question: what happens to my body when my metabolism speeds up? If I haven’t increased my activity level then how does that extra energy get spent?
comment: Caffeine is a stimulant, and will increase your resting heart rate. Cold temperatures will force your body to generate more heat by ramping up cell chemistry rates and/or shivering major muscle groups. Both of these cost energy, but the effect isn't really that significant. If you're looking to lose weight, it begins in the kitchen. Anything else is just damage control. Humans are highly energy efficient and even actual running burns a disappointingly low amount of calories. Slamming Red Bull in the freezer barely burns anything.
passages: This table outlines the estimated distribution of energy consumption at different intensity levels for a healthy 20-year-old with a Max Heart Rate (MHR) of 200.
  
  These estimates are valid only when glycogen reserves are able to cover the energy needs. If a person depletes glycogen reserves after a long workout (a phenomenon known as "hitting the wall") or during a low carbohydrate diet, the body will shift into ketosis and use mostly fat and muscle for energy. Intermittent fasting can be used to train the body to shift easily into ketosis.
  
  Section::::See also.
  
  BULLET::::- Exercise physiology
  
  BULLET::::- Human power
   Metabolic window
  
  The metabolic window (also called the anabolic window or protein window) is a term used in strength training to describe the 30-minute (give or take, dependent on the individual) period after exercise during which nutrition can shift the body from a catabolic state to an anabolic one. Specifically, it is during this period that the intake of protein and carbohydrates can aid in the increase of muscle mass.
   This energy expenditure is very large compared to the basal resting metabolic rate of the adult human body. This rate varies somewhat with size, gender and age but is typically between 45 W and 85 W.
  
  Section::::Metabolic changes.
  
  Section::::Metabolic changes.:Rapid energy sources.
   Regular exercise is required to maintain the state of recovery from weight loss management. If resistance training is employed to maintain muscle mass for better glucose-disposal and glucose-control capability, a 12 to 48 hours of rest between sessions is a required time for the muscles to recover depending on intensity of exercise or training load. A change in hormone levels occurs in case of drastic dietary changes, like leptin - a satiety hormone, made by fat cells showed declination in levels, its function is to regulate energy balance by inhibiting hunger and at the same time, there is also a rise in levels of ghrelin – a hormone secreted in the gastrointestinal tract when a person's stomach is empty and informs one they are hungry. Changes in production of these hormones along with other satiating hormones in extreme weight loss managements showed suppressed resting metabolic rate (RMR) which resulted many subjects regaining much of the lost weight.
   Depending on the intensity and duration of the sport, insulin pump users typically use a temporary basal rate to reduce the amount of insulin delivered to match their reduced need of insulin as a result of exercise. The reduction is determined by trial and error with blood glucose monitoring. Some users suspend the basal rate entirely or disconnect for exercise.
  
  In some cases, the insulin pumper may want to wear the pump during sports to be able to increase and decrease insulin delivery as needed. This is when the basal rate of the pump is reduced.
   In his approach, the power output by muscles during exercise is continuously adjusted in regard to calculations made by the brain in regard to a safe level of exertion. These neural calculations factor in earlier experience with strenuous exercise, the planning duration of the exercise, and the present metabolic state of the body. These brain models ensure that body homeostasis is protected, and an emergency reserve margin is maintained. This neural control adjusts the number of activated skeletal muscle motor units, a control which is subjectively experienced as fatigue. This process, though occurring in the brain, is outside conscious control.
   BULLET::::- stoichiometric constraints on production
  
  BULLET::::- organizational uncoupling of metabolic modules (assimilation, dissipation, growth)
  
  BULLET::::- strong and weak homeostasis (composition of compartments is constant; composition of the organism is constant when the food is constant)
  
  BULLET::::- substrate(s) from the environment is/are first converted to reserve(s) before being used for further metabolism
   The fact that weight loss and dieting reduce the metabolic rate is supported by research. In one study, heat production was reduced 30% in obese men after a weight loss program, and this led to resistance to further lose body weight. Whether body mass increases or decreases, adjustments in the thermic effect of food, resting energy expenditure, and non-resting energy expenditure all oppose further change.
  
  Section::::Transitions in body composition.:Plateaus during strength training.
   Cerebral autoregulation usually ensures the brain has priority to cardiac output, though this is impaired slightly by exhaustive exercise. During submaximal exercise, cardiac output increases and cerebral blood flow increases beyond the brain’s oxygen needs. However, this is not the case for continuous maximal exertion: "Maximal exercise is, despite the increase in capillary oxygenation [in the brain], associated with a reduced mitochondrial O content during whole body exercise" The autoregulation of the brain’s blood supply is impaired particularly in warm environments
  
  Section::::Brain.:Glucose.
   Cortisol decreases amino acid uptake by muscle tissue, and inhibits protein synthesis. The short-term increase in protein synthesis that occurs subsequent to resistance training returns to normal after approximately 28 hours in adequately fed male youths. Another study determined that muscle protein synthesis was elevated even 72 hours following training.
   Section::::Energy usage in the human body.
  
  The human body uses the energy released by respiration for a wide range of purposes: about 20% of the energy is used for brain metabolism, and much of the rest is used for the basal metabolic requirements of other organs and tissues. In cold environments, metabolism may increase simply to produce heat to maintain body temperature. Among the diverse uses for energy, one is the production of mechanical energy by skeletal muscle to maintain posture and produce motion.
   Certain drugs also may be associated with insulin resistance (e.g., glucocorticoids).
  
