Human Nutrition

Carbohydrates

Protein sparing, meaning if there aren’t enough carbs in the diet, the body will convert protein into protein into glucose to meet energy needs.

• Definition: Carbohydrates are "hydrated carbons" – for every carbon atom, there is one molecule of water.

• Primary Fuel Source: Carbohydrates are the body's main source of energy, especially for the CNS, brain, and red blood cells.

• Energy Content: Carbs provide 4 calories per gram.

• Glucose: The carbohydrate we consume is converted into glucose, which is transported through the blood as "blood sugar." It is stored as glycogen in muscles and the liver.

• Excess Carbohydrates: When carbs are consumed in excess, they are converted and stored as fat.

• Blood Glucose Regulation:

  • Insulin: Lowers blood glucose levels.

• Glucagon: Increases blood glucose levels.

Blood Glucose Levels

• Normal: 70–99 mg/dL

• Pre-Diabetes: 100–125 mg/dL

• Diabetes: 126+ mg/dL

• Hypoglycemia: Low blood glucose levels (<70 mg/dL)

• Hyperglycemia: High blood glucose levels (>100 mg/dL)

Types of Carbohydrates

• Monosaccharides

• Disaccharides

• Oligosaccharides

• Polysaccharides

• Glycogen

Monosaccharides

• Single sugar molecules.

  • Fructose: Known as "fruit sugar," found in fruits, vegetables, honey, and high-fructose corn syrup.

  • Galactose: Most commonly consumed as part of lactose in dairy.

Disaccharides

• Two monosaccharides linked together.

  • Maltose: Glucose + Glucose (alpha bond), found in sprouting seeds and malted beverages.

  • Sucrose: Glucose + Fructose (alpha bond), known as "table sugar," found in sugarcane, sugar beets, and maple syrup.

  • Lactose: Glucose + Galactose (beta bond), found in dairy products.

Oligosaccharides

1. Complex carbohydrates made up of 3 to 10 monosaccharides.

   • Fructans/Fructo-oligosaccharides – Chains of fructose with glucose at the end.

   • Galactans/Galacto-oligosaccharides – Chains of galactose with glucose at the end.

   • Raffinose – A trisaccharide composed of galactose, glucose, and fructose.

   • Stachyose – A tetrasaccharide composed of two galactose, one glucose, and one fructose.

   • Oligosaccharides act as fiber and prebiotics since we cannot digest them

Fructans/Fructo-oligosaccharides

Chains of fructose with glucose at the end

Galactans/Galacto-oligosaccharides

Chains of galactose with glucose at the end

Raffinose

A trisaccharide composed of galactose, glucose , and fructose

Stachyose

A tetrasaccharide composed of two galactose, one glucose, and one fructose

Lactose Intolerance

• Cause: Insufficient lactase enzyme production, which decreases after childhood (around 3-5 years old).

• Symptoms: Undigested lactose attracts water into the GI tract and is fermented by bacteria, causing gas, bloating, cramping, and diarrhea.

• Primary Lactose Intolerance: Natural decline in lactase production with age.

• Secondary Lactose Intolerance: Caused by diseases (e.g., Crohn's or Celiac disease) that damage lactase-producing cells.

• Management: Some people can tolerate low-sugar dairy (e.g., hard cheeses, yogurt), as the lactose is broken down during fermentation.

Polysaccharides

1. Complex carbohydrates composed of multiple sugar units.

   • Digestible Polysaccharides (Starch)

     • Amylose – Linear and unbranched; glucose linked by alpha 1-4 bonds.

     • Amylopectin – Highly branched; glucose linked by alpha 1-4 and alpha 1-6 bonds.

   • Indigestible Polysaccharides (Fiber)

     • Soluble Fiber – Dissolves in water, becomes gel-like, and is fermented by probiotics.

       • Aids in blood sugar control.

       • Lowers blood cholesterol levels.

       • Acts as a prebiotic, promoting gut health and diversity.

       • Promotes satiety and aids in weight control.

     • Insoluble Fiber – Does not dissolve in water and is not fermented by probiotics.

