Nutrition Science and Dietetics

Summary

Nutrition and dietetics, a multidisciplinary field that involves acquiring and using nutrients from food sources to sustain life and growth, incorporates the science of economically producing and making foods available to a global society. Illnesses may result from inadequate or poor food choices, and certain health conditions require diet modifications to maintain or restore health.

Definition and Basic Principles

Nutrition is the science of providing and processing nutrients from food for survival and growth. It involves assimilating nutrients and turning food consumed into energy. Approximately fifty nutrients are essential for human life and health.

Dietetics is the science and art of procuring, planning, and preparing foods to supply nutrients in a palatable, pleasing, and economical way. It incorporates principles of nutrition and the interactions among nutrients. In a broader scope, dietetics includes the social, cultural, and psychological aspects of food acquisition and consumption.

Background and History

Antoine-Laurent Lavoisier, the father of nutrition, recognized the relationship between food and respiration in the 1700s. In 1830, Dutch chemist Gerard Johann Mulder classified proteins. W. O. Atwater, the father of American nutrition, published the first table of food values in 1896. Two decades later, American biochemist E. V. McCollum referred to vitamins and minerals as “protective foods.”

Most vitamins were discovered in the early 1900s, although their presence in certain foods had been noted. Scientists first recognized vitamin A in 1913. Since the Middle Ages, an unidentified substance in cod liver was known to prevent rickets, and in the 1920s, this substance, vitamin D, was isolated from vitamin A. As early as 1753, English physician James Lind had noted that sailors fed citrus fruits avoided scurvy. It was not until 1928, however, that vitamin C was first isolated. Deficiencies of substances, later named B vitamins, were known to result in beriberi, pellagra, and other diseases. Scientists classified B vitamins by numbers (B₁, B₂, B₃, and so on) as they isolated specific types. In 1917, Lenna F. Cooper founded the American Dietetic Association (ADA) to help the government conserve food and improve the nation's health and nutrition during World War I. As the twentieth century progressed, the importance of nutrition and developing a healthy diet full of vitamins and nutrients grew.

How It Works

Energy Metabolism.Calories are units of heat measure used for body energy. One pound of body weight equals 3,500 calories. Body metabolism and activity levels determine daily calorie needs. Most adult women need 1,900 to 2,100 calories, while adult men need about 2,100 to 2,400 calories daily. Calorie requirements decrease with age because metabolism naturally slows about 5 percent per decade after age forty. Only the energy nutrients—carbohydrates, fats, and proteins—provide calories to the body.

Carbohydrates, also known as sugars and starches, are primary sources of calories. Each gram of carbohydrate yields about four calories. The simple sugar glucose is the major fuel source and the only sugar found in the body. Two other simple sugars are fructose, found mostly in fruits, and galactose, a component of the double sugar lactose. Sucrose, a double sugar known as table sugar, is the most common sugar in the diet. Complex glucose molecules, called starches, come primarily from potatoes and grains.

Lipids or fats yield about nine calories per gram. Fats act as carriers for fat-soluble vitamins. Dietary fat improves palatability and provides satiety. Two common types of fats that are significant in health are saturated and unsaturated fatty acids. Saturated fats, primarily from animal sources, are generally solid at room temperature. These fats may cause build-up of fatty plaques in the blood and contribute to blood clots.

Unsaturated fats, found in plants, are better choices for a healthful diet. These fats, usually soft or liquid at room temperature, vary from monounsaturated (the major fatty acid in olive oil) to polyunsaturated fatty acids (found in cottonseed, soybean, corn, and canola oils). Hydrogenation, which changes fatty acids from liquid to solid, creates trans fats. Trans fats raise blood cholesterol levels and may contribute to heart disease.

Protein comes from the Greek word meaning “to take first place.” Proteins, found in every living cell, are composed of amino acids. Of the twenty-two known amino acids, nine are essential in the diet. Nonessential (dispensable) amino acids are derived from the essential ones or manufactured in the body. Protein, which yields about four calories per gram, is inefficient as an energy source. However, with insufficient carbohydrates, the body converts protein into glucose for energy. Protein builds and repairs body tissue. Amino acids may function as precursors for transport substances such as lipoprotein. Complete proteins found in meats, eggs, and milk contain all essential amino acids. Plant sources such as legumes and nuts lack at least one essential amino acid and are incomplete proteins.

