A Review of the Fundamentals of Diet

Glob Adv Health Med. 2013 Jan; 2(1): 58–63.
Published online 2013 Jan 1. doi: 10.7453/gahmj.2013.2.1.010
PMCID: PMC3833586
PMID: 24381826

A Review of the Fundamentals of Diet


Una revisiуn de los aspectos bбsicos de la alimentaciуn


Dietary recommendations should be individualized for each patient, but certain basic principles apply to most people. A healthful diet should include a wide variety of whole, unprocessed foods that are free of additives and, if possible, grown without the use of pesticides, herbicides, and other potentially toxic agricultural chemicals. For people who do not have specific food intolerances, such a diet generally includes liberal amounts of fresh fruits and vegetables, whole grains, nuts, seeds, and legumes. For most people, animal foods such as eggs, fish, chicken, beef, and dairy products can be healthfully consumed in moderation. It is not necessary to consume animal foods to maintain good health. In fact, compared with omnivores, vegetarians have a lower risk of developing a number of chronic diseases. However, vegetarians must carefully plan their diet so as not to develop nutritional deficiencies.

Key Words: Diet, whole foods, phytochemicals, vitamins, minerals


Dietary recommendations should be individualized for each patient, but certain basic principles apply to most people. A healthful diet should include a wide variety of whole, unprocessed foods that are free of additives and, if possible, grown without the use of pesticides, herbicides, and other potentially toxic agricultural chemicals. For people who do not have specific food intolerances, such a diet generally includes liberal amounts of fresh fruits and vegetables, whole grains, nuts, seeds, and legumes. For most people, animal foods such as eggs, fish, chicken, beef, and dairy products can be healthfully consumed in moderation. It is not necessary to consume animal foods to maintain good health. In fact, compared with omnivores, vegetarians have a lower risk of developing a number of chronic diseases. However, vegetarians must carefully plan their diet so as not to develop nutritional deficiencies.

A balanced, whole-foods diet provides the nutrients that are essential for life and good health, including protein, carbohydrates, fat, vitamins, and minerals. In addition, whole foods contain fiber and a wide range of phytochemicals that may have health benefits. These include flavonoids (which enhance tissue integrity), indole-3-carbinol (which may help prevent cancer), lignans (compounds with possible anticancer activity that are present in the fiber component some plants),1 oligosaccharides (which support the growth of beneficial intestinal bacteria), sterols (which lower serum cholesterol levels), hippuric acid (an antibiotic), and alkylresorcinols (see below). Each new scientific discovery regarding phytochemicals reminds us of the enormous complexity of whole food and of the futility of attempting to duplicate their effects with “nutraceutical” pills and potions.


Whole grains contain a wide range of vitamins and minerals, as well as fiber, essential fatty acids, and accessory food factors. Refining of whole wheat to white flour depletes most of the fiber and results in substantial losses of vitamins and minerals (as noted in Tables 1 and ?and22).2 In addition, more than half of the betaine is lost in the refining of whole wheat.3 Betaine lowers homocysteine levels and might be of value for preventing cardiovascular disease.4 Whole wheat and some other whole grains (but not their refined counterparts) also contain alkylresorcinols, a class of phenolic lipids that can be incorporated into cell membranes.5 In rats, administration of alkylresorcinols increased tissue concentrations of gammatocopherol,6 a naturally occurring form of vitamin E that appears to have cardioprotective effects. In observational studies, consumption of whole grains (as compared with refined grains) has been associated with reduced risk of cardiovascular disease, stroke, and diabetes, and increased longevity.7,8 For these reasons, whole grains are strongly preferable to refined grains.

Table 1

Losses of Vitamins in the Refining of Flour2

Vitamin Amount Lost
Thiamine 77%
Riboflavin 80%
Niacin 81%
Vitamin B6 72%
Pantothenic acid 50%
Folic acid 67%
Vitamin E 86%
Choline 30%

Table 2

Losses of Minerals in the Refining of Flour2

Vitamin Amount Lost
Magnesium 85%
Potassium 77%
Calcium 60%
Iron 76%
Zinc 78%
Copper 68%
Manganese 86%
Chromium 40%
Selenium 16%
Molybdenum 48%


Consumption of beans and other legumes (eg, lentils) has been reported to improve blood glucose regulation and to lower serum cholesterol levels. Beans form a complete protein when combined with grains in a 1:3 ratio (dry weight).

