All creatures need fuel in order to function, and humans are no exception. Diet influences long-term health within the range set by genetic inheritance. We get our fuel from food in the form of chemical compounds that are collectively known as nutrients.
These nutrients work together to provide energy, growth, and maintenance, and to regulate numerous body processes.
Three of the six classes of nutrients—carbohydrates, fats (part of the larger class of lipids), and protein—provide energy in the form of kilocalories. Two other classes of nutrients, vitamins and minerals, help regulate many body processes, including metabolism. Some also play other supporting roles.
The last class of nutrient, water, is found in all foods and beverages, and is so vital to life that you couldn’t live more than a few days without it.
Foods also provide nonnutrient compounds like phytochemicals and other substanc
es that help maintain and repair your body in order to keep it healthy.We will explore each of these nutrients in more depth later in this chapter, and in much more depth throughout the book.
Beyond the basic need to replenish our bodies with daily fuel are other factors that drive our food choices.
Nutrients Compoundsin foods that sustain your body processes. There are six classes of nutrients: carbohydrates, fats (lipids), proteins, vitamins, minerals, and water.
Kilocalories The measurement of energy in foods commonly referred to as calories.
Metabolism The numerous reactions that occur within the cell. The calories in foods are converted to energy in the cells of the body.
Phytochemicals Nonnutritive compounds in plant foods that may playa role in fighting chronic diseases.
Macronutrients The energy containing essential nutrients that you need in higher amounts: carbohydrates, lipids (fats), and proteins.
Micronutrients Essential nutrients that you need in smaller amounts: vitamins and minerals.
Carbohydrates, fats (lipids), and proteins are the energy-providing nutrients, because they contain calories. When we talk about energy, we mean that your body breaks down these nutrients and “burns” them to fuel your activities and internal functioning.
One calorie equals the amount of energy needed to raise the temperature of 1 kilogram (a liter) of water 1 degree Celsius. Carbohydrates and protein provide 4 calories per gram, and
fats provide 9 calories per gram.
The number of calories in a given food can be determined by measuring the weight, in grams, of each of the three nutrients in one serving of the food.
You need vitamins and minerals to use carbohydrates, fats, and proteins and to sustain numerous chemical reactions. A deficiency of vitamins and minerals can cause ill effects ranging from fatigue to stunted growth, weak bones, and organ damage.
Many vitamins and minerals aid enzymes, which are substances that speed upreactions in your body.
Vitamins are organic compounds that usually have to be obtained from your foods. Your body is able to make some vitamins, such as vitamin D, but sometimes cannot make enough of it to maintain good hea
lth. In these situations, your diet has to supplement your body’s efforts.
Minerals are inorganic substances that play a role in body processes and are key to the structure of some tissues, such as bone. A deficiency of any of the minerals can cause disease symptoms. Anyone who has ever suffered from iron-deficiency anemia can tell you that falling short of your daily iron needs, for example, can cause fatigue and interfere with your ability to function.
Healthy eating involves the key principles of balance, variety, and moderation.
A balanced diet includes healthy proportions of all nutrients. For instance, a student subsisting largely on bread, bagels,muffins, crackers, chips, and cookies might be eating too much carbohydrate and fat but too little protein, vitamins, and minerals.
A varied diet includes many different foods. A student who habitually chooses the same foods for
breakfast, lunch, and dinner is not likely to be consuming the wide range of phytochemicals, fiber, and other benefits that a more varied diet could provide.
A moderate diet provides adequateamounts of nutrients and energy. Both crash diets and over-consumption are immoderate.
In short, you need to consume a variety of foods, some more moderately than others, and balance your food choices to meet your nutrient and health needs.
A diet that lacks variety and is unbalanced can cause under-nutrition, a state in which you are not meeting your nutrient needs. If you were to consume only grains like white bread and pasta, and avoid other foods such as milk products, fruits, vvegetables, and meats, your body wouldn’t get enough fiber, calcium, protein, and other important nutrients. You would eventually become malnourished.
In contrast, over-nutrition occurs when a diet provides too much of anutrient such as iron,which can be toxic in high amounts, or too many calories,which can lead to obesity. A person who is overnourishedcan also be malnourished. For example, a person can be overweight on a diet laden with less nutritious snack foods and
sweets—foods that should be eaten in moderation—because he or she is taking in more calories than needed. These foods often displace more nutrient-rich choices, leaving the person malnourished.
Food labels don’t just make food shopping easier; they also serve important functions that make them helpful tools for anyone who wants to eat a healthy diet. First and foremo
st, they tell you what’s inside the package. Second, they contain a Nutrition Facts panel, which identifies the calories and nutrients in a serving of the food.
Third, they list Daily Values (DVs), which help you determine how those calories and nutrients will fit into your overall diet.
To help consumers make informed food choices, the Food and Drug Administration (FDA) regulates the labeling of all packaged foods in the United States.7 Currently, the FDA has mandated that every packaged food be labeled with: