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"A calorie is a calorie" is a tautology used to convey the thermodynamic concept that a "calorie" is a sufficient way to describe the energy content of food.
In 1878, German nutritionist Max Rubner crafted what he called the "isodynamic law". [1] The law claims that the basis of nutrition is the exchange of energy, [2] and was applied to the study of obesity in the early 1900s by Carl von Noorden. Von Noorden had two theories about what caused people to develop obesity. The first simply avowed Rubner's notion that "a calorie is a calorie". The second theorized that obesity development depends on how the body partitions calories for either use or storage. [1] Since 1925, the calorie has been defined in terms of the joule; the current definition of the calorie was formally adopted in 1948. [3]
The related concept of "calorie in, calorie out" might be contested, [4] despite having become a commonly held belief in nutritionism.[ citation needed ]
Calorie amounts found on food labels are based on the Atwater system. [5] The accuracy of the system is disputed, despite no real proposed alternatives. For example, a 2012 study by a USDA scientist concluded that the measured energy content of a sample of almonds was 32% lower than the estimated Atwater value. [6] The driving mechanism behind caloric intake is absorption, which occurs largely in the small intestine and distributes nutrients to the circulatory and lymphatic capillaries by means of osmosis, diffusion and active transport. Fat, in particular is emulsified by bile produced by the liver and stored in the gallbladder where it is released to the small intestine via the bile duct. A relatively lesser amount of absorption—composed primarily of water—occurs in the large intestine.
A kilocalorie is the equivalent of 1000 calories or one dietary Calorie, which contains 4184 joules of energy. The human body is a highly complex biochemical system that undergoes processes which regulate energy balance. The metabolic pathways for protein are less efficient than the metabolic pathways for carbohydrates and fat.[ citation needed ] Protein contains four calories per gram, although a large part of the calories are lost as heat when metabolised by the body. [7]
The calorie is a unit of energy that originated from the obsolete caloric theory of heat. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, dietary calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius. The small calorie or gram calorie was defined as the amount of heat needed to cause the same increase in one gram of water. Thus, 1 large calorie is equal to 1000 small calories.
Dieting is the practice of eating food in a regulated way to decrease, maintain, or increase body weight, or to prevent and treat diseases such as diabetes and obesity. As weight loss depends on calorie intake, different kinds of calorie-reduced diets, such as those emphasising particular macronutrients, have been shown to be no more effective than one another. As weight regain is common, diet success is best predicted by long-term adherence. Regardless, the outcome of a diet can vary widely depending on the individual.
Food energy is chemical energy that animals derive from their food to sustain their metabolism, including their muscular activity.
Adipose tissue (also known as body fat, or simply fat) is a loose connective tissue composed mostly of adipocytes. In addition to adipocytes, adipose tissue contains the stromal vascular fraction(SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and a variety of immune cells such as adipose tissue macrophages. Adipose tissue is derived from preadipocytes. Its main role is to store energy in the form of lipids, although it also cushions and insulates the body. Far from being hormonally inert, adipose tissue has, in recent years, been recognized as a major endocrine organ, as it produces hormones such as leptin, estrogen, resistin, and cytokines (especially TNFα). In obesity, adipose tissue is also implicated in the chronic release of pro-inflammatory markers known as adipokines, which are responsible for the development of metabolic syndrome, a constellation of diseases, including type 2 diabetes, cardiovascular disease and atherosclerosis. The two types of adipose tissue are white adipose tissue (WAT), which stores energy, and brown adipose tissue (BAT), which generates body heat. The formation of adipose tissue appears to be controlled in part by the adipose gene. Adipose tissue – more specifically brown adipose tissue – was first identified by the Swiss naturalist Conrad Gessner in 1551.
Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Proper measurement requires a strict set of criteria to be met. These criteria include being in a physically and psychologically undisturbed state and being in a thermally neutral environment while in the post-absorptive state (i.e., not actively digesting food). In bradymetabolic animals, such as fish and reptiles, the equivalent term standard metabolic rate (SMR) applies. It follows the same criteria as BMR, but requires the documentation of the temperature at which the metabolic rate was measured. This makes BMR a variant of standard metabolic rate measurement that excludes the temperature data, a practice that has led to problems in defining "standard" rates of metabolism for many mammals.
Cat food is food specifically designed for consumption by cats. As obligate carnivores, cats have specific requirements for their dietary nutrients, namely nutrients found only in meat, such as taurine, arginine, and Vitamin B6. Certain nutrients, including many vitamins and amino acids, are degraded by the temperatures, pressures and chemical treatments used during manufacture, and hence must be added after manufacture to avoid nutritional deficiency.
Weight gain is an increase in body weight. This can involve an increase in muscle mass, fat deposits, excess fluids such as water or other factors. Weight gain can be a symptom of a serious medical condition.
Calorie restriction is a dietary regimen that reduces the energy intake from foods and beverages without incurring malnutrition. The possible effect of calorie restriction on body weight management, longevity, and aging-associated diseases has been an active area of research.
