Nutrition: Eating for a Healthier You – Essential Nutrients, Dietary Guidelines, and Food Safety

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Essential Nutrients for Health

Introduction to Nutrients

Nutrition is the science that investigates the relationship between physiological function and the essential elements of foods eaten. Nutrients are the constituents of food that sustain human physiology, including water, proteins, carbohydrates, fats, vitamins, and minerals.

Hunger: A physiological response that prompts us to seek food for energy.
Appetite: The learned desire to eat, more psychological than physiological.
Digestive process: The process by which the body breaks down foods into smaller components for absorption or excretion.

Calories and Kilocalories

Calorie: A unit of measure indicating the amount of energy obtained from food.
Kilocalorie (kcal): 1 kilocalorie = 1,000 calories. Nutrition labels typically use "calories" to refer to kilocalories.

Water: A Crucial Nutrient

Functions and Importance

Humans can survive longer without food than without water.
Dehydration can cause serious health problems within hours; death can occur within days.
Excess water can cause hyponatremia, a condition of low sodium levels.
The human body is composed of 50–70% water by weight.
Water is obtained from both foods and beverages.

Estimated Daily Calorie Needs

Calorie Requirements by Age, Sex, and Physical Activity

Calorie needs vary based on age, sex, and activity level. The following tables summarize estimated daily calorie needs:

Group	Age	Sedentary	Moderately Active to Active
Children	2–3 years	1,000	1,400
Females	4–13 years	1,200–1,800	1,400–2,200
Females	14–18 years	1,800	2,000–2,400
Females	19–25 years	2,000	2,000–2,400
Females	26–50 years	1,800	2,000–2,200
Females	51–75 years	1,600–1,800	1,800–2,200
Males	4–12 years	1,200–1,800	1,600–2,400
Males	13–18 years	2,000–2,400	2,600–3,200
Males	19–20 years	2,600	2,600–3,000
Males	21–40 years	2,400	2,600–3,000
Males	41–60 years	2,200	2,400–2,800
Males	61–75 years	2,000	2,400–2,600

Proteins

Functions and Sources

Proteins are the most abundant substances in the body after water.
Functions include repairing bone, muscle, skin, and blood cells, and forming antibodies.
Proteins help transport iron, oxygen, and nutrients to all body cells.

Structure and Sources

Amino acids are the building blocks of proteins. Nine are essential (must be obtained from food), and eleven are non-essential (produced by the body).
Complete proteins supply all essential amino acids (e.g., animal sources).
Incomplete proteins lack one or more essential amino acids (e.g., plant sources).
Combining different plant foods (e.g., legumes and grains) can provide all essential amino acids (complementary proteins).

Protein Intake Recommendations

Recommended intake: 0.8 grams protein per kilogram of body weight.
To calculate: Divide body weight in pounds by 2.2 to get kilograms, then multiply by 0.8.

Example: A 150 lb person: kg; grams protein/day.

Carbohydrates

Functions and Types

Carbohydrates supply energy for daily activity and are metabolized faster than protein.
Converted to glucose, the main energy source for the body.
Essential for the functioning of internal organs, nervous system, and muscles.

Forms of Carbohydrates

Simple carbohydrates: Monosaccharides (glucose, fructose) and disaccharides (sucrose, lactose, maltose).
Complex carbohydrates: Polysaccharides such as starches (grains, cereals, vegetables) and fiber.
Fiber: Indigestible portion of plant foods that aids digestion.

Fiber

Dietary fiber: Nondigestible carbohydrates from plant parts (leaves, stems, seeds).
Functional fiber: Nondigestible carbohydrates with health benefits, from plants or manufactured.
Total fiber: Sum of dietary and functional fiber.

Types of Fiber

Insoluble fiber: Found in bran, whole grains, fruits, and vegetables; reduces cancer risk.
Soluble fiber: Found in oat bran, dried beans, some fruits and vegetables; lowers blood cholesterol and cardiovascular risk.

