Science And Nutrition :: You Are What You Ate
Over two thousand years ago, Hippocrates theorized that the body was composed of four fluids or humours including blood, phlegm, choler (yellow bile) and black bile (melancholy). Avicenna later suggested in the ninth century that these humours were derived from the process of digestion and so classified them as well as humans and all foods as hot/moist, hot/dry, cold/moist and cold/dry. Similarly, in ancient China body fluids identified resembled those put forward by Hippocrates. Additionally, the Chinese classified human characteristics, as well as foods, into yin and yang. Indian traditional medicine (ayurveda) categorizes people into three doshas or humours with their corresponding characteristics: vata (active and enthusiastic although a worrier), pitta (sharp intellectual, with a tendency to become irritable under stress) and kapha (balanced and conservative). All of these systems make a reference to the importance of balancing the internal environment of the body and, while their outlook varied, they coincide in the fact that illness was regarded as an imbalance of these components. The human body is amazing in how it protects itself and preserves life. It is indeed true that a certain level of balance or equilibrium is required to sustain life. It is critical for conditions such as temperature, hydration and energy supply to be maintained at all times. This last concept, energy supply, is a direct result of our eating habits. Out of all of these amazing chemical reactions, lets look at one group more closely: glucose metabolism. Under normal circumstances, the human body uses carbohydrates as its number one source of energy. When carbohydrates are not available in sufficient quantities to supply the body with the required energy (in the form of glucose), alterna Continue reading >>
How The Body Uses Carbohydrates, Proteins, And Fats
How the Body Uses Carbohydrates, Proteins, and Fats The human body is remarkably adept at making do with whatever type of food is available. Our ability to survive on a variety of diets has been a vital adaptation for a species that evolved under conditions where food sources were scarce and unpredictable. Imagine if you had to depend on successfully hunting a woolly mammoth or stumbling upon a berry bush for sustenance! Today, calories are mostly cheap and plentifulperhaps too much so. Understanding what the basic macronutrients have to offer can help us make better choices when it comes to our own diets. From the moment a bite of food enters the mouth, each morsel of nutrition within starts to be broken down for use by the body. So begins the process of metabolism, the series of chemical reactions that transform food into components that can be used for the body's basic processes. Proteins, carbohydrates , and fats move along intersecting sets of metabolic pathways that are unique to each major nutrient. Fundamentallyif all three nutrients are abundant in the dietcarbohydrates and fats will be used primarily for energy while proteins provide the raw materials for making hormones, muscle, and other essential biological equipment. Proteins in food are broken down into pieces (called amino acids) that are then used to build new proteins with specific functions, such as catalyzing chemical reactions, facilitating communication between different cells, or transporting biological molecules from here to there. When there is a shortage of fats or carbohydrates, proteins can also yield energy. Fats typically provide more than half of the body's energy needs. Fat from food is broken down into fatty acids, which can travel in the blood and be captured by hungry cells. Fatty aci Continue reading >>
How Our Bodies Turn Food Into Energy
All parts of the body (muscles, brain, heart, and liver) need energy to work. This energy comes from the food we eat. Our bodies digest the food we eat by mixing it with fluids (acids and enzymes) in the stomach. When the stomach digests food, the carbohydrate (sugars and starches) in the food breaks down into another type of sugar, called glucose. The stomach and small intestines absorb the glucose and then release it into the bloodstream. Once in the bloodstream, glucose can be used immediately for energy or stored in our bodies, to be used later. However, our bodies need insulin in order to use or store glucose for energy. Without insulin, glucose stays in the bloodstream, keeping blood sugar levels high. Insulin is a hormone made by beta cells in the pancreas. Beta cells are very sensitive to the amount of glucose in the bloodstream. Normally beta cells check the blood's glucose level every few seconds and sense when they need to speed up or slow down the amount of insulin they're making and releasing. When someone eats something high in carbohydrates, like a piece of bread, the glucose level in the blood rises and the beta cells trigger the pancreas to release more insulin into the bloodstream. When insulin is released from the pancreas, it travels through the bloodstream to the body's cells and tells the cell doors to open up to let the glucose in. Once inside, the cells convert glucose into energy to use right then or store it to use later. As glucose moves from the bloodstream into the cells, blood sugar levels start to drop. The beta cells in the pancreas can tell this is happening, so they slow down the amount of insulin they're making. At the same time, the pancreas slows down the amount of insulin that it's releasing into the bloodstream. When this happens, Continue reading >>
