Nutrition Science

Grade 9 · Health · Study Guide

An advanced exploration of macronutrients, micronutrients, metabolism, and how dietary choices affect adolescent health and performance.

Nutrition science is the study of how food and its components affect health, growth, and disease. The nutrients in food are broadly classified as macronutrients — carbohydrates, proteins, and fats — which provide energy, and micronutrients — vitamins and minerals — which support biochemical processes without directly providing energy.

Carbohydrates are the body's primary energy source. They are broken down into glucose, which fuels cellular respiration, particularly in the brain and muscles. Complex carbohydrates (whole grains, legumes) provide sustained energy and dietary fiber, while simple carbohydrates (sugar) cause rapid blood glucose spikes followed by crashes. The glycemic index (GI) measures how quickly a carbohydrate raises blood glucose.

Proteins are made of amino acids and are essential for building and repairing tissues, producing enzymes and hormones, and supporting immune function. Of the 20 amino acids, 9 are essential, meaning they must be obtained from food. Complete proteins (meat, dairy, eggs) provide all 9 essential amino acids; most plant proteins are incomplete and must be combined.

Dietary fats include saturated fats (solid at room temperature, associated with cardiovascular risk when consumed in excess), unsaturated fats (mono- and polyunsaturated, heart-protective), and trans fats (industrially produced, strongly linked to heart disease). Omega-3 fatty acids, found in fish and flaxseed, reduce inflammation and support brain development.

Adolescents have elevated needs for calcium (bone density), iron (especially menstruating females), vitamin D, and zinc due to rapid growth. The MyPlate model recommends filling half the plate with fruits and vegetables, a quarter with grains (preferably whole), and a quarter with protein foods.

Key terms

Macronutrients: Nutrients required in large amounts that provide energy: carbohydrates (4 kcal/g), proteins (4 kcal/g), and fats (9 kcal/g).
Glycemic index (GI): A scale ranking carbohydrate-containing foods by how quickly they raise blood glucose relative to pure glucose (GI = 100).
Essential amino acids: The 9 amino acids the body cannot synthesize and must obtain from dietary protein: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Unsaturated fats: Heart-healthy fats that are liquid at room temperature; include monounsaturated fats (olive oil) and polyunsaturated fats (omega-3 and omega-6 fatty acids).
Micronutrients: Vitamins and minerals required in small amounts that regulate metabolic processes, immune function, and growth without providing caloric energy.
Basal metabolic rate (BMR): The number of calories the body requires at rest to maintain vital functions such as breathing, circulation, and cell production.

Flashcards

Carbohydrates: Organic molecules (sugars, starches, fiber) that are the body's primary energy source; broken down into glucose for cellular respiration.
Protein: A macronutrient composed of amino acid chains; essential for tissue repair, enzyme and hormone synthesis, and immune function.
Saturated fat: A fat with no double bonds between carbon atoms; solid at room temperature; found in animal products; raises LDL cholesterol when consumed in excess.
Omega-3 fatty acids: Polyunsaturated fats (EPA, DHA, ALA) with anti-inflammatory properties; found in fatty fish, walnuts, and flaxseed; important for brain and heart health.
Vitamin D: A fat-soluble vitamin synthesized in skin exposed to UV light; essential for calcium absorption and bone health; deficiency is common in teens.
Iron: A mineral critical for hemoglobin synthesis (oxygen transport in red blood cells); deficiency causes anemia; menstruating individuals have higher requirements.
Dietary fiber: Indigestible plant carbohydrates that promote gut health, regulate blood glucose, and lower cholesterol; found in vegetables, fruits, legumes, and whole grains.
Complete protein: A protein source containing all 9 essential amino acids in sufficient quantities; found in animal products and some plant foods like quinoa and soy.

Questions

Which macronutrient provides the most energy per gram?
1. Carbohydrates (4 kcal/g)
2. Proteins (4 kcal/g)
3. Fats (9 kcal/g)
4. Fiber (2 kcal/g)
Show answer
Answer: Fats (9 kcal/g)
Fats provide 9 kilocalories per gram — more than double the 4 kcal/g provided by both carbohydrates and proteins — making them the most energy-dense macronutrient.
All 20 amino acids must be obtained from food because the body cannot produce any of them.
Show answer
Answer: False
Only 9 of the 20 amino acids are essential (must come from food). The remaining 11 are non-essential because the body can synthesize them from other compounds.
The glycemic ______ measures how quickly a carbohydrate food raises blood glucose levels compared to pure glucose.
Show answer
Answer: index
The glycemic index ranks foods 0-100 based on blood glucose response; high-GI foods (white bread, sugary drinks) cause rapid spikes while low-GI foods (oats, lentils) produce gradual rises.
During adolescence, which mineral is especially critical for building peak bone density?
1. Iron
2. Sodium
3. Calcium
4. Potassium
Show answer
Answer: Calcium
About 90% of peak bone mass is acquired by age 18; adequate calcium intake (1300 mg/day for teens) and vitamin D during adolescence significantly reduces osteoporosis risk later in life.
Trans fats found in partially hydrogenated oils are associated with increased LDL cholesterol and cardiovascular disease risk.
Show answer
Answer: True
Industrial trans fats raise LDL (bad) cholesterol and lower HDL (good) cholesterol, dramatically increasing cardiovascular disease risk; the FDA banned partially hydrogenated oils in 2018.

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