How Fat Cells Work
In the last section, we learned how fat in the body is broken down and rebuilt into chylomicrons, which enter the bloodstream by way of the lymphatic system. Chylomicrons do not last long in the bloodstream -- only about eight minutes -- because enzymes called lipoprotein lipases break the fats into fatty acids. Lipoprotein lipases are found in the walls of blood vessels in fat tissue, muscle tissue and heart muscle. Insulin When you eat a candy bar or a meal, the presence of glucose, amino acids or fatty acids in the intestine stimulates the pancreas to secrete a hormone called insulin. Insulin acts on many cells in your body, especially those in the liver, muscle and fat tissue. Insulin tells the cells to do the following: The activity of lipoprotein lipases depends upon the levels of insulin in the body. If insulin is high, then the lipases are highly active; if insulin is low, the lipases are inactive. The fatty acids are then absorbed from the blood into fat cells, muscle cells and liver cells. In these cells, under stimulation by insulin, fatty acids are made into fat molecules and stored as fat droplets. It is also possible for fat cells to take up glucose and amino acids, which have been absorbed into the bloodstream after a meal, and convert those into fat molecules. The conversion of carbohydrates or protein into fat is 10 times less efficient than simply storing fat in a fat cell, but the body can do it. If you have 100 extra calories in fat (about 11 grams) floating in your bloodstream, fat cells can store it using only 2.5 calories of energy. On the other hand, if you have 100 extra calories in glucose (about 25 grams) floating in your bloodstream, it takes 23 calories of energy to convert the glucose into fat and then store it. Given a choice, a fat cell w Continue reading >>
We Really Can Make Glucose From Fatty Acids After All! O Textbook, How Thy Biochemistry Hast Deceived Me!
Biochemistry textbooks generally tell us that we can’t turn fatty acids into glucose. For example, on page 634 of the 2006 and 2008 editions of Biochemistry by Berg, Tymoczko, and Stryer, we find the following: Animals Cannot Convert Fatty Acids to Glucose It is important to note that animals are unable to effect the net synthesis of glucose from fatty acids. Specficially, acetyl CoA cannot be converted into pyruvate or oxaloacetate in animals. In fact this is so important that it should be written in italics and have its own bold heading! But it’s not quite right. Making glucose from fatty acids is low-paying work. It’s not the type of alchemy that would allow us to build imperial palaces out of sugar cubes or offer hourly sweet sacrifices upon the altar of the glorious god of glucose (God forbid!). But it can be done, and it’ll help pay the bills when times are tight. All Aboard the Acetyl CoA! When we’re running primarily on fatty acids, our livers break the bulk of these fatty acids down into two-carbon units called acetate. When acetate hangs out all by its lonesome like it does in a bottle of vinegar, it’s called acetic acid and it gives vinegar its characteristic smell. Our livers aren’t bottles of vinegar, however, and they do things a bit differently. They have a little shuttle called coenzyme A, or “CoA” for short, that carries acetate wherever it needs to go. When the acetate passenger is loaded onto the CoA shuttle, we refer to the whole shebang as acetyl CoA. As acetyl CoA moves its caboose along the biochemical railway, it eventually reaches a crossroads where it has to decide whether to enter the Land of Ketogenesis or traverse the TCA cycle. The Land of Ketogenesis is a quite magical place to which we’ll return in a few moments, but n Continue reading >>
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When Does Glucose Convert To Fat?
