Diseasespecific Guidelines

Dietary advice for persons with one or more risk factors for a particular condition, or those with an established disease, differ from national guidelines, which target the population as a whole and focus on the prevention of chronic disease in essentially healthy persons. Such disease-specific guidelines are often issued as consensus statements or recommendations by health agencies, professional associations, and other authoritative groups. For example, the earliest advice linking diet and health came from the American Heart Association (AHA) in a series of position statements released periodically beginning in 1957.531 Since then, numerous authoritative bodies and agencies have issued recommendations related to the secondary prevention and treatment of specific disease conditions.

A. Heart Disease Guidelines

Coronary Heart Disease (CHD) is the major cause of death in industrialized and emerging nations and is the most common and serious form of cardiovascular disease. Elevated blood lipids and related disorders of lipoprotein metabolism are implicated in the progression of atherosclerosis and subsequent obstruction of coronary blood vessels and development of atherosclerotic heart disease. Atherosclerosis is infrequently hereditary in origin and there is an extensive body of epidemiologic, laboratory, and clinical evidence of an association between diet and the incidence of CHD. Recent clinical trials provide evidence that reducing serum cholesterol levels through diet, drugs, or both decreases the incidence of CHD. Although much attention has been focused on the effect of dietary fat and cholesterol on blood lipids, diet may influence other steps in the pathogenic sequence leading to atherosclerosis or to a cardiac event. For example, dietary factors may influence the propensity toward thrombosis (essential fatty acids, omega-3 fatty acids), lipoprotein oxidation (antiox-idant nutrients), and endothelial damage (folate), among others.31,32

1. Risk-Reduction Strategies

Millions of individuals in the U.S. and throughout the world have some manifestations of atherosclerotic disease and are at risk for a fatal or nonfatal myocardial infarction. From a public health perspective, it is most important to emphasize secondary prevention measures that reduce the likelihood of serious later illness. The AHA guidelines,31 and the National Cholesterol Education Program (NCEP) Adult Treatment Panel II (ATP II),32 recommend that cholesterol-lowering therapy be initiated in individuals with CHD if their LDL cholesterol level is more than 100 mg/dL. The guidelines confirm diet therapy as primary intervention for lowering cholesterol; drug therapy is reserved for persons who do not respond to diet, or who are high risk. High risk is defined as LDL cholesterol at baseline > 130 mg/dL.

Dietary modifications for the management of elevated blood lipids do not differ much from the dietary guidelines. These diets limit total fat intake to 30% or less of total calories. Step I and Step II diets progressively restrict intake of saturated fat and cholesterol. Step I limits saturated fat to 8% to 10% and cholesterol to no more than 300 mg per day. Step II restricts saturated fat to 7% and cholesterol to less than 200 mg per day. Typical response to the diet in free-living individuals is a reduction in blood cholesterol of 3-10% for Step I and 5-15% for Step II.32-35

2. Low-Fat and Very-Low-Fat Diets

To obtain maximum reductions in cholesterol-raising nutrients, especially saturated fatty acids, low fat (< 20% of energy), and very low fat (< 10% of energy) diets have been tested by Connor, Pritikin, and Ornish, among others.32,36 Such lower fat diets usually provide a greater percentage of energy from carbohydrate. Although these diets facilitate weight reduction and reverse advanced atherosclerotic lesions, their use remains controversial. In many individuals, reduction in total cholesterol and LDL cholesterol is accompanied by a decrease in high-density lipoprotein cholesterol (HDL) and often an increase in plasma triglycerides.37 Unlike the data for LDL cholesterol and HDL cholesterol, which show strong, consistent, and opposing correlations with CHD risk, the evidence for an independent association between triglyceride concentrations and risk of heart disease is equivocal. There is, however, some indication that elevated blood triglyceride is an independent risk factor in certain subgroups such as older women and individuals with type 2 diabetes. On the other hand, the risk may be indirect and secondary to the decreased HDL cholesterol and increased levels of the highly atherogenic small-dense LDL cholesterol particles that accompany the rise in blood triglyceride levels.38

Hypertriglyceredemia secondary to low fat intake is not seen with lower energy or calorie content of diets, or when accompanied by weight loss.39,40 It is also not seen if the diet is high in plant foods with ample whole grains and fiber, or among populations in developing countries consuming mostly unrefined plant-based diets containing low quantities of animal foods.41

