The Body's Requirement for Calories

Many people are interested in losing weight. However, many do not understand the differences between whether the weight is lost as fat or muscle. There is also a great deal of confusion and misinformation about caloric deficit and starvation. Actually, many people also believe that they are the same thing. The truth is that a caloric deficit is necessary for any real fat loss, while starvation will quickly neutralize the effectiveness of any fat loss program. In order to understand the difference, it is important to have a very basic understanding of the body’s caloric needs. The intent of this article is to provide just that.

The caloric nutrients have different functions in the human metabolism. Protein  is needed for tissue repair, enzyme production, and other vital functions. Although protein has a caloric value, it is being used more as a structural component and not as an energy source. If there is not enough protein in the diet to perform these vital functions, the body will take protein from where it is least needed (usually muscle) to supply it where it is most needed (enzymes, internal organs, etc.). This qualifies as starvation because it is caused by the deficiency of a vital nutrient (protein) which forces the body to catabolize lean tissue to get the vital nutrient.

Carbohydrates are needed by the entire nervous system (including the brain), as well as by the red blood cells and the kidneys. Although carbohydrates are being used as an energy source, there is no substitute for the minimum amounts that are needed. If the diet is deficient in carbohydrates, it will catabolize lean tissue and use the protein to make carbohydrates for vital functions (as mentioned in another article). This also qualifies as starvation because the body is forced to catabolize lean tissue to manufacture a vital nutrient (carbohydrates).

Omega 3 and omega 6 fatty acids are essential in the diet for many cellular functions. Also, just like the previous cases, there are no substitutes for these vital nutrients. Lack of these nutrients is linked to cardiovascular disease, nervous system disorders, and other health problems. Although much research still needs to be done, it is clear that these nutrients are needed in the diet. It is also clear that these nutrients are not used as energy sources, but more like structural components.

It is important to know that these nutrients are needed by the body at all times. Whenever we eat these nutrients, they can take over an hour to reach the liver. Also, the supply of nutrients from a meal is usually depleted between 4 to 5 hours after eating the meal. This leaves about a 2 to 3 hour period where the body is being supplied with nutrients from that given meal. If there is not another supply reaching the liver when the old supply runs out, the body will begin to catabolize lean tissue for the nutrients. This explains why it is best to eat every 2 to 3 hours (5 to 6 times daily). It also explains why we are in a starvation state when we wake up in the morning. In addition, the longer we go without eating, the more lean tissue will be catabolized. This clearly explains why skipping breakfast is so bad.

In addition to the nutrient requirements, the body needs calories for the mitochondria to produce ATP via the Krebs cycle. The body can use carbohydrates, amino acids (protein), fats, or even alcohol to provide the energy for this. The body will choose the calorie source based on what is more available. If there is a shortage, then the body will tap into its fat stores for the calories to meet the requirement. This energy needed for the Krebs cycle is the window of fat loss because this is the maximum caloric deficit you can create without depriving your body of a vital nutrient. This window gets bigger with physical exercise, increased muscle mass, and increased thyroid activity. Conversely, this window decreases with loss of lean mass, hypothyroidism, and intake of empty calories. However, a normal person has some window that allows some fat loss. The only exception is for an extremely lean person who is at his or her minimum acceptable body fat level in which case, the body will begin to catabolize lean tissue. Also, once the body has received its requirement of a vital caloric nutrient, the extra is likely to be used to fuel the Krebs cycle. If any is still left over after fueling the Krebs cycle, it can be converted to fat and stored. Because the body has no requirement for alcohol, all of the consumed amounts have to be burned off. This burning off of the alcohol will take place instead of fat burning.

This all goes to show that a caloric deficit is a shortage of calories which causes the body to tap into its energy stores to balance the need. It also shows that a starvation state is a deficiency in a vital nutrient which causes the body to catabolize lean tissue. These two states are separate from each other and can occur independently. When we need a minimum amount of calories to keep out of starvation mode, it is because the sum of the vital nutrients has this number as their total caloric value. Also, a starvation state can exist in a caloric equilibrium, a caloric deficit, or even a caloric surplus if the person is short of a vital caloric nutrient. In the latter case, the person would be getting fatter while slowly starving, which can happen if the person is ingesting excessive amounts of grease or alcohol while depriving himself of carbohydrates or proteins.