RGI.20 Dietary Imbalance Notes

Dietary Imbalance

Learning Outcomes

• Define dietary imbalance.
• Explain the effects of excessive calorie intake, including metabolic syndrome and obesity.
• Contrast Type 2 Diabetes Mellitus with Type 1 Diabetes Mellitus.
• Recall the effects of calorie deficiency.
• Identify the effects of micronutrient deficiencies.

Nutrition

• Nutrition involves the digestion and absorption of foods, and their utilization for growth and cell replacement.

Malnutrition

• Malnutrition occurs when the diet lacks the correct amount of nutrients for daily requirements.
• Dietary imbalances:
  • Undernutrition: Insufficient nutrient intake.
  • Overnutrition: Excessive nutrient intake.

Undernutrition

• Micronutrient Malnutrition:
  • Deficiencies in vitamins A, D, C, and B complex.
  • Mineral deficiencies.
• Macronutrient or Protein Energy Malnutrition (PEM):
  • Underconsumption of calories or protein, globally the most important form of malnutrition.
  • Kwashiorkor: Extreme protein deficiency, leading to oedema and a swollen abdomen.
  • Marasmus: Extreme calorie deficiency, causing muscle wasting.
• Secondary malnutrition:
  • Impaired nutrient digestion or absorption due to:
    • Loss of appetite (aging).
    • Altered metabolism (fever/infection).
    • Prevention of nutrient absorption (diarrhoea).
    • Diversion to parasites.

Overnutrition

• Results from excessive calorie consumption, leading to:
  • Obesity.
  • Metabolic syndrome.
  • Diabetes.
  • Hypertension.
  • Cardiovascular disease.
  • Increased cancer risk.
• Excessive intake of some micronutrients (especially lipid-soluble vitamins) can cause adverse effects, often due to supplement overdose (e.g., Vitamin D poisoning).

Balanced, Healthy Diet

• Emphasis on fruits, vegetables, and whole grains.
• Fat-free or low-fat milk and milk products.
• Includes lean meats, poultry, fish, beans, eggs, and nuts.
• Low in saturated fats, cholesterol, salt (sodium), and added sugars.
• Dietary supplements are generally unnecessary with a balanced, varied diet.

Principles of Nutrition

• Adequacy: Sufficient essential nutrients.
• Balance: Avoid over-reliance on a single food type.
• Energy Control: Balance caloric intake and expenditure.
• Moderation: Avoid excesses or deficiencies.
• Variety: Include a wide range of foods.
• Aim for a healthy weight.
• Engage in physical activity (30 minutes daily).

Dietary Reference Intakes (DRI)

• Reference values for nutrient intakes for healthy people:
  • Estimated Average Requirement (EAR).
  • Recommended Dietary Allowance (RDA).
  • Adequate Intakes (AI).
  • Tolerable Upper Intake Levels (UL).

Nutrient Classification

• Macronutrients (large quantities): Carbohydrates, fats (lipids), and proteins (all organic).
• Micronutrients (small amounts): Vitamins (organic) and minerals (inorganic).
• Energy Yielding: Macronutrients
• Regulator nutrients: Vitamins and minerals

Macronutrients

• Carbohydrates (CH_2O): Sugars (sucrose, lactose, fructose, glucose) and starches.
  • Oxidation yields energy.
• Lipids: Mainly triglycerides (3 fatty acids esterified to 1 glycerol).
  • Lipid oxidation yields more energy than carbohydrates.
• Proteins: Source of amino acids.
  • Non-essential amino acids: Alanine, Arginine, Aspartic acid, Cysteine, Glutamic acid, Glutamine, Glycine, Proline, Serine, Tyrosine.
  • Essential amino acids: Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, Valine.

Micronutrients - Vitamins

• Refer to Lippincott’s: Chapter 28.

Vitamin Functions and Deficiencies

Micronutrients - Minerals

Mineral Functions and Deficiencies

The Calorie

• The calorie measures the energy available from food through digestion.
• A kcal (kilocalorie) is widely used in nutrition.
• The SI unit for energy is the kilojoule (kJ).
  • 1 kcal = 4.2 kJ
  • 1 kJ = 0.24 kcal
• 1 kJ is the heat required to raise the temperature of 1kg (L) water by 1^\circ C.

