Carbohydrates: Plant-Derived Energy Nutrients

Types of Carbohydrates

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen. They are classified based on the number of sugar units they contain.

• Monosaccharides: The simplest form of carbohydrates, consisting of a single sugar unit. Examples include glucose, fructose, and galactose.

• Disaccharides: Composed of two monosaccharide units joined by a glycosidic bond. Examples include sucrose (glucose + fructose), lactose (glucose + galactose), and maltose (glucose + glucose).

• Polysaccharides: Long chains of monosaccharide units. Examples include starch (plant storage), glycogen (animal storage), and cellulose (plant fiber).

Example: Table sugar is sucrose, a disaccharide composed of glucose and fructose.

Dietary Fiber

Fiber is a type of carbohydrate that cannot be digested by human enzymes. It is classified as either soluble or insoluble.

• Soluble Fiber: Dissolves in water to form a gel-like material. Found in oats, peas, beans, apples, and citrus fruits. Helps lower blood cholesterol and glucose levels.

• Insoluble Fiber: Does not dissolve in water. Found in whole-wheat flour, wheat bran, nuts, and vegetables. Promotes movement of material through the digestive system and increases stool bulk.

Example: Oatmeal is rich in soluble fiber, while whole wheat bread is high in insoluble fiber.

Functions of Carbohydrates in the Body

• Primary Energy Source: Glucose is the main fuel for the brain and muscles during exercise.

• Spares Protein: Adequate carbohydrate intake prevents the body from using protein for energy.

• Prevents Ketosis: Sufficient carbohydrate prevents excessive fat breakdown and ketone production.

• Promotes Digestive Health: Fiber supports bowel regularity and gut health.

Digestion and Absorption of Carbohydrates

Carbohydrate digestion begins in the mouth and continues in the small intestine.

• Mouth: Salivary amylase breaks down starch into maltose.

• Small Intestine: Pancreatic amylase continues starch breakdown; enzymes (maltase, sucrase, lactase) split disaccharides into monosaccharides.

• Absorption: Monosaccharides are absorbed into the bloodstream via the intestinal wall and transported to the liver.

Health Risks of High Sugar Diets

• Obesity: Excess sugar intake contributes to weight gain.

• Dental Caries: Sugar promotes tooth decay.

• Increased Risk of Chronic Diseases: High sugar diets are linked to type 2 diabetes and cardiovascular disease.

High Fructose Corn Syrup (HFCS) and Other Sweeteners

• HFCS: A sweetener made from corn starch that has been processed to convert some glucose into fructose. Used widely in processed foods and beverages.

• Metabolism: Both HFCS and sucrose are broken down into glucose and fructose in the body, but HFCS may contain a higher proportion of fructose.

• Artificial Sweeteners: Non-nutritive sweeteners such as aspartame, sucralose, and saccharin provide sweetness with little or no calories.

Example: Diet sodas often contain artificial sweeteners instead of sugar.

Diabetes: Causes, Symptoms, and Prevention

• Type 1 Diabetes: Autoimmune destruction of insulin-producing cells; requires insulin therapy.

• Type 2 Diabetes: Insulin resistance and eventual insulin deficiency; associated with obesity and lifestyle factors.

• Gestational Diabetes: Develops during pregnancy; increases risk of type 2 diabetes later in life.

• Symptoms: Frequent urination, excessive thirst, unexplained weight loss, fatigue.

• Prevention: Healthy diet, regular physical activity, maintaining a healthy weight.

Fats: Essential Energy-Supplying Nutrients

Types of Lipids in Foods

• Triglycerides: The most common type of fat in foods and the body; composed of three fatty acids attached to a glycerol backbone.

• Phospholipids: Contain a phosphate group; important for cell membrane structure.

• Sterols: Include cholesterol; important for hormone synthesis and cell membranes.

Sources of Healthy Fats

• Monounsaturated Fats: Olive oil, avocados, nuts.

• Polyunsaturated Fats: Fatty fish, flaxseeds, walnuts.

• Omega-3 and Omega-6 Fatty Acids: Essential fatty acids found in fish, flaxseed, and certain plant oils.

Saturated, Unsaturated, and Trans Fats

• Saturated Fats: No double bonds; solid at room temperature; found in animal fats and some tropical oils.

• Unsaturated Fats: One or more double bonds; liquid at room temperature; includes monounsaturated and polyunsaturated fats.

