Food Energy Sources
There are three primary sources of energy the human body can use. These include sugars (and there are different types of these), proteins, and fats. All three of these sources are vital for proper function and optimum health, in their proper amounts of course. There is also a fourth, alcohol, which is usually categorized as a sugar.
When we say sugar it is important to understand that there are many types, not just the table sugar we put in our teas and coffees. Many foods have sugars. Some of these sugars are referred to as simple sugars (such as table sugar) some as complex sugars, or complex carbohydrates (such as in whole grain rice, whole grain bread, most fruits, and many vegetables).
Simple sugars are broken down and absorbed very quickly into the bloodstream and can cause a spike in sugar levels, resulting in a spike in insulin production, which in turn can lead to these sugars being absorbed and stored as fat. These types of sugars are found in processed and refined foods and in junk food.
More complex sugars take much longer to break down and to be absorbed. This is beneficial because they provide energy over a much more extended period of time and don't have the same harmful effects as simple sugars.
Some types of sugars include: glucose, galactose, dextrose, fructose, lactose, sucrose (table sugar). About 30% of calories should be obtained from sugar, with most of that coming from complex carbohydrates as opposed to simple sugars.
Unused sugars are converted into body fat so moderation is important. Most of us, probably without realizing it, consume excessive amounts of refined sugars as they are found in almost all processed foods. One gram of sugar has about 4 calories.
Proteins' primary use is for the building of body tissue, such as skin, muscle, nails, etc. But protein also provides energy, especially when sugar levels are low. Some examples of foods that contain protein include meat, fish, eggs, milk, soy products, nuts, beans, lentils, and chickpeas. About 30-40% of calories should come from protein sources. Often people believe that a high intake of protein is beneficial, but this can lead to obesity as unused calories from protein are converted into fat. Another caution is that many foods that are high in protein may also be high in saturated fats (e.g. certain types of meat). One gram of protein has about 4 calories.
Fats are the third primary source of calories. Although we think of fats as harmful, they are critical for proper health. Fats can be found primarily in nuts, oils, dairy products, and meat. One gram of fat has about 9 calories which is more than twice as much as a gram of sugar or protein. About 30% of calories should come from fats, with most ideally coming from mono or polyunsaturated fats. Although unused sugars and proteins can be converted into fat, fat can't be converted to sugar or protein. You may have heard someone say that they want to convert their excess fat into muscle. This is simply not possible. But, with an increase in exercise excess fat will be used up as energy, while the individual simultaneously increases their muscle mass.
Alcohol has about 7 calories per 1 gram. And, just like simple sugars, alcohol is absorbed into the blood stream very quickly. This can lead to obesity from too much alcohol intake. In addition, alcohol does not have much nutritional value.