Proximal principles of Nutrition
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Proximate Principles of Nutrition
The term "proximate principles" refers to the three macronutrients - proteins, fats, and carbohydrates - so named because they form the main bulk of food. They are the primary energy-yielding nutrients and are distinguished from micronutrients (vitamins and minerals), which are required in much smaller amounts.
Park's Textbook of Preventive and Social Medicine - these are formally defined under the heading of Macronutrients: "Proteins, fats and carbohydrates... are often called 'proximate principles' because they form the main bulk of food."
Energy Contribution (Indian Dietary)
| Proximate Principle | % of Total Energy Intake |
|---|---|
| Proteins | 10-15% |
| Fats | 15-30% |
| Carbohydrates | 50-80% |
1. Proteins
- The word "protein" by derivation means "that which is of first importance"
- Complex organic nitrogenous compounds composed of C, H, O, N, and S; some also contain phosphorus and iron
- Nitrogen content is approximately 16%
- Constitute about 20% of body weight in an adult
- Energy yield: 4 kcal per gram
Essential Amino Acids (9 total)
The body cannot synthesize these in adequate amounts; must be obtained from diet:
Leucine, Isoleucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine, and Histidine
Protein Quality
| Term | Meaning |
|---|---|
| Complete proteins | Contain all essential amino acids in adequate proportions (e.g., eggs, milk, meat, fish) |
| Partially incomplete | Deficient in one or more EAAs but can maintain life (e.g., most plant proteins) |
| Incomplete proteins | Cannot support life or growth (e.g., zein in maize - lacks lysine and tryptophan) |
Biological Value (BV)
Measures the proportion of absorbed nitrogen actually retained by the body:
- Egg: ~100 (reference standard)
- Milk: ~85
- Meat/Fish: ~75-80
- Pulses: ~65
- Cereals: ~60
Protein Requirements (Indian RDA)
| Group | Requirement |
|---|---|
| Adult man | ~0.83 g/kg body weight/day (safe level) |
| Pregnant woman | Additional +23 g/day (2nd & 3rd trimester) |
| Lactating woman | Additional +19 g/day (first 6 months) |
| Infants | ~1.69 g/kg/day |
Protein-Energy Malnutrition (PEM)
- Kwashiorkor: Protein deficiency with adequate caloric intake - edema, skin lesions, fatty liver
- Marasmus: Deficiency of both protein and calories - extreme wasting
- Marasmic Kwashiorkor: Combined features
Sources
- Animal (high BV): Milk, eggs, meat, fish, poultry
- Plant: Pulses, legumes, nuts, oilseeds, cereals
2. Fats (Lipids)
- Most concentrated source of energy: 9 kcal per gram (more than double proteins/carbohydrates)
- Composed of C, H, and O; characterized by their fatty acid content
- Enable absorption of fat-soluble vitamins (A, D, E, K)
- Provide essential fatty acids (EFAs)
- Contribute to palatability and satiety of food
Classification of Fatty Acids
| Type | Nature | Health Effect | Examples |
|---|---|---|---|
| Saturated (SFA) | No double bonds | Raise LDL cholesterol; atherogenic | Butter, ghee, coconut oil, palm oil |
| Monounsaturated (MUFA) | One double bond | Neutral/beneficial; lower LDL | Olive oil, groundnut oil |
| Polyunsaturated (PUFA) | Two or more double bonds | Lower cholesterol; anti-atherogenic | Sunflower, safflower, corn oil |
| Trans fatty acids | Artificially hydrogenated | Raise LDL, lower HDL; most harmful | Vanaspati (PHVO), margarine |
Essential Fatty Acids (EFAs)
Cannot be synthesized by the body; must come from diet:
| EFA | Major Dietary Sources |
|---|---|
| Linoleic acid (LA, omega-6) | Safflower oil (73%), corn oil (57%), sunflower oil (56%), soyabean oil (51%) |
| Linolenic acid (ALA, omega-3) | Soyabean oil (7%), leafy greens |
| Arachidonic acid | Meat, eggs, milk fat |
| EPA (Eicosapentaenoic acid) | Fish oil (10%) |
Visible vs. Invisible Fats
- Visible fats: Separated from their natural source (ghee, cooking oils) - easy to measure
- Invisible fats: Present in almost all foods (cereals, pulses, nuts, milk, eggs) - difficult to estimate; major contributor to total fat intake in Indian diet
Fat Requirements (Indian Adults - Visible Fat)
| Group | Sedentary | Moderate Activity | Heavy Activity |
|---|---|---|---|
| Adult man | 25 g/day | 30 g/day | 40 g/day |
| Adult woman | 20 g/day | 25 g/day | 30 g/day |
Minimum total fat should provide at least 20% of total energy intake.