Soy products, in addition to having the beneficial effects mentioned above, have been shown in some, but not all, studies to improve menopausal hot flashes and other menopause-related symptoms. Soy foods have also demonstrated an antihypertensive effect. In addition, soy may help prevent osteoporosis and some types of cancer, although the evidence is conflicting. Some of the effects of soy appear to be due to its content of isoflavones, which have both estrogenic and anti-estrogenic effects.

On the negative side, soy is a relatively common allergen. In addition, some practitioners have observed that processed soy can be difficult to digest, resulting in various gastrointestinal symptoms. Soy products (particularly isolated soy protein) have been shown to inhibit iron absorption, and soy appears to inhibit the absorption of levothyroxine as well. In one study, treatment with a relatively high dose of soy isoflavones (150 mg/ day) for 5 years caused endometrial hyperplasia in 3.9% of women, although no endometrial hyperplasia was seen after 2.5 years.9


Fruits and vegetables are rich sources of vitamins, potassium and other minerals, carotenoids, flavonoids, fiber, and phytochemicals. Some vegetables are also good sources of essential fatty acids. Consumption of abundant amounts of fruits and vegetables may be useful for preventing or treating cardiovascular disease, stroke, some cancers, hypertension, osteoporosis, and other diseases.

With regard to specific fruits and vegetables, cruciferous vegetables such as broccoli, Brussels sprouts, cabbage, kale, and cauliflower contain isothiocyanates and indole-3-carbinol, which have demonstrated anticancer effects. In addition, indole-3-carbinol has been reported to be an effective treatment for cervical dysplasia. Onions may inhibit platelet aggregation, increase fibrinolytic activity, and lower blood pressure. Each of these effects would be expected to reduce the risk of cardiovascular disease. Administration of tomato extracts has been shown to inhibit platelet aggregation and to lower blood pressure. In addition, tomatoes are a major food source of lycopene, which may help prevent prostate cancer. Spinach, kale, and other dark green leafy vegetables are good sources of lutein, a carotenoid that may help prevent age-related macular degeneration. However, spinach is also high in oxalate and may therefore be contraindicated in people with calcium oxalate kidney stones. Blueberries are a good source of anthocyanosides, which enhance capillary integrity and play a role in visual function. Cranberries contain compounds that inhibit the binding of pathogenic Escherichia coli to uroepithelial cells. Cranberry juice and cranberry extracts have been found to be effective for preventing urinary tract infections. Olives are rich in cardioprotective monounsaturated fatty acids. Olives and extra virgin olive oil (but not refined olive oil) also contain a number of phenolic antioxidants (oleuropein, hydroxytyrosol, vanillic acid, and verbascoside), which may have anti-inflammatory and cardioprotective effects.


Nuts are a good source of protein, essential fatty acids, magnesium, and fiber. Consumption of various types of nuts has been shown to lower serum cholesterol levels. In observational studies, eating nuts was associated with a lower incidence of cardiovascular disease. Since the polyunsaturated fatty acids in nuts can become oxidized to form potentially toxic lipid peroxides, nuts should be stored in an airtight container in the refrigerator. Nuts are best consumed raw and unsalted.


Fish is a good source of protein, omega-3 fatty acids, and other nutrients. Consumption of fish or fish oil has been found to reduce the incidence of cardiovascular disease. Fish oil has an anti-inflammatory effect and has been shown to be beneficial for the prevention and treatment of a wide range of illnesses. Fish are at the top of the food chain and contain mercury and other toxins. However, the bulk of the evidence suggests that the benefits of moderate fish consumption (such as 2–3 servings a week) outweigh the risks.


