What is Food?
The foods we eat contain nutrients. Nutrients are substances required by the body to perform its basic functions. Nutrients must be obtained from the diet since the human body does not synthesize them. Nutrients are used to produce energy, detect and respond to environmental surroundings, move, excrete wastes, respire (breathe), grow, and reproduce.
There are six classes of nutrients required for the body to function and maintain overall health. These are carbohydrates, lipids, proteins, water, vitamins, and minerals. Foods also contain no nutrients that may be harmful (such as cholesterol, dyes, and preservatives) or beneficial (such as antioxidants).
There are two types of major Nutrients –
Nutrients that are needed in large amounts are called macronutrients. There are three classes of macronutrients:
These can be metabolically processed into cellular energy. The energy from macronutrients comes from their chemical bonds. This chemical energy is converted into cellular energy that is then utilized to perform work, allowing our bodies to conduct their basic functions. A unit of measurement of food energy is the calorie. On nutrition food labels, the amount given for “calories” is actually equivalent to each calorie multiplied by one thousand. A kilocalorie (1000 calories, denoted with a small “c”) is synonymous with the “Calorie” (with a capital “C”) on nutrition food labels. Water is also a macronutrient in the sense that you require a large amount of it, but unlike the other macronutrients, it does not yield calories.
Carbohydrates are molecules composed of carbon, hydrogen, and oxygen. The major food sources of carbohydrates are grains, milk, fruits, and starchy vegetables like potatoes. Non-starchy vegetables also contain carbohydrates but in lesser quantities. Carbohydrates are broadly classified into two forms based on their chemical structure:
- Fast-releasing carbohydrates (Simple sugars)
- Slow-releasing carbohydrates (Complex Carbs)
Fast-releasing carbohydrates consist of one or two basic units. Examples of simple sugars include sucrose, the type of sugar you would have in a bowl on the breakfast table, and glucose, the type of sugar that circulates in your blood.
Slow-releasing carbohydrates are long chains of simple sugars that can be branched or unbranched. During digestion, the body breaks down all slow-releasing carbohydrates to simple sugars, mostly glucose. Glucose is then transported to all our cells where it is stored, used to make energy, or used to build macromolecules. Fiber is also a slow-releasing carbohydrate, but it cannot be broken down in the human body and passes through the digestive tract undigested unless the bacteria that inhabit the gut break it down.
One gram of carbohydrates yields four kilocalories of energy for the cells in the body to perform work. In addi8on to providing energy and serving as building blocks for bigger macromolecules, carbohydrates are essential for the proper functioning of the nervous system, heart, and kidneys. As men8oned, glucose can be stored in the body for future use. In humans, the storage molecule of carbohydrates is called glycogen. Glycogen is a slow-releasing carbohydrate.
1 gram of Carbs = 4 calories
Lipids are also a family of molecules composed of carbon, hydrogen, and oxygen, but unlike carbohydrates, they are insoluble in water. Lipids are found predominately in butter, oils, meats, dairy products, nuts, and seeds, and in many processed foods. The main job of lipids is to store energy. Lipids provide more energy per gram than carbohydrates (nine kilocalories per gram of lipids versus four kilocalories per gram of carbohydrates). In addition to energy storage, lipids serve as cell membranes, surround and protect organs, aid in temperature regulation, and regulate many other functions in the body
1 gram of Fat = 9 calories
Proteins (Type of Proteins)
Proteins are macromolecules composed of chains of subunits called amino acids. Amino acids are simple subunits composed of carbon, oxygen, hydrogen, and nitrogen. The food sources of proteins are meats, dairy products, seafood, and a variety of different plant-based foods, most notably soy. Proteins provide four kilocalories of energy per gram; however, providing energy is not protein’s most important function. Proteins provide structure to bones, muscles, and skin play a role in conducting most of the chemical reactions that take place in the body. The Estimate is greater than one-hundred thousand different proteins that exist within the human body.
1 gram of Protein = 4 calories
There is one other nutrient that we must have in large quantities: water. Water does not contain carbon but is composed of two hydrogens and one oxygen per molecule of water. More than 60 percent of your total body weight is water. Without it, nothing could be transported in or out of the body, chemical reactions would not occur, organs would not be cushioned, and body temperature would fluctuate widely. On average, an adult consumes just over 2 liters of water per day from food and drink. According to the “rule of threes,” a generalization supported by survival experts, a person can survive three minutes without oxygen, three days without water, and three weeks without food.
Average Intake = 2.5 Liters || Healthy Intake = 2.5 to 3.5 Liters