Carbohydrates, Lipids, and Proteins: Core Concepts for Nutrition Students

Carbohydrates (Carbs)

Types of Diabetes

Diabetes is a metabolic disorder characterized by high blood glucose levels due to issues with insulin production or function. There are several types, each with distinct causes and management strategies.

Type	Description	Key Points
Type 1	Autoimmune—body destroys insulin-producing cells	Childhood onset, insulin required, symptoms: thirst, urination, fatigue
Type 2	Insulin resistance or not enough insulin	Most common, linked to obesity, can be managed with diet/exercise
Prediabetes	Slightly high blood sugar	Warning stage, reversible with lifestyle change
Gestational	During pregnancy	Usually temporary, raises future risk of Type 2

Types of Carbs

Carbohydrates are classified based on the number of sugar units they contain. They serve as the body's main energy source and are found in a variety of foods.

Type	Example	Notes
Monosaccharides (1 sugar)	Glucose, Fructose, Galactose	Basic units of carbs
Disaccharides (2 sugars)	Sucrose = Glucose + Fructose Maltose = Glucose + Glucose Lactose = Glucose + Galactose	Broken down by enzymes
Polysaccharides (many sugars)	Starch, Glycogen, Fiber	Complex carbs

• Enzymes break down disaccharides: Sucrose → sucrase → glucose + fructose Maltose → maltase → 2 glucose Lactose → lactase → glucose + galactose

Glucose, Glycogen, Starch, Fiber

These are key carbohydrate forms with distinct functions in the body.

Term	Function
Glucose	Main energy source
Glycogen	Stored glucose in animals
Starch	Stored glucose in plants
Fiber	Nondigestible plant carb; aids digestion & heart health

Blood Sugar Regulation

Maintaining blood glucose within a healthy range is essential for metabolic health.

• Hypoglycemia: <70 mg/dL → shaky, dizzy; fixed with simple sugars

• Hyperglycemia: High blood sugar—common in diabetes

Digestion of Carbs

Carbohydrate digestion involves several steps and organs.

1. Mouth – Salivary amylase starts breakdown

2. Small Intestine – Pancreatic amylase finishes digestion

3. Fiber – Passes through undigested

Benefits of Fiber

Dietary fiber is crucial for digestive and overall health.

• Prevents constipation & diverticulitis

• Promotes heart health

• Controls blood sugar

• Prevents obesity & some cancers

• Goal: 14g per 1,000 calories (~28g/day)

Sugars & Health

Sugars are classified as natural or added, with different health impacts.

Type	Example	Note
Natural	Fruit (fructose), Milk (lactose)	Nutrient-dense
Added	Soda, candy, desserts	Limit to <10% of calories (≤6 tsp women, 9 tsp men)

• Tooth Decay: Bacteria feed on sugar → cavities Tips: Brush after meals, avoid sticky snacks, drink water

Sugar Substitutes

Alternative sweeteners provide sweetness with fewer or no calories.

Type	Notes
Polyols	Sugar alcohols (xylitol, sorbitol); fewer calories
Saccharin	"Sweet'N Low"
Aspartame	"Equal" 200× sweeter
Neotame	Not metabolized
Acesulfame K	"Sunett"; body can't digest
Sucralose	"Splenda"; made from sugar
Steviol Glycosides	"Stevia"; "Truvia"
Monk Fruit	Natural sweetener
Advantame	Very sweet, heat stable

Lipids (Fats)

Types & Roles

Lipids are a diverse group of compounds that serve as energy storage, structural components, and signaling molecules.

Type	Function
Triglycerides	Most common; energy storage
Phospholipids	Make up cell membranes
Sterols (Cholesterol)	4 carbon rings; make hormones, vitamin D, bile

Fatty Acids

Fatty acids are classified by the presence and number of double bonds, affecting their physical properties and health effects.

Type	Bonds	Example
Saturated	No double bonds	Butter
Unsaturated	≥1 double bond	Oils

• Essential Fatty Acids: Omega-6 (Linoleic acid) Omega-3 (Alpha-linolenic acid) – good for heart & brain health

Digestion & Absorption

Lipid digestion involves emulsification and enzymatic breakdown.

1. Mouth – Lingual lipase starts

2. Stomach – Gastric lipase continues

3. Small Intestine – Bile emulsifies fat; pancreatic lipase breaks it down

Lipoproteins

Lipoproteins transport lipids in the blood, influencing cardiovascular health.

Type	Function
VLDL	Carries fat from liver to cells
LDL ("bad")	Delivers cholesterol to tissues; can clog arteries
HDL ("good")	Removes cholesterol to liver for disposal

Heart Disease

Dietary fats and lipoproteins play a major role in cardiovascular health.

• Atherosclerosis: Plaque buildup → blocked arteries

• Metabolic Syndrome: ≥3 risk factors (abdominal fat, high BP, high triglycerides, low HDL)

• Risk factors: Non-modifiable: Age, sex, family history Modifiable: Diet, exercise, blood sugar, smoking

Blood Pressure: Normal = 120/80 Systolic = pumping pressure Diastolic = resting pressure

Fat Substitutes

Fat substitutes are used to reduce calorie content in foods.

Type	Example	Function
Carb-based	Fiber, gums	Add texture
Protein-based	Milk or egg protein	Creamy feel (not heat stable)
Fat-based	Olestra	Not absorbed, 0 calories

Proteins

Roles in Body

Proteins are essential macromolecules involved in structure, function, and regulation of the body's tissues and organs.

• Build, repair, and maintain cells

• Make enzymes, hormones, and antibodies

• Transport nutrients

• Provide energy (last resort)

Protein Structure

• Amino acids = building blocks

• Peptide bonds link them together

• Protein Turnover: Continuous breakdown & rebuilding of proteins

Denaturation

Denaturation is the process by which proteins lose their structure due to heat, acid, or salt, potentially causing permanent loss of function.

Digestion Process

Protein digestion involves several steps and enzymes.

1. Stomach: HCl unfolds protein

2. Pepsin breaks into peptides

3. Small Intestine: Trypsin, chymotrypsin, carboxypeptidase → break down further

4. Absorption: Amino acids absorbed → liver → used for energy or new proteins

Protein Types

Type	Notes
Animal-based	Complete proteins (all amino acids)
Plant-based	Incomplete; combine foods (beans + rice)

Nitrogen Balance

Nitrogen balance reflects protein status in the body.

• Positive: Growth, pregnancy, muscle gain

• Negative: Illness, malnutrition, muscle loss

Low Protein & Health Issues

• Muscle wasting

• Weak immune system

• Edema (fluid imbalance)

Protein Requirements

Protein needs vary by age, activity, and health status.

• Formula: $0.8 \times \text{body weight (kg)}$

• Example: 70 kg = 56g protein/day

Important Proteins

• Actin & Myosin – muscle movement

• Collagen – skin & connective tissue

• Enzymes & Hormones – control body processes