Despite the fact that eating a jelly doughnut seems to deposit fat directly on your hips, converting sugar to fat is actually a relatively complex chemical process. Sugar conversion to fat storage depends not only upon the type of foods you eat, but how much energy your body needs at the time you eat it. Video of the Day Your body converts excess dietary glucose into fat through the process of fatty acid synthesis. Fatty acids are required in order for your body to function properly, playing particularly important roles in proper brain functioning. There are two kinds of fatty acids; essential fatty acids and nonessential fatty acids. Essential fatty acids refer to fatty acids you must eat from your diet, as your body cannot make them. Nonessential fatty acids are made through the process of fatty acid synthesis. Fatty Acid Synthesis Fatty acids are long organic compounds having an acid group at one end and a methyl group at the other end. The location of their first double bond dictates whether they are in the omega 3, 6, or 9 fatty acid family. Fatty acid synthesis takes place in the cytoplasm of cells and requires some energy input. In other words, your body actually has to expend some energy in order to store fat. Glucose is a six-carbon sugar molecule. Your body first converts this molecule into two three-carbon pyruvate molecules through the process of glycolysis and then into acetyl CoA. When your body requires immediate energy, acetyl CoA enters the Citric Acid Cycle creating energy molecules in the form of ATP. When glucose intake exceeds your body's energy needs--for example, you eat an ice-cream sundae and then go relax on the sofa for five hours--your body has no need to create more energy molecules. Therefore, acetyl CoA begins the process of fatty acid syn Continue reading >>
Carbohydrate, Protein And Lipid Metabolism Notes
Part 1 – Metabolism Concepts and Measurement Carbohydrates, protein and fat are macronutrients. In the human body metabolism is the oxidization of carbohydrates, protein and fat to give CO2, H2O and energy. What is Metabolic Rate? Metabolic Rate is the amount of energy liberated per unit time. The Basal Metabolic Rate is the rate of energy expenditure at rest in a neutrally temperate environment, in the post-absorptive state (meaning that the digestive system is inactive, which requires about twelve hours of fasting in humans). The Basal Metabolic Rate is the largest component of total caloric expenditure in humans: 70% Physical activity contributes: 20% Thermogenesis & digestion contributes: 10% Units used for Metabolic Energy calorie (cal – note lowercase) is the standard unit of metabolic heat energy, being the amount of energy needed to raise 1g of water by 1 degree, from 15o to 16o C. Calorie (kilocalorie, kcal, big calorie, large calorie, kilogram calorie) is more commonly used, representing 1000 calorie. Joule is the SI unit for energy, such that 1 calorie = 4.2 joule. To convert from Calories (kilocalories) to kilojoules, multiply by 4.2. How do we measure Metabolic Energy and Metabolic Rate? Direct calorimetry A Bomb Calorimeter, or constant-volume calorimeter, is used to measure the energy released by food during complete oxidization. The food is placed in a sealed metal container surrounded by water in an insulated container. The food is ignited by an electrical spark and the temperature change of a known volume of water is used to calculate the energy released by the food. Standard caloric values for macronutrients are: Carbohydrates: 4.1 kcal/g Protein: 5.3 kcal/g (but in the body is only 4.1 kcal/g due to incomplete oxidation) Fat: 9.3 kcal/g Ethanol: Continue reading >>
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How Sugar, Not Fat, Raises Your Cholesterol
Excess carbohydrates and sugar lead to cholesterol and weight gain, explains Dr. Doni Wilson, which is why balancing blood sugar levels every day is so important. When you go to the doctor and get a cholesterol reading, you may be cautioned against eating high-fat foods. But very little fat from foods becomes cholesterol in your blood. What produces cholesterol is rather the excessive consumption of carbs at any one time. The cholesterol and triglycerides in your bloodstream come not from consuming excess fat, but rather, from consuming excess glucose. I’m not just talking about excess glucose over the course of a week or even a day. I’m talking about what happens when you consume excess glucose in one sitting. Let’s take a closer look at exactly happens when your body gets too many carbs at one particular meal. First, you digest the carb-containing food, breaking it down into the individual glucose molecules that are small enough to cross the cells of your intestinal walls and enter your bloodstream. Because you have eaten too many carbs, you have far too much glucose stuck in your blood. You don’t have enough insulin to move all that glucose into your cells. So what happens to that excess glucose? Some of it is stored in your liver as a substance known as glycogen, to be released when you don’t eat. Harking back to our hunter-gatherer days, our bodies created a backup system to ensure that even if we can’t get any food for a couple of days, we won’t starve to death. The liver can only hold so much glycogen, however. So what about the glucose that doesn’t fit? Your body has three choices: convert the glucose into body fat, which translates into weight gain, most likely around your middle; convert the glucose into lipids (fats), which remain in your bloo Continue reading >>