Fat-Soluble Vitamins. Vitamins, organic substances the body needs in minute quantities, are categorized into fat-soluble and water-soluble. Each vitamin has specific functions. Generally, vitamins regulate cell metabolism in conjunction with enzymes and contribute toward the construction of body tissue. The fat-soluble vitamins—A, D, E, and K—can be stored in fatty tissues in the body.

Vitamin A (retinoid), necessary for the growth and development of skeletal and soft tissues and maintenance of normal epithelial structures, is called the anti-infective vitamin. Major sources are dark green and deep yellow fruits and vegetables. Few sources other than cod liver oil provide significant amounts of vitamin D. Therefore, almost all forms of milk are fortified at a level of 400 international units (IU) per quart. Vitamin D helps form normal bones and teeth and provides other functions. Vitamin E (tocopherol) is an antioxidant that is important for protecting cells from oxidation. Sources include vegetable oils, margarine, whole-grain products, seeds, and nuts. Vitamin K, important in blood clotting, is found in most green leafy vegetables.

Water-Soluble Vitamins. Vitamin C (ascorbic acid) functions in forming collagen, wound healing, metabolic functions, and other roles. Foods high in vitamin C include citrus fruits, strawberries, cantaloupe, and cruciferous vegetables. B vitamins are important in energy metabolism. Thiamin (B₁) is called the antineuritic vitamin. Riboflavin (B₂), rarely deficient in the diet, is found most abundantly in milk and dairy products. Niacin (B₃) is prevalent in meats, poultry, fish, peanut butter, and other foods. Other major B vitamins include folic acid (B₉), B₆, and B₁₂.

Minerals. Minerals have varied functions in building tissue. The major minerals found in larger quantities in the body include calcium, phosphorus, magnesium, and iron. More than 99 percent of calcium and 85 percent of phosphorus in the body is in the bones. Calcium, essential in blood coagulation, is involved in nerve, enzyme, and hormone functions and other activities. Iron is primarily involved in oxygen transport within the blood. Although many trace elements have been identified as essential, the best known are copper, zinc, manganese, cobalt, selenium, chromium, and molybdenum.

Applications and Products

Even with sufficient global food supplies, much of the world fails to acquire appropriate nutrition to sustain good health. Food insecurity (a lack of nutritious food) or excessive weight problems often result from limited knowledge, skills, or the financial means to procure more healthful foods.

Food Insecurity. According to the 2023 edition of the United Nations' State of Food Security and Nutrion World Report, food insecurity affected between 691 and 783 million people worldwide in 2022. Almost 12.8 percent of American households were food insecure in 2022, according to the US Department of Agriculture (USDA). Of these people, about 7.7 percent had very low food security, causing reduced food intake and disruption of normal eating patterns. The remainder use a variety of coping strategies, including participation in various food programs. The COVID-19 pandemic of 2020-2021 led to unemployment and increasing food insecurity worldwide. In the 2020s, inflation, which specifically affected food and grocery prices, also contributed to food insecurity. USDA’s yearly data on food insecurity highlighted growing food shortages because of limited financial resources.

Food insecurity is more prevalent in households with incomes near or below the federal poverty line, single-parent households, and Black and Latino households. In the United States, numerous agencies exist to alleviate food insecurity. The three largest federal food and nutrition assistance programs are the National School Lunch Program, the Supplemental Nutrition Assistance Program (also known as SNAP and formerly the Food Stamp Program), and the Special Supplemental Nutrition Program for Women, Infants, and Children. Efforts to drastically reduce hunger depend on forming new partnerships at every level. That involves improved coordination among existing USDA programs, expansion of technical assistance, increasing public awareness of causes for food insecurity, and finding solutions.

Hunger and malnutrition affect individuals, nations, and the world community, affecting labor productivity and economic development. Multifaceted factors contributing to hunger include greed, overpopulation, unemployment, political and civil unrest, and limited productive resources. Elimination of worldwide hunger requires efforts from agriculture, the development of human capital, and improved infrastructures. Advanced seed varieties increase crop production in developing countries, creating a need for additional workers who then acquire food from their incomes. However, a lack of costly irrigation systems, fertilizers, and pesticides makes advanced technologies unsuitable for many poor farmers.

The US government runs the Women, Infants, and Children (WIC) program, which provides nutritional food for impoverished and pregnant women. Another such program is the Summer Food Service Program, which provides free nutritional meals to children and teenagers from economically disadvantaged families.

