Science of Nutrition

What Is Nutrition?

Nutrition is the scientific study of 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.

• Nutrition: The science of food, nutrients, and their impact on health.

• Key processes: Digestion, absorption, transport, metabolism, storage.

Tools for Healthful Eating

Factors Influencing Food Choices

Food choices are driven by a complex interplay of biological, psychological, social, and environmental factors.

• Taste and enjoyment: Most important factor; preferences for sweet, salty, and fatty foods begin in infancy and are influenced by genetics and age.

• Culture and environment: Cultural background and living environment affect food selection; availability and accessibility are key.

• Social life and trends: Eating with others increases food intake; popular trends (e.g., organic foods, convenience foods) shape choices.

• Nutrition knowledge: Perceptions of healthiness influence choices (e.g., avoiding high-sodium foods).

• Advertising: Major influence, especially on children; most advertising targets processed foods.

• Time, convenience, and cost: Busy schedules favor quick, prepared foods; cost can drive choices toward less nutritious options.

• Habits and emotions: Daily routines and emotional states can dictate eating patterns.

The Human Body & Digestion

Nutrients: Essential Compounds in Food

Nutrients are compounds in foods that serve as building blocks for body components and sustain body processes. The six categories of nutrients are:

• Carbohydrates

• Fats (Lipids)

• Proteins

• Vitamins

• Minerals

• Water

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

Organic vs. Inorganic Nutrients

• Organic nutrients: Contain carbon (carbohydrates, proteins, lipids, vitamins).

• Inorganic nutrients: Do not contain carbon (minerals, water).

Essential vs. Nonessential Nutrients

• Essential nutrients: Must be obtained from food; cannot be synthesized in sufficient quantities by the body.

• Nonessential nutrients: Can be made by the body; may become essential under certain conditions (conditionally essential).

Carbohydrates, Lipids, Proteins, Vitamins, Water, and Minerals

Energy-Yielding Nutrients

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

• Carbohydrates: 4 kcal/gram

• Proteins: 4 kcal/gram

• Fats (Lipids): 9 kcal/gram

• Alcohol (not a nutrient): 7 kcal/gram

Macronutrients and Micronutrients

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

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

Functions of Major Nutrients

Carbohydrates

• Composition: Carbon, hydrogen, oxygen

• Function: Supply glucose, the primary energy source for body cells

• Sources: Plant foods (grains, legumes, fruits, vegetables); dairy is the only significant animal source

Lipids

• Composition: Carbon, hydrogen, oxygen

• Types: Triglycerides, sterols, phospholipids

• Function: Provide energy, structural component of cell membranes

• Sources: Margarine, butter, oils, animal products

Proteins

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

• Function: Build and maintain tissues, act as enzymes, neurotransmitters, immune function, secondary energy source

• Sources: Animal (meat, poultry, fish, dairy); plant (legumes, soy, nuts, seeds)

Vitamins

• Composition: Carbon, hydrogen, oxygen

• Function: Coenzymes in metabolic reactions; do not provide energy

• Types: Water-soluble (B-complex, C), fat-soluble (A, D, E, K)

Minerals

• Composition: Single elements

• Function: Regulate body processes, structure of tissues

• Types: Major (≥100 mg/day), trace (<100 mg/day)

Water

• Function: Medium for metabolism, digestion, absorption, transport, temperature regulation, lubrication, cushioning organs

• Cannot be stored; must be replenished daily

Tools for Healthful Eating

Balanced Diet and Functional Foods

A balanced diet includes a variety of whole foods: whole grains, fruits, vegetables, lean meats, and low-fat dairy. It also provides beneficial compounds such as phytochemicals (plant-based, disease-fighting) and zoochemicals (animal-based, e.g., omega-3 fatty acids).

Supplements and Fortified Foods

• Supplements may be necessary for individuals unable to meet nutrient needs through food alone (e.g., lactose intolerance).

Energy Balance: Body Weight, Obesity, & Eating Disorders

Diet and Health

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

• Helps maintain healthy weight and supports gene expression (nutritional genomics).

Current State of the American Diet

• Excess intake: Added sugar, saturated fat

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

• Most men meet vitamin/mineral recommendations; women often low in iron

• Poor dietary practices: Eating on the go, prepared meals, eating in front of screens

Tools for Healthful Eating

Assessing Nutritional Status: The ABCD Method

The ABCD method is used to assess the nutrient status of individuals and populations:

• Anthropometric: Body measurements (e.g., BMI, waist circumference)

• Biochemical: Lab tests (e.g., blood, urine)

• Clinical: Physical signs (e.g., mouth, skin, eyes)

• Dietary: Food intake records, surveys

Population Surveys

• NHANES: National Health and Nutrition Examination Survey

• Framingham Heart Study: Long-term cardiovascular data

Obesity Trends

• Over 35% of adults are obese; 41.9% as of 2020

• 73.6% of Americans are above a healthy weight

• Childhood obesity rates: 12.7% (2-5 yrs), 20.7% (6-11 yrs), 22.29% (12-19 yrs)

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

Food Safety & Regulation

Reliable Nutrition Information

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

• Be wary of single reports and popular trends.

• Registered Dietitian Nutritionists (RDNs) are qualified sources for nutrition information.

Example: Identifying Reliable Sources

• Medical professionals and RDNs are more reliable than salespersons or unqualified individuals.

Additional info:

• Equations for energy calculation:

• Functional foods, phytochemicals, and zoochemicals are emerging areas in nutrition science.