Fundamentals of Human Nutrition/Lipid storage
6.2 Lipid Storage
Lipids, which include steroids, like cholesterol, fatty acids, and triglycerides, are either synthesized by the body or derived from the foods that one consumes in their diet. They are stored in adipocytes, which unlike other cells, have a fairly unlimited amount of storage capacity, making consuming excess fat dangerous to one’s health. Overconsumption can impair the function of these cells and other bodily processes.
Looking first at dietary lipids, or lipids that come from the foods we consume, these macronutrients begin to be digested first in the mouth. As they move throughout the digestive system, they eventually reach the small intestine where they are mixed with a secretion of bile acids and broken down into cholesterol, fatty acids, and glycerides. The cholesteryl esters and triglycerides are then prepared for transport through the body by being packed into chylomicrons along with phospholipids, cholesterol, and protein. These lipoproteins, known as chylomicrons, can then be transported through the lymph, thoracic duct, and ultimately into the bloodstream. The triglyceride portions of the chylomicrons are absorbed by different organs and tissues, such as the heart and muscle, and stored in the cells as lipid droplets.
As discussed previously, lipids can also be synthesized by your body from the remnants of other macronutrients like carbohydrates and proteins. This process occurs in the liver where either amino acids from proteins or glucose from carbohydrates can be used to form lipids. These synthesized lipids can either be stored or used in the liver, or shipped via VLDL (very low density lipoproteins) to other tissues to be stored as lipid droplets.
Lipid Digestion Underneath the three layers, of skin (epidermis, dermis, hypodermis) is adipose tissue. Adipose tissue is made up of adipocyte cells held together by collagen. There are two types of adipose tissue, white and brown. White adipose is most prevalent. Adipose tissue is in charge of collecting, storing and releasing lipids as the body sees fit. Lipids are fat-like substances that do not dissolve in water. They contain various fats, waxes, steroids, phospholipids, and triglycerides as well as others (How Are Lipids Stored in the Body) . The purpose of lipids is to produce hormones, absorb fat-soluble vitamins, provide structure to cell membranes, protect the nerves and provide the body with energy and energy storage. Lipids are the major form of energy reserve for the body.
Lipid Absorption The body only uses the amount of nutrients and energy it needs to function, any excess after that is what is stored in the adipose tissue. Lipids are stored in the body in different forms such as, triglycerides, fat cells, cell membranes and lipoproteins. Any excess energy consumed is converted to triglycerides which together with globules make up 90% of the fat cells. These fat cells contain enough energy storage to keep the body functioning for 30 days. In the cell membranes lipids are stored as phospholipids, this is what helps give cell membranes their structure, and it also serves as a barrier. In the liver lipoproteins are made. Lipoproteins are broken down into HDL and LDL. Together they are transported in the bloodstream through other lipids and help keep cholesterol under control.
Disorders and diseases
As with all bodily processes, disorders can appear along different parts of the path and for a variety of reasons in lipid storage. For the most part however, these diseases involve either mutated enzymes that do not properly break down lipids or their bodies simply don’t produce enough of the needed enzyme to be effective. These disorders can be genetically passed down as autosomal recessive or sex-linked recessive. If the disorder is autosomal recessive, in order for the offspring to inherit the trait, both parents have to be carriers and there is still only a 25% chance they will express the disorder. If the disorder is sex-linked recessive, the offspring will have a higher chance of inheriting it if it is a male than female. As a male, if the mom is a carrier, the offspring as a male will have a 50% chance of inheriting the disease.
One of the most common lipid storage disorders is Gaucher disease which is caused when the body cannot produce enough of the enzyme glucocerebrosidase. This disorder is marked by extra fatty accumulation in the brain, liver, bone marrow, and other organs. There are three different types of it which range in symptoms and severity. Typically, the disorder can be diagnosed through biopsies, genetic testing, or looking for common symptoms which include liver enlargement, liver malfunction, swollen lymph nodes, anemia, and yellow eye spots.
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How Does the Body Digest Lipids?
