Introduction to Nutrition: Core Concepts and Dietary Reference Intakes

Introduction to Nutrition

Overview of Nutritional Sciences

Nutritional sciences is the study of nutrients in food, their role in the body, and human behavior in relation to food. This foundational knowledge is essential for understanding how diet influences health and disease.

• Nutrition: The science that studies nutrients in food, nutrients in the body, and human behavior in relation to food.

• Nutritional Genomics: An emerging field combining nutrition, genomics, and molecular biology to study how nutrients and genes influence each other.

Key Nutrition Terms

Definitions and Classifications

• Diet: The foods and beverages a person consumes.

• Food: Edible substances with physical and chemical properties, accepted based on preference, and providing energy and nutrients for survival and growth.

• Nutrients: Components of food needed for body function, energy, building material, maintenance, repair, and development.

Six Classes of Nutrients

• Carbohydrates

• Fats (Lipids)

• Proteins

• Vitamins

• Minerals

• Water

Macronutrients vs. Micronutrients

• Macronutrients: Carbohydrates, fats, proteins (required in large amounts, provide energy).

• Micronutrients: Vitamins and minerals (required in small amounts, do not provide energy).

• Water: Essential for life, does not provide energy but is required in large amounts.

Types of Nutrients in Detail

• Vitamins (organic):

  • Water-soluble: Vitamin C, B vitamins (Thiamin, Riboflavin, Niacin, Biotin, Pantothenic acid, Vitamin B6, Folate, Vitamin B12)

  • Fat-soluble: Vitamins A, D, E, K

• Minerals (inorganic):

  • Major minerals: Sodium, Potassium, Chloride, Phosphorus, Calcium, Magnesium, Sulfur

  • Trace minerals: Selenium, Fluoride, Iodine, Chromium, Manganese, Iron, Zinc, Copper

Organic nutrients contain carbon; inorganic nutrients do not.

Other Key Terms

• Essential Nutrients: Nutrients that must be obtained from food because the body cannot synthesize them (e.g., certain amino acids, vitamins, minerals).

• Dietary Supplements: Purified nutrients in pills, powders, or liquids.

• Nutraceuticals: Food products with medicinal or therapeutic effects.

• Functional Foods: Foods that provide health benefits beyond basic nutrition due to physiologically active components.

• Non-nutrients: Substances in food that do not provide nutrition but affect characteristics like color, taste, and smell.

• Phytochemicals: Non-nutrient compounds in plants with biological activity (e.g., flavonoids, carotenoids).

• Processed Foods: Foods intentionally changed by adding substances or using methods like cooking, preserving, or milling.

• Ultra-processed Foods: Foods significantly altered and made from substances not typically consumed as food (e.g., oils, sugars, additives).

Malnutrition

• Malnutrition: Inadequate, excessive, or imbalanced intake of energy and/or nutrients.

• Undernutrition: Insufficient energy or nutrients, leading to wasting, stunting, or underweight.

• Overnutrition: Excessive energy intake, leading to obesity and related health conditions.

Influences on Dietary Choice

Factors Affecting Food Choices

• Personal (Intrapersonal): Preferences, habits, emotions, values, body image, knowledge of nutrition and health benefits.

• Social (Interpersonal): Cultural traditions, social interactions, parental/family influence.

• Setting: School environment, food availability (retail).

• Environment/Policy: Food availability, advertisements, labeling, and policies.

Example: A student's food choices may be influenced by family traditions, peer preferences, school cafeteria options, and food marketing.

Caloric Value of Energy-Yielding Nutrients

Understanding Calories

• Calorie: A unit of energy; specifically, the amount of heat required to raise the temperature of 1 liter of water by 1°C.

• "Cal" and "kcal" are commonly used abbreviations (1 kcal = 1,000 cal).

