Metabolism - Carbs, Proteins, and Fats Defined

Metabolism - Carbs, Proteins, and Fats Defined

A typical high school biology course commences with an understanding of the four major groups of macromolecules, which are the fundamental building blocks of all living things. These groups are:

  • Fats, which encompass fatty acids, numerous vitamins, and cholesterol-based compounds, including steroids, play a vital role in our bodies. These molecules, with their limited solubility in water, are known as hydrophobic.
  • Carbohydrates or carbs are essentially sugars. Sugars are very soluble in water, so they are referred to as hydrophilic. Carbohydrates can be simple sugars, usually between 5 to 7 carbon atoms long, like ribose (5 carbon) and glucose (6 carbon). Individual sugars can be linked together to form larger macromolecules. Starches are long chains of sugars linked together and include glycogen (glucose polymer used to store sugar in muscle, liver, and the brain). Plants contain amylose, again a polymer of glucose but with a different pattern of sugar linkages compared to animal glycogen. We consume both of these starches in our diets and convert the large molecules into glucose when we need more energy. Plants also make a glucose polymer called cellulose, which is the major constituent of fiber in our diets. We cannot break the bonds holding the glucose molecules together, so it is not digestible by animals. It is digested by several bacteria that live in cow stomachs to break down the cellulose in the grass that they eat.
  • Proteins are a hugely diverse class of macromolecules made of amino acids. All cells make proteins using information coded in their genes. The code lists the particular amino acids that are linked together, end-to-end, to form each individual protein. Some proteins are hydrophobic and tend to concentrate in the fatty membranes around cells. Some proteins are hydrophilic and tend to be found in the fluid inside and around each cell. Some proteins are both hydrophilic and hydrophobic.
  • Nucleic Acids are the stuff that your DNA is made out of, the G, C, A, and T bases that make up the code. However, they are also intimately involved in metabolism and a huge variety of cellular functions. Adenosine triphosphate (ATP) takes center stage as the energy currency of our cells. In fact, your body makes and then consumes around 70 kg (150 pounds) of ATP each and every day, and around 70% of that energy is used by all the cells in your body to pump sodium out and potassium in. Cool stuff.

Nucleic acids are found in all foods, so they are not considered an important macronutrient. On the other hand, fats, carbs, and proteins are present at significantly different levels in different types of foods. Your average breakfast cereal will be very high in carbs compared to fats or protein. A slice of chicken is relatively low in fat and sugar but high in protein. A slice of bacon contains very little carbohydrates but is high in both protein and fat.

There are many sources of information concerning the relative fat, protein, and carbohydrate content of the foods you eat. The Ven diagram above shows a simple way of thinking about macronutrient content of most major food groups.

My next blog will give some detail of how these molecules fit into your metabolism. Once we explain this a bit, we can get onto the topic all want to know more about. What is the difference between all the various diets out there, and is there one that is right for me?

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