3. High Monounsaturated Fat (Mediterranean) Diet

From a practical point of view, saturated fat in the diet can be replaced by either carbohydrate or by monounsaturated fatty acids. Substantial reductions in total cholesterol and LDL cholesterol can be obtained by substituting sources of saturated fat in the diet (meat, poultry, eggs, whole-fat dairy products) with foods rich in monounsaturated fatty acids (olive oil, canola oil, nuts). This dietary pattern is similar to that observed in some Mediterranean regions. The dietary pattern in those areas is associated with low risk for heart disease. Although moderately high in fat

(30-40% of kcals), the Mediterranean diet is relatively low in saturated fat and effectively helps lower LDL cholesterol levels without reducing HDL cholesterol or increasing plasma triglycerides. In the mind of nutritionists, the Mediterranean diet is one in which olive oil is the dominant fat and the diet includes plenty of vegetables (including legumes) cereals, fruits and vegetables, nuts, and small amounts of cheese, fish, and meat; or, it is a plant-rich vegetarian-like diet.19

4. Vegetarian Diets

The relationship between diet and coronary heart disease is more complex than one that simply considers the influence of dietary saturated fat and cholesterol on blood lipid levels. Processes such as plaque formation, thrombosis, endothelial function, and antioxidant status may be influenced by a number of dietary components and interactions. Vegetarian diets that include small amounts of non-fat or low-fat dairy products, or vegetarian diets based entirely on plant foods (vegan) may provide greater overall benefits that go beyond those obtained by simply reducing fat or saturated fat.

a. Vegetarian Diets and Heart Disease

Compared with non-vegetarians, vegetarians in Western countries have lower mean plasma cholesterol levels and lower mortality from CHD.42,43 In a recent pooled analysis of five cohort studies from the U.S., Britain, and Germany, vegetarians had a 24% reduction in mortality from this disease.43 It is suggested that much of the reduction in heart disease among vegetarians is due to the lower intake of saturated fat and cholesterol. The data shows that, among vegetarians, consumption of total animal fat and dietary cholesterol are strongly associated with CHD mortality. However, it is also likely that other foods commonly consumed by vegetarians in large amounts offer additional protective effects. Such foods are fruits, vegetables, whole grain cereals, legumes, and nuts. Dietary patterns that emphasize plant foods provide a unique set of nutritive and non-nutritive components such as plant protein, plant sterols, and phytochemicals, which may positively influence certain biological processes and reduce disease risk.

Fruits and vegetables. Recent cohort studies highlight the protective role of fruits and vegetables in CHD. A high fruit intake is associated with reduced risk for both coronary artery and cerebrovascular disease.44 Oxidized lipoproteins are key in provoking inflammation and deposition of cholesterol in the vascular endothelium. Physiologically active components in fruits and vegetables such as vitamin C, carotenoids, and flavonoids may reduce the risk of heart disease by reducing the oxidation of cholesterol in the arteries.45-48 Sulfur-containing compounds found in garlic, onions, and leeks help reduce blood cholesterol levels.49 Trace minerals found in plants such as selenium, manganese, and copper enhance the activity of antioxidant enzyme systems and offer additional antioxidant protection.

Elevated blood homocysteine concentrations are toxic to endothelial cells and have been implicated as a risk factor for heart disease and other vascular disorders.50 Cross-sectional studies have shown a strong inverse association between dietary folate, blood folate, and blood homocysteine concentration. Plant foods are rich sources of folate, and both the consumption of fruits and vegetables and folic acid supplements lower elevated blood homocysteine levels.51,52

Fruits, vegetables, and especially legumes are rich sources of soluble fiber. Eating foods high in viscous and soluble fiber significantly lowers blood cholesterol and LDL concentrations. Soluble fiber sources that have been especially effective are pectin, oat bran, and legumes in lowering total and LDL cholesterol.53-57

Whole grains. Epidemiological studies show that fiber intake, independent of fat intake, is associated with a reduced risk of heart attacks in men. The protective effect is due mostly to cereal fiber obtained from whole grains.58 Consumption of whole grains is associated with reduced mortality in older women.59 Whole grains contain a wide variety of possibly beneficial nutrients and other constituents that are lost in the refining process.

Nuts. Nuts, including peanuts, are considered by vegetarians to be an important component of their diet and a valuable source of energy, protein, and essential fat. This is in contrast to the general perception of nuts as snack foods or attractive ingredients in candies and cookies.