Resting metabolic rate (RMR) is whole-body mammal metabolism during a time period of strict and steady resting conditions that are defined by a combination of assumptions of physiological homeostasis and biological equilibrium. RMR differs from basal metabolic rate (BMR) because BMR measurements must meet total physiological equilibrium whereas RMR conditions of measurement can be altered and defined by the contextual limitations. Therefore, BMR is measured in the elusive "perfect" steady state, whereas RMR measurement is more accessible and thus, represents most, if not all measurements or estimates of daily energy expenditure.
Specific dynamic action (SDA), also known as thermic effect of food (TEF) or dietary induced thermogenesis (DIT), is the amount of energy expenditure above the basal metabolic rate due to the cost of processing food for use and storage. Heat production by brown adipose tissue which is activated after consumption of a meal is an additional component of dietary induced thermogenesis. The thermic effect of food is one of the components of metabolism along with resting metabolic rate and the exercise component. A commonly used estimate of the thermic effect of food is about 10% of one's caloric intake, though the effect varies substantially for different food components. For example, dietary fat is very easy to process and has very little thermic effect, while protein is hard to process and has a much larger thermic effect.
Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, stored heat and other thermodynamic properties of substances such as specific internal energy, specific enthalpy, specific Gibbs free energy, and specific Helmholtz free energy. It may also be used for the kinetic energy or potential energy of a body. Specific energy is an intensive property, whereas energy and mass are extensive properties.
Max Rubner was a German physiologist and hygienist.
Lipid metabolism is the synthesis and degradation of lipids in cells, involving the breakdown and storage of fats for energy and the synthesis of structural and functional lipids, such as those involved in the construction of cell membranes. In animals, these fats are obtained from food and are synthesized by the liver. Lipogenesis is the process of synthesizing these fats. The majority of lipids found in the human body from ingesting food are triglycerides and cholesterol. Other types of lipids found in the body are fatty acids and membrane lipids. Lipid metabolism is often considered as the digestion and absorption process of dietary fat; however, there are two sources of fats that organisms can use to obtain energy: from consumed dietary fats and from stored fat. Vertebrates use both sources of fat to produce energy for organs such as the heart to function. Since lipids are hydrophobic molecules, they need to be solubilized before their metabolism can begin. Lipid metabolism often begins with hydrolysis, which occurs with the help of various enzymes in the digestive system. Lipid metabolism also occurs in plants, though the processes differ in some ways when compared to animals. The second step after the hydrolysis is the absorption of the fatty acids into the epithelial cells of the intestinal wall. In the epithelial cells, fatty acids are packaged and transported to the rest of the body.
The term "infectobesity" refers to the hypothesis that obesity in humans can be caused by pathogenic organisms, and the emerging field of medical research that studies the relationship between pathogens and weight gain. The term was coined in 2001 by Dr. Nikhil V. Dhurandhar, at the Pennington Biomedical Research Center.
Proteins are essential nutrients for the human body. They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 4 kcal per gram; in contrast, lipids provide 9 kcal per gram. The most important aspect and defining characteristic of protein from a nutritional standpoint is its amino acid composition.
Gary Taubes is an American journalist, writer, and low-carbohydrate / high-fat (LCHF) diet advocate. His central claim is that carbohydrates, especially sugar and high-fructose corn syrup, overstimulate the secretion of insulin, causing the body to store fat in fat cells and the liver, and that it is primarily a high level of dietary carbohydrate consumption that accounts for obesity and other metabolic syndrome conditions. He is the author of Nobel Dreams (1987); Bad Science: The Short Life and Weird Times of Cold Fusion (1993); Good Calories, Bad Calories (2007), titled The Diet Delusion (2008) in the UK and Australia; Why We Get Fat: And What to Do About It (2010); The Case Against Sugar (2016); and The Case for Keto: Rethinking Weight Control and the Science and Practice of Low-Carb/High-Fat Eating (2020). Taubes's work often goes against accepted scientific, governmental, and popular tenets such as that obesity is caused by eating too much and exercising too little and that excessive consumption of fat, especially saturated fat in animal products, leads to cardiovascular disease.
A protein-sparing modified fast or PSMF diet is a type of a very-low-calorie diet with a high proportion of protein calories and simultaneous restriction of carbohydrate and fat. It includes a protein component, fluids, and vitamin and mineral supplementation.
Diet plays an important role in the genesis of obesity. Personal choices, food advertising, social customs and cultural influences, as well as food availability and pricing all play a role in determining what and how much an individual eats.
Weight management refers to behaviors, techniques, and physiological processes that contribute to a person's ability to attain and maintain a healthy weight. Most weight management techniques encompass long-term lifestyle strategies that promote healthy eating and daily physical activity. Moreover, weight management involves developing meaningful ways to track weight over time and to identify ideal body weights for different individuals.
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