Lipids are essential fats that have much importance to the human body. Lipids are biological molecules that are insoluble in aqueous solutions and soluble in organic solvents are classified as lipids. The lipids of physiological importance for humans have four major functions:

1. They serve as structural components of biological membranes.

2. They provide energy reserves, predominantly in the form of triacylglycerols.

3. Both lipids and lipid derivatives serve as vitamins and hormones.

4. Lipophilic bile acids aid in lipid solubilization

Essential sources of lipids or fats are ghee, butter, milk, oil. But fats need to be consumed in balanced amounts so as to avoid heart related problems.

After talking about the various nutrients, let us now see what the author has to say about calories and energy yielding nutrients. All the calories in the human diet are provided by three classes of nutrients: proteins, carbohydrates, and lipids. Calories are units of energy, not units of weight.

In nutrition, a calorie (sometimes written as Calorie) is the amount of energy it takes to raise the temperature of 1,000 grams of water by 1 degree Celsius.

Calories: calorie is a unit of measurement. In a popular use of the term calorie, dietitians loosely use it to mean the kilocalorie, sometimes called the kilogram calorie, or large Calorie (equal to 1,000 calories.

• Proteins, carbohydrates, and lipids sometimes are referred to as the energy-yielding nutrients in because of the fact that they alone provide the body with energy.

• Quantities of energy-yielding nutrients that we consume but do not burn up end up being stored within us, mostly as fat tissue.

• Foods are caloric in accordance with how much energy they contain per unit of weight.

• Lipids are much more caloric than either proteins or carbohydrates.

• Each gram of lipids yields 9 calories of energy.