Two large cohort studies have shown that higher nut consumption reduced the risk for heart disease.60,61 Clinical intervention trials have shown that substituting nuts for a portion of healthful diets results in lowering of plasma lipids in individuals with normal and elevated blood lipid levels.62,63

Legumes. Beans are a staple in vegetarian dietary patterns as a source of protein and essential nutrients such as iron, zinc, and folate. As a rich source of soluble fiber, bean consumption has been shown to lower blood lipids in hypercholesterolemic individuals.53 Among carbohydrate foods, cooked beans exhibit the lowest glycemic load, and so have beneficial effects in blood sugar modulation, satiety, and weight control. Protease inhibitors, phytic acid, oligosaccharides, and saponins found in beans are being studied for their anti-cancer and anti-tumor properties.56

Plant protein. The type of dietary protein (plant or animal) may influence blood lipids and risk of cardiovascular disease. Clinical studies on human subjects have shown soy protein to lower blood cholesterol. The vegetable protein of legumes and nuts are rich in arginine and glutamine, amino acid regulators of vascular and cardiac function.

Dietary lipids. Recent research suggests that the influence of dietary lipids on blood lipids and coronary artery function is complex. Dietary saturated fatty acids and cholesterol are known to raise blood lipid. The major source of saturated fat and cholesterol in the diet is meats and dairy foods, whereas the fat of plants is mostly unsaturated. However, trans fatty acids produced during the partial hydrogenation of vegetable oils also adversely influence blood lipids. Monounsaturated fatty acids as found in olive oil, nuts, and avocados are rather neutral with respect to heart disease mortality. The optimal intake of polyunsaturated fatty acids and the ratio of omega-3 to omega-6 fatty acids remains controversial.

The impact of fatty acids on thrombosis is unclear. A higher proportion of omega-3 relative to omega-6 inhibits platelet aggregation and thrombus formation. Although fish consumption is somewhat protective, fish oil supplements may not provide a beneficial effect.67 Omega-3 fatty acids are lower in erythrocyte, platelet, and serum phospholipids of vegetarians, especially vegans, who also show increased platelet aggregation compared with meat eaters.68,69 Although potential sources of omega-3 fatty acids other than fish and marine animals exist in plant foods (walnuts, flaxseed, algae), they may not be consumed in adequate amounts by all vegetarians.

Dietary cholesterol. The impact of dietary cholesterol on altering blood lipids is small. The average change in plasma total cholesterol levels is 2.2 mg/dL for every 100-mg change in dietary cholesterol. Also, there is much variability among individuals in response to consuming dietary cholesterol.70 Most individuals compensate for increases in dietary cholesterol by suppression of endogenous cholesterol production to maintain near-constant plasma cholesterol levels. Others are unable to compensate and demonstrate enhanced cholesterol absorption and increased plasma cholesterol with high dietary cholesterol intake.

Since dietary cholesterol is derived exclusively from animal foods, vegan diets are devoid of cholesterol, whereas vegetarian diets that include dairy products may contain some cholesterol, albeit at lower amounts compared with the general population.

Plant sterols. The main plant sterols present in the diet are sitosterol, stigmasterol, and campesterol. Plant sterols are poorly absorbed in humans and interfere with the absorption of dietary cholesterol. They have also been shown to increase LDL-receptor activity. Their effectiveness has been recently demonstrated in a trial in which participants consumed a margarine containing a sitosterol derivative (sitostanol) for a year and maintained a mean decrease of 10% in plasma cholesterol.71

Body weight. The favorable effect of vegetarian diets on blood lipids may be partially mediated through the effects of the diet on body weight. Weight loss lowers total cholesterol, triglyceride, and VLDL, and raises HDL. A metanalysis showed that an 11-lb weight loss was associated with a decline of 10 mg/dL triglycerides.72

b. The Vegetarian Diet as Intervention

The advantage of a vegetarian diet is that substantial reduction in lipid levels can be obtained without resorting to severe fat restriction. Controlled metabolic studies, in which vegetarian diets were fed to non-vegetarians, with crossover control to omnivorous diets, resulted in lower total and LDL cholesterol levels but no change in HDL levels.73,74 This is in contrast to very low fat interventions, which result in reduced HDL cholesterol.

Can vegetarian dietary practices be used instead of angioplasty or bypass surgery to manage and reverse heart disease? Ornish et al. demonstrated in the Life-Style Heart Trial that major life-style changes that included a vegetarian diet (~10% energy from fat, <5% from saturated fat, and <100 mg cholesterol) retards progression of coronary plaques and promotes regression documented by angiography.36 Total cholesterol was reduced by 24% and LDL cholesterol by 37%. What is not known at present is whether vegetarian diets with a moderate content of fat are similarly effective in reversing atherosclerosis.

