In nutrition, which class of food is described as “nitrogenous food” because it is rich in nitrogen containing compounds needed for growth and tissue repair?

Introduction / Context:
Different classes of nutrients play different roles in the human body. Some primarily provide energy, while others are essential for building and repairing tissues. Nutritional science often uses the term nitrogenous food for foods that contain a high proportion of nitrogen, mainly in the form of amino groups. This question asks which class of food is commonly referred to as nitrogenous food.

Given Data / Assumptions:

We are looking for the class of food rich in nitrogen containing substances. Options include proteins, carbohydrates, mineral salts, lipids and simple sugars. We assume standard definitions of macronutrients and their chemical composition.

Concept / Approach:
Proteins are large biological molecules composed of amino acids. Amino acids contain amino groups that include nitrogen, making proteins the primary nitrogen containing macronutrients in the diet. They are essential for growth, tissue repair, enzyme formation and many structural functions. In contrast, carbohydrates and lipids consist mainly of carbon, hydrogen and oxygen and contain very little or no nitrogen. Mineral salts include many inorganic ions but are not considered nitrogenous foods in the traditional nutritional sense. Therefore, proteins are the class of food described as nitrogenous food.

Step-by-Step Solution:
Step 1: Recall that amino acids, the building blocks of proteins, have an amino group containing nitrogen. Step 2: Recognise that proteins are the main dietary source of nitrogen for the body. Step 3: Compare this with carbohydrates (such as starch and sugars) and lipids, which primarily contain carbon, hydrogen and oxygen. Step 4: Note that mineral salts provide various ions like sodium, potassium, calcium and iron, but they are not classified as nitrogenous foods. Step 5: Conclude that proteins are correctly described as nitrogenous foods in basic nutrition terminology.

Verification / Alternative check:
Textbook discussions of nutrients often divide them into energy giving foods (mainly carbohydrates and fats), body building foods (primarily proteins) and protective foods (vitamins and minerals). In the body building category, proteins are specifically called nitrogenous foods because of the presence of nitrogen in their amino acid structure. Labels on high protein foods like pulses, meat, eggs and milk sometimes highlight their protein content as important for growth and repair. These references confirm that proteins are the nitrogen rich class of food.

Why Other Options Are Wrong:
Carbohydrates such as starch, sucrose and glucose are composed mainly of carbon, hydrogen and oxygen and serve primarily as energy sources, not as nitrogen rich building blocks. Lipids are also composed of carbon, hydrogen and oxygen and provide energy and insulation, but are not rich in nitrogen. Mineral salts include inorganic ions that are essential in small amounts but do not make a food nitrogenous in the usual sense. Simple sugars are a subset of carbohydrates and also lack significant nitrogen. Therefore, these options do not correctly describe nitrogenous food.

Common Pitfalls:
Students sometimes confuse energy rich foods with body building foods, assuming that all energy sources are equally important for growth. Another pitfall is to overlook the chemical composition of nutrients and think only in terms of calories. To avoid these errors, remember that proteins are unique among the major macronutrients because they contain a significant amount of nitrogen in amino acid structures. This is why they are emphasised in diets for children, athletes and patients recovering from illness.

Final Answer:
Nitrogenous food refers primarily to proteins, which are rich in nitrogen containing amino acids.