People often hear nutrition being discussed in the context of determining which foods are "healthy" and which are "junk foods". The science of nutrition discusses many factors which affect the population every day. Much of the study of nutrition can be used at a personal level to help maintain a healthy weight and to help avoid diseases that can cause your body harm.
In general, nutrition is associated with taking in foods that your body needs to remain healthy. Basic nutrients include water, minerals, carbohydrates, fats and proteins. More modern definitions include supplements and physical activity as part of keeping up with good nutrition. Much of this study revolves around determining how much of each of these items the body needs to take in on a regular basis in order to function at the optimum level.
More broadly, nutrition is the science of food, and determining what nutrients are in different products. This science will also determine how your body ingests, digests, absorbs, metabolizes, transports, stores and excretes different food products to determine what overall effects these nutrients have on the body. Nutritional scientists also study the environment, psychology and behavior that is associated with eating and how these factors play a role in how the body processes foods and which foods people choose to consume.
Nutritional choices are often discussed in terms of how many servings of different food options you should take or limit yourself to. Different foods have different serving sizes based on the amount of calories are in each item, the nutritional value of each item and how it has been prepared. Most prepared foods have serving sizes listed on the packaging to help you make these determinations when you organize your diet.
In years' past, many people pointed to the food pyramid to help people organize their diet properly. Recently, the pyramid has been adjusted by different nutritional experts. While these different presentations differ in which foods are counted in different sections, the general advice of each nutritional chart is quite similar.
Grains. Most nutritional experts agree that the main portion of your diet should include plenty of grains. Whole grains are often recommended over processed grains. These include items like bread, pasta, rice, cereals and the like. These items provide carbohydrates that provide the body with quick, accessible energy.
Protein. The body also requires plenty of protein to help maintain muscles and to provide the body with long-term energy. Two to three servings of protein are often recommended per day. Protein is often referred to as meat sources such as poultry, red meat, or fish but it can also come from leaner or vegetarian sources such as tofu, eggs, or beans.
Dairy products. Two to three servings of dairy were traditionally recommended, but some nutritional experts are now saying that less dairy is optimal, especially for those with digestive issues. The key here is to get plenty of calcium and vitamin D, most notably to maintain skeletal health. Leaner calcium sources such as yogurt or low fat milk are often recommended over fattier sources like cheese or whole milk.
Fruits and vegetables. At least 2-3 servings each of fruits and vegetables per day are recommended. Some of the most commonly recommended fruits and vegetables include green, leafy vegetables, apples, and bananas, fruits rich in vitamin C such as citrus fruits, and unsweetened fruit and vegetable juice. Many fruits and vegetables contain more nutrients and are healthier when eaten raw, but some, such as tomatoes produce more nutrients when cooked.
Things you'd better eat less. Foods such as oils, sugars and fats should be eaten sparingly and avoided when possible. Many modern nutritionists also count processed or prepackaged foods such as fast foods or frozen meals in this category. Foods that are very high in sodium should also be consumed sparingly due to the damage high levels of these ingredients can do to your circulatory system and other parts of the body.