Energy Yields

Basal Metabolic Rate (BMR)

• Energy consumed by a person at rest, awake, in a thermo-neutral environment, and 12 hours after the last meal.
• Defines the energy required for normal body functions.
• BMR \approx 24kcal per kg of weight per day.
• Higher in males, children, people with fever and hyper-thyroidism.
• Lower in females, hypo-thyroidism, and starvation.
• BMR decreases with age.

Basic Caloric Requirements

• Calories needed to maintain BMR:
  • Male = 1800 kcal/day
  • Female = 1300 kcal/day
• Recommended Dietary Allowances (RDA) for adults <50 years old and moderately active:
  • Male = 2,800 kcal/day
  • Female = 2,100 kcal/day
  • + 300 during pregnancy
  • + 500 during lactation

Metabolic Fuels

• Metabolic energy: carbohydrates, lipids, proteins (and alcohol).
• End products: carbon dioxide, water, and urea.
• Energy intake = energy expenditure (1st Law of Thermodynamics).
• Isocaloric balance: When energy (kilocalories) input equals energy output, body weight remains constant.
• Negative caloric balance: When energy output exceeds energy input, body weight decreases.
• Positive caloric balance: When energy input exceeds energy output, body weight increases.

Body Mass Index (BMI)

• BMI = body weight (kg) \div height (meters)^2 = kg/m^2
• Correlates with percentage of body fat and body fat mass.
• Identifies adults at increased risk for morbidity and mortality due to obesity.

BMI Ranges

• BMI < 16 kg/m^2: possible eating disorder
• BMI < 18.5 kg/m^2: underweight
• BMI = 18.5 to 24.9 kg/m^2: healthy/low health risks
• BMI = 25 to 29.9 kg/m^2: overweight/increased risk of disease
• BMI = 30 to 34.9 kg/m^2: obese (class I)/further increased risk of disease
• BMI = 35 to 39.9 kg/m^2: obese (class II)/higher risk of disease
• BMI $\geq$ 40 kg/m^2 extremely or morbidly obese (class III)

Obesity Epidemic

• Obesity is a disorder of body weight regulation characterized by an accumulation of body fat.
• Human evolution has favored the ability to store excess calories during times of high food availability.
• Modern sedentary lifestyles with unlimited calorie availability have contributed to the obesity epidemic.

Body Fat Deposition

• The gynoid (pear) shape, more common in women, has a lower metabolic disease risk.
• 80-90\% of body fat is subcutaneous, around the abdomen or gluteal-femoral region.
• 10-20\% of body fat is visceral, located in the abdominal cavity.
• Abdominal subcutaneous and visceral adipocytes are metabolically more active; lipolysis releases more fatty acids into circulation.
• Adipocytes can expand to 2-3 times normal size; further lipid storage requires pre-adipocyte proliferation.
• Weight loss reduces adipocyte size, but not number. Small adipocytes drive appetite and efficiently accumulate fat, promoting weight regain.

Metabolic Syndrome

• Includes:
  • Abdominal Obesity
  • Hyperglycaemia
  • Insulin Resistance (T2DM)
  • Dyslipidaemia
  • Excess Insulin
  • Hypertension
• Metabolic syndrome increases the risk of cardiovascular disease and type 2 diabetes.
• Adipocytes release IL-6 and TNF-$\alpha$, resulting in low-level chronic inflammation, contributing to insulin resistance.
• Associated with Fatty Liver Disease, Cancer and Dementia Risks.

Diabetes Mellitus (DM)

• DM is a collection of conditions characterized by high blood glucose.
• Underlying causes are multifactorial: genetic and lifestyle.
• DM results from deficiency or insensitivity to the hormone insulin.
• DM is the most common cause of blindness and limb amputations in US adults.
• Insulin is released by the beta cells of the pancreas in response to high blood glucose.
• Insulin acts on the liver, muscle, and adipocytes to reduce blood glucose.

Type 1 and Type 2 Diabetes Mellitus

Insulin Resistance

• A decline in the ability of the body’s tissues to respond to insulin.
• Obesity is the most common cause of insulin resistance and can lead to T2DM.
• Initially, increased insulin production can compensate for insulin resistance.
• Defects in β-cell function result in a loss in this compensation.
• As insulin production declines, T2DM develops.
• Excess abdominal fat is a major risk factor for insulin resistance.