Gluconeogenesis
Not to be confused with Glycogenesis or Glyceroneogenesis. Simplified Gluconeogenesis Pathway Gluconeogenesis (GNG) is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. From breakdown of proteins, these substrates include glucogenic amino acids (although not ketogenic amino acids); from breakdown of lipids (such as triglycerides), they include glycerol (although not fatty acids); and from other steps in metabolism they include pyruvate and lactate. Gluconeogenesis is one of several main mechanisms used by humans and many other animals to maintain blood glucose levels, avoiding low levels (hypoglycemia). Other means include the degradation of glycogen (glycogenolysis)[1] and fatty acid catabolism. Gluconeogenesis is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms.[2] In vertebrates, gluconeogenesis takes place mainly in the liver and, to a lesser extent, in the cortex of the kidneys. In ruminants, this tends to be a continuous process.[3] In many other animals, the process occurs during periods of fasting, starvation, low-carbohydrate diets, or intense exercise. The process is highly endergonic until it is coupled to the hydrolysis of ATP or GTP, effectively making the process exergonic. For example, the pathway leading from pyruvate to glucose-6-phosphate requires 4 molecules of ATP and 2 molecules of GTP to proceed spontaneously. Gluconeogenesis is often associated with ketosis. Gluconeogenesis is also a target of therapy for type 2 diabetes, such as the antidiabetic drug, metformin, which inhibits glucose formation and stimulates glucose uptake by cells.[4] In ruminants, because dietary carbohydrates tend to be metabolized by rumen organisms, gluconeogenesis occurs Continue reading >>
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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Converting Carbohydrates To Triglycerides
Consumers are inundated with diet solutions on a daily basis. High protein, low fat, non-impact carbohydrates, and other marketing “adjectives” are abundant within food manufacturing advertising. Of all the food descriptors, the most common ones individuals look for are “fat free” or “low fat”. Food and snack companies have found the low fat food market to be financially lucrative. The tie between fat intake, weight gain, and health risks has been well documented. The dietary guidelines suggest to keep fat intake to no more than 30% of the total diet and to consume foods low in saturated and trans fatty acids. But, this does not mean that we can consume as much fat free food as we want: “Fat free does not mean calorie free.” In many cases the foods that are low in fat have a large amount of carbohydrates. Carbohydrate intake, like any nutrient, can lead to adverse affects when over consumed. Carbohydrates are a necessary macronutrient, vital for maintenance of the nervous system and energy for physical activity. However, if consumed in amounts greater than 55% to 65% of total caloric intake as recommended by the American Heart Association can cause an increase in health risks. According to the World Health Organization the Upper Limit for carbohydrates for average people is 60% of the total dietary intake. Carbohydrates are formed in plants where carbons are bonded with oxygen and hydrogen to form chains of varying complexity. The complexity of the chains ultimately determines the carbohydrate classification and how they will digest and be absorbed in the body. Mono-and disaccharides are classified as simple carbohydrates, whereas polysaccharides (starch and fiber) are classified as complex. All carbohydrates are broken down into monosaccharides before b Continue reading >>
How Does Fat Get Converted To Calories?
Opinions expressed by Forbes Contributors are their own. Answer by Bart Loews , passionate exercise enthusiast, on Quora : How is fat being converted into calories at cellular level? First lets get some term clarification: A calorie is a measure of energy, specifically heat. Its a measurement of an indirect use of your biological fuels. Your body doesnt really convert things to calories, it converts them to ATP which is used as energy. Calories are, sadly, the best way we have to measure this process.Ill assume that the point of this question is: How does fat turn into energy? Fat is a term used interchangeably with lipids and with adipose tissue. Lipids are molecules that consist of a hydrophobic tail with a hydrophilic head. Because of this polarized set up, they are able to cluster together to form barriers between water and non water, like bubbles. Your cell membranes are composed of lipids. Adipose tissue is what makes you fat. Adipose tissue stores lipids in the form of triglycerides or 3 fatty acid chains with a glycerol backbone. These triglycerides are what is broken down to be used for energy. Adipose tissue is made up of collections of adipocytes or fat cells. Adipose tissue is used for insulation, cushioning, and energy storage. You get a particular number of fat cells (between 30 and 300 billion) during adolescence and childhood. You don't lose them naturally, but you can gain more if they grow more than 4 fold from their original size. They grow and shrink as they take on more energy. Fat cells have a few other roles in the endocrine system, they release the hormone, Leptin when they receive energy from insulin. Leptin signals to your body that you're full. The more fat cells you have, the more leptin is released. It's been found that obese people are lep Continue reading >>
Evolving Health: Why Can't We Convert Fat To Glucose?