B. Obesity Guidelines

The prevalence of overweight and obesity is reaching epidemic proportions nationally and worldwide.75,76 In the U.S., 55% of adults aged 20 years and older are either overweight or obese. Overweight is defined as having a body mass index (BMI) of 25.0 to 29.9 kg/m2; and obesity as BMI equal to or greater than 30 kg/m2. Similar trends are observed in children and adolescents with a doubling of the number of obese children from 20 years ago.75 Obesity is a major risk factor for coronary heart disease, hypertension, type 2 diabetes, stroke, gallbladder disease, osteoar-thritis, respiratory problems, and some cancers. In addition to the enormous health consequences that result in increased health care costs, there are significant social and psychological burdens for obese individuals and their families.77

1. Risk Reduction Strategies

It is generally recognized that overweight and obesity result from a complex interaction between genetic and environmental factors characterized by long-term energy imbalance due to a sedentary life-style and excessive caloric consumption. To promote healthful eating patterns and discourage dieting as such, dietary guidelines have focused on lowering fat and increasing carbohydrate intake as the population-based dietary strategy for the problem. Even though reducing fat intake was primarily a message to reduce saturated fat and lower blood cholesterol, it was considered to be a useful guideline for also addressing the obesity problem. Unfortunately, public awareness of the importance of reducing fat and increasing carbohydrate does not appear to have been accompanied by sufficient knowledge about how to successfully achieve this without increasing body weight. Whereas the percentage of dietary energy derived from fat has fallen steadily in the U.S. during the past 20 years, caloric intake and the rates of obesity have risen.

Because of the growing problem, the National Heart, Lung, and Blood Institute (NHLBI) recently initiated the Obesity Education Initiative.78 Guidelines from the initiative's expert panel on the identification, evaluation, and treatment of overweight and obesity in adults emphasize that, although reducing dietary fat is a practical way to reduce calories, the strategy must be accompanied by caloric restriction to be effective in weight management. As shown in Table 15.3, the focus of the initiative is on dietary caloric reduction and increased physical activity.

2. Vegetarian Diets

Studies have consistently found that vegetarians are, on the average, thinner and have lower BMIs than non-vegetarians within the same cohort.21-23 Adult populations that subsist on mostly vegetarian diets not greatly impacted by Westernization are often quite lean.76 Low fat diets that adhere to the dietary guidelines and emphasize plant foods have been found to be effective in reducing weight without caloric restriction.79

The foremost advantage of the vegetarian diet in weight control is the emphasis on consumption of minimally processed foods derived mainly from plant sources. Such unadorned whole plant foods (grains, fruits, vegetables, legumes) can be consumed in relative abundance during weight loss interventions. Such ample quantity and variety is necessary to provide a wide complement of nutrient and non-nutrient substances found in plants and needed by humans. This high-volume, low-energy dietary pattern is vital for achieving fullness and satiety, as recently affirmed in the studies conducted by Bell and colleagues.80

Table 15.3 Dietary Guidelines for Weight Control*

Dietary Component

Guidelines

Energy

Food energy reduction to achieve a

weight loss of 1 to 2 lbs per week

Low-calorie diet (800 to 1,500 kcal per

day), or

A reduction of 500 to 1,000 kcal/day

Fat

Total fat

30% or less of total calories

Saturated fatty acids

8% to 10% of total calories

Monounsaturated fatty acids

Up to 15% of total calories

Polyunsaturated fatty acids

Up to 10% of total calories

Cholesterol

< 300 mg per day

Protein

Approximately 15% of total calories

Carbohydrate

55% or more of total calories

Sodium chloride

Approximately 6 g per day

Calcium

1,000 to 1,500 mg

Fiber

20 to 30 g

  • From the National Institute of Health's Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults, 1998.78
  • From the National Institute of Health's Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults, 1998.78

The physiological advantage of an emphasis on plant foods may also stem from the influence of these foods on blood sugar control, where there is renewed interest in the role of foods with a lower glycemic index. Whole foods and foods rich in unrefined starch and fiber produce a more blunted postprandial blood sugar response and effectively control hunger than those based on highly refined carbohydrate foods.

C. Hypertension Guidelines

High blood pressure is one of the most common health problems in industrialized countries. Among U.S. adults, about one fourth suffer from hypertension. Certain subgroups within the population, such as African-Americans and the elderly, exhibit a markedly greater prevalence of hypertension. Elevated blood pressure is a significant risk factor for stroke, end-stage renal disease, congestive heart failure, and sudden death.81

1. Risk Reduction Strategies

Dietary factors have long been known to affect blood pressure control and have been the subject of years of investigation to determine their specific roles in the prevention and treatment of hypertension. Current public policy expressed in the Dietary Guidelines recommends moderate sodium restriction for the entire population to prevent hypertension and stroke. In its 6th report, the National Institutes of Health (NIH) Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI) outlines dietary and life-style modifications effective in the prevention and treatment of hypertension.82 Dietary modifications that have been demonstrated as beneficial are shown in Table 15.4 and include:

