of these foods also may
contain components that are not consumed in optimal amounts in some diets.
Although current knowledge already provides general guidance toward healthy
diets, the accumulated evidence strongly indicates a powerful, yet complex,
impact of diet on health and the need for further investigation.
# 02
Legumes and Soybeans: An Overview of Health Effects -- Mark Messina
The contribution of legumes to overall dietary intake varies greatly among
populations as legume intake differs markedly throughout the world. Not
surprisingly, those countries that consume more plant-based diets also consume
relatively more legumes. In fact, other than the obvious distinction of not
including flesh products, the greater consumption of legumes by western
vegetarians in comparison to omnivores may be the most distinguishing feature
of vegetarian diets. Legumes are an excellent source of dietary fiber and on a
caloric basis, are generally no more than 10% fat (the main exceptions being
soybeans and peanuts) and between 20% and 30% protein. The glycemic index of
beans is extremely low which suggests legumes may be a particulary important
food for diabetics and for individuals who are at risk of becoming insulin
resistant. Also, the bacterial metabolism of the indigestible oligosaccharides
in legumes may produce beneficial health effects. Finally, legumes offer a
variety of potentially beneficial phytochemicals such as saponins (found in a
variety of legumes) and isoflavones (primarily found in soybeans). Recent data
suggest isoflavones may promote bone health, and reduce risk of both
cardiovascular disease and some forms of cancer.
# 03
Cereals and Legumes: An Epidemiologic Approach -- Lawrence Kushi
There is growing evidence that cereals and legumes play important roles in the
prevention of chronic diseases. Early epidemiologic studies of these
associations focused on dietary fiber rather than intake of grains or legumes.
Generally, such studies indicate an inverse association of dietary fiber and
risk of coronary disease; this observation has been replicated in recent cohort
studies. Studies focused on grain or cereal intake are fewer in number; they
tend to support an inverse association of whole grains with coronary heart
disease. The association of dietary fiber with colon and other cancers have
generally shown inverse associations; whether these are attributable to cereal
or to other fiber sources or other factors is less clear. Although legumes have
been demonstrated to lower blood cholesterol levels, epidemiologic studies are
few and inconclusive regarding the association of legumes with risk of coronary
heart disease. Legumes, in particular soy, have been hypothesized to decrease
risk of some cancers, but epidemiologic studies are equivocal in this regard.
Overall, there is substantial epidemiologic evidence that dietary fiber and
whole grain intake is associated with decreased risk of coronary heart disease
and some cancers, while the role of legumes in these diseases is promising but
inconclusive.
# 04
Health Benefits of Whole Grains -- Joanne Slavin
Dietary guidance recommends consumption of whole grains in the prevention of
chronic diseases. Recent studies find that whole grain consumption protects
against cardiovascular disease, cancer, and diabetes. Components in whole
grains that may be protective are diverse and include compounds that effect the
gut environment, e.g. dietary fiber, resistant starch, and oligosaccharides.
Whole grains are also rich in compounds that function as antioxidants such as
trace minerals and phenolic compounds, and compounds that are phytoestrogens
with potential hormonal effects. Whole grains also are rich sources of
compounds formerly thought of as antinutrients, for example phytic acid. Phytic
acid may function as an antioxidant in human foods and therefore be protective,
rather than detrimental to human health. Other potential mechanistic effects of
whole grains include binding of carcinogens and modulation of glycemic index.
Clearly the range of protective substances in whole grains is impressive and
advice to consume additional whole grains is appropriate. Further study is
needed on the mechanisms for this protection so the most potent protective
components of whole grains are not lost in processing and preparation of whole
grains into acceptable foods for the public.
# 05
Soy Protein Intake and Risk for Atherosclerotic Cardiovascular Disease -- James W. Anderson
Ingestion of vegetable protein in place of animal protein appears to be
associated with the lower risk for coronary heart disease. This effect may be
related to changes in serum lipid concentrations. The cholesterol lowering
effects of soy protein as compared with animal protein have been recognized in
animal models for more than 80 years. These studies indicate that soy protein
intake protects from development of atherosclerosis.