Dietary Recommendations
- Use blended oils (combining oils with different fatty acid profiles)
- Limit butter/ghee
- Avoid partially hydrogenated vegetable oils (PHVO/vanaspati)
- For frying, use thermally stable oils (palm oil, sesame, ricebran)
3. Carbohydrates
- The third major proximate principle and the main source of energy
- Energy yield: 4 kcal per gram
- Essential for oxidation of fats (prevent ketosis) and synthesis of certain non-essential amino acids
- Forms the largest fraction of the Indian diet (50-80% of total energy)
Classification
| Class | Examples |
|---|---|
| Monosaccharides | Glucose, fructose, galactose |
| Disaccharides | Sucrose (glucose + fructose), lactose (glucose + galactose), maltose |
| Polysaccharides | Starch (digestible), cellulose/dietary fiber (non-digestible) |
Dietary Fiber
- The non-digestible polysaccharide component of plant foods
- Reduces constipation, lowers risk of colorectal cancer, helps manage blood glucose and cholesterol
- Recommended intake: >40 g/day (ICMR)
- Sources: whole grains, legumes, fruits, vegetables
Sources of Carbohydrates
- Starches: Cereals (rice, wheat, maize), roots and tubers (potato, tapioca)
- Sugars: Jaggery, sugar, fruits, milk (lactose)
- Cellulose/Fiber: All plant foods, especially bran, vegetables, legumes
Carbohydrate Requirements
- Should provide 50-80% of total energy intake in the Indian dietary pattern
- Complex carbohydrates (starches) preferred over simple sugars
- Free sugars should be limited to <10% of total energy (WHO recommendation)
Summary: Key Comparisons
| Feature | Proteins | Fats | Carbohydrates |
|---|---|---|---|
| Energy (kcal/g) | 4 | 9 | 4 |
| % in Indian diet | 10-15% | 15-30% | 50-80% |
| Key elements | C, H, O, N, S | C, H, O | C, H, O |
| Unique property | Contains nitrogen | Most energy-dense | Main energy source |
| Deficiency disease | PEM (Kwashiorkor, Marasmus) | EFA deficiency, fat-soluble vitamin deficiency | Hypoglycemia, ketosis |
| Body composition | ~20% body weight | ~15-20% body weight | Glycogen stores (~500g) |
Source: Park's Textbook of Preventive and Social Medicine (Park's PSM)
Briefly about proximal principles from imp points from park
Based on the content already retrieved from Park's PSM in our previous session, here is a concise high-yield summary:
Proximate Principles - High-Yield Points (Park's PSM)
Definition
- Proteins, Fats & Carbohydrates = "Proximate Principles"
- Called so because they form the main bulk of food
- They are Macronutrients (vs. micronutrients = vitamins + minerals)
Energy Contribution in Indian Diet
| Nutrient | Energy/gram | % of Indian Diet |
|---|---|---|
| Proteins | 4 kcal/g | 10-15% |
| Fats | 9 kcal/g | 15-30% |
| Carbohydrates | 4 kcal/g | 50-80% |
PROTEINS - Key Points
- Means "first importance" (by derivation)
- Contains nitrogen ~16% (unique among proximate principles)
- Makes up ~20% of adult body weight
- Essential amino acids = 9 (Leu, Ile, Lys, Met, Phe, Thr, Trp, Val, His)
- Limiting amino acid in most cereals = Lysine; in pulses = Methionine
- BV of egg = 100 (reference protein)
- Safe intake = 0.83 g/kg/day (adult)
- Deficiency: Kwashiorkor (protein deficiency) vs. Marasmus (protein + calorie deficiency)
FATS - Key Points
- Most energy-dense macronutrient (9 kcal/g)
- Required for absorption of fat-soluble vitamins A, D, E, K
- Essential Fatty Acids (must come from diet):
- Linoleic acid (omega-6) - richest source: Safflower oil (73%)
- Linolenic acid (omega-3) - Soyabean oil (7%)
- Trans fats (PHVO/Vanaspati) = most harmful - raise LDL, lower HDL
- Invisible fat > Visible fat in contribution to Indian diet
- Minimum fat = 20% of total energy
- Avoid PHVO; use blended oils
CARBOHYDRATES - Key Points
- Main energy source in Indian diet (50-80%)
- Prevent ketosis (needed for fat oxidation)
- Dietary fiber recommendation: >40 g/day (ICMR)
- Free sugars should be <10% of total energy (WHO)
- Prefer complex carbs (starches) over simple sugars
One-liner Comparisons (Exam Favourite)
| Point | Answer |
|---|---|
| Highest energy/gram | Fat (9 kcal/g) |
| Only N-containing proximate principle | Protein |
| Main energy source in India | Carbohydrates |
| Reference protein (BV=100) | Egg |
| Most harmful dietary fat | Trans fat (PHVO) |
| EFA richest vegetable source | Safflower oil (linoleic acid) |
| Fiber recommendation (ICMR) | >40 g/day |
Park's Textbook of Preventive and Social Medicine
Caused and ris factors for pem park spm briefly
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Causes & Risk Factors of PEM - Park's PSM (Brief)
Definition (Park's)
PEM = inadequate intake of protein and energy, leading to Kwashiorkor, Marasmus, or both.