As evident by many sugar-laden soda pop "potbellies" of North America, lipogenesis can obviously occur from drinking and eating too much sugar (1). Wouldnt it be just grand to reverse the process and be able to lose all that fat via gluconeogenesis? Unfortunately mammals do not have the ability to synthesize glucose from fats (1). The fact is that once glucose is converted to acetyl coA there is no method of getting back to glucose. The pyruvate dehydrogenase reaction that converts pyruvate to acetyl CoA is not reversible (1p252). Because lipid metabolism produces acetyl CoA via beta-oxidation, there can be no conversion to pyruvate or oxaloacetate that may have been used for gluconeogenesis (1p252). Further, the two carbons in the acetyl CoA molecule are lost upon entering the citric acid cycle (1p252). Thus, the acetyl CoA is used for energy (1p252). There are some fatty acids that have an odd number of carbon atoms that can be converted to glucose, but these are not common in the diet (1p253). Maybe they should be made more common. Do they taste good? 1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009. Continue reading >>
The Science Behind Fat Metabolism
Per the usual disclaimer, always consult with your doctor before experimenting with your diet (seriously, go see a doctor, get data from blood tests, etc.). Please feel free to comment below if you’re aware of anything that should be updated; I’d appreciate knowing and I’ll update the content quickly. My goal here is to help a scientifically curious audience know the basic story and where to dive in for further study. If I’m successful, the pros will say “duh”, and everyone else will be better informed about how this all works. [UPDATE: based on a ton a helpful feedback and questions on the content below, I’ve written up a separate article summarizing the science behind ketogenic (low-carb) diets. Check it out. Also, the below content has been updated and is still very much applicable to fat metabolism on various kinds of diets. Thanks, everyone!] tl;dr The concentration of glucose in your blood is the critical upstream switch that places your body into a “fat-storing” or “fat-burning” state. The metabolic efficiency of either state — and the time it takes to get into one from the other — depends on a large variety of factors such as food and drink volume and composition, vitamin and mineral balances, stress, hydration, liver and pancreas function, insulin sensitivity, exercise, mental health, and sleep. Carbohydrates you eat, with the exception of indigestible forms like most fibers, eventually become glucose in your blood. Assuming your metabolism is functioning normally, if the switch is on you will store fat. If the switch is off, you will burn fat. Therefore, all things being equal, “diets” are just ways of hacking your body into a sufficiently low-glycemic state to trigger the release of a variety of hormones that, in turn, result in Continue reading >>
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How Are Carbohydrates Converted Into Fat Deposits?
How are carbohydrates converted into fat deposits? There are two ways that carbohydrates and body fat interact. One is directly by turning into body fat, and the other is via insulin. Turning into body fat is like adding fat into the fat cells, whereas carbohydrates spiking insulin does not add anything to fat cells per se, but hinders the release. The former is like a + equation, where the latter is a double negative which results in something that seems positive. There is a process called de novo lipogenesis (literally: Creation of fat from non-fat sources) that can occur in the body. This process turns glucose into lipids, which are then stored as body fat. This process is normally quite inefficient in the body [1] , which suggests that carbohydrates cannot be stored as fat to a high degree. The process can be upregulated (enhanced) if dietary fat comprised almost none of the diet (lesser than 10%, as a rough estimate), if carbohydrate intake is excessively high for a period of a few days, or if one follows an obesogenic diet (diet that is likely to make you fat) for a prolonged period of time. [1] [2] [3] Carbohydrates spike insulin , which is a hormone that mediates glucose metabolism. Insulin is not good or bad, insulin is insulin. It can be thought of as a lever that switches the body from fat burning mode into carbohydrate burning mode. This allows carbohydrates (and glycogen) to be burnt at a greater rate, but directly reduces the ability of fat to be lost. Overall metabolic rate (calories burnt over the course of a day) does not change significantly, just where the calories come from. When insulin is spiked in presence of ingested dietary fat, the dietary fat can go into body fat stores and not be released since glucose from glycogen is being used in place of Continue reading >>
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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Does Fat Convert To Glucose In The Body?