Carbohydrate Choices

Whole grains and high-fiber diets protect against obesity, cancer, heart disease, constipation, and possibly type II diabetes.
Recommended fiber intake: 22–28 grams/day (women), 28–34 grams/day (men).
Choose whole grains, fresh fruits, legumes, vegetables, nuts, and seeds over refined carbohydrates.

Fats (Lipids)

Functions and Types

Fats maintain healthy skin, insulate organs, regulate temperature, promote cell function, and carry fat-soluble vitamins (A, D, E, K).
Triglycerides make up most body fat; excess calories are stored as triglycerides.
Cholesterol is a fat-like substance; the HDL/LDL ratio determines heart disease risk.

Types of Dietary Fat

Saturated fats: Mainly from animal sources; solid at room temperature.
Unsaturated fats: Mainly from plant sources; liquid at room temperature.
Monounsaturated fatty acids (MUFAs): Found in peanut and olive oils; lower LDL, raise HDL.
Polyunsaturated fatty acids (PUFAs): Found in corn, sunflower, safflower oils.

Trans Fatty Acids

Created by hydrogenating liquid oils to make them solid.
Increase LDL (bad cholesterol), lower HDL (good cholesterol).
Increase risk of coronary heart disease and sudden cardiac death.
Look for "partially hydrogenated oils" on labels to identify trans fats.

Fat Intake Recommendations

Less than 10% of total calories from saturated fat; no more than 35% from all fats.
Eat fatty fish; use plant oils (soy, olive, peanut, canola); add leafy vegetables, walnuts, flaxseed.
Reduce intake of trans fats and saturated fats; choose lean meats and low-fat dairy.

Vitamins

Types and Functions

Potent, essential organic compounds that promote growth and maintain health.
Fat-soluble vitamins: A, D, E, K; absorbed with fats, stored in the body, risk of toxicity if consumed in excess.
Water-soluble vitamins: B-complex, C; dissolve in water, generally excreted, low toxicity risk.

Essential Vitamins

Vitamin D: Formed in skin by sunlight; improves bone strength, immunity, lowers blood pressure.
Folate: Essential for DNA synthesis; required in fortified foods to prevent birth defects.

Table: Guide to Vitamins

Vitamin Name	Primary Functions	Recommended Intake	Reliable Food Sources
Thiamin	Carbohydrate and protein metabolism	Men: 1.2 mg/day Women: 1.1 mg/day	Pork, fortified cereals, grains, legumes
Vitamin C	Collagen synthesis, iron absorption, immune function	Men: 90 mg/day Women: 75 mg/day	Citrus fruits, peppers, broccoli
Vitamin D	Calcium absorption, bone health	Adults: 600 IU/day	Sunlight, fortified milk, fatty fish
Folate	DNA synthesis	400 mcg/day	Leafy greens, fortified grains

Minerals

Major and Trace Minerals

Inorganic elements essential for body function; vitamins cannot be absorbed without minerals.
Major minerals: Needed in large amounts (sodium, calcium, phosphorus, magnesium, potassium, sulfur, chloride).
Trace minerals: Needed in small amounts (iron, zinc, manganese, copper, iodine).
Imbalances can cause serious health problems.

Sodium and Calcium

Sodium: Regulates blood and body fluids, nerve impulses, heart activity; recommended intake is about 0.65 tsp/day, but most Americans exceed this.
Calcium: Builds bones and teeth, muscle contraction, blood clotting, nerve transmission; found in broccoli, cauliflower, peas, beans; recommended intake is 1,000–1,300 mg/day.

Iron

Most common nutrient deficiency globally.
Women (19–50): 18 mg/day; Men (19–50): 8 mg/day.
Iron-deficiency anemia: Reduced oxygen delivery to cells.
Iron toxicity: Excess supplementation can increase risk of cardiovascular disease and cancer.