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Chapter 5 Cell Respiration and Metabolism To place this chapter in perspective, we must realize that all living cells have a continuous need for energy (ATP) to perform routine functions. These include such vital functions as transporting materials across cell membranes and generating membrane potentials (chapter 6); transmitting these electrical impulses (chapters 7-10); synthesizing and secreting hormones (chapter 11); and contracting muscles (chapters 12-14). Ultimately, the energy for these cellular activities comes from the fuel foods we consume, digest, and absorb (digestion: chapter 17); deliver to our cells (circulation: chapters 13 and 14); and combust or metabolize along enzymeâ€‘catalyzed pathways. As we learned in the previous chapter, much of this chemical energy is lost as heat energy (measured in calories) as the residual energy is transferred to the synthesis of ATP. The ATP then serves to drive or â€œenergizeâ€ cellular functions. We are prepared now to ask questions about the processes that comprise cell respiration and to analyze the combustion reactions that occur continuously in all living cells. In this way, food consumption provides the high-energy raw materials that active cells require to produce the ATP that drives the cellâ€™s activities and that ultimately maintains overall body homeostasis. When we breathe in, where in the body does the oxygen go? And, where does the carbon dioxide come from that we exhale? And how does this exchange of gases relate to the combustion of fuel food molecules such as glucose, fat (triglycerides), and amino acids; and to the subsequent transfer of energy to ATP? Answers to these questions and others regarding cell respiration are discussed here. Also, this chapter illustrates how the metabolic d Continue reading >>
Approximately What Percentage Of The Weight Of Triglycerides Cannot Be Converted To Glucose?
"glycerol can yield glucose, but that represents only 3 of the 50 or so carbon atoms in a triglyceride-about 5% of its weight. The other 95% cannot be converted to glucose." Understanding Nutrition 11th Ed. pg 223 Hope that helps... I had that question too... 3 people found this useful Continue reading >>
Ann L. Albright and Judith S. Stern Department of Nutrition and Internal Medicine University of California at Davis Davis, CA USA Morphology and Development of Adipose TissueAdipose-Tissue MetabolismAdipose Tissue DistributionDefinition and Causes of ObesityFurther Reading Albright, A.L. and Stern, J.S. (1998). Adipose tissue. In: Encyclopedia of Sports Medicine and Science, T.D.Fahey (Editor). Internet Society for Sport Science: 30 May 1998. Adipose tissue is specialized connective tissue that functions as the major storage site for fat in the form of triglycerides. Adipose tissue is found in mammals in two different forms: white adipose tissue and brown adipose tissue. The presence, amount, and distribution of each varies depending upon the species. Most adipose tissue is white, the focus of this review. White adipose tissue serves three functions: heat insulation, mechanical cushion, and most importantly, a source of energy. Subcutaneous adipose tissue, found directly below the skin, is an especially important heat insulator in the body, because it conducts heat only one third as readily as other tissues. The degree of insulation is dependent upon the thickness of this fat layer. For example, a person with a 2-mm layer of subcutaneous fat will feel as comfortable at 15°C as a person with a 1-mm layer at 16°C. Adipose tissue also surrounds internal organs and provides some protection for these organs from jarring. As the major form of energy storage, fat provides a buffer for energy imbalances when energy intake is not equal to energy output. It is an efficient way to store excess energy, because it is stored with very little water. Consequently, more energy can be derived per gram of fat (9 kcal.gm-1) than per gram of carbohydrate (4 kcal.gm-1) or protein (4 kcal.g Continue reading >>
Section 16.1oxidation Of Glucose And Fatty Acids To Co2