Our group recently completed a meta-analysis of the effects of soy protein
intake on serum lipids. We analyzed outcomes reported by 29 controlled clinical
studies. In most of these studies, the intake of energy, fat, saturated fat, and
cholesterol was similar when the subjects ingested control and soy-containing
diets. Soy protein intake averaged 47 grams per day. Ingestion of soy protein
was associated with the following net changes in serum lipid concentrations
from the concentrations reached with the control diets: total cholesterol, a
decrease of 9.3 percent; LDL cholesterol, a decrease of 12.9 percent;
triglycerides, a decrease of 10.5 percent; and HDL a nonsignificant increase of
2.4 percent.
# 06
Effects of Fruit and Vegetable Consumption on Chronic Diseases and Longevity -- Gladys Block
- Unavailable -
# 07
Health Effects of Vegetables and Fruit -- Johanna Lampe
There are a number of biologically plausible reasons why consumption of
vegetables and fruit might slow or prevent the onset of chronic diseases.
Vegetables and fruit are rich sources of a variety of nutrients, including
vitamins, trace minerals and dietary fiber, and many classes of non-nutritive,
biologically active compounds, such as carotenoids, coumarins, the
sulfur-containing dithiolthiones, indoles, isothiocyanates and allyl sulfides,
flavonoids, phenols, plant sterols, isoflavones and lignans, and monoterpenes.
These substances have complementary and overlapping mechanisms of action,
including the induction of detoxification enzymes, stimulation of the immune
system, alteration of platelet aggregation, modulation of cholesterol synthesis
and hormone metabolism, dilution and binding of carcinogens in the intestinal
tract, and antibacterial, antiviral, and antioxidant effects. However, no
single compound acts through all proposed mechanisms and, even within
phytochemical classes, the biologic activity of compounds varies widely.
Consumption of vegetables and fruit contributes variety and complexity to the
diet. There is the potential for inhibitory, additive or synergistic biologic
interactions of compounds from within one plant food, as well as interactions
with other dietary components. Epidemiologic data support the association
between a high intake of vegetables and fruit and lowered risk of chronic
disease; the complexity of such a diet cannot be ignored in the attempt to
understand the mechanisms of action.
# 08
Nut Consumption, Cardiovascular Disease Prevention and Longevity -- Joan Sabaté
Perhaps one of the most unexpected and novel findings in nutritional
epidemiology in the last 5 years has been that nut consumption protects against
ischemic heart disease (IHD)--the leading cause of death for male and female
adults world-wide. Frequency and quantity of nut consumption has been
documented to be higher among vegetarian than in non-vegetarian populations.
Nuts also constitute an important part of traditional plant-based diets, such
as the Mediterranean and Asian Diets.
In a prospective epidemiological study of approximately 31,000 California
Adventists, we found that frequency of nut consumption had a substantial and
highly significant inverse association with risk of myocardial infarction and
death from IHD. The Iowa Women's Health Study has also documented an
association between nut consumption and decreased risk of IHD.
The protective effect of nuts on CHD has been found in both men and women,
adults, and the elderly, Caucasion and African Americans. Importantly, nuts
have similar associations in both vegetarian and non-vegetarian Adventists.
Finally, the protective effect of nut consumption on IHD is not offset by an
increased mortality from other causes. Unpublished results from the California
Adventist Health Study indicates that frequency of nut consumption is inversely
related to all-cause mortality in African Americans and the elderly. Thus, nut
consumption may not only offer protection against IHD, but also increase
longevity.
# 09
Nuts, Serum Lipids, and Beyond -- Penny Kris-Etherton
Many studies have shown that reducing saturated fatty acids (SFA) elicits a
marked total and low density lipoprotein cholesterol (LDL-C) lowering effect
and, as a result, decreases risk of coronary heart disease. The pressing
question to be resolved is what nutrient or nutrients should replace SFA
calories in the diet? The present report reviews the existing literature that
has examined the effects of high carbohydrate, low SFA diets and high fat diets
(low SFA) that are high in unsaturated fatty acids with emphasis on studies that
have used nuts to achieve nutrient targets. The nuts that have been studied
principally have been almonds, which are a rich source of monounsaturated fatty
acids (MUFA), and walnuts, which are high in polyunsaturated fatty acids (PUFA).