       • Promotes bowel regularity.

       • Adds bulk to stool and prevents constipation.

       • Promotes satiety and aids in weight control.

Amylose

Linear and unbranched; glucose linked by alpha 1-4 bonds. (Digestible polysaccharide: aka Starch)

Amylopection

Highly branched; glucose linked by alpha 1-4 and alpha 1-6 bonds. (Digestible Polysaccharides: Aka Starch)

Soluble FIber

Dissolves in water, becomes gel-like, and is fermented by probiotics

• Aids in blood sugar control.

• Lowers blood cholesterol levels.

• Acts as a prebiotic, promoting gut health and diversity.

• Promotes satiety and aids in weight control.

• Indigestible Polysaccharides (Fiber)

Insoluble FIber

Does not dissolve in water and is not fermented by probiotics.

• Promotes bowel regularity.

• Adds bulk to stool and prevents constipation.

• Promotes satiety and aids in weight control.

• Indigestible Polysaccharide (fiber)

Glycogen

Storage Form of Glucose in Humans

• Structure is similar to amylopectin, with glucose linked by alpha bonds.

• Liver glycogen – Maintains blood sugar levels.

• Muscle glycogen – Used by muscles for energy.

Sugar Alcohols

Also known as Polyols or Polyhyrdric Alcohols

• Contain an -OH (hydroxyl) group.

• Common sugar alcohols: Sorbitol, Mannitol, Xylitol, Erythritol, Maltitol.

• Often end in "-ol."

• FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols).

  • FODMAPs produce gas.

  • Consuming sugar alcohols in large amounts may cause gas, bloating, and GI distress.

  • Foods containing sorbitol or mannitol must include a warning on their label:
    “Excess consumption may have a laxative effect.”

FODMAPS

Fermentable Oligosaccharides, Disaccharides, Monosaccharides, And Polyols.

• FODMAPS Produce gas

• May cause bloating, gas, and GI distress

• ***Foods containing sorbitol or mannitol must include a warning on their label: “Excess consumption may have a laxative effect.”

Sweeteners

• Nutritive Sweeteners – Provide calories.

• Non-Nutritive Sweeteners – Do not provide calories (e.g., artificial sweeteners).

  • Extremely sweet and calorie-free.

  • FDA-approved artificial sweeteners recognized as safe:

    • Saccharin

    • Aspartame

    • Sucralose

    • Neotame

    • Acesulfame-Potassium

    • Advantame

Nutritive Sweeteners

Provide calories

Non-Nutritive Sweeteners

Do not provide calories (artificial sweeteners)

FDA approved artificial Sweeteners

• Saccharin

• Aspartame

• Sucralose

• Neotame

• Acesulfame-Potassium

• Advantame

Orthorexia

An unhealthy obsession with healthy eating

Functions of Carbohydrates

• Primary source of energy for the body

• Brain/CNS prefers glucose as an energy source

• Carbohydrates spare protein, preserving body protein/muscle

• Prevents ketosis (excessive ketone production from fat breakdown)

• Ketones: Alternative energy source formed from fatty acids (acidic)

Ketones

Alternative energy source formed from fatty acids (acidic)

Carbohydrate Digestion and Absorption

1. Mouth – Salivary amylase begins breaking starch into polysaccharides and disaccharides

2. Stomach – No carbohydrate digestion (amylase inactivated by stomach acid)

3. Pancreas – Releases pancreatic amylase and dextrinase to break starch into disaccharides

4. Small Intestine – Enzymes break disaccharides into monosaccharides, which are absorbed

5. Liver – Monosaccharides travel via the portal vein to the liver

6. Large Intestine – Some soluble fiber is fermented into acids and gases

7. Rectum/Anus – Insoluble fiber is excreted in feces

Mouth

Salivary amylase begins breaking starch into polysaccharides and disaccharides

Stomach

No carbohydrate digestion (amylase inactivated by stomach acid)

Pancreas

Releases pancreatic amylase and dextrinase to break starch into disaccharides

Small Intestine

Enzymes break disaccharides into monosaccharides, which are absorbed

Liver

Monosaccharides travel via the portal vein to the liver

Large Intestine

Some soluble fiber is fermented into acids and gases

Rectum/Anus

Insoluble fiber is excreted in feces

Glucose & Galactose

Actively absorbed (requires ATP)

Fructose

Slowly diffuses across the GI Tract

Non-glucose monosaccharides

In the Liver non-glucose monosaccharides are converted to glucose and glucose can be released into the bloodstream, stored as glycogen, and converted to fat.

