11. Macronutrient

What are the 3 main roles of nutrients?

Energy (carbs, fats, proteins), structural materials (organic + inorganic like Ca, PO₄), and catalytic molecules (vitamins, minerals).

What are the main nutrient classes?

Macronutrients (carbs, proteins, fats) + micronutrients (vitamins, minerals).

What is EAR?

Intake that meets needs of 50% of a population; used for population-level assessment.

What is RDA?

Intake sufficient for ~97–98% of individuals; goal for individuals.

What is UL?

Maximum intake unlikely to cause toxicity.

Key difference EAR vs RDA?

EAR = midpoint; RDA = safe level for nearly everyone.

What is a Calorie?

1 kcal (“big calorie”) = 4200 J (4.2 kJ).

What is Resting Metabolic Rate (RMR)?

Energy required for basic physiologic functions at rest (no activity).

What do Harris-Benedict & Mifflin-St Jeor equations estimate?

Daily maintenance calories based on weight, height, age, sex.

What is RQ?

Ratio of CO₂ produced to O₂ consumed (VCO₂/VO₂).

RQ values for macronutrients?

Carbs = 1.0, Protein = 0.8, Fat = 0.7.

What does RQ >1 indicate?

What does RQ <0.7 indicate?

Fat synthesis (lipogenesis).

Ketosis or underfeeding.

Calories per gram of macronutrients?

Fat = 9 kcal/g, Carbs = 4 kcal/g, Protein = 4 kcal/g, Alcohol = 7 kcal/g.

Factors affecting caloric needs?

Height, weight, age, sex, activity, lean mass, health, genetics, pregnancy/lactation.

BMI formula?

BMI categories?

Weight (kg) / height (m²).

Normal: 18.5–24.9, Overweight: 25–29.9, Obese: ≥30.

Why is BMI limited?

Doesn’t distinguish muscle vs fat; varies with age/sex.

What are the BMI categories and grades of obesity?

• Normal: 18.5–24.9

• Overweight: 25–29.9

• Obesity Class I: 30–34.9

• Obesity Class II: 35–39.9

• Obesity Class III (severe): ≥40

Types of carbohydrates?

% of calories from carbs?

Simple sugars and polysaccharides.

45–65%.

Are carbohydrates essential?

No (body can produce glucose via gluconeogenesis).

What is glycemic index?

How is GI measured?

Blood glucose response to food relative to glucose ×100.

Give glucose → compare blood sugar rise to another food.

What lowers GI?

Fat slows absorption → lowers apparent GI.

What is glycemic load?

GI × quantity of carbohydrate consumed.

Why is glycemic load more useful than GI?

Accounts for portion size, not just food type.

Types of fiber?

Insoluble (cellulose, hemicellulose) and soluble (pectins, gums, mucilage).

Function of insoluble fiber?

Adds bulk, speeds transit, prevents constipation.

Function of soluble fiber?

Fermented → short chain fatty acids SCFAs (acetate, propionate, butyrate) → nourish gut.

What is the difference between starch and fiber?

• Starch: Digestible polysaccharide → broken down into glucose for energy.

• Fiber: Indigestible polysaccharide → not absorbed; adds bulk, speeds transit, and can be fermented by gut bacteria to produce beneficial SCFAs.

What are FODMAPs? Why are FODMAPs important clinically?

Fermentable oligo-, di-, mono-saccharides and polyols.

Cause GI symptoms (bloating, gas, diarrhea).

Daily protein requirement?

% of calories from protein?

~0.8 g/kg/day.

10–35%.

Essential amino acids (mnemonic)?

“PVT TIM HALL” → phe, val, trp, thr, ile, met, his, arg, leu, lys.

What are conditionally essential amino acids?

Needed during stress (e.g., illness, trauma).

What is a complete protein?

Examples of complete proteins?

Contains all essential amino acids in adequate amounts.

Animal sources, soy, quinoa.

Why combine plant proteins?

Individually incomplete → combined to meet AA needs (e.g., rice + beans).

Do you need to combine at every meal?

No, as long as total daily intake is balanced.

Why are high-protein diets problematic in renal disease?

Increase nitrogen waste → kidney strain.

What did rat studies show about protein intake?

High protein/casein (20%) → ↑ liver cancer vs low protein/casein (5%).

Epidemiologic finding (Philippines)?

Higher protein intake correlated with ↑ liver cancer (due to aflatoxin exposure).

Aflatoxin Mechanism?

Aflatoxin enters cell, ↑ CYP450 activity, ↑ toxin activation, ↑ cell proliferation, ↑ DNA adducts, ↑cancer.

Key conclusion of China Study?

Diets high in animal protein associated with chronic disease risk. best diet is low fat plant based

What is the difference between N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac)?

• Neu5Gc: Found in most mammals (e.g., red meat); not naturally produced in humans → can trigger immune/inflammatory responses when consumed.

• Neu5Ac: The form humans naturally produce and use in cell surface glycoproteins.
  👉 Key concept: dietary Neu5Gc (from animal products) may be linked to chronic disease via inflammation.

Essential fatty acids?

Linoleic (ω-6) and α-linolenic (ω-3).

When is arachidonic acid essential?

When linoleic acid is deficient.

Functions of essential fatty acids?

Membrane structure, cholesterol transport, lipoprotein formation, prevent fatty liver.

What is phrynoderma?

“Toad skin” from EFA deficiency.

What is DHA?

Why is DHA important?

Omega-3 fatty acid (22:6).

Essential for brain, retina, and visual development in infants.

Where is DHA highly concentrated?

Retina (20%), rod outer segments (35%), brain cortex (~9%).

Effect of polyunsaturated fatty acids on metabolism?

↑ fat breakdown (β-oxidation), ↓ fat synthesis (lipogenesis)

How do PPAR and SREBP-1 differ in lipid metabolism?

• PPAR: Activated by fatty acids → ↑ fat breakdown (β-oxidation), ↓ fat synthesis → promotes lipid catabolism

• SREBP-1: Transcription factor → ↑ fatty acid & triglyceride synthesis → promotes lipid storage
  👉 Opposite effects: PPAR = burn fat, SREBP-1 = make/store fa

What happens to polyunsaturated fatty acids during partial hydrogenation?

• PUFAs normally have cis double bonds → liquid at room temp

• Partial hydrogenation adds H → makes fat more solid

• This process converts some cis bonds → trans bonds
  👉 Result: formation of trans fats (more rigid, harmful).

What do trans fats do in the body and what are their effects?

• ↑ LDL (“bad” cholesterol), ↓ HDL (“good” cholesterol)

• Promote inflammation and endothelial dysfunction

• Increase risk of atherosclerosis and cardiovascular disease
  👉 Overall: strongly harmful fats linked to heart disease.