  • reducing dietary sodium consumption
  • avoiding excessive alcohol intake
  • restricting calories to reach an optimal weight if overweight
  • increasing dietary potassium, calcium and magnesium

Table 15.4 Dietary Guidelines for Blood Pressure Management*

Aspect

Guidelines

Weight reduction Alcohol intake Physical activity

Dietary Sodium Dietary potassium

Dietary calcium Dietary magnesium Dietary fats

Tobacco avoidance

Caloric restriction and increased activity in individual with BMI** > 27 Limit to 2 drinks*** per day for men; 1 drink per day for women Moderately intense physical activity (40%-60% of maximum oxygen consumption) for 30-45 minutes on most days 100 mmol/day (approximately 6 g sodium chloride or 2400 mg sodium) 90 mmol/day of potassium from food

(approximately 3600 mg) Additional potassium from potassium salt-

substitutes or supplements in hypokalemia Adequate intake for health Adequate intake for health Reduce intake of dietary saturated fat and cholesterol for cardiovascular health

  • From the 6th report of the Joint National Committee on Detection, Evaluation, and Treatment of High Blood Pressure (JNC VI)82
  • BMI is body mass index or weight in kilograms divided by height in meters squared
  • A "drink" contains 15 ml of alcohol

2. The DASH Diet

As a result of increasing awareness of the impact and complexity of dietary interactions, The National Institutes of Health initiated a multi-center, randomized clinical trial called Dietary Approaches to Stop Hypertension (DASH) that examined the effects of the guidelines on blood pressure.83 The subjects were randomized into one of three dietary treatment groups. The control group received a typical American diet with four servings of fruits and vegetables and half a serving of dairy products per day. The fruit and vegetable group received 8.5 servings of fruits and vegetables that provided increased magnesium and potassium, but the diet was otherwise similar to the control diet. The combination group received 10 servings of fruits and vegetables including legumes and nuts, and 2.7 servings of low-fat dairy products. The combination diet provided higher amounts of magnesium, potassium, and calcium. Sodium intake and body weight were kept constant for all groups. Both the high fruit and vegetable diet and the combination diet (fruit, vegetable and low-fat dairy) produced substantial reductions in blood pressure, with the combination diet being more effective.

3. Vegetarian Diets

Within populations, vegetarians exhibit lower blood pressure than non-vegetarians,84,85 and replacing a mixed diet with a vegetarian diet reduces blood pressure in both normotensive and hypertensive individuals.86 The effect has been shown in individuals who follow a lacto-vegetarian diet characterized by a relatively low intake of saturated fat, and high intake of fruit, vegetables, and other fiber-containing foods. High fruit and vegetable intake has been linked to low stroke mortality.44,87 Vegetarian diets and dietary patterns that emphasize plant-based foods provide the best strategies for the prevention and control of high blood pressure. The beneficial effect of plant-rich diets could be due to type of fat (monoun-saturated and polyunsaturated), fiber, antioxidant vitamins, carotenoids, flavonoids, and mineral contribution of the diet, especially calcium, magnesium, and potassium.

D. Diabetes Guidelines

Diabetes mellitus is a chronic condition that contributes to disease and death worldwide. Type 1 diabetes occurs less frequently and results from an autoimmune destruction of the insulin-producing pancreatic beta cells. Type 2 diabetes is the more common disease. In the U.S., it is estimated that at least 90 to 95% of the 15 million persons with diabetes mellitus have type 2 diabetes. Complications from diabetes are serious and disabling. Diabetes is the leading cause of end-stage renal disease, lower-extremity amputations, and blindness in adults. Other complications include heart disease, stroke, hypertension, nervous system disease, dental disease, and complications of pregnancy.

The management of individuals with diabetes relies heavily on dietary control along with hypoglycemic agents and insulin. The goals of therapy are the optimization of blood glucose control and minimization of the risk of hypoglycemia in individuals treated with insulin, and the prevention or delay of the onset of chronic complications for all diabetics. Clinical trials have demonstrated the benefit of aggressive treatment to achieve glycemic control in delaying complications.89

1. Insulin Resistance

It is proposed that most individuals with type 2 diabetes have had a less severe abnormality of carbohydrate metabolism before progressing to diabetes.90 The transition from normal glucose tolerance to type 2 diabetes in genetically susceptible persons involves manifestations described as insulin resistance, a condition in which body cells lose sensitivity to insulin action, and insulin-stimulated glucose disposal is compromised. Insulin resistance is associated with a metabolic syndrome characterized by a cluster of atherogenic risk factors including hyperinsulinemia, obesity with an abdominal pattern of distribution, some degree of carbohydrate intolerance, hypertension, and an abnormal blood lipoprotein profile of increased triglycerides and decreased HDL cholesterol. Other features of the syndrome include easily oxidized small LDL particles, heightened blood-clotting activity (plasminogen-activating inhibitor-1), and elevated serum uric acid concentration.