Fiber

Binds minerals in the digestive tract

• Recommended Intake:

  • Before age 50: 25g/day (women), 38g/day (men)

  • After age 50: 21g/day (women), 30g/day (men)

  • Adequate Intake: 14g per 1000 kcal

• High Fiber Risks:

  • Low liquid intake → Constipation

  • Insufficient calorie intake → Micronutrient deficiencies

  • Early satiety → Can limit overall nutrient intake

Blood Glucose Regulation

Organs Involved:

• Liver: Determines glucose release into bloodstream, stores excess as glycogen

• Pancreas: Releases hormones for blood glucose regulation

Key Hormones:

• Insulin (Anabolic Hormone):

  • Lowers blood glucose levels (facilitates glucose uptake into cells)

  • Acts as a "key" for glucose entry into cells

• Glucagon:

  • Increases blood glucose by breaking down glycogen

  • Stimulates glucose production from non-carbohydrate sources

• Other Hormones That Raise Blood Glucose:

  • Cortisol, Epinephrine, Norepinephrine, Growth Hormone

Insulin (Anabolic Hormone)

• Lowers blood glucose levels (Facilitates glucose uptake into cells

• Acts as a key for glucose entry into cells

Glucagon

• Increases blood glucose by breaking down glycogen

• Stimulates glucose production from non-carbohydrate sources

Other Hormones that Raise Blood Glucose

• Cortisol

• Epinephrine

• Norepinephrine

• Growth Hormone

Dietary Carbohydrate Recommendations

• RDA: 130g/day

  • Supplies adequate glucose for the brain/CNS

  • Prevents excessive ketone production

• AMDR: 45-65% of total energy intake

• Athletes/Active Individuals: Should consume a higher proportion of carbs

• Added Sugar:

Limit to ≤10% of total daily energy intake

Type 1 Diabetes (5% of cases)

• Cause: Autoimmune destruction of pancreatic cells

• Symptomes

  • Ketosis: Ketones are formed from fatty acids and are an alternative energy source for the body (Ketones are acidic)

  • Weight loss

  • Increased thirst, hunger, urination

  • Fruity/acetone breath

• Treatment:

  • Insulin therapy

  • Diet & exercise

  • Monitor: Blood glucose, urine ketones, HbA1c

Type 2 Diabetes (90% of cases)

• Cause: Insulin resistance

• Symptoms:

  • Fatigue

  • Nighttime urination

  • Ketosis usually absent

• Treatment:

  • Exercise & Diet

  • Oral medication to lower blood glucose

  • Monitor: Blood glucose, HbA1c

Glycemic Index (GI)

Ranks carbs (0-100) based on their impact on blood sugar

• High Gi foods—>Rapid blood sugar spike

Glycemic Load (GL)

Takes into account both carbohydrate quantity and quality

• Low GL meals —> Better blood sugar control

Functions of Lipids

• Energy source (9 kcal/g)

• Insulation & protection (preserve body heat, protect organs)

• Aid in absorption & transport of fat-soluble vitamins (A, D, E, K)

• Structural component of cells & hormones

• Enhance food flavor and texture

Types of Lipids

1. Triglycerides (most common in food & body)

   • Composed of glycerol + 3 fatty acids

2. Phospholipids (major component of cell membranes)

3. Sterols (e.g., cholesterol)

Fatty Acid Types

• Saturated Fatty Acids (SFA) – No double bonds (solid at room temp)

