VEG Diet:A Convergence of Science & Philosophy

[Guest guest]

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.