2. Risk Reduction Strategies

Despite the public health significance of type 2 diabetes, little is known about the dietary risk factors in the development of the disease.91 Although genetic predisposition is a determinant of insulin resistance, diet and lifestyle are thought to play a role in the development of the syndrome. Animal studies suggest that a high-fat, high-refined carbohydrate, low fiber diet (typical Western diet) induces insulin resistance and precedes other aspects of the syndrome including obesity. Epidemiological studies of groups such as the Pima Indians have shown decreased prevalence with high-carbohydrate native diets, and increased with Westernized high-fat diets. Risk of diabetes has also been associated with low fiber intake and large glycemic response of foods.92

The negative effects are not limited to excess consumption but also to a sedentary life-style. The incidence of type 2 diabetes is lower in physically active persons than in those who are inactive. Physical activity enhances insulin sensitivity, decreases abdominal obesity, and may prevent the development of type 2 diabetes in susceptible persons.93,94

Current dietary recommendations for persons with diabetes shown in Table 15.5 are similar to those advocated for health promotion in the general populace. They hinge on diet, exercise, and weight loss. Recommendations to decrease caloric intake and increase energy expenditure are of primary importance for people with diabetes whose BMI > 25kg/m2. The clinical disturbances of type 2 diabetes associated with obesity improve with weight reduction. To prevent the atherogenic complications of diabetes, the ADA guidelines have in the past advocated the restriction of total and saturated fat intake, and an emphasis on carbohydrates and dietary fiber. Recent findings that low fat diets tend to increase blood triglycerides and reduce HDL in diabetics have shifted the recommendations toward an individualized approach suggesting lower carbohydrate and higher monounsaturated fatty acid diets for diabetics whose blood triglycerides are high.95

3. Vegetarian and Plant Rich Diets

Although the evidence is not strong, vegetarians may have lower rates of type 2 diabetes.96 There have been a number of large cohort studies that show an inverse association between incidence of diabetes and intakes of cereal grains and dietary fiber.97-99 High risk of diabetes was associated with a large glycemic index of foods consumed by participants.97 The glycemic index is an indicator of carbohydrates' ability to raise blood glucose levels. These relationships are physiologically substantiated by the clinical trials of J.W. Anderson and others, who demonstrated that a high carbohydrate, albeit high fiber, diet composed of low glycemic foods (whole grains, fruits, vegetables, legumes, nuts) decreased postprandial glucose and insulin concentrations, and improved insulin sensitivity.100,101 Similar results were obtained recently with a low fat vegetarian diet that emphasized plant food.102

E. Cancer Guidelines

In the U.S., cancer is the second leading cause of death after cardiovascular disease and is responsible for one out of four deaths. Existing scientific evidence suggests that about one third of the 5,000,000 cancer deaths that occur in the U.S. each year are due to dietary and life-style factors, and another third can be blamed on cigarette smoking. The evidence also

Table 15.5 Dietary Guidelines for Type 2 Diabetes*

Component

Patient Characteristics

Guidelines

Energy

Overweight

Moderate caloric restriction to

achieve moderate weight loss (5

kg to 9 kg)

A reduction of 250 to 500 calories

per day.

Protein

Normal renal function

10% to 20% of calories

Nephropathy

0.6 g ■ kg-1 ■ day-1 to 0.8 g ■ kg-1 ■

day-1

Total fat

Normal blood lipids

NCEP Step 1 diet (< 30% calories

fat)

Elevated triglycerides

>30% calories fat, mainly

or VLDL

monounsaturated fat (10% to

15% of calories)

Saturated fat and

Normal blood lipids

NCEP Step 1 diet (saturated fat 8%

cholesterol

to 10% of calories, cholesterol

<300 mg per day)

