Macronutrients

Carbohydrate:
4 Calories per gram

A carbohydrate is made up of starches, sugars, and possibly even fibers. It is known as the usual source of energy in food. After being consumed the digestive system usually breaks them down into glucose or sugar molecules which then enters the bloodstream. Blood cells use glucose to function properly and carry out their daily tasks. The other 2 macronutrients do not break down into glucose. Fruits, milk, grains, and vegetables are all foods that contain carbohydrates. An average person should consume about 250 grams of carbohydrates each day.

Good Carbs Vs. Bad
Good Carbs are found in foods that have not been altered by humans or machines, basically they are in their organic form. These foods are high in nutrients, vitamins, and minerals and also "fill" your stomach. The foods with good carbs will not increase your blood sugar.

Bad Carbs are foods that have been altered or refined. These foods have almost no nutritional value which therefore makes it unhealthy to eat. These carbs are generally harder for your body to digest and also increases the blood sugar, not to mention that eating high quantities of these carbs will most likely gain weight. People who eat lots of bad carbs are more likely vulnerable to being diagnosed with obesity, diabetes, and heart problems.

Sources:
http://www.mamashealth.com/diets/goodcarbs.asp
http://nutrition.about.com/od/askyournutritionist/f/howmanycarbs.htm
"Carbohydrates." Harvard School of Public Health Nutrition Source. 2006. Harvard School of Public Health. 29 Nov 2006


Protein:
4 Calories Per Gram

10-15% of our daily calorie intake should consist of proteins
Good sources of proteins include meat, fish, shellfish, poultry and dairy produce, basically animal foods.

What is protein?
Proteins are long chains of amino acids. An amino acid are chemical compounds made up of carbon, hydrogen, oxygen and nitrogen. These molecules combine in different orders and structures to create a variety of proteins that are body uses. There are 22 amino acids in all that our bodies use and need to function properly.
In terms of health, Protein is needed in order for body growth, and in order to repair cells. Protein is also a major part of all tissues and muscles found in our bodies, and without it, many processes would not be able to occur. For example protein is needed for metabolism and even the movement of nutrients and oxygen throughout the blood stream. Another important role that protein plays in our life is the production of antibodies. Antibodies help prevent the body from infections and sickness. However, protein may be good when consumed in healthy amounts but when you consume to much protein is when it may become harmful for your body. Your cholesterol level may rise which will lead to heart problems, also eating to much protein makes the kidneys and liver work very hard to remove the nitrogen found in the protein. Causing the kidneys and liver to work very hard to filter out this nitrogen may lead to disorders of those organs or even may limit filtering capabilities which is very dangerous for your health. Consuming to much protein may also lead to many other problems besides a rise in cholesterol and functioning of your kidneys and liver.

Sources:
http://www.helpwithcooking.com/nutrition-information/protein-guide.html


Fat:
9 Calories Per Gram

Fat is a major source of energy that is stored throughout your body. As you can see, fat gives you more than twice as much calories per gram than carbohydrates and proteins. Along with being an efficient energy source, fat has many other functions. First, a special form of fat, known as fatty acids, are a main part of the cell membranes that surround every cell in the body. The membrane itself is essential to how the cell functions. Fat also keeps your skin healthy, keeping it watertight and moist. Another critical function of fat is that it helps nerves transmit signals throughout your body. Fat is also required for certain vitamins. Vitamins A and E both need fat for your body to properly use those vitamins. In general, fat has different forms, Saturated Fats, Polyunsaturated Fats, and Monounsaturated Fats. Saturated fats are mostly found in meat and dairy foods. Polyunsaturated Fats are found in plant foods. Monounsaturated Fats are found in both animal and plant foods.
As you may no already, to much fat in the body may lead to heart disease, obesity, cancer, stroke, and even diabetes. However, to little fat in the body may lead to a weakened immune system, dry skin, and loss of muscle mass.

Sources:
http://ezinearticles.com/?Weight-Loss-News!--Fat-Serves-A-Purpose&id=199045