Energy-Yielding Nutrients

• Carbohydrates: 4 kcal/g

• Fats (Lipids): 9 kcal/g

• Proteins: 4 kcal/g

• Alcohol: 7 kcal/g (not a nutrient, used for energy only)

Example Calculation

1 slice of bread with 1 Tbsp peanut butter contains:

• 16g carbohydrate × 4 kcal/g = 64 kcal

• 7g protein × 4 kcal/g = 28 kcal

• 9g fat × 9 kcal/g = 81 kcal

Total: 64 + 28 + 81 = 173 kcal

Practice Problem

Mrs. L. consumed 2000 kcals today:

• 55% from carbohydrates (CHO)

• 25% from protein (PRO)

• 20% from fat

1. CHO: 2000 × 0.55 = 1100 kcal / 4 kcal/g = 275g CHO

2. PRO: 2000 × 0.25 = 500 kcal / 4 kcal/g = 125g PRO

3. FAT: 2000 × 0.20 = 400 kcal / 9 kcal/g = 44g FAT

Energy Density

Low vs High Energy Density Meals

• Energy Density: The amount of energy (kcal) per weight of food (g).

• Low energy density: More food volume for fewer calories (e.g., fruits, vegetables).

• High energy density: Less food volume for more calories (e.g., pastries, fried foods).

Example: 500 kcal breakfast: 450g (energy density = 1.1 kcal/g) vs. 144g (energy density = 3.5 kcal/g).

Dietary Reference Intakes (DRIs)

Overview

DRIs are a set of reference values used to plan and assess nutrient intakes of healthy people. They are based on scientific evidence and are specific to age, sex, and life stage.

• Refer to general nutrient adequacy, not prevention or treatment of deficiencies.

• Apply to healthy individuals and vary by sex and age.

Types of DRIs

1. Estimated Average Requirement (EAR): Average daily nutrient intake estimated to meet the requirement of half (50%) of healthy individuals in a group.

2. Recommended Dietary Allowance (RDA): Average daily intake sufficient to meet the nutrient requirements of nearly all (97-98%) healthy individuals.

3. Adequate Intake (AI): Established when evidence is insufficient for an EAR/RDA; based on observed or experimentally determined estimates of nutrient intake by healthy people.

4. Tolerable Upper Intake Level (UL): Highest daily intake unlikely to cause adverse health effects in most individuals.

5. Chronic Disease Risk Reduction Intake (CDRR): Intake levels expected to reduce the risk of chronic disease (e.g., sodium).

Graphical Representation

DRIs are often illustrated with a bell curve showing EAR at the midpoint, RDA at the higher end, and UL as the upper safe limit. Intakes below EAR or above UL may be associated with increased risk of deficiency or toxicity, respectively.

Energy and Macronutrient Recommendations

• Estimated Energy Requirement (EER): Average dietary energy intake predicted to maintain energy balance in a healthy individual, considering age, sex, weight, height, and activity level.

• Acceptable Macronutrient Distribution Ranges (AMDR):

  • Protein: 10-35% of total calories

  • Fat: 20-35% of total calories

  • Carbohydrate: 45-65% of total calories

Summary Table: Main Nutrient Categories

Nutrient	Type	Energy Yield (kcal/g)	Examples
Carbohydrates	Macronutrient	4	Bread, rice, fruits
Fats (Lipids)	Macronutrient	9	Oils, butter, nuts
Proteins	Macronutrient	4	Meat, beans, eggs
Vitamins	Micronutrient	0	Vitamin C, Vitamin D
Minerals	Micronutrient	0	Calcium, Iron
Water	Essential	0	Drinking water, fruits

Key Equations

• Energy from Macronutrients:

$\text{Total kcal} = (\text{g CHO} \times 4) + (\text{g PRO} \times 4) + (\text{g FAT} \times 9)$

• Energy Density:

$\text{Energy Density} = \frac{\text{Total kcal}}{\text{Weight of food (g)}}$

• Macronutrient Grams from Calories:

$\text{Grams of nutrient} = \frac{\text{Calories from nutrient}}{\text{Energy yield per gram}}$

Additional info: This guide covers foundational concepts from the first week of an introductory human nutrition course, including definitions, nutrient classifications, energy calculations, and dietary reference standards.