Elevated LDL

NCEP Step 2 diet (saturated fat 7%

of calories, cholesterol <200 mg

per day

Carbohydrate

Normal blood lipids

Approximately 50% to 60% of

calories

Elevated triglycerides

< 50% of calories

or VLDL

Sugar (sucrose,

Moderate part of total

fructose)

carbohydrate

Fiber

20 to 35 g per day from soluble

and insoluble fiber sources

Sodium

Mild to moderate

< 2,400 mg per day

hypertension

Hypertension and

< 2,000 mg/day

nephropathy

Alcohol intake

Limit to 2 drinks** per day for

men; 1 drink per day for women

*From the American Diabetes Association Nutrition recommendations and principles for people with diabetes mellitus. 1998. **A "drink" contains 15 ml of alcohol indicates that, although genetics is a factor in the development of cancer, behavioral factors such as cigarette smoking, dietary choices, and physical activity can modify the risk of cancer at all stages of its development.103 A recent report commissioned by the World Cancer Research Fund and the American Institute for Cancer Research (AICR), in which an exhaustive collection of the relevant worldwide research on this topic was reviewed, estimated that "recommended diets, together with maintenance of physical activity and appropriate body mass, can in time reduce cancer incidence by 30-40%." The AICR report specifically identified the preventive contribution of a diet rich in plant foods. This is of particular relevance to vegetarian diets which are based mostly or entirely on plant foods.104

1. Risk Reduction Strategies

Cancer development in man is a multistage process involving multiple steps and interactions. Habitual dietary patterns can influence cancer development in various ways and at different levels. For example, food may be the source of genotoxic or carcinogenic chemicals capable of forming DNA adducts and altering genetic material, or food components may act as tumor promotors and enhance the carcinogenetic process. On the other hand, food may contain a number of preventive substances that inhibit the development of tumors.

a. Carcinogens in Food

Carcinogens may occur naturally in the diet, such as the pyrrolizidine alkaloids that exist in some plants consumed as food or herbal remedies. Some foods may be contaminated either intentionally or unintentionally by harmful agents, possible pesticide residues, additives to food, or chemicals from packaging materials. Cancer-causing substances may be produced during food storage, cooking, or processing. Aflatoxins are carcinogenic metabolites produced by Aspergillus flavus and other molds if grains and peanuts are inadequately stored. Nitrosamines, polycyclic aromatic hydrocarbons, and oxidized lipids form during cooking or processing of various foods. In developed countries, vigilance by the food industry and government regulatory agencies has been effective in maintaining negligible levels of these contaminants in the food supply and in reducing the exposure of the public to such substances. Recently, however, a new class of potent genotoxic substances called heterocyclic amines has been identified in meat cooked at high temperatures.104

b. Meat and Heterocyclic Amines

Frequent consumption of cooked meats has been associated with an increased risk of colorectal, pancreatic, and urothelial cancer.105,106 The charred surface of the meat contains heterocyclic amines such as dime-thylimidazo quinoxaline (MeIQx), and phenylimidazo pyridine (PhIP), which are produced during frying, broiling, or cooking of meat and fish. These compounds are multi-site animal carcinogens and form DNA adducts in humans. Their metabolites are detected in various body tissues and fluids. The carcinogenic potential of heterocyclic amines may differ in individuals based on inherited variation (polymorphism) in genes that influence the activation or inactivation of dietary carcinogens.107,108

c. Dietary Modulators

Dietary factors that do not of themselves exhibit a genotoxic effect may modulate the carcinogenic response of caloric intake and dietary fat. Studies in laboratory animal model systems show the component of the diet with the most dramatic effect on cancer risk is caloric intake. Restriction of energy from carbohydrate, or carbohydrate and fat, inhibits a number of cancers and results in a considerably longer life span in the restricted than in the fully fed animals. Human epidemiological studies also provide strong support for the role of dietary energy and energy balance in cancer. Observations consistently indicate that increased body weight and obesity are risk factors for cancer, especially that of the colon, endometrium, prostate, and breast, whereas higher levels of physical activity are protective in the prevention of the same cancers.104

The role of dietary fat in cancer modulation has been extensively studied in animal models. In general, diets rich in polyunsaturated fat have enhanced the development of cancer more than saturated or monounsaturated fat. This effect has been attributed to the role of linoleic acid as an essential nutrient in tumor development.105

d. Protective Substances

Foods and dietary patterns may inhibit or retard the development of cancer. The classic animal studies of L.W. Wattenberg110 first awakened the scientific community to the potential role of certain foods and their components in the prevention of cancer. Epidemiological studies demonstrated that diets containing higher amounts of plant-derived foods (fruits and vegetables) are associated with relatively low risk of cancer. Fruit and vegetable intake consistently lowered risk of a variety of tumors, especially epithelial cancers of the respiratory and GI tract (lung, esophagus, stomach, colon). Protective properties of plant foods can most likely be attributed to their rich composite of beneficial nutrients and biologically active compounds referred to as phytochemicals.

