Fundamentals of Nutrition pg 3

Phytochemicals are nonnutrient compounds in plants that have biological activity in the body. Some examples of these substances are carotenoids in deeply pigmented fruits and vegetables, allyl sulfides in garlic and onions, sulforaphane in cabbage family plants, and flavonoids in fruits, vegetables, and tea. In addition to imparting flavor and color to foods, phytochemicals can have profound physiological effects, including the suppression of the development of cancer.

There are several modes of action of phytochemicals. Some, such as carotenoids and flavonoids, act as antioxidants. Others, such as limonene in citrus fruits and allyl sulfides in garlic and onions, trigger enzyme production to facilitate carcinogen excretion. Caffeic acid in fruits triggers enzyme production to make carcinogens water-soluble, facilitating excretion. There are many active hormone-like substances found in plants such as isoflavones in soy protein. The isoflavones, genistein and daidzein, are selective estrogen response modifiers. They are proestrogenic in bone and brain, and anti-estrogenic in breast and uterus. Isoflavones are also antioxidants, and tyrosine kinase inhibitors capable of inhibiting breast and prostate tumor cell growth in vitro.

Xenobiotics

Xenobiotics are external elements providing a signal to the cell. Often these xenobiotics have a precursor form which requires activation by oxidation. These reactions are carried out by so-called drug metabolizing enzymes (DME’s). Other DME’s carry out inactivation of the oxygenated ligand providing a regulatory mechanism. Apoptosis, or cell death, differentiation, and neuroendocrine functions can be carried out in response to the expression of specific genes triggered by active oxygenated ligands derived from xenobiotics.

Potentially carcinogenic dietary constituents and potentially protective dietary constituents interact in pathways of DNA oxidation and damage leading to carcinogenesis. These pathways are well-studied for smoking related carcinogens and there is emerging evidence on the applicability of this common pathway to drugs and food constituents. Potentially carcinogenic dietary constituents and potentially protective dietary constituents also co-exist in the food supply. While pesticides are considered a potential source of carcinogens, the protective substances found in foods may counteract the harmful effects of other toxins.

While man evolved on earth about 50,000 to 100,000 years ago, the drug-metabolizing enzymes were developed hundreds of millions of years ago in simple bacteria. For example, cytochrome P450 has over 150 isoforms in different species. Agriculture only evolved 10,000 years ago and modern western diets have been here only a few hundred years. There is a gene-environment imbalance for individuals eating a typical high fat diet.

The Pima Indians of Northern Mexico and Southern Arizona demonstrate the impact of nutrition on genetic expression of chronic diseases such as obesity and non-insulin dependent diabetes mellitus (NIDDM) . Pimas in Arizona have the highest reported prevalence of obesity and non-insulin dependent diabetes, while the incidence is low in Pimas living in Northern Mexico. Pima Indians living in the mountains of Northern Mexico were separated some 700 to 1000 years ago from the Pimas living today in Arizona. The Northern Mexico inhabitants continue to live a traditional lifestyle, eating a diet with much less animal fat and more complex carbohydrates, and have higher activity levels, than Pimas in Arizona. This population demonstrates increased body weight, height (which is a biomarker of prepubertal nutrition), increased body mass index, increased cholesterol and increased incidence of NIDDM. The "thrifty gene" hypothesis states that genes for conserving energy, while adaptive in a traditional environment, are responsible for the high prevalence of obesity and diabetes in individuals exposed to overnutrition and underactivity

Recommendations for dietary intake among populations often take the form of pyramids, with the base of the pyramid determining the basis of the diet. In the USDA pyramid developed in the late 1980’s the base consists of cereals and grains without an emphasis on the fiber content of those grains. The fruits and vegetables appear on the second level and are two separate groups. In a new pyramid developed in 1997 by the UCLA Center for Human Nutrition, a modified plant-based diet is recommended. The base consists of 5 to 11 servings of fruits and vegetables to provide unique phytonutrients for chronic disease prevention. The second level is 6 to 9 servings of high fiber cereals and grains to provide the benefits of fiber from this level as well as from fruits and vegetables. The protein level is made up of low fat protein choices including protein from the plant kingdom (beans and rice or soybean protein) and the animal kingdom (egg whites, breast of chicken and turkey, low-fat fish and seafood, and non-fat milk products). The top tier of the USDA pyramid has only dots representing fats and sweets with the mixed message "use sparingly". The top tier of the new California Pyramid emphasizes taste enhancers including olives, avocados, garlic, onion, nuts, cheese, chili peppers, and as much monounsaturate or omega-3-rich oils as needed to enhance taste. The overall fat recommendation of the USDA pyramid is 30% or less of calories from fat, while the new pyramid reflects the decreased fat intake in the population by recommending 20% or less of calories from fat. This exercise illustrates how the science of nutrition can be used to influence dietary recommendations