Causes of PEM
A. Dietary Causes
| Cause | Detail |
|---|---|
| Inadequate protein intake | Low protein/energy ratio in diet |
| Low concentration of essential amino acids | Main direct cause per Park's |
| Inadequate total caloric intake | Causes marasmus |
| Early cessation of breastfeeding | Premature weaning without adequate substitutes |
| Faulty weaning practices | Late or inappropriate weaning foods |
| Monotonous cereal-based diet | Low in protein quality (especially in poor communities) |
B. Socioeconomic Causes
| Cause | Detail |
|---|---|
| Poverty | Unable to afford protein-rich foods |
| Ignorance/lack of nutrition education | Poor feeding practices |
| Large family size / high parity | Food shared among too many members |
| Food insecurity | Inadequate food availability at household level |
| Low maternal education | Directly affects child feeding practices |
C. Biological/Host Causes
| Cause | Detail |
|---|---|
| Infections | Increase metabolic demand, reduce appetite, impair absorption |
| Recurrent diarrhea | Nutrient loss, malabsorption |
| Low birth weight (LBW) | <2500 g at birth - already nutritionally compromised |
| Close birth intervals | Inadequate nutrition recovery between pregnancies |
Risk Factors (Park's PSM)
Child-related
- Age 6 months to 5 years (peak vulnerability)
- LBW babies (birth weight <2500 g)
- Not breastfed or early weaning
- Male sex (marginally higher risk)
- Recurrent infections (measles, diarrhea, respiratory infections)
Maternal/Family-related
- Maternal malnutrition during pregnancy
- Maternal anaemia
- Short maternal stature, very young maternal age
- High parity and close birth spacing
- Low maternal education and poor child care knowledge
Environmental/Social
- Rural poor and urban slum dwellers (most at risk in India)
- Lack of safe water and sanitation (promotes infections)
- Poverty - single most important underlying determinant
- Food insecurity at household level
The Malnutrition-Infection Cycle (Park's Key Concept)
Malnutrition → Impaired immunity → More infections
↑ ↓
Reduced food intake ← Loss of appetite, nutrient loss
Park describes this as a vicious cycle - malnutrition and infection mutually reinforce each other.
Quick Comparison: Kwashiorkor vs Marasmus
| Feature | Kwashiorkor | Marasmus |
|---|---|---|
| Deficiency | Protein (with adequate calories) | Both protein + energy |
| Edema | Present (hallmark) | Absent |
| Weight | Moderate loss | Severe wasting |
| Liver | Enlarged, fatty | Normal |
| Serum albumin | Low | Low/normal |
| Subcutaneous fat | Preserved | Severely depleted |
| Skin/hair changes | Present (depigmentation) | Usually absent |
Early Detection Methods (Park's)
- Growth charts - first indicator = underweight for age
- MUAC (Mid-Upper Arm Circumference):
-
13.5 cm = Normal
- 12.5-13.5 cm = Mild-Moderate malnutrition
- <12.5 cm = Severe malnutrition
-
Source: Park's Textbook of Preventive and Social Medicine
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