  • Found in meat, dairy, coconut oil, palm oil

• Monounsaturated Fatty Acids (MUFA) – One double bond

  • Found in olive oil, avocado, nuts

• Polyunsaturated Fatty Acids (PUFA) – Two or more double bonds

  • Includes Omega-3 (EPA, DHA) and Omega-6

Found in fish, flaxseeds, walnuts

Fatty Acid Length

• Long-Chain FA (>12 C): Beef, pork, lamb, fish, plant oils (slow digestion)

• Medium-Chain FA (6-10 C): Coconut oil, dairy (rapid digestion)

• Short-Chain FA (<6 C): Butter, gut-fermented fiber (quick digestion)

Lipid Metabolism Processes

• Esterification: Formation of triglycerides

• De-esterification: Release of fatty acids (hydrolysis)

• Re-esterification: Reattachment of fatty acids

Recommended Fat Intake

• No RDA (Recommended Dietary Allowance) for adults

• AI (Adequate Intake) established for infants

• AMDR (Acceptable Macronutrient Distribution Range): 20-35% of total kcal

• Omega-3 Adequate Intake (as ALA)

  • Males (19-50 years old): 1.6 g

  • Females (19-50 years old): 1.1 g

• Dietary Guidelines for Americans (DGAs):

  • Consume more unsaturated fats

  • Limit saturated fat to <10% of total calories

  • Avoid artificial trans fats

Saturated Fat

• Sources

  • Animal Products (butter, ghee, lard, red meat, dairy)

  • Tropical oils (coconut oil, palm oil, palm kernel oil)

  • Baked goods & Ultra processed foods

Monounsaturated Fat (MUFA)

• Sources

  • Plant-based oils (olive oil, canola oil, peanut oil, avocado oil)

  • Whole foods (olives, avocados, nuts, seeds, nut butters)

Polyunsaturated Fat (PUFA)

• Sources

  • Plant oils (safflower, sunflower, corn, soybean)

  • Nuts & seeds (walnuts, flaxseeds, chia seeds)

  • Fish & seafood (salmon, mackerel, sardines)

Trans Fat

• Naturally found in dairy

• Artificial sources: Partially hyrogenated oils, fast food, fried food

• PHOs (Partially Hydrogenated Oils) banned in 2020

Essential Fatty Acids (EFAs)

• Body cannot synthesize EFAs—> Must come from food

• Alpha-Linolenic Acid (ALA) (18:3) w3)- Omega 3 PUFA

• Linoleic Acid (LA) (18:2 w6)- Omega-6 PUFA

Alpha-Linolenic Acid (ALA) (18:3 ω3) – Omega-3 PUFA

• Used to make: EPA & DHA + certain eicosanoids

• Sources: Nuts, seeds, flaxseed oil, chia seeds, walnuts, canola oil, soy-based foods

Linoleic Acid (LA) (18:2 ω6) – Omega-6 PUFA

• Used to make: Arachidonic Acid (ARA) + certain eicosanoids

Omega-3 Fatty Acids

Eicosapentaenoic Acid (EPA) (20:5 ω3)

• Synthesized from ALA or obtained from diet

• Needed for:

  • Fetal development

  • Healthy aging

Docosahexaenoic Acid (DHA) (22:6 ω3)

• Synthesized from EPA or obtained from diet

• Supports:

  • Brain & eye development/function

  • Nervous system function

  • Memory & cognition

• Deficiency linked to: Depression, suicidal behavior, anger, hostility

• Sources of EPA & DHA:

  • Fatty fish (herring, salmon, mackerel, sardines, trout, tuna)

  • Seafood (oysters, crab)

  • Omega-3 supplements (fish oil, krill oil, cod liver oil, algal oil)

Eicosapentaenoic Acid (EPA) (20:5 ω3)

• Synthesized from ALA or obtained from diet

• Needed for:

  • Fetal development

  • Healthy aging

Docosahexaenoic Acid (DHA) (22:6 ω3)

• Synthesized from EPA or obtained from diet

• Supports:

  • Brain & eye development/function

  • Nervous system function

  • Memory & cognition

• Deficiency linked to: Depression, suicidal behavior, anger, hostility

• Sources of EPA & DHA:

  • Fatty fish (herring, salmon, mackerel, sardines, trout, tuna)

  • Seafood (oysters, crab)

  • Omega-3 supplements (fish oil, krill oil, cod liver oil, algal oil)

Functions of Triglycerides

• Energy source: 9 kcal/g

• Main fuel source when resting or doing light activity

• Body stores excess calories as fat

• Protects vital organs & maintains body temperature

• Aids in absorption of fat-soluble vitamins (A, D, E, K)

• Transports essential nutrients in the bloodstream

Fat Cell Growth

• Hypertrophy: Increase in cell size

• Hyperplasia: Increase in cell number

• Weight gain → Fat droplets enlarge

• Weight loss → Fat droplets shrink

Phospholipids

• Two major roles:

  • Cell membrane component

  • Functions as an emulsifier

• Sources:

  • Dietary: Lecithin (egg yolks, wheat germ, peanuts)

  • Synthesized by the body

  • Unrefined plant oils (vegetable, nut, olive oil)

• Structure:

  • Phosphate "head" – Hydrophilic

  • Fatty acid "tails" – Hydrophobic

• In water, phospholipids form micelles

Sterols & Cholesterol

• Sterols: Type of steroid (multi-ringed structure)

• Best known sterol: Cholesterol

• Functions of cholesterol:

  • Used to make steroid hormones (testosterone, estrogen)

  • Adrenal hormones (aldosterone, cortisol)

  • Cell membranes

  • Vitamin D

  • Bile acids

Sources: Found in animal-based foods or synthesized by the body

Eicosanoids: Hormone-like compounds

• Regulate:

  • Blood pressure & clotting

  • Sleep/wake cycles

  • Body temperature

  • Inflammation & immune response

  • Kidney function & fluid balance

• Omega-3-derived eicosanoids: Anti-inflammatory

• Omega-6-derived eicosanoids: Pro-inflammatory

Phytosterols

• Plant stanols & sterols (cholesterol-like compounds)

• Function:

  • Lower LDL cholesterol by interfering with dietary cholesterol absorption

  • 2 g/day can reduce LDL by 8-10%

Fatty Acid Nomenclature

Two Naming Systems:

1. Omega (ω) System

   • Methyl end (CH₃) = Omega end

   • Number indicates first double bond closest to methyl end

   • Example: Linoleic Acid (18:2 ω6)

2. Delta (Δ) System

   • Describes fatty acids from carboxyl end (COOH)

   • Indicates all double bond locations

   • Example: Linoleic Acid (18:2 Δ9,12)

Hydrogenation & Trans Fats

• Hydrogenation: Process of adding hydrogen to unsaturated fats

• Fully Hydrogenated Oils:

  • All double bonds → single bonds

  • Converts liquid oil → solid fat

• Partially Hydrogenated Oils (PHOs):

  • Some double bonds → single bonds

  • Forms trans fats

• PHOs banned in 2020 (no longer GRAS by FDA)

Lipoproteins

Lipoproteins: Transporters of Lipids in the Blood

• Chylomicrons

  • Primary Component: Triglyceride

  • Key Role: Transports dietary fat from the small intestine (SI) to the cells

• Very-Low-Density Lipoprotein (VLDL)

  • Primary Component: Triglyceride

  • Key Role: Produced by the liver – Carries lipids from the liver to the cells

• Intermediate-Density Lipoprotein (IDL)

• Low-Density Lipoprotein (LDL) – "Bad" Cholesterol

  • Arises from VLDL

  • Primary Component: Cholesterol

  • Key Role: Carries cholesterol made by the liver and from other sources to the cells

• High-Density Lipoprotein (HDL) – "Good" Cholesterol

  • Primary Component: Protein

  • Key Role: Reverse Cholesterol Transport

    • Helps remove cholesterol from the cells and excretes it from the body

    • Can prevent LDL from being oxidized

Lipoprotein Lipase (LPL)