1.4 Health Factors and Their Impact

Everyone starts out in life with the genes handed down to them from the families of their mother and father. GenesThe sequences of DNA that code for all the proteins in your body. are responsible for your many traits as an individual and are defined as the sequences of DNA that code for all the proteins in your body. The expression of different genes can determine the color of your hair, skin, eyes, body size, and if you have an increased risk for a certain disease. The sequence of DNA that makes up your genes determines your genetic makeup, also called your genomeEntire genetic information contained in an individual that is inherited from their parents., which is inherited from your mother and father. In 2003, the Human Genome Project was completed, and now the entire sequence of DNA in humans is known. It consists of about three billion individual units and contains between twenty-five and thirty thousand genes. The human genome that was sequenced was taken from a small population of donors and is used as a reference DNA sequence for the entire population. Each of us has a similar but unique DNA sequence. Only identical twins and cloned animals have the exact same DNA sequence.

Now that we understand the map of the human genome, let’s enter the fields of nutrigenetics and nutrigenomics and epigenetics. Recall that nutrigenetics refers to the study of how variation in one’s genes leads to different responses to one’s nutrient intake. NutrigenomicsAn emerging scientific discipline that studies how nutrients affect gene expression and how genes affect our nutritional requirements.  is an emerging scientific discipline that examines how nutrients affect gene expression. Chemical reactions in the body can turn genes “on” and “off,” causing changes in the amounts and types of proteins expressed. It is a subfield of epigeneticsA rapidly advancing scientific field in which researchers study how nongene factors affect gene expression. , which is a rapidly advancing scientific field in which researchers study how chemical reactions turn genes “on” and “off” and the factors that influence the chemical reactions. Some of these factors are now known to be nutrients. Researchers at the Genetic Science Learning Center at the University of Utah conducted an experiment in which some pregnant mice were fed a diet containing folate, choline, vitamin B₁₂, and betaine, and other pregnant mice were fed a diet that did not contain these nutrients and chemicals. Both groups of pregnant mice were also fed bisphenol A (BPA), a chemical in plastic, which alters DNA by inhibiting a specific chemical reaction. The mice born from the mother fed the supplemented diet were brown, thin, and healthy. The mice born from the mother fed the unsupplemented diet were yellow, fat, and unhealthy. This is a dramatic example of how nutrients change not the sequence of DNA, but which genes are expressed. These two mice look different, but have identical DNA sequences. Thus, not only do the things you eat determine your health, but so do the things your mother ate during pregnancy. Moreover, other studies have demonstrated what your dad ate—and what your grandmother ate while she was pregnant with your mother!—also can affect your gene expression and, consequently, your health. But while genetics—and epigenetics—are important in determining your health, they are certainly not the only determinant.

The life cycleThe stages of life one passes through until death. of human beings originates from a fertilized egg, which develops into a fetus that is eventually born as a baby. A baby develops into a child, transitions through adolescence, becomes an adult, and then advances into old age and eventually death (refer to Figure 1.4). The current average life expectancy in America is approaching eighty years (though this varies by sex and race). To see how this compares with other countries, refer to “Interactive: Global Life Expectancy”.

A person’s stage of life influences their health and nutritional requirements. For example, when you are an adolescent, your bones grow quickly. More calcium, a bone-building nutrient, is required in the diet during this life stage than at other stages. As you get older, the aging process affects how your body functions. One effect of aging, apparently occurring earlier in women than in men, is the deterioration of bone tissue. As a result, women over age fifty-one need more calcium in their diet than do younger adult women. Another life-cycle stage, pregnancy, requires several adjustments to nutrition compared to those who are not pregnant. It is recommended that pregnant people consume more protein than nonpregnant people to support growth and development, and to consume more of some vitamins, such as folate, to prevent certain birth defects. Healthy aging requires eating a diet that matches one’s life stage to support the body’s specific physiological requirements.

Your environment has a large influence on your health. Scientists say that the majority of your expressed traits are a product of the interaction of your genes and environment, of which nutrition is a component. An example of this interaction can be observed in people who have the rare genetic disorder phenylketonuria (PKU). The clinical signs of PKU are intellectual disability, behavioral problems, and seizures and are caused by the build-up of the amino acid phenylalanine and its metabolites (i.e., breakdown products produced during metabolism) in the body. The high level of phenylalanine in a person who has PKU is the result of a change in the gene that encodes for an enzyme that converts phenylalanine into the amino acid tyrosine. This genetic change, called a mutation, causes the enzyme to not function properly. In this country and many others, all new-born babies are screened for PKU, and other mutations, to diagnose and treat the disease before the development of mental retardation and brain damage. Once diagnosed, PKU is treated by strict adherence to a diet low in phenylalanine, consisting mostly of fruits, vegetables, grains, and special medical foods that contain all essential amino acids except phenylalanine. Adhering to this diet throughout their life cycle allows an individual with PKU to lead a normal life without suffering the consequences of intellectual disability, behavioral problems, and seizures. In the example of PKU, the consequences of a genetic mutation are modified by diet. Thus, a person’s genes can make them more susceptible to a particular disease, or cause a disease, and their environment can decrease or increase the progression and severity of the condition.

Lifestyle refers to the way in which a person or group lives. One facet of lifestyle is your dietary habits. Recall that we discussed briefly how nutrition affects health. A greater discussion of this will follow in subsequent chapters in this book as there is an enormous amount of information regarding the effects of nutrition on health. Dietary habits include what a person eats, how much a person eats during a meal, how frequently meals are consumed, and how often a person eats out at restaurants. Other aspects of lifestyleComponents of lifestyle are dietary habits, physical activity level, recreational drug use, and sleeping patterns, all of which play a role in health and impact nutrition. include physical activity level, recreational drug and alcohol use, and sleeping patterns, all of which play a role in health and impact nutrition. Following a healthy lifestyle improves your overall health. It’s important to remember, though, that how easy or difficult it is to follow a healthy lifestyle depends on one’s environment. For example, socioeconomic factors such as income, employment, geographic location, and discrimination can affect whether a person has access to healthy food, the ability to afford healthy food, access to safe places to engage in physical activity, whether options for physical activity are accessible to people with disabilities, and access to health care, just to name a few.

Many things affect our choices around what, when, and how much to eat. In addition to nourishing our bodies, food also has psychological, cultural, and religious significance. The social implications of food have a great deal to do with what people eat, as well as how and when. Special events in individual lives—from birthdays to funerals—are commemorated with equally special foods. Being aware of these can help people make healthier food choices—and still honor the traditions and ties they hold dear. Typically, eating kosher food means a person is Jewish; eating fish on Fridays during Lent means a person is Catholic; fasting during the ninth month of the Islamic calendar means a person is Muslim. On New Year’s Day, people from New England like to combine pork and sauerkraut as a way to eat their way to luck. Several hundred miles away in the southern United States, people eat Hoppin’ John, a favorite local dish made with black-eyed peas and pork, while eating soba noodles at midnight on New Year’s symbolizes longevity and prosperity for Japanese Americans. National food traditions are carried to other countries when people immigrate. American cuisine would not be what it is today without the contributions of Italian, Chinese, Mexican, and other cultures.