To date, there have been only several studies conducted with nuts. They have
been designed to evaluate the effects of nuts on plasma lipids and lipoproteins
in diets that are both high and relatively low in total fat.
Collectively the studies that have compared the plasma lipid/lipoprotein
responses of a high carbohydrate diet low in SFA to a high fat, high MUFA diet
low in SFA (using nuts) have reported similar total and LDL-cholesterol
lowering effects. In addition, the high MUFA diet either increased or
maintained HDL-cholesterol levels in contrast to the high carbohydrate diet in
which a typical HDL-cholesterol lowering effect was observed. There also is
evidence to show beneficial plasma lipid/lipoprotein effects of a Step-One diet
relatively high in PUFA provided by walnuts. In this study the high walnut diet
resulted in even greater reductions in total and LDL-cholesterol levels than
did the typical Step-One diet, and the ratio of LDL-cholesterol to HDL
cholesterol decreased.
Additional studies are needed to corroborate these findings and to resolve the
question of whether there are other biologically active molecules in nuts that
promote lipid lowering or confer other beneficial health effects. In this
regard, we need to know whether there are distinctive biological effects
observed for the different nuts and importantly, what constituents in nuts
account for these responses.
# 10
Percent Fat vs Type of Dietary Fat - A Low Fat Approach -- Lee Lipsenthal
It is estimated that dietary and lifestyle modification could halve the rate of
CHD. However, the current dietary guidelines of the AHA (30% fat, 200-300 mg
dietary cholesterol) may not be sufficient to stop the progression of coronary
heart disease. Hunninghake demonstrated only a 5% improvement in LDL
cholesterol from a step 2 AHA diet compared to 27% improvement from lovastatin
in the same patients. Patients randomly assigned to the control group in a
number of regression trials were consuming a step 1 or step 2 diet, yet the
majority of these patients continued to show progression of disease. However,
regression of coronary atherosclerosis may occur when dietary intake of fat and
cholesterol are much lower.
Dietary intake of fat and cholesterol may have short-term as well as long-term
effects, for better and for worse. Even a single high-fat, high cholesterol
meal may cause acute enhancement of platelet reactivity as well as sludging in
arterial beds. These changes may result from a shift in the
thromboxane/prostacyclin balance to favor thromboxane production. In animals
with atherosclerosis induced by high-cholesterol diets, platelets synthesize
thromboxane A2 in increased amounts. Since cholesterol is contained only in
foods of animal origin, a vegetarian diet may shift the balance away from
thromboxane formation, which would make both coronary spasm and platelet
aggregation less likely to occur.
# 11
Role of Dietary Fat in Plant-Based Diets -- Ann Coulston
We face an obsession in the U.S. that low-fat, high-carbohydrate diets are
essential for health, driven largely by an effort to reduce heart disease and
more recently certain types of cancer. The "fat phobia" line of reasoning is
much clearer for heart disease than it is for cancer. We have learned over the
past several years that all fats are not alike, and specifically that saturated
fatty acids are more closely associated with risk factors for heart disease. The
other broad classifications of dietary fats, polyunsaturated and
monounsaturated, do not have as strong an associated risk. An examination of
fat-containing foods leads to the conclusion that unsaturated fatty acids are
largely found in plant-based foods, and saturated fatty acids in animal foods.
In general, plant foods are thought to be rich in carbohydrates, low in fats
and low in protein. However, populations that meet all of their nutrition needs
from plants, consume plant-based foods that are rich in fat, i.e. nuts, seeds,
and oils from plants and seeds, and rich in protein, ie mature beans, peas, and
other legumes. Fat is an essential nutrient and, in the body, for example,
becomes an important component of cell membranes in the formation of
prostaglandins and leukotrienes. The human body can synthesize fat from
carbohydrate. Scientists are now beginning to appreciate a relationship between
the amount and type of dietary fats to the types of fats found in body fat
depots.