Nutrients and Their Energy Values

Part 1-Nutrients

• Nutrient: A substance in food needed for growth, maintenance, and repair.
• Five categories of nutrients.
• Three macronutrients (carbohydrates, lipids, and proteins) form the majority of the diet.
• Two micronutrients (vitamins and minerals) are also important, but in smaller amounts.
• Most nutrients are used for metabolic fuel or building molecules and cells.
• Water accounts for roughly 60% of the food volume.
• Essential nutrients (approximately 40 molecules) must be consumed in the diet.
• The body can't produce essential nutrients on its own.
• Body cells, especially liver cells, can convert one molecule type to another.
• This allows the body to adapt to varying food intakes.

Part 1-Nutrients (Energy Value)

• Energy value of nutrients is measured in kilocalories (kcal).
• One kcal is the amount of heat needed to raise the temperature of 1 kg of water by 1°C.
• 1 kcal = 1 calorie.
• Carbohydrates and proteins provide 4 kcal/g, while lipids provide almost 9 kcal/g.
• MyPlate guidelines are shown as portions on a dinner plate.
• Basic Dietary Principles:
  • Eat only what you need
  • Eat plenty of fruits, vegetables, and whole grains
  • Avoid junk food

Carbohydrates

• Dietary sources: Mostly plants (except milk sugar (lactose) and small amounts of glycogen).
• Sugars (monosaccharides and disaccharides): fruits, sugarcane, sugar beets, honey, and milk.
• Starch (polysaccharide): grains and vegetables.
• Insoluble fiber: present in vegetables and increases stool bulk aiding in defecation.
• Soluble fiber: found in apples and citrus, reduces blood cholesterol levels.

Carbohydrates (Uses in the body)

• Glucose: the carbohydrate molecule used by cells to produce ATP.
• Fructose and galactose are converted to glucose by the liver before entering circulation.
• Many cells use fats for energy, but neurons and red blood cells mostly rely on glucose.
• Excess glucose is converted to glycogen or fat for later use.
• Other uses: building nucleic acids (with pentose sugars), and cell's glycocalyx (with short-chain sugars).

Carbohydrates (Dietary Requirements)

• Recommended daily carbohydrate intake is 45–65% of total calories.
• Typical American adults consume about 46% of their calories from carbohydrates.
• Diets should primarily include complex carbohydrates from whole grains and vegetables instead of simple carbohydrates.
• Large amounts of refined, sugary foods contribute to obesity and nutritional deficiencies.
• Starchy foods (e.g., rice, pasta, breads) are often less expensive than high-protein foods.

Lipids

• Dietary sources: Primarily triglycerides (neutral fats) in saturated, trans, and unsaturated forms.
• Saturated fats:Meat, dairy, some tropical plants (e.g., coconut)
• Trans fats:hydrogenated oils (e.g., margarine and shortening)
• Unsaturated fats:seeds, nuts, olive oil, and most vegetable oils
• Cholesterol:egg yolk, meats, organ meats, shellfish, and milk products
• The liver manufactures approximately 85% of the blood's cholesterol.
• Two essential fatty acids synthesized by the liver (linoleic acid (omega-6) and linolenic acid (omega-3)).

Lipids (Uses in the body)

• Adipose tissue: provides cushioning, insulation, and energy storage.
• Phospholipids: essential components of myelin sheaths (neurons) and cell membranes.
• Cholesterol: stabilizes cell membranes and is a precursor of bile salts and steroid hormones.
• Prostaglandins: regulatory molecules made from linoleic acid involved in smooth muscle contraction, blood pressure regulation, inflammation.
• Triglycerides: major energy source for skeletal muscle and liver cells.
• Help absorb fat-soluble vitamins.

Lipids (Dietary Requirements)

• Fats should represent 20–35% of total caloric intake (typically 40% in American diets).
• Limit saturated fats to 10% or less of total fat intake.
• Cholesterol can be synthesized by the body and isn't required in the diet.
• Often recommended to keep cholesterol intake as low as possible, especially for individuals with high blood cholesterol levels.
• High cholesterol levels are associated with cardiovascular disease.

Proteins

• Dietary sources: primarily animal products (eggs, milk, fish, meats, soybeans) .
• Legumes, nuts, and cereal grains contain incomplete proteins that are low in one or more essential amino acids.
• Ingesting combinations of cereal grains and legumes provides all essential amino acids.

Essential Amino Acids

• Essential amino acids are a small percentage of the total recommended protein intake.
  • Histidine and arginine are essential for infants, but not adults.
• Incomplete proteins from different sources (e.g., corn and beans) can be combined in one meal to provide all essential amino acids.

Proteins (Nitrogen Balance)

• Homeostatic state: rate of protein synthesis equals rate of protein breakdown and loss.
• Positive nitrogen balance: synthesis exceeds breakdown (normal in growing children and pregnant women, tissue repair)
• Negative nitrogen balance: breakdown exceeds synthesis (occurs during stress, burns, infection, injury; low dietary protein intake).

Proteins (Dietary Requirements)

• Essential amino acids are obtained from the dietary intake.
• The amount of protein needed depends on age, size, metabolic rate, and current nitrogen balance.
• A rule of thumb suggests a daily intake of 0.8 g of protein per kg of body weight.

Vitamins

• Vitamins are organic compounds needed in small amounts.
• Not an energy source; needed for macronutrient use.
• Coenzymes or parts of coenzymes that carry out biochemical reactions when combined with enzymes during use of nutrients like glucose.
• Made in the body or from ingested sources.
• Vitamin D is made in the skin.
• Vitamins B and K are synthesized by intestinal bacteria.
• Beta-carotene from carrots can be converted to vitamin A.
• A balanced diet avoids deficiencies.

Vitamins (Types)

• Two types of vitamins based on solubility (Water-soluble, and Fat-soluble).
• Water-soluble vitamins (e.g., B complex and C) are absorbed with water and are not stored in the body; excess can be excreted.
• Fat-soluble vitamins (e.g., A, D, E, and K) are absorbed with lipids in the intestines and can be stored in the body.

Minerals

• Seven minerals needed in moderate amounts, plus trace amounts of others.
• (Calcium, phosphorus, potassium, sulfur, sodium, chlorine, and magnesium)
• Like vitamins, minerals work with nutrients to support bodily functions.
• Mineral incorporation makes body structures stronger.
• Most minerals are ionized or bound to organic compounds to create phospholipids, hormones, and other proteins.
• Iron is part of hemoglobin, which binds oxygen; sodium and chloride are essential electrolytes; iodine is needed for thyroid hormone synthesis.
• Uptake and excretion are balanced to prevent excessive mineral accumulation.
• Natural sodium is beneficial. Processed foods add high amounts of sodium contributing to fluid retention and high blood pressure.

Part 2-Metabolism

• Metabolism: the total sum of all biochemical reactions in the body.
• Metabolism involves the building up (anabolism) of compounds and the breaking down (catabolism) of compounds.
• Body requires energy even when resting, used for essential functions like breathing and absorbing nutrients from food.