• Trans Fats: Produced by hydrogenation; increase LDL cholesterol and risk of heart disease.

Example: Butter is high in saturated fat, while canola oil is high in unsaturated fat.

Digestion of Fats

• Mouth and Stomach: Minimal fat digestion occurs.

• Small Intestine: Bile emulsifies fats; pancreatic lipase breaks triglycerides into fatty acids and monoglycerides.

• Absorption: Fatty acids and monoglycerides are absorbed into intestinal cells and reassembled into triglycerides for transport.

Functions of Fat in the Human Body

• Energy Storage: Fats provide a concentrated source of energy.

• Cell Structure: Essential for cell membrane integrity.

• Insulation and Protection: Fats cushion organs and help regulate body temperature.

• Absorption of Fat-Soluble Vitamins: Necessary for absorption of vitamins A, D, E, and K.

Essential Fatty Acids: Linoleic and Alpha-Linolenic Acid

• Linoleic Acid (Omega-6): Found in vegetable oils, nuts, and seeds.

• Alpha-Linolenic Acid (Omega-3): Found in flaxseed, walnuts, and fatty fish.

• Both are essential for health and must be obtained from the diet.

Recommended Dietary Intake (RDI) and Acceptable Macronutrient Distribution Range (AMDR) for Fats

• AMDR for Fats: 20-35% of total daily calories should come from fat.

• Saturated Fat: Should be limited to less than 10% of total calories.

Food Sources for Different Fats

Fats and Chronic Diseases

• Cardiovascular Disease: High intake of saturated and trans fats increases risk.

• Diabetes: Excess fat, especially visceral fat, is linked to insulin resistance.

• Obesity: High-fat diets can contribute to excessive calorie intake and weight gain.

Proteins: Crucial Components of All Body Tissues

Structure of Amino Acids

Amino acids are the building blocks of proteins, each containing a central carbon, an amino group, a carboxyl group, a hydrogen atom, and a unique side chain (R group).

• General Structure:

Essential vs. Non-Essential Amino Acids

• Essential Amino Acids: Cannot be synthesized by the body; must be obtained from the diet (e.g., lysine, leucine).

• Non-Essential Amino Acids: Can be synthesized by the body (e.g., alanine, glutamine).

Complete and Incomplete Proteins

• Complete Proteins: Contain all essential amino acids in adequate amounts (e.g., animal proteins, soy).

• Incomplete Proteins: Lack one or more essential amino acids (e.g., most plant proteins).

Example: Quinoa is a plant-based complete protein.

Proteins vs. Other Energy Nutrients

• Proteins: Provide 4 kcal/g; used for tissue building, enzymes, hormones, and immune function.

• Carbohydrates and Fats: Primarily used for energy; proteins are not stored for energy in the same way.

Protein Digestion and Absorption

• Stomach: Pepsin and hydrochloric acid denature and break proteins into smaller peptides.

• Small Intestine: Pancreatic enzymes (trypsin, chymotrypsin) further digest peptides to amino acids.

• Absorption: Amino acids are absorbed into the bloodstream and transported to the liver.

Functions of Protein in the Body

• Structural: Build and repair tissues (muscle, skin, hair).

• Enzymatic: Catalyze biochemical reactions.

• Transport: Hemoglobin transports oxygen; albumin maintains fluid balance.

• Immune Function: Antibodies are proteins.

Protein Sparing

When sufficient carbohydrates and fats are available, protein is spared from being used for energy and can be used for tissue building and repair.

Calculating Protein RDA

• General Formula:

• Needs increase for athletes, pregnant women, and during illness.

Risks of High-Protein Diets

• Kidney Strain: Excess protein increases kidney workload.

• Dehydration: Increased urea production requires more water for excretion.

• Potential Nutrient Imbalances: May lead to low intake of fiber and certain vitamins.

Protein-Related Diseases

• Kwashiorkor: Protein deficiency with adequate energy intake; causes edema and fatty liver.

• Marasmus: Severe deficiency of both protein and energy; causes wasting and stunted growth.

Vegetarian Diets: Benefits and Risks

• Benefits: Lower risk of heart disease, hypertension, type 2 diabetes, and certain cancers; higher intake of fiber and antioxidants.

• Risks: Potential deficiencies in vitamin B12, iron, zinc, calcium, and omega-3 fatty acids if not well planned.

Example: Lacto-ovo vegetarians consume dairy and eggs, reducing risk of some nutrient deficiencies compared to vegans.