Carbohydrates | Composition of Carbohydrates | Recommended Daily Allowances (RDA) | Functions of Carbohydrates |

 

Carbohydrates: An Overview

Carbohydrates are an essential macronutrient and the primary source of energy for the body. They are organic compounds made up of carbon, hydrogen, and oxygen, with a general formula of $C_nH_{2n}O_n$.

Composition of Carbohydrates

1. Starch:

   • A complex carbohydrate and a polysaccharide made of long chains of glucose molecules.
   • Found in foods like rice, wheat, potatoes, and corn.
   • Provides a slow and sustained release of energy.

2. Sugar:

   • A simple carbohydrate.
   • Includes monosaccharides like glucose and fructose, and disaccharides like sucrose (table sugar) and lactose.
   • Found in fruits, honey, milk, and processed foods.

3. Cellulose:

   • A structural carbohydrate and a polysaccharide.
   • Found in the cell walls of plants.
   • Indigestible by humans but acts as dietary fiber, aiding in digestion and bowel movements.

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Recommended Daily Allowances (RDA)

• Adults: Approximately 45-65% of total daily calorie intake should come from carbohydrates. For a 2,000-calorie diet, this equals 225-325 grams per day.
• Children: Similar proportions as adults, depending on age and activity level.
• Fiber: 25-30 grams per day, primarily from whole grains, fruits, and vegetables.

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Dietary Sources of Carbohydrates

1. Natural Sources:

   • Starch: Rice, wheat, oats, barley, potatoes, sweet potatoes, and legumes.
   • Sugar: Fruits (e.g., bananas, apples), honey, and milk.
   • Cellulose (Fiber): Vegetables (e.g., broccoli, carrots), fruits (e.g., apples with skin), and whole grains.

2. Processed Sources:

   • Bread, pasta, breakfast cereals, and sugary snacks like cookies and cakes.

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Functions of Carbohydrates

1. Energy Production:

   • Carbohydrates are broken down into glucose, the primary energy source for the body and brain.
   • Each gram provides 4 calories.

2. Protein Sparing:

   • Prevents the body from using proteins for energy, allowing proteins to perform their primary functions of growth and repair.

3. Fat Metabolism:

   • Helps in the oxidation of fats. Without adequate carbohydrates, incomplete fat metabolism can lead to the formation of ketones, which can cause ketosis.

4. Dietary Fiber Benefits:

   • Improves digestion by adding bulk to stool.
   • Reduces the risk of constipation, colon cancer, and heart disease.
   • Helps regulate blood sugar levels by slowing glucose absorption.

5. Storage as Glycogen:

   • Excess glucose is stored as glycogen in the liver and muscles for use during periods of fasting or intense physical activity.

Carbohydrate Energy

Carbohydrates are one of the primary macronutrients that provide energy for the human body. They are composed of carbon, hydrogen, and oxygen and are found in foods such as grains, fruits, vegetables, and dairy products. When consumed, carbohydrates are broken down into glucose, the body’s primary energy source.

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Unit of Energy: Kilocalorie (Kcal)

• Definition: A kilocalorie (Kcal) is the unit used to measure the amount of energy provided by food and expended by the body.
• Energy Contribution:
  • 1 gram of carbohydrate provides approximately 4 Kcal of energy.
• Role of Carbohydrates: Carbohydrates are the quickest and most efficient source of energy for the body, especially for brain and muscle functions.

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Basal Metabolic Rate (BMR)

• Definition:
  The Basal Metabolic Rate is the amount of energy expended by the body at rest to maintain basic physiological functions, such as breathing, circulation, cell production, and body temperature.
• Measurement:
  BMR accounts for approximately 60-70% of the total energy expenditure in a day.
• Calculation:
  There are various equations (e.g., Harris-Benedict Equation) to calculate BMR based on age, gender, weight, and height.

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Factors Affecting BMR

1. Age:
   • BMR decreases with age as lean body mass reduces.
2. Gender:
   • Men generally have a higher BMR than women due to more muscle mass.
3. Body Composition:
   • Lean muscle mass increases BMR, while higher fat content reduces it.
4. Genetics:
   • Hereditary factors influence individual metabolic rates.
5. Hormonal Levels:
   • Thyroid hormones significantly regulate metabolism.
6. Physical Activity:
   • Regular exercise increases muscle mass, thereby boosting BMR.
7. Environmental Temperature:
   • Extreme cold or heat can elevate BMR as the body works harder to maintain temperature.
8. Dietary Habits:
   • Starvation or very low-calorie diets can lower BMR as the body adapts to conserve energy.

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Importance of Carbohydrate Energy and BMR

Carbohydrates play a critical role in meeting the body’s energy needs, especially during physical activity or mental tasks. Understanding BMR helps in:

• Diet Planning: Designing calorie intake according to individual energy requirements.
• Weight Management: Balancing calorie consumption and expenditure to maintain or modify weight.
• Health Monitoring: Identifying metabolic disorders or energy imbalances.

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Carbohydrates, as a primary source of energy, work in tandem with the body’s metabolic processes. Proper understanding of energy units, BMR, and influencing factors allows healthcare providers and individuals to manage health effectively.