Macronutrients

• Macronutrients:

Carbohydrates, proteins, and fats: metabolism and roles in the body

1. Carbohydrates are broken down into glucose during digestion. Glucose is the sugar you get when you consume food, and it is the most common sugar found in blood. The glucose is then used as a primary energy source for cellular activities. If there is excess, glucose can be stored in the liver and muscles as glycogen, a storage form of carbohydrates, for later use.

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The roles of carbohydrates include energy sources, protein spares, and brain function. Carbohydrates are used as an energy source because of their conversion into glucose. Like carbohydrates, proteins are also an energy source; however, carbohydrates can replace proteins because they can be metabolized quickly into glucose. In addition, glucose is the preferred energy source for the brain, allowing it to function and for optimal brain health.  

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2. Protein metabolism begins with digestion, breaking down the protein into amino acids. Digestive enzymes like pepsin and trypsin separate proteins into peptides and amino acids. Then amino acids, these building blocks are absorbed across the intestinal lining into the bloodstream. They are transported to various tissues and organs throughout the body. Protein synthesis (anabolism) occurs with the assembly of new proteins according to the genetic instructions given by the DNA. Another process is protein degradation (catabolism), the breakdown of proteins into amino acids or smaller peptide fragments. This process is crucial for regulating protein levels within cells and tissues and recycling amino acids for new protein synthesis. Finally, certain amino acids are metabolized for energy production.

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Proteins help build and repair tissue, support immune function, and transport nutrients; they also serve as enzymes and hormones.  Proteins are long chains of amino acids, “small organic molecules that consist of an alpha (central) carbon atom linked to an amino group, a carboxyl group, a hydrogen atom, and a variable component called a side chain.” Amino acids build and repair tissue. Proteins build antibodies (immunoglobins) to support immune function to bind to unwanted substances.  Proteins are also transporters. Transport or carrier proteins deliver substances like nutrients, vitamins, and sugar throughout the bloodstream into cells, out of cells, and within cells.

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3. Fats are broken down into fatty acids and glycerol during the digestion process. Like protein, these components are absorbed into the bloodstream and used for energy or stored in adipose (fat) tissue. 

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Fat is a crucial macronutrient because it stores energy, insulates heat, protects organs, and absorbs fat-soluble vitamins. Fats are an energy source, providing more than twice the energy per gram compared to carbohydrates or proteins. Fats also insulate the heat and protect organs. Adipose tissue (fat tissue) acts as an insulation material, helping to regulate body temperature, and providing cushioning for organs. Finally, fat-soluble vitamins (K, A, D, and E) absorb better when consumed with fats.

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Energy balance and macronutrient requirements

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The definition of energy balance is when the amount of calories consumed is equivalent to the number of calories burned.  This balance can be imbalanced such as eating more calories and burning fewer calories consumed or burning more calories than consumed. In addition, this balance may be different because it also depends on factors like physical activity, genetics, body fat percentage, and muscle. 

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Example: You consume 100 calories, and you burn 100 calories = energy balance

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Macronutrient requirements for adults: 

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Dietary references suggest that adults should consume 45% to 65% of their total calories from carbohydrates, 20% to 35% from fat, and 10% to 35% from protein. Thus, adults should consume more carbohydrates than fat or protein. These ranges are estimated because they depend on an individual’s diet. 

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Questions:

1. What are the three macronutrients?
2. What is energy balance?
3. True or False: can your energy balance be imbalanced? 
4. What is an adipose tissue and what does it do?

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