People Can Eat the Same Food Yet Some Stay Thin While Others get Fat

Annette Nay, Ph.D.

Copyright 1999

Sedentary individuals make a different type of fat than physically fit people. They can eat the same amount of fats and calories but it adds up to more stored fat. A regularly-exercised body treats fat differently than an unexercised body does. When cholesterol (fat) comes through the blood stream it enters the liver. The liver wraps strands of protein around the cholesterol so the body can use it. The fit body's liver grabs the cholesterol and quickly wraps many strands of protein around it. This forms HDL or high-density cholesterol. HDL cholesterol is easily used by the body (Bailey, 1991).

The unfit body's liver is too tired to do much with the cholesterol. It slowly wraps a few proteins strands around the cholesterol and sends it back into the blood stream. This cholesterol is called LDL or low-density cholesterol. LDLs are harder for the body to break down. LDL cholesterol is hard to get rid of. When the liver is finished with the cholesterol it sends it back into the blood stream to find a fat storage cell.

There are two enzyme systems within the fat cells; each with a different job to do. The first is a lypo-genesis enzyme. Its job is to capture LDLs or HDLs and glue them together so they are too big to get out of the storage cell. The second type of enzymeis the lypo-lysis. Its job is to unglue the cholesterol and release it for the body to use for energy. The exercised body has more lypo-lysis enzyme than lypo-genesis. The unexercised body has the opposite (Bailey, 1991).

When there are more enzymes binding cholesterol than those releasing it, the person has a lot of fat deposits. Once stored these deposits are difficult to release it for use. This is how the fat get fatter and the thin stay thin even though they eat the same kinds and amounts of foods (Bailey, 1991).

Obese or overweight people tend not to do aerobic exercise. The lack of aerobic exercise makes one more prone to being overweight or obese (Bailey, 1991). They have no external way to help the body burn fats. Fat burning exercise must have a sustained level of activity, an elevated rise in heart rate, and incorporate a large quantity of oxygen. Without all of these components the fat will not be burned. When a person cannot breath and carry on a conversation without panting, there is not enough oxygen in the body for the process of burning fat (Bailey, 1991).

The overweight or obese individual may not be exercising long enough to burn full fats instead of glycogen (Smith, 1988). Glycogen is a starch that is available to the body for instant energy. As exercise is sustained for longer periods of time, less glycogen is burned and more fat is used up. After thirty minutes of aerobic exercise, the body is burning all fat. Most exercise plans call for a thirty minute workout. Increasing the workout to forty-five minutes will allow fifteen minutes of full fat burning and greater weight loss.

Besides the difference that the lack of sufficient exercise makes in the type of fats that are made in the body, individuals differ in their ability to stay trim because of the rate that their metabolism naturally burns fat. Some individuals are born with a metabolism that burns fat more quickly that those with a average metabolism. These people naturally burn fat faster than

More muscle means an ability to burn more fat. This is because the sites for burning fat are located in the muscles. Therefore the more muscle one gains, the more fat is burned. Resistive exercises such as weightlifting and isometrics cause the body to make more muscle and build stronger bones to support the additional muscle.

There are then at least four reasons why some people can eat the same food and some stay thin and others gain weight. They are:

  1. Sedentary people make a low-density cholesterol (fat) that the body likes to store instead of burn.
  2. People who maintain a regular exercise routine make a high-density cholesterol (fat) that the body readily burns and easily takes out of storage.
  3. Some individuals are born with a metabolism that burns fat more quickly that those with a average metabolism. These people naturally burn fat faster than people with a normal metabolism. This is usually a hereditary characteristic.
  4. The more muscle a person has the more s/he is able to burn more fat.


Bailey C. (1991). Fit or fat for the 90's. [Film]. CA: Pacific Art Video Publishing.

Knepper, Michelle, CPT. (1999). Unpublished correspondence.

Smith, K. (1988). Kathy smith's fat burning workout. Bernstein J. (Producer), Hay, S. (Director). [film]. CA: Fox Hills Video

Annette Nay, Ph.D.

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