Meat and poultry contain substantial amounts of protein and heme iron (particularly red meat), as well as B vitamins, minerals, and carnitine. However, these foods are also high in cholesterol and saturated fat and, being at the top of the food chain, tend to accumulate pesticides and other toxic substances. Cooking meat and poultry at high temperatures results in the production of carcinogens and advanced glycation end products (which may promote the development of cardiovascular disease and other diseases). The available evidence suggests that meat and poultry should be used in moderation and cooked at low temperatures, preferably in the presence of moisture. Meat from animals raised organically, without the use of antibiotics and hormones, is preferable.


Eggs are a good source of high-quality protein, lutein, choline, and other nutrients. Although eggs are high in cholesterol, egg consumption has little or no effect on serum cholesterol levels in most people. In observational studies, eating eggs was associated with an increased risk of heart disease in diabetics but not in nondiabetics. Eggs should be cooked in such a way as to minimize the formation of angiotoxic cholesterol oxides (ie, boiling or poaching as opposed to scrambling or frying).


Cow’s milk is a good source of protein, calcium, and vitamin D. However, cow’s milk is also one of the most common food allergens and, as such, is a frequent etiological or triggering factor in a wide range of illnesses. In addition, cow’s milk consumption may play a role in the pathogenesis of type 1 diabetes.


The available evidence suggests that people should minimize their consumption of trans fatty acids. People should also avoid using polyunsaturated fatty acids for frying or high-temperature cooking in order to minimize the formation of potentially toxic lipid peroxides. Saturated fats may not be as harmful as is commonly believed, although some foods that are high in saturated fat may be atherogenic for reasons largely unrelated to their saturated fat content.


Refined grains should, whenever possible, be replaced by whole grains (eg, whole grain bread instead of white bread and brown rice instead of white rice). Refining of grains removes the nutrient-rich germ portion and the nutrient- and fiber-rich bran portion of the grain. Refined grains, which comprise approximately 30% of the calories in the American diet, contain substantially lower amounts of vitamins, minerals, and fiber than do their unrefined counterparts. In addition, the carbohydrates in refined grains are absorbed relatively rapidly and may therefore lead to less-than-optimal blood glucose control.


In addition to emphasizing the use of health-promoting foods, it is important for patients to restrict their intake of foods that cause symptoms and promote illness. At the top of the list of undesirable foods is refined sugar, which is most commonly consumed as sucrose and high-fructose corn syrup (HFCS). Nearly 20% of the calories in a typical American diet are derived from added sugars (not including the sugars that occur naturally in fruit, milk, and other foods). This translates, according to one estimate, to an average of about 40 teaspoons of added sugar per person per day,10 and many people consume much more than that. Since refined sugar contains virtually no vitamins, minerals, or other micronutrients, sugar consumption decreases overall micronutrient intake by an average of almost 20%. In addition, refined sugars are energy-dense (ie, they provide a large number of calories in a small volume) and contain no fiber. Because it takes a relatively large number of calories from energy-dense foods to produce a feeling of fullness, excessive intake of sweets can lead to overeating and obesity.

It is generally agreed that excessive sugar consumption contributes to obesity and tooth decay. However, it is not widely appreciated that high sugar intake or sensitivity to refined sugar is in some cases a major contributing factor to a diverse array of symptoms and conditions, including fatigue, anxiety, depression, migraines, tension headaches, premenstrual syndrome, and candidiasis. Excessive consumption of sucrose and HFCS appears to be an important contributing factor to many of the chronic health problems that are prevalent in Western society. Excessive intake of refined sugar may promote or exacerbate obesity, type 2 diabetes, nonalcoholic fatty liver disease, hypertension, hypertriglyceridemia, cardiovascular disease, kidney stones, chronic diarrhea/irritable bowel syndrome, gall-bladder disease, tooth decay, fatigue, anxiety, depression, attention deficit-hyperactivity disorder, migraines, tension headaches, premenstrual syndrome, candidiasis, and other conditions.


Historically, sucrose and other refined sugars were consumed only in small quantities. For example, estimated annual per capita sucrose consumption was 6 lbs to 8 lbs in the 1750s. This increased to about 25 lbs in the 1850s and to 120 lbs in the 1950s.11 Over the past few decades, a significant amount of the sucrose in the Western diet has been replaced by HFCS. As of 1997, mean annual per capita sucrose consumption had decreased to 67 lbs, but mean total intake of these refined sugars combined (sucrose plus HFCS) had increased to 129 lbs or about 40 teaspoons of added sugar per day. That level of intake corresponds to an average of 17-18%12 to more than 20% of total calories, depending on the method of calculation. Many people consume refined sugar in amounts well above the average.