Before lipids can be stored in the body, they first have to be digested (“Digestion”, n.d.). The goal of digestion is to take triglycerides, which is the form that most of the fat in our diets is in, and break them apart into monoglycerides and fatty acids. (“Digestion”, n.d.). Digestion of lipids begins in the mouth, where body temperature starts to melt some hard fats (Rolfes & Whitney, 2016). The enzyme lingual lipase is secreted from a gland at the base of the tongue (Rolfes & Whitney, 2016). Lingual lipase helps break down milk fats, which is especially important for infants (Rolfes & Whitney, 2016). Next, the fat travels down the esophagus to the stomach. Because of the hydrophobic nature of lipids, they do not dissolve well in the liquid of the stomach (“Digestion”, n.d.). However, in the stomach, the churning of the stomach breaks up the fat globules into small droplets. This is done in order to increase the surface area of the fat, making it easier for the enzymes gastric lipase to work on the droplets (“Digestion”, n.d.). Gastric lipase hydrolyzes the droplets, but only a little of the fat. Lipid digestion occurs mostly in the small intestine (Rolfes & Whitney, 2016). Once the fat leaves the stomach via the pyloric sphincter and travels to the small intestine, the hormone cholecystokinin triggers the release of bile from the gallbladder. Bile is made of bile salts and phospholipids (“Digestion”, n.d.). Bile is amphipathic, meaning that it works like a detergent to suspend the fat droplets in water and separate from each other (Joyce, 2008). This make it easier for pancreatic lipase from the pancreas can remove the fatty acids from the lipids and fully digest them. (Joyce, 2008). After the pancreatic lipase acts upon the lipids, the result is monoglycerides (Rolfes & Whitney, 2016).
How Does the Body Absorb Lipids?
The next phase after lipid digestion is absorption. Some molecules of fat, because they are small, can pass into the intestinal cells, or enterocytes, and enter the bloodstream (Rolfes & Whitney, 2016). Other molecules, such as monoglycerides and long-chain fatty acids, are too large to go this route. They must mix with bile salts to form micelles (“Digestion”, n.d.). Micelles are spherical transporters that can enter the enterocytes. Micelles also contain cholesterol and fat-soluble vitamins (“Digestion”, n.d.). Inside the enterocytes, the fats are reassembled into new triglycerides (Rolfes & Whitney, 2016). These triglycerides and cholesterol combine with protein into transporters called chylomicrons. The chylomicrons travel through the lymph system (also kwon as lacteal) until they are able to enter the blood (Rolfes & Whitney, 2016). As the chylomicrons travel through the body, cells remove triglycerides from the chylomicrons as they float by, making the chylomicrons smaller (Rolfes & Whitney, 2016). The liver removes whatever remaining pieces are left from the chylomicrons.
These chylomicron pieces, called chylomicron remnants, which the liver picks up can be dangerous for the body (Cooper, 1997). According to Cooper (1997, p. 2174), “the accumulation of these particles [in the liver] for prolonged periods or in high concentrations may have particularly deleterious consequences”. Chylomicron remnants are removed using apolipo- protein (apoE) and LDL receptors (Cooper, 1997). The study concludes that “delayed removal of chylomicron remnants has been documented in diabetes, renal failure, and familial combined hyperlipemia”.
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Metabolism is a chemical process that converts food into energy to help us for everything that we do. Lipid consists of fat; speeding up metabolism helps an individual burn fat. There are three important factors that help speed up lipid metabolism: exercise, sleeping habits, and eating habits.
Decreasing sedentary actions and replacing them with physical activities helps to increase metabolism. Exercising keeps the body moving, increasing calorie loss. For adults that go to the gym frequently, any type of cardio such as swimming, aerobic exercising, or running promote calorie loss. Resistance training, lifting weights, has been recommended to speed up metabolism because bigger muscles are created. More muscle in the body equals faster metabolism. An individual doesn’t have to go to the gym to get exercise. Any physical hobby such as walking, dancing, or climbing will keep the body moving and enhance metabolism. Making small changes in your everyday life can help your metabolism as well. For example, instead of driving to the drive-thru to get food, park your car and walk inside. Walking instead of driving in your community keeps the body active; metabolism will be working at all times. Working out for at least thirty minutes, three to five times a week is efficient.
Taking too long to eat between meals hinders your metabolism. It is recommended to reduce your larger portions to smaller ones, eating up to about five to six meals a day. Eating smaller meals regulates your blood and your metabolism doesn’t have to conserve energy since it is being provided more frequently throughout the day. Ensure that every meal has a variety of carbohydrates, proteins, and fats; avoid high-saturated fat foods! Adding spices to meals will help improve metabolism as well. Staying hydrated helps the body stay active; it is recommended that an adult consume at least eight ounce, eight cups of cool water every day. Cool water is recommended because the body will spend more time trying to warm the water to your body temperature, burning more calories as a result.
Sleep is essential to not only for the mind, but for the body as well. When an individual doesn’t get enough sleep, hormones get disrupted. Ghrelin, the hormone that lets the body know that it is time to eat, rises when you don’t get enough sleep. Leptin, the hormone that lets the body know that you’re full, lowers. As a result, the body compensates by eating more than what is recommended to get energy. It is recommended for an adult to get at least seven to nine hours of sleep to maintain a healthy hormone balance.
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Why Is Sleep Important? (n.d.). Retrieved December 2, 2015, from http://www.nhlbi.nih.gov/health/health-topics/topics/sdd/why
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