The complete aerobic oxidation of glucose is coupled to the synthesis of as many as 36 molecules of ATP: Glycolysis, the initial stage of glucose metabolism, takes place in the cytosol and does not involve molecular O. It produces a small amount of ATP and the three-carbon compound pyruvate. In aerobic cells, pyruvate formed in glycolysis is transported into the mitochondria, where it is oxidized by O to CO. Via chemiosmotic coupling, the oxidation of pyruvate in the mitochondria generates the bulk of the ATP produced during the conversion of glucose to CO. In this section, we discuss the biochemical pathways that oxidize glucose and fatty acids to CO and HO; the fate of the released electrons is described in the next section. Go to: Cytosolic Enzymes Convert Glucose to Pyruvate A set of 10 enzymes catalyze the reactions, constituting the glycolytic pathway, that degrade one molecule of glucose to two molecules of pyruvate (Figure 16-3). All the metabolic intermediates between glucose and pyruvate are watersoluble phosphorylated compounds. Four molecules of ATP are formed from ADP in glycolysis (reactions 6 and 9). However, two ATP molecules are consumed during earlier steps of this pathway: the first by the addition of a phosphate residue to glucose in the reaction catalyzed by hexokinase (reaction 1), and the second by the addition of a second phosphate to fructose 6-phosphate in the reaction catalyzed by phosphofructokinase-1 (reaction 3). Thus there is a net gain of two ATP molecules. The balanced chemical equation for the conversion of glucose to pyruvate shows that four hydrogen atoms (four protons and four electrons) are also formed: (For convenience, we show pyruvate in its un-ionized form, pyruvic acid, although at physiological pH it would be largely dissociat Continue reading >>
Ketosis: Metabolic Flexibility In Action
Ketosis is an energy state that your body uses to provide an alternative fuel when glucose availability is low. It happens to all humans when fasting or when carbohydrate intake is lowered. The process of creating ketones is a normal metabolic alternative designed to keep us alive if we go without food for long periods of time. Eating a diet low in carb and higher in fat enhances this process without the gnawing hunger of fasting. Let’s talk about why ketones are better than glucose for most cellular fuel needs. Legionella Testing Lab - High Quality Lab Results CDC ELITE & NYSDOH ELAP Certified - Fast Results North America Lab Locations legionellatesting.com Body Fuel Basics Normal body cells metabolize food nutrients and oxygen during cellular “respiration”, a set of metabolic pathways in which ATP (adenosine triphosphate), our main cellular energy source is created. Most of this energy production happens in the mitochondria, tiny cell parts which act as powerhouses or fueling stations. There are two primary types of food-based fuel that our cells can use to produce energy: The first cellular fuel is glucose, which is commonly known as blood sugar. Glucose is a product of the starches and sugars (carbohydrates) and protein in our diet. This fuel system is necessary, but it has a limitation. The human body can only store about 1000-1600 calories of glucose in the form of glycogen in our muscles and liver. The amounts stored depend on how much muscle mass is available. Men will be able to store more because they have a greater muscle mass. Since most people use up about 2000 calories a day just being and doing normal stuff, you can see that if the human body depended on only sugar to fuel itself, and food weren’t available for more than a day, the body would run Continue reading >>
All About Fructose
What is fructose? Fructose is a monosaccharide, the simplest form of carbohydrate. As the name implies, mono (one) saccharides (sugar) contain only one sugar group; thus, they can’t be broken down any further. Each subtype of carbohydrate has different effects in the body depending on the structure and source (i.e. what food it comes from). The chemical structure affects how quickly and/or easily the carbohydrate molecule is digested/absorbed. The source affects whether other nutrients are provided along with the carbohydrate. For example, both high fructose corn syrup (HFCS) and fruit contain fructose, but their effects in the body are different. HFCS is essentially a simple fructose delivery system – there’s nothing else to it, while fruit contains additional nutrients along with fibre, which affect digestion and absorption of the fructose. Plus, the amount of fructose in the average apple is much less than, say, the average can of soda. Fructose has a unique texture, sweetness, rate of digestion, and degree of absorption that is different from glucose, which is the sugar that most of our ingested dietary carbohydrates become when they hit the bloodstream. Fructose is absorbed through the intestine via different mechanisms than glucose Fructose has a slower rate of uptake Unlike glucose, fructose does not stimulate a substantial insulin release Fructose is transported into cells via a different transporter than glucose Once fructose is in the liver, it can provide glycerol, the backbone of fat, and increase fat formation Some people may be unable to completely absorb fructose when given in a high dose of around 50 grams (Note: that’s an extremely high amount of fructose. We’re talking 4-5 medium apples. Yet a 16 oz juice with HFCS can provide around 45 grams Continue reading >>