Fruits, vegetables, grains, legumes. Of the many studies on the topic of dietary pattern, the higher consumption of plant foods provides the best protection against the risk of developing cancer. The mechanism to explain the health benefits derived from eating plant foods and their relation to cancer is yet to be determined, but likely to be multiple in origin. There are many potentially anticarcinogenic substances in plant foods. Vitamin C, found in citrus and other fruits, and vitamin E in whole grains and nuts, are important antioxidants and may protect cell membranes and DNA from oxidative damage. Green leafy vegetables, legumes, and citrus fruit are sources of folic acid, which may have a protective role at the molecular level in cancer development. The sulfur-containing compounds in cabbage family vegetables (dithiolthiones, isothiocynates) and onion family vegetables (allyl sufides) enhance the activity of enzymes involved in detoxifying carcinogens and other xebiotics in the body.111-114 Carotenoids from food, not from supplements. Interest in caro-tenoids as anti-cancer agents were based on evidence from epidemiologic studies consistently suggesting that diets rich in fruits and vegetables are associated with reduced risk of cancer. Because of the strong supportive evidence from several animal models and cell culture systems,115 it was assumed that the protective component in fruits and vegetables was the plant pigment beta-carotene. Studies also showed that higher blood concentrations of beta-carotene are associated with decreased risk for cancer, especially lung and stomach cancer.116 In addition to beta-carotene, lyco-pene in tomato sauce has recently received attention for its role in preventing prostate cancer.117

The efficacy of beta-carotene as a chemo-preventive agent was tested in several large clinical trials. Results from two of these trials revealed that individuals at high risk for developing lung cancer (heavy smokers and asbestos workers) who use high-dose supplemental beta-carotene had an increased relative risk (18-23%) for developing lung cancer than control subjects. Provided as a high-dose supplement, beta-carotene may have a different effect than the same agent acquired in a food. Beta-carotene is only one of a large number of carotenoids and other phytochemicals found in fruits and vegetables. The chemo-preventive effect of whole plant foods seems to be greater than that of a single food component.118 Soy foods. Cancer of the breast is the most common cancer in women. Because genetics is believed to account for only 10-15% of cases, the search for environmental factors assumes considerable importance. Studies of Asian women suggest that those who consume a traditional diet high in soy products have a low incidence of breast cancer. Genistein, an isoflavone found in soy, is being examined as a possible protective factor for breast cancer. Exposure of immature rats to genistein promotes cellular differentiation, which results in a less active epidermal growth factor in adulthood and suppression in the development of mammary cancer in those animals.119 The consumption of soy may also reduce the risk of prostate cancer incidence. In the Adventist Health Study, men with a high consumption of soy beverage were at reduced risk of prostate cancer.120

2. Vegetarian Diets

Vegetarians in developed countries show lower cancer mortality rates for certain cancer sites than non-vegetarians.122-124 In several large cohort studies, the consumption of red meat was associated with a greater risk for colon cancer.125 In the Nurses Health Study, animal fat intake was correlated to risk of breast cancer.116 Among California Seventh-Day Adven-tists, colon cancer was 88% higher and prostate cancer 54% higher in non-vegetarians compared with vegetarians.123 In the cohort studied, both red-meat and white-meat consumption increased the risk of colon cancer, whereas legume consumption had a protective effect. Vegetarian diets are associated with lower levels of mutagenic activity and reactive oxygen species (free radical formation) especially in the digestive tract.127,128 This is possibly a consequence of higher fiber content and nutritive and nonnutritive antioxidants found in plant foods. Plant foods are rich in folate, a nutrient that is associated with lower colon cancer risk.125

The risk of fatal pancreatic cancer is also lower in vegetarian Seventh-Day Adventists, with significant protective association found for consumption of dried fruits, legumes, and vegetarian meat substitutes, some of which are derived from soy.123

a. Vegetarian Diets and the Cancer Guidelines

Nutrition guidelines to advise the public about dietary practices that reduce cancer risk are published by authoritative organizations such as the American Cancer Society.103 Table 15.6 shows these along with the guidelines published by World Cancer Research Fund and the American Institute for Cancer Research.104 The guidelines are consistent with vegetarian dietary practices. Vegetarians tend to be leaner than non-vegetarians. Their food patterns emphasize a variety of whole plant foods and the avoidance of meat intake as expressed in the cancer prevention guidelines.

Good Carb Diet

Good Carb Diet

WHAT IT IS A three-phase plan that has been likened to the low-carbohydrate Atkins program because during the first two weeks, South Beach eliminates most carbs, including bread, pasta, potatoes, fruit and most dairy products. In PHASE 2, healthy carbs, including most fruits, whole grains and dairy products are gradually reintroduced, but processed carbs such as bagels, cookies, cornflakes, regular pasta and rice cakes remain on the list of foods to avoid or eat rarely.

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