Worldwide hunger is linked to price fluctuations in world markets and changing agricultural policies. Prices of imported items, such as fuel and manufactured goods, rise faster than exported food products, causing international debt to accumulate in developing countries. The economic crisis of 2009 differed from previous food crises. Simultaneous effects on large portions of the world hindered traditional coping strategies. The 2006 to 2008 food and fuel crisis intensified economic difficulties. Although food commodity prices decreased, they remained high by historical standards. The impoverished spent as much as 40 percent of their income on food.

The United Nations considers access to food a basic human right. Ethnic and political conflicts intertwined with cultural, religious, economic, and social systems remain problems in abating hunger.

The Weight Epidemic. The World Health Organization reports that worldwide, nearly two billion people were overweight in 2016, and 650 million of these people were obese. In the United States, the percentage of obesity remained relatively stable from 1960 to 1980. Between 1980 and 2018, however, the prevalence of obesity more than doubled. Slightly more than 70 percent of Americans were considered overweight in 2018, and about 42 percent were obese, according to the US Centers for Disease Control and Prevention (CDC). In 2020, 74 percent of Americans were considered overweight and 43 percent obese. In 2021, a study suggested that a Western high-fat diet could increase the chances of various disorders in people who are already suffering from diseases like diabetes.

For adults, excessive weight ranks second only to smoking as a lifestyle choice affecting health and longevity. Overweight and obesity intensify and increase risks for chronic illnesses, including heart disease, stroke, certain cancers, and type 2 diabetes. Excessive weight has been linked to other health conditions and increased morbidity. Children and teens with weight problems show increased susceptibility to potential forerunners of heart disease. Additionally, excessive weight in children leads to lower self-esteem.

One recognized standard for determining a person's healthy weight is the body mass index (BMI). A BMI score between nineteen and twenty-four suggests a healthy weight. A score under nineteen indicates that the person is underweight. Scores between twenty-five and twenty-nine are classified as overweight, and scores over thirty signify obesity. Values above thirty-five indicate stage one obesity, and scores of forty or greater reflect stage three obesity. The BMI has been criticized, however, for oversimplification and a lack of recognition of different body types, as well as ethnic and gender disparities.

Weight management constitutes a balance between calories taken in and calories used. Overweight and obesity occur when more calories are consumed than the body uses. Being sedentary and exercising less can lead to weight gain. The appeal and convenience of high-calorie fast foods have caused them to replace more nutritious fruits and vegetables in people's diets. Oversized portions worsen the problem.

The expense and limited availability of more wholesome foods make the food insecure more vulnerable to becoming overweight or obese. Making nutritious foods and beverages more affordable and readily available in all communities may help prevent obesity. Ways to accomplish this include offering healthier choices in different settings, competitively priced foods in low-income areas, and incentives for food purveyors and retailers to service those areas.

Careers and Course Work

Dietetics provides opportunities in multifaceted areas, including improving the nutritional state of healthy and diseased people and dealing with societal issues related to food supply, distribution, and consumption. Career choices continue to expand in education, research, media, healthcare sites, and industry. Aspirants can work as clinical dieticians and nutritionists. Many dietitians work in corporate settings. Others opt to launch independent practices, working with individuals in fitness centers and businesses such as supermarkets and creating and conducting employee wellness programs. Universities, such as George Mason University in Virginia and Illinois State University, offer Bachelor's and Master's courses in family and consumer sciences and nutritional sciences.

A dietitian must have at least a Bachelor's degree from an accredited institution, with approved coursework and training from the ADA. A registered dietitian (RD) has successfully completed a national examination for credentialing. Many states have their own licensing systems.

Social Context and Future Prospects

Cultural attitudes and beliefs, social influences, marketing, media, and other factors affect food choices, but taste preference remains a significant influence. Although people tend to eat primarily according to their preferences, most Americans try to eat a healthy diet to avoid future health problems. Heart disease, high blood pressure, diabetes, obesity, and other diseases and disorders in which diet plays a role remain common in the United States. Dietitians can play a significant role in helping people attain better health and physical well-being. As the roles that diet and nutrition play in human health are better understood, dietitians and nutritionists can make dietary recommendations to improve the health of the general public and people with special nutritional needs. In addition, they can advise companies in the food industry so that these companies can prepare processed and packaged foods that are not only healthful but also appealing.

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