Nutrition Ch. 7
Sort Which of the following accounts for the higher energy density of a fatty acid compared with the other energy-yielding nutrients? a. Fatty acids have a lower percentage of hydrogen-carbon bonds b. Fatty acids have a greater percentage of hydrogen-carbon bonds c. Other energy-yielding nutrients have a lower percentage of oxygen-carbon bonds d. Other energy-yielding nutrients undergo fewer metabolic reactions, thereby lowering the energy yield b. Fatty acids have a greater percentage of hydrogen-carbon bonds Lillie has been losing weight by following a very-low-carbohydrate diet for 2 months. Her primary care physician just diagnosed ketosis through a urine sample. Which of the following symptoms would be another way the physician might have suspected ketosis in Lillie? Fruity odor on breath Continue reading >>
Example of an unsaturated fat triglyceride (C55H98O6). Left part: glycerol; right part, from top to bottom: palmitic acid, oleic acid, alpha-linolenic acid. A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from tri- and glyceride). Triglycerides are the main constituents of body fat in humans and other animals, as well as vegetable fat. They are also present in the blood to enable the bidirectional transference of adipose fat and blood glucose from the liver, and are a major component of human skin oils. There are many different types of triglyceride, with the main division between saturated and unsaturated types. Saturated fats are "saturated" with hydrogen — all available places where hydrogen atoms could be bonded to carbon atoms are occupied. These have a higher melting point and are more likely to be solid at room temperature. Unsaturated fats have double bonds between some of the carbon atoms, reducing the number of places where hydrogen atoms can bond to carbon atoms. These have a lower melting point and are more likely to be liquid at room temperature. Chemical structure Triglycerides are chemically tri esters of fatty acids and glycerol. Triglycerides are formed by combining glycerol with three fatty acid molecules. Alcohols have a hydroxyl (HO–) group. Organic acids have a carboxyl (–COOH) group. Alcohols and organic acids join to form esters. The glycerol molecule has three hydroxyl (HO–) groups. Each fatty acid has a carboxyl group (–COOH). In triglycerides, the hydroxyl groups of the glycerol join the carboxyl groups of the fatty acid to form ester bonds: HOCH2CH(OH)CH2OH + RCO2H + R′CO2H + R″CO2H → RCO2CH2CH(O2CR′)CH2CO2R″ + 3H2O The three fatty acids Continue reading >>
Can Fats Be Turned Into Glycogen For Muscle?
The amount of fat in the average diet and the amount of stored fat in the average body make the notion of converting that fat into usable energy appealing. Glycogen, a form of energy stored in muscles for quick use, is what the body draws on first to perform movements, and higher glycogen levels result in higher usable energy. It is not possible for fats to be converted directly into glycogen because they are not made up glucose, but it is possible for fats to be indirectly broken down into glucose, which can be used to create glycogen. Relationship Between Fats and Glycogen Fats are a nutrient found in food and a compound used for long-term energy storage in the body, while glycogen is a chain of glucose molecules created by the body from glucose for short-term energy storage and utilization. Dietary fats are used for a number of functions in the body, including maintaining cell membranes, but they are not used primarily as a source of fast energy. Instead, for energy the body relies mostly on carbohydrates, which are converted into glucose that is then used to form glycogen. Turning Fats Into Glucose Excess glucose in the body is converted into stored fat under certain conditions, so it seems logical that glucose could be derived from fats. This process is called gluconeogenesis, and there are multiple pathways the body can use to achieve this conversion. Gluconeogenesis generally occurs only when the body cannot produce sufficient glucose from carbohydrates, such as during starvation or on a low-carbohydrate diet. This is less efficient than producing glucose through the metabolizing of carbohydrates, but it is possible under the right conditions. Turning Glucose Into Glycogen Once glucose has been obtained from fats, your body easily converts it into glycogen. In gl Continue reading >>