Chapter 1: What Is Nutrition? — Foundations of Nutritional Science

What Drives Our Food Choices?

Factors Influencing Food Selection

Food choices are shaped by a variety of factors, each playing a significant role in dietary habits and nutritional status.

• Taste and Enjoyment: Taste is the most important factor in food selection. Preferences for sweet, salty, high-fat, and specific textures begin early in life and are influenced by genetics and age. Texture also affects enjoyment; for example, nearly 30% of adults dislike slippery foods.

• Culture and Environment: Cultural background and environmental factors, such as living environment, availability, accessibility, size and shape of plates, packaging, and lighting, influence the types and amounts of food consumed.

• Social Life and Trends: Eating with others increases food intake (meal size can increase by over 40% in groups). Popular trends, such as the rise of frozen vegetables in the 1950s or prewashed produce today, also affect choices.

• Nutrition Knowledge: Perceptions of foods as healthy or unhealthy, and current health status, influence choices (e.g., avoiding high-sodium foods to reduce blood pressure).

• Advertising: Food advertising, especially for children and adolescents, strongly influences selection. Most advertising dollars are spent on breakfast cereals, candy, gum, and soft drinks, with little spent on fruits and vegetables.

• Time, Convenience, and Cost: Busy schedules lead to a preference for quick, convenient foods. Fast foods are often perceived as cheaper, increasing their selection and risk for obesity.

• Habits and Emotions: Daily routines and emotions can drive food choices, sometimes leading to unhealthy eating patterns.

What is Nutrition?

Definition and Scope

Nutrition is the science that studies how nutrients and compounds in foods nourish the body and affect body functions and overall health. It explores how food is digested, absorbed, transported, metabolized, and used or stored in the body.

Nutrients: Essential Compounds in Food

Categories and Functions

• Nutrients are compounds in foods that serve as building blocks for body components and sustain body processes. The same nutrients found in foods are also present in the body.

• There are six categories of nutrients:

  • Carbohydrates

  • Fats (lipids)

  • Proteins

  • Vitamins

  • Minerals

  • Water

• Foods also contain nonnutrient compounds, such as nondigestible fiber and additives (for color, flavor, texture, and shelf life).

We Are What We Eat

Major Nutrient Composition

• Water is the most abundant nutrient in foods and the body.

• Carbohydrates, fats, proteins, vitamins, and minerals make up the rest.

• Animal foods do not contain carbohydrates by the time we consume them.

Organic and Inorganic Nutrients

Chemical Classification

• Organic nutrients contain carbon: carbohydrates, proteins, lipids, and vitamins.

• Inorganic nutrients do not contain carbon: minerals and water.

Table: Chemical Composition of Nutrients

Nutrient	Carbon	Hydrogen	Oxygen	Nitrogen	Single Elements
Carbohydrates	X	X	X
Lipids	X	X	X
Proteins	X	X	X	X
Vitamins	X	X	X	Some
Minerals					X
Water		X	X

Essential vs. Nonessential Nutrients

Definitions

• Essential nutrients: Must be consumed from food, support good health, and cannot be made in sufficient quantities by the body.

• Nonessential nutrients: Can be made in sufficient quantities by the body.

• Conditionally essential nutrients: Nonessential nutrients that become essential under certain circumstances.

Energy-Yielding Nutrients

Sources and Measurement

• Energy is the capacity to do work. The body derives energy from nutrients in foods that store energy in chemical bonds, released as adenosine triphosphate (ATP) when bonds are broken.

• Energy-yielding nutrients:

  • Carbohydrates

  • Lipids (fats)

  • Proteins

• Nonnutrient source of energy: Alcohol

Energy Content per Gram

• Carbohydrate: 4 kcal/gram

• Protein: 4 kcal/gram

• Fat (lipid): 9 kcal/gram

• Alcohol: 7 kcal/gram

Kilocalorie (kcal): The amount of energy required to raise the temperature of 1 kilogram of water by 1 degree Celsius. 1 kcal = 1,000 calories (lowercase 'c'). On nutrition labels, 'Calorie' (uppercase 'C') is used.

Primary Roles of the Individual Nutrients

Functions

• Supply energy

• Regulate metabolism

• Provide structure

Macronutrients and Micronutrients

Definitions

• Macronutrients: Needed in large amounts (carbohydrates, fats, proteins, water)

• Micronutrients: Needed in smaller amounts (vitamins, minerals)

Table: Functions of the Major Nutrients by Type

Nutrient	Provides Energy	Growth/Maintenance/Structure	Regulates Body Processes
Carbohydrates	Yes	No	No
Protein	Yes	Yes	Yes
Fats	Yes	Yes	Yes
Water	No	Yes	Yes
Vitamins	No	No	Yes
Minerals	No	Yes	Yes

Carbohydrates

Primary Energy Source

• Composition: Carbon, hydrogen, oxygen

• Function: Supply glucose, the primary energy source for many body cells, including red blood cells and brain cells

• Food sources: Plants (breads, cereals, legumes, nuts, fruits, vegetables); animal (dairy products)