Your body is an amazing machine that is able to extract energy from just about anything you eat. While glucose is your body's preferred energy source, you can't convert fat into glucose for energy; instead, fatty acids or ketones are used to supply your body with energy from fat. Video of the Day Fat is a concentrated source of energy, and it generally supplies about half the energy you burn daily. During digestion and metabolism, the fat in the food you eat is broken down into fatty acids and glycerol, which are emulsified and absorbed into your blood stream. While some tissues -- including your muscles -- can use fatty acids for energy, your brain can't convert fatty acids to fuel. If you eat more fat than your body needs, the extra is stored in fat cells for later use. Fat has more than twice as many calories per gram as carbs and protein, which makes it an efficient form of stored energy. It would take more than 20 pounds of glycogen -- a type of carbohydrate used for fuel -- to store the same amount of energy in just 10 pounds of fat. Your Body Makes Glucose From Carbs Almost all the glucose in your body originated from carbohydrates, which come from the fruit, vegetables, grains and milk in your diet. When you eat these carb-containing foods, your digestive system breaks them down into glucose, which is then used for energy by your cells. Any excess glucose is converted into glycogen, then stored in your muscles and liver for later use. Once you can't store any more glucose or glycogen, your body stores any leftover carbs as fat. Glucose is your brain's preferred source of energy. However, when glucose is in short supply, your brain can use ketones -- which are derived from fat -- for fuel. Since your brain accounts for approximately one-fifth of your daily calori Continue reading >>
Fat-to-glucose Interconversion By Hydrodynamic Transfer Of Two Glyoxylate Cycle Enzyme Genes
Fat-to-glucose interconversion by hydrodynamic transfer of two glyoxylate cycle enzyme genes 1Department of Nutrition and Food Sciences, Physiology and Toxicology, University of Navarra, Pamplona, Spain 2Laboratory of Animal Physiology and Nutrition, School of Agronomy, Public University of Navarra, Pamplona, Spain Received 2008 Sep 29; Accepted 2008 Dec 10. Copyright 2008 Cordero et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The glyoxylate cycle, which is well characterized in higher plants and some microorganisms but not in vertebrates, is able to bypass the citric acid cycle to achieve fat-to-carbohydrate interconversion. In this context, the hydrodynamic transfer of two glyoxylate cycle enzymes, such as isocytrate lyase (ICL) and malate synthase (MS), could accomplish the shift of using fat for the synthesis of glucose. Therefore, 20 mice weighing 23.37 0.96 g were hydrodinamically gene transferred by administering into the tail vein a bolus with ICL and MS. After 36 hours, body weight, plasma glucose, respiratory quotient and energy expenditure were measured. The respiratory quotient was increased by gene transfer, which suggests that a higher carbohydrate/lipid ratio is oxidized in such animals. This application could help, if adequate protocols are designed, to induce fat utilization for glucose synthesis, which might be eventually useful to reduce body fat depots in situations of obesity and diabetes. Thousands of different life-related biochemical processes, such as cell respiration and many other metabolic reactions, can lead to the producti Continue reading >>
Conversion Of Carbohydrate To Fat In Adipose Tissue: An Energy-yielding And,therefore, Self-limiting Process.
Conversion of carbohydrate to fat in adipose tissue: an energy-yielding and,therefore, self-limiting process. A theoretical analysis of the energy metabolism associated with the conversion ofglucose to fat is presented. In tissues where the pentose cycle furnishes some ofthe NADPH required for fatty acid synthesis, this conversion is an ATP-yieldingprocess. In rat adipose tissue the maximal rate of glucose conversion to fat can be quantatively predicted on the basis of the tissue's ability to use the ATPwhich is generated in excess during this conversion. The energy-generating natureof this process provides the means for a type of regulation which depends onmetabolic state and which, during fasting, contributes to the sparing ofcarbohydrate. Impairment of lipogenesis in the fasting state is attributed to adecrease in the activity of the malate cycle and to the presence of free fattyacids. However, rather than by inhibiting specific enzymes, it is by virtue oftheir quality as substrates for energy production that free fatty acids and theirCoA derivatives appear to inhibit de novo lipogenesis. The regulatory phenomenadiscussed here may explain the failure of the attempts made to identify therate-limiting step for de novo lipogenesis in adipose tissue. Continue reading >>
