The living body requires energy for its maintenance, metabolism, vital activities and to perform work. Food serves the role to meet the energy requirements of the body. Food comprises various substrates which when subjected to oxidation releases energy. Food contains macronutrients as well as micronutrients. Example: carbohydrates, fats, proteins, lipids, etc. Each substrate upon oxidation releases energy at a different rate and extent. The order of oxidation is Carbohydrates, Fats, and Proteins. Carbohydrates are the preferred substrates of oxidation. Energy also gets stored in the body in the form of high-energy phosphate bonds in the molecules of ATP, which when required by the body gets released by breaking bonds of ATP.
A brief outline of the topic:
Fats are one of the main sources of energy fuel for metabolism in the body. Fats are a rich source of energy as they provide 9 Cal per gram of food. On the contrary, fat contributes to various health disorders but in reality, it is essential for maintaining the normal health and functioning of the body. Fats provide more than twice the calories per gram as proteins and carbohydrates. ‘Calorific value’ is the term that denotes the extent of released energy when different substrates(carbohydrates, fats, proteins, vitamins, and minerals) are oxidized. Calorific value can be of two types: Gross calorific value and physiologic calorific value. Gross calorific Value can be defined as – Upon combustion, the heat energy being released when one gram of food is combusted in a bomb calorimeter(it is a device used to measure calorific value in the laboratory). Gross Calorific values: carbohydrate = 4.1 Kcal/g, proteins= 5.65 Kcal/g and fats= 9.45 Kcal/g.
Calories are the amount of energy released when your body breaks down (digests and absorbs) food. The more calories a food contains, the more energy it can provide to your body. When you consume more calories than you require, your body stores the excess calories as body fat. Even fat-free foods can contain a lot of calories.
- Amount of fat required by the body.
- Measuring The Calorific Value Of Fats using the direct and indirect methods.
- Daily calories requirement of different categories of person.
A brief note:
Fats and Calories
Calories are defined as the amount of released energy when the body oxidizes the food. The energy requirements of different individuals are different depending on gender, age, weight, and other factors. The calorific value is measured in the kilojoule (kJ) and the kilocalorie (kcal). The higher the calories, the higher will be the energy the food provides. When a food contains extra calories than required, the body accumulates it as ‘body fat’ in the form of adipose tissues.
Fatty foods (such as sausage, bacon, and potato chips) are rich in calories and have saturated fats with few essential nutrients than other low-calorie foods. Saturated fat increases low-density lipoprotein (LDL) or bad cholesterol in the blood and is not required by the body. Bad cholesterol is one of the major contributing risk factors to many cardiovascular diseases such as CHF, atherosclerosis, etc
Good cholesterol is required by the body for healthy living. Sources of unsaturated fats are majorly the protein sources like lean meat, fish, seafood, poultry without skin, beans, lentils, tofu, dairy products, cottage cheese, and flax seeds contain unsaturated fat and also Omega-3-fatty acids.
Fat contains more than twice the calories as carbohydrates and proteins present per gram of substrate. One gram of fat contains about 9 calories, while one gram of carbohydrate or protein contains nearly 4 calories.
Dietary intake including moderate fat content is important for maintaining body weight and health and for the prevention of diseases by providing essential and adequate nutrients. According to the Institute of Medicine and the American Heart Association, the recommended fat intake level should be 25-35% of the total calories. For the majority of the population, approximately 1500-2000 calories per day in a diet are sufficient to maintain the healthy and normal function of the body.
Measuring The Calorific Value Of Fats
There are two methods used to measure the calorific value of food containing carbohydrates, fats and proteins-
- Direct Method
- Indirect Method
By this method, the caloric value of food can be calculated by measuring the heat produced, when a given amount of substrate is completely burnt in oxygen. It is performed with the help of a ‘bomb calorimeter’ where the oxygen is under constant pressure. A commonly used bomb calorimeter is the ‘Atwater bomb calorimeter’.It involves a heavy steel bomb, with platinum or gold plated copper lining, it also has a cover tightly held by a strong screw-collar. The sample is weighed, placed and the bomb is charged with an oxygen valve. The valve is then closed and the bomb is immersed in the amount of water being weighed. The burning of the substrate is terminated by an electric spark and the liberated heat is measured by the rise in temperature of the surrounding water, the temperature variation can be measured by a differential thermometer which can read up to one-thousandth of a degree.
By this method, the caloric value can be determined indirectly by burning the food in oxygen in an oxy-calorimeter. The volume of oxygen that is utilized to burn the food sample is measured and the caloric value can be determined. The amount of energy produced is directly proportional to oxygen utilization. The principle used to calculate the calorific value is that when 1 liter of oxygen is consumed in the oxidation of organic nutrients, approximately 4.8 Kcal of heat is released. Oxygen consumption can be determined which is quite a simple technique and is now applied universally to estimate the metabolic rate.
Daily Calorie Requirement
The daily requirement of calories varies from person to person depending on activity level, age, gender, health status, lifestyle, pregnancy, etc.
- People with a sedentary lifestyle: usually between 12 and 15 calories per pound requirement.
- Moderately active: usually between 14 and 17 calories per pound requirement.
- Very active: usually between 16 and 18 calories per pound requirement.
- Women usually require a lesser range than men.
- Pregnant females require high amounts of calories.
Frequently Asked Questions (FAQs):
Question 1: What are the gross calorific values and physiologic calorific values of fat?
Answer: 9.45 Kcal/g and 9.0 Kcal/g respectively.
Question 2: Which apparatus is used to measure the gross calorific value of fat?
Answer: Bomb calorimeter
Question 3: Which fat is not required by the body?
Answer: Low-density lipoprotein (LDL) or bad cholesterol.
Question 4: Mention the devices which are used to determine the calorific value using direct and indirect methods respectively?
Answer: For the direct method – Bomb calorimeter
For the indirect method – Oxy- calorimeter