Refined sugar is absorbed rapidly into the bloodstream; a phenomenon the human body was not apparently programmed to handle efficiently. An abrupt rise in blood glucose levels may trigger the pancreas to release an excessive amount of insulin, which can lead to reactive hypoglycemia and a compensatory increase in the levels of blood sugar–raising compounds such as epinephrine and cortisol.13 These and other disruptions of homeostatic mechanisms may contribute to the development of some of the symptoms and chronic diseases listed above.


Consumption of large amounts of sucrose may cause adverse changes in various cardiovascular disease risk factors, including an increase in serum levels of triglycerides, insulin, and uric acid; a rise in blood pressure; an increase in platelet adhesiveness; and a decrease in HDL-cholesterol levels.14,15 Approximately one-third of the population is susceptible to these adverse effects of sucrose, and sucrose sensitivity appears to be clustered in people who have, or are at increased risk of developing, cardiovascular disease.16 Fructose consumption has been reported to increase triglyceride and uric acid levels and to promote insulin resistance.17


Ingestion of 100 g (25 teaspoons) of sucrose, glucose, or fructose by healthy volunteers caused a transient decrease in the capacity of their neutrophils to engulf bacteria.18,19 Ingestion of 75 g of glucose by healthy volunteers also transiently decreased measures of cell-mediated immune function.20 These findings raise the possibility that limiting consumption of refined sugar would be useful for preventing or treating infections.


Fructose malabsorption appears to be a common, though underappreciated, cause of diarrhea and other symptoms often attributed to irritable bowel syndrome. The amount of fructose that can be absorbed as a bolus varies widely among healthy volunteers, from 5 g to more than 50 g.21 Glucose enhances fructose absorption, and malabsorption of fructose typically occurs only if more fructose than glucose is present.22 Thus, gastrointestinal symptoms may be more likely to occur with HFCS (which has a fructose-to-glucose ratio of 1.31:1), than with sucrose (which has a 1:1 ratio). However, sucrose consumption has also been reported to cause chronic diarrhea, possibly through a mechanism unrelated to fructose malabsorption.


Serum fructose concentrations increase in a dose-dependent manner after ingestion of sucrose or fructose. A 20-oz soft drink, which contains 33 g of fructose, would be expected to increase the fasting serum fructose concentration by approximately four-fold. In healthy volunteers, peak serum fructose levels were 36% to 41% lower after consumption of sucrose (0.5 g/kg and 1.0 g/kg of body weight) than after consumption of equivalent amounts of fructose (0.25 g/kg and 0.5 g/kg, respectively).23 The blunted rise in serum fructose levels after ingestion of sucrose (as compared with fructose) is probably related to the fact that the fructose portion of sucrose is not available for absorption until sucrose is hydrolyzed by intestinal brush border enzymes. The fructose portion of sucrose is, therefore, presumably absorbed more slowly than fructose ingested as the monosaccharide.

There appears to be no evolutionary precedent for the substantial increase in plasma fructose concentrations that results from eating high-fructose (and, to a somewhat lesser extent, high-sucrose) diets. Fructose is a powerful reducing sugar, and therefore promotes the formation of advanced glycation end products, which may contribute to the aging process and to the pathogenesis of cardiovascular disease and diabetic complications. In rats, ingestion of fructose or sucrose (but not glucose) increased tissue concentrations of advanced glycation end products.24 In addition, hyperfructosemia may deplete hepatic adenosine triphosphate (ATP) levels with potential deleterious consequence both for liver health and general metabolism.


While excessive consumption of all types of refined sugar should be discouraged, a case can be made that HFCS is somewhat more harmful than sucrose. One possible disadvantage of HFCS relative to sucrose is the higher ratio of fructose to glucose in the former. This higher ratio would be expected to produce higher serum fructose concentrations, with potenti

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