Lipids

Energy and Structure

• Composition: Carbon, hydrogen, oxygen

• Categories: Triglycerides, sterols, phospholipids

• Function: Provide energy to cells, structural component of cell membranes

• Food sources: Margarine, butter, oils, animal products

Proteins

Building Blocks for Tissue Synthesis

• Composition: Carbon, hydrogen, oxygen, nitrogen (some contain sulfur)

• Function:

  • Basic building blocks (amino acids) for synthesizing, growing, and maintaining tissues

  • Primary source of tissues in muscles, bones, skin

  • Participate as neurotransmitters, play a role in the immune system, act as enzymes

  • Can be used as an energy source, but not primary

• Food sources: Animal (meat, poultry, fish, dairy); plant (legumes, soy, nuts, seeds; minimal in whole grains, vegetables, fruits)

Vitamins and Minerals

Vital Roles in Metabolism

• Vitamins: Carbon, hydrogen, oxygen; function as coenzymes, help enzymes catalyze reactions

• Minerals: Single elements; assist in body processes, essential for structure of tissues

• Deficiencies: Fatigue, stunted growth, weak bones, organ damage

Vitamin Classifications

• Water-soluble: Not stored in the body, need daily (B-complex, vitamin C)

• Fat-soluble: Stored in the body (A, D, E, K)

Mineral Classifications

• Major: Need at least 100 mg/day, found in amounts ≥5 grams in the body

• Trace: Need less than 100 mg/day, found in amounts <5 grams in the body

Water

Critical for Numerous Functions

• Primary form of all body fluid, part of every cell

• Key functions: Essential during metabolism, digestion, absorption, transport of nutrients and oxygen, excretion of waste, maintenance of body temperature, lubrication, cushioning organs

• Cannot be stored; must be replenished daily

The Best Approach: A Balanced Diet

Dietary Recommendations

• Eat a well-balanced diet with a variety of whole foods: whole grains, fruits, vegetables, lean meats, low-fat dairy

• Provides beneficial dietary compounds: phytochemicals (plant chemicals), zoochemicals (animal compounds), fiber

• Functional foods: Foods that provide health benefits beyond basic nutrition (e.g., omega-3 fatty acids, antioxidants)

Table: Your Guide to Functional Foods

Compound	Found in	Health Benefit
Beta-carotene	Carrots, pumpkin, cantaloupe, broccoli	Antioxidant
Lycopene	Tomatoes, tomato sauce	May lower prostate cancer risk
Soy protein	Tofu, soy milk	Lowers heart disease risk
Beta-glucan	Oatmeal, oats, oat bran	Lowers blood cholesterol
Plant sterol and stanol esters	Fortified margarines, Benecol spreads	Lowers blood cholesterol
Omega-3 fatty acids	Salmon, sardines, tuna, walnuts, wheat bran, brown rice	May reduce risk of heart disease
Whole grains	Whole-wheat bread, brown rice, popcorn	May reduce risk of some cancers and heart disease
Flavanols	Dark chocolate, green apples	May contribute to heart health
Antho-cyanins	Berries, red grapes, cherries	Antioxidants, may contribute to brain function
Probiotics	Active cultures in yogurt	Support intestinal health

How Diet Influences Health

Chronic Disease and Gene Expression

• A healthy diet reduces the risk of chronic diseases (heart disease, cancer, stroke, diabetes).

• Diet helps achieve and maintain a healthy weight, decreasing chronic disease risk.

• Gene expression is influenced by nutrition (nutritional genomics studies this relationship).

Assessing Nutritional Status

Definitions and Methods

• Nutritional status can be: healthy, malnourished, undernourished, or overnourished.

• Registered Dietitian Nutritionists (RDNs) assess nutritional status using the ABCD method:

  • Anthropometric: Growth, weight, body mass index, waist circumference

  • Biochemical: Blood, urine, feces, tissue concentrations

  • Clinical: Hair, fingernails, skin, lips, mouth, muscles, joints, overall appearance

  • Dietary intake: Diet history, food frequency questionnaires, 24-hour recalls

Table: The ABCDs of Nutrition Assessment

Type of Assessment	Examples	What They Determine
Anthropometric	Height, weight, BMI, waist circumference	Growth, obesity, risk of chronic diseases
Biochemical	Blood, urine, feces, tissue concentrations	Protein, mineral, vitamin status
Clinical	Hair, skin, nails, mouth, muscles, joints	Signs of nutrient deficiencies or excesses
Dietary Intake	Diet history, food frequency, 24-hour recall	Usual nutrient intake, deficiencies, or excesses

Current State of the American Diet

Trends and Concerns

• Excess intake: Added sugars, sodium, saturated fat, calories

• Too little intake: Fiber, some vitamins (D), minerals (potassium, calcium)

• High rates of overweight and obesity: 41.9% of adults obese (2020), 73.6% above healthy weight, increasing rates in children and adolescents

• Associated risks: Type 2 diabetes, heart disease, cancer, stroke

Reliable Nutrition Information

Evaluating Sources

• Sound advice is based on consensus from multiple research findings.

• Be wary of results from a single report or non-expert sources.

• Registered Dietitian Nutritionists (RDNs) are the most reliable professionals for nutrition information.

Additional info: Nutritional genomics is an emerging field that explores how individual genetic variation affects response to nutrients and impacts health outcomes.