In nutrition, the term macronutrients refers to the three energy-yielding nutrients: protein, carbohydrates, and lipids (fat).
Each of the macronutrients, carbohydrate, protein, and fat, has a unique set of properties that influence health, but all are a source of energy. Most macronutrients are not essential because they can be supplied by both food and the body. In other words, you can eat a macronutrient like a carbohydrate (e.g., from foods like pasta) for energy. Still, when that energy source runs out, your body can convert fat into carbohydrates to get more energy.
Carbohydrates:
The term carbohydrate includes a wide variety of energy-yielding compounds that contain carbon, hydrogen, and oxygen atoms. With the exception of fiber, carbohydrates yield 4 calories per gram (similar to protein) and are an important fuel source for the body, especially when the body is fueling physical activity.
To be used for energy, carbohydrates must be broken down into smaller units and absorbed by the body. This process takes place in the gastrointestinal tract, primarily in the small intestine. Simple sugars are easily digested and absorbed through the intestinal lining, because they are small units of single or double sugars. Starch, however, is comprised of long polysaccharide chains that must first be broken down into smaller units by enzymes for absorption. For example, when an individual consumes a source of starch, such as grains, potatoes, or bread, the starch is physically broken into smaller pieces in the mouth and stomach and then broken down into monosaccharides and disaccharides by enzymes in the small intestine. These small units travel to the liver, which converts most fructose and galactose to glucose, and then directs glucose to other tissues and organs to be taken up by cells and used for energy. Some glucose is stored as glycogen in the liver and skeletal muscle to meet future energy requirements (Figure 9-4). Any excess carbohydrate is converted to fat and stored in the liver, muscle, and adipose tissue for future energy needs.
 Carbohydrates |  Proteins |  Fats |
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The primary role of dietary carbohydrates is to provide energy for the body. Yet, many controversies exist regarding carbohydrates. Are they healthy? Are they needed for optimal sports performance? Do they contribute to weight gain?
Carbohydrates are often referred to as sugars and starches or as simple and complex carbohydrates.
Starches: grains, corn, rice, barley, vegetables, beans, and wheat, whereas examples of sugars include sweets (candy), sugar (cane sugar), fruit, and milk
Except for lactose, milk sugar, and glycogen, the storage form of carbohydrates in the body, all carbohydrates are plant-derived.
Carbs are considered the body’s primary fuel source yet are often labeled as the cause of weight gain. Carbohydrates frequently take a back seat to protein following exercise by those who fail to recognize the importance of this nutrient. Blame for these belief systems can be attributed to misinformation or even misunderstandings.
Though carbohydrates are not considered key for survival, considering how the body can synthesize the amounts of glucose needed to survive from non-carbohydrate sources, they are generally required in specific quantities to optimize health and performance.
Added sugars
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Raw, brown, and white sugar (sucrose)
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Corn sweetener and syrups
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Malt syrup
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Turbinado sugar
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Rice syrup
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Date sugar
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Glucose
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Fructose
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Lactose
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Dextrin
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High fructose corn syrup
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Invert sugar
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Maple sugar or syrup
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Agave sugar
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Maltose
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Honey
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Trehalose
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Maple Sugar or Syrup
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Caramel
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Dextrose
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Molasses
Added sugars are sugars added to foods or food products, not sugars that are naturally contained in the food. Naturally occurring sugars, such as those found in fruit or milk, are generally considered healthier options because the foods that contain natural sugars also include other vital nutrients like vitamins and fiber. Added sugars are not naturally occurring in food groups and include syrups and other caloric sweeteners found in candy (sweets) and sweetened beverages (soda).
Fiber
Fiber represents most of the indigestible portions of plant food; it is not a single compound. It is a group of compounds that share similar characteristics and are generally classified as either soluble or insoluble. Soluble fiber originates from the inside of the plant cell, including Pectins, gums, and mucilages. They are called soluble because they either dissolve or swell when placed in water, and most can be digested by the bacteria living within the large intestine. Therefore, they are also sometimes called fermentable.
Soluble fibers are found in oat bran, oatmeal, beans, fruits (e.g., apples or pears), vegetables (e.g., artichoke, leeks, or sweet potatoes), and many commercial products like salad dressings, jams, and jellies.
Several benefits include the following
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Weight loss can delay gastric emptying (from the stomach) and promote an overall feeling of fullness, potentially reducing caloric intake.
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Reducing risk for cardiovascular disease—It can bind to cholesterol particles. It can prevent its absorption and help remove this compound from the body.
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Bowel movement and intestinal health—It attracts water and promotes bulk to the stool, safeguarding against constipation.
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Diabetes protection—This carbohydrate is not absorbed. It can, therefore, reduce potential blood sugar spikes.
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Improved absorption of foods—It slows the movement of food through the small intestine. It can enhance nutrient absorption.
Insoluble fiber
Insoluble fiber (water-insoluble) form the structural parts of plants and include compounds like cellulose, hemicellulose, and lignin, and are often found in the outermost portion of grains, vegetables, fruits, and seeds (e.g., whole-grain wheat, celery, brown rice, quinoa, apple peels, or broccoli).
They are called insoluble or non-fermentable because they do not dissolve in water and are easily digested by intestinal bacteria. When many of these compounds have their outermost portions removed, this produces processed starch (e.g., whole-wheat kernel to white bread or brown rice to white rice).
Like the soluble fibers, insoluble fiber also provides many health benefits that include the following
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Digestive health—It adds bulk and draws water into the GI tract. It improves regularity in the large intestine to avoid constipation and other bowel-related health problems (e.g., hemorrhoids).
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Reduces risk of cancer—It improves movement through the large intestine. It reduces the risk of colon cancer and other prominent intestinal diseases (e.g., diverticulosis).
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Weight loss—Delaying gastric emptying (from the stomach) promotes an overall feeling of fullness, reducing caloric intake.