NASM CNC Chapter 7: Carbohydrates

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Chapter Goals:

• Explain the function and the structure of carbs.
• Discuss the absorption and digestion of carbs.
• Discuss the role hormones play in regulating blood sugar levels.
• Know the carb metabolism pathway.
• Find the requirements for total daily carbohydrates.
• Discuss the role dietary fiber plays.
• Find the myths that relate to carbohydrates.

Introduction

Carbs are often called starches, sugars, or complex and simple carbohydrates. 

Some normal starches we see are grains, wheat, veggies, barley, rice, and corn.

Some normal sugars that we see are sweets, sugar, fruits, and milk. 

Besides lactose and glycogen, all carbs will come from plants. They are considered the primary fuel for the body, but they are victimized due to their role in weight gain. 

Carbohydrate Structure

These carbohydrates are often put into their scientific classifications of mono, di, and polysaccharides. Monosaccharides are single sugar units. Disaccharides are paired up with units of sugar. And then, the polysaccharides are the longer sugar unit chains. Oligosaccharides are sugar units that are 3 – 10 units long. 

Monosaccharides

Again, these are the sugars made of one unit of sugar. They are the most basic and the only carbohydrate form absorbed into the body. So, the bigger sugars need to be broken down to get to this form for their use.

The important monosaccharides for humans are glucose, fructose, and galactose. 

Disaccharides

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Like the monosaccharides, we call the simple disaccharides sugars also. These are the sugars that contain two pairs of sugar units.

The three important disaccharides are sucrose, lactose, and maltose. These are different combinations of glucose with either glucose or another simple sugar added to it. 

Oligosaccharides

These are much less discussed than the other three categories of carbohydrates. These sugars contain 3 – 10 sugar units. 

Polysaccharides

These are our complex sugars and they include the starches, glycogen, and the fibers we take in. these sugar units contain more than 10 units and maybe as much as a few thousand sugar units. 

These polysaccharides can be straight chain structures that are called amylose, they may be branched structures called amylopectin, and lastly, they may be fiber. 

Fiber

Fiber represents more indigestible parts of plants, but it is not one single type of compound. These groups of compounds share characteristics with each other, and they are considered soluble or insoluble fiber. 

Soluble fiber is a type of dietary fiber that will dissolve into water and then form a type of gel. This type is often associated with many heart health benefits and glucose control. It also can see increases in intestinal health, protection from diabetes, and potentially some weight loss.

Insoluble fibers are the second form of fiber we take in. These fibers do not dissolve in water at all, and they are most associated with the regularity of bowel movements. They also are seen about reduced cancer risks, weight loss, and the health of your digestive system.

Functional fiber is one compound that comes from isolated, non-digestible carbs that might provide a benefit psychologically.

Glycogen

The storage form of glucose in all animals. This is like starch, which is the storage form of carbs. This large molecule has a pinwheel orientation centered on a core made from protein, which may range from 100 to somewhere near 30,000 units of glucose. There is no fructose in the glycogen molecules, only glucose. 

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Glycogenolysis is the process of breaking down glycogen molecules into their own glucose molecules to use them in their energy pathway when needed. 

Glycogenesis is the actual process of making glycogen molecules from glucose molecules being put together. 

We store most of the glycogen in our body within our muscles. This is because we are most likely to use and need glycogen in this location. We often use this model for more intense physical activity. The liver is the next biggest storage area for glycogen in the body. And lastly, blood glucose contains some glycogen molecules for quick transport and basic ready usage. 

Summary of Carbohydrate Classifications

The carbs essentially follow a classification system where they are just classified based on how many sugar units there are in the compound. We ingest many carbs in our diet of varying types, and it is important also to know that when we absorb sugar into the body, we do this with simple sugars. These are the monosaccharides. 

Carbohydrate Roles Within the Body

The main role of all carbs that enter the body is to provide us with the energy we need immediately, and then if not used, it is stored for energy production later in the muscles and the liver. This is due to the liver being able to circulate glucose and insulin metabolism helping to manage everything. 

Triglycerides are the form of fats that are stored. The excess carbs are stored as this. These triglycerides are the body’s main storage and transportable form of fats. They are made up of free fatty acids that are bound to a glycerol backbone.

Ketones are groups of fat fragments that are not completely metabolized and are usually made during fat metabolism without the proper amount of carbs.

Gluconeogenesis is a metabolic pathway that produces glucose from carbon substrates other than carbohydrates like lactate, glycerol, and glucogenic amino acids.

Carbohydrate Digestion and Absorption

This begins in the mouth, as it does for all food items and drinks. The mouth emits salivary amylase in the saliva, an enzyme that begins this digestion and breakdown process. The salivary amylase works to cleave off the large chain polysaccharides into smaller parts. Chewing, of course, also aids in this, along with the addition of adding fluid volume to the food. The surface area of the food products is increased through those processes. The small round food that we swallow is known as a bolus.

The stomach is the next location of digestion, which sees the gastric juices and the high acid content continuing the breakdown. The food then leaves and enters the small intestine, where chyme is neutralized by things released from the pancreas, and digestion moves forward in the jejunum. Here, the carbohydrates reach their mono and disaccharide forms, and then the majority will be taken into the body in the ileum. The absorbed cells enter the hepatic portal vein and are transported to the liver, and then serve the purpose they are meant for. This is either through use as immediate energy or storage. 

Non-Alcoholic Fatty Liver Disease is the development of a fatty liver that results from a large number of fats coming from something other than the intake of alcohol. 

Hormonal Regulation of Glucose

We have two main hormones that are used for the preservation of blood glucose:

Insulin is made in the pancreas and it is used for preventing hyperglycemia by lowering the level of blood sugars and facilitating glucose to be taken into the fat cells, muscle, and liver. So, we all have insulin escorting the glucose back to the liver, muscle, and fat cells.

Glucagon is the other vital hormone for glucose regulation. The pancreas also releases this. It serves the opposing role to the insulin in the body essentially. This means it prevents hypoglycemia by raising the blood glucose level. Glycolysis and gluconeogenesis are promoted, along with the inhibition of lipogenesis. 

During Exercise

When exercising, regulating blood sugar via hormones is a tad more complex. Norepinephrine and epinephrine in circulation will bind to the receptors and inhibit insulin production for the body. 

All of the hormones here will increase for the stimulation of glycogenolysis and glucose to be released from the liver and into the blood. This allows more energy to be available for use in exercise. 

Glycemic Index

The glycemic index is a ranking of the effect a food has on blood glucose levels two hours following its consumption of it. The score is assigned based on a 100 representing glucose. The reference food would be like a 50, which gives half the amount of blood glucose elevation of glucose. 

Current Versus Recommended Intakes

The RDA for carbs for adults that are over 19 years of age is 130 grams per day. This is the minimum that is needed for normal metabolism and the use of fuels. 

Current Intakes

In that order, the average intake is 47.4 – 49.6 % of total calories for men and women.

Current Recommendations

Again, the RDA is 130 grams per day. And the percent of total calories that carbs should represent is 45 – 65%.