  The presence of insulin leads to a kind of insulin resistance; every time a cell is exposed to insulin, the production of GLUT4 (Glucose transporter type 4) on the membrane of the cell decreases somewhat. In the presence of a higher than usual level of insulin (generally caused by insulin resistance), this down-regulation acts as a kind of positive feedback, increasing the need for insulin. Exercise reverses this process in muscle tissue, but if it is left unchecked, it may contribute to insulin resistance.
   The metabolic rate can be affected by some drugs, such as antithyroid agents, drugs used to treat hyperthyroidism, such as propylthiouracil and methimazole, bring the metabolic rate down to normal and restore euthyroidism. Some research has focused on developing antiobesity drugs to raise the metabolic rate, such as drugs to stimulate thermogenesis in skeletal muscle.
  
  The metabolic rate may be elevated in stress, illness, and diabetes. Menopause may also affect metabolism.
  
  Section::::Cardiovascular implications.
   Excessive gain in body weight contributes to the metabolic syndrome, which may include elevated fasting blood sugar (or glucose), resistance to the action of insulin, elevated low-density lipoprotein (LDL cholesterol) or decreased high-density lipoprotein (HDL cholesterol), and elevated blood pressure. Although obesity by itself is not considered a disease, it increases the risk for Diabetes mellitus type II. Because body mass, fat mass and fat free mass all change exponentially during weight reduction, it is a reasonable hypothesis to expect that symptoms of metabolic syndrome will also adjust exponentially towards normal values.
  
  Section::::The plateau principle in compartmental modeling.
   Section::::Aerobic.
  
  In trained long term aerobic exercisers, basal levels are unchanged, or decreased. Acutely, endurance based aerobic efforts cause testosterone to rise.
   To prevent hyperglycemia and noticeable organ damage over time, the body produces insulin when glucose starts to be released into the bloodstream, primarily from the digestion of carbohydrates in the diet. Under normal conditions of insulin reactivity, this insulin response triggers glucose being taken into body cells, to be used for energy, and inhibits the body from using fat for energy, thereby causing the concentration of glucose in the blood to decrease as a result, staying within the normal range even when a large amount of carbohydrates is consumed.
   Metabolism involves two biochemical processes that occur in living organisms. The first is anabolism, which refers to the build up of molecules. The second is catabolism, the breakdown of molecules. These two processes work to regulate the amount of energy the body uses to maintain itself. During non-REM sleep, metabolic rate and brain temperature are lowered to deal with damages that may have occurred during time of wakefulness.
  
  Section::::Normal metabolism.
  
  After eating, the pancreas releases insulin. Insulin signals muscle and fat cells to absorb glucose from food. As a result, blood glucose levels return to normal.
   Although many factors influence insulin secretion, the most important control is the amount of glucose moving from the blood into the beta cells of the pancreas. In healthy people, even small rises in blood glucose result in increased insulin secretion. As long as the pancreatic beta cells are able to sense the glucose level and produce insulin, the amount of insulin secreted is usually the amount required to maintain a fasting blood glucose between 70 and 100 mg/dL (3.9–5.6 mmol/L) and a non-fasting glucose level below 140 mg/dL (7.8 mmol/L).
   BULLET::::- Food is transformed into reserve, which fuels all other metabolic processes. The feeding rate is proportional to the surface area; food handling time and the transformation efficiency from food to reserve are independent of food density.
   Changes in body temperature – either hotter or cooler – increase the metabolic rate, thus burning more energy. Prolonged exposure to extremely warm or very cold environments increases the basal metabolic rate (BMR). People who live in these types of settings often have BMRs 5–20% higher than those in other climates.
  
  Section::::See also.
  
  BULLET::::- Atwater system
  
  BULLET::::- Basal metabolic rate
  
  BULLET::::- Chemical energy
  
  BULLET::::- Food chain
  
  BULLET::::- Food composition
  
  BULLET::::- Heat of combustion
  
  BULLET::::- List of countries by food energy intake
  
  BULLET::::- Nutrition facts label
  
  BULLET::::- Table of food nutrients
  
  Section::::External links.
   Insulin signal transduction pathway
  
  The insulin transduction pathway is a biochemical pathway by which insulin increases the uptake of glucose into fat and muscle cells and reduces the synthesis of glucose in the liver and hence is involved in maintaining glucose homeostasis. This pathway is also influenced by fed versus fasting states, stress levels, and a variety of other hormones.
   Different water sports place different demands on the patient. Sailing might be thought of as long dry periods of sitting down — interrupted by unpredictable wet periods. Swimming laps is a great aerobic activity. Yet a toddler in a pool partially filled with water may get the most intense workout of any. Each situation demands that the pump user adjusts the basal rate. If a portion of the basal insulin is combined with a long-acting insulin there can be even more trial-and-error. This allows the pump to be removed for longer periods and blood glucose control is adequately maintained.
   Because the AMPK response to exercise decreases with increased training duration, many questions arise that would challenge the AMPK role with respect to biochemical adaptations to exercise and endurance training. This is due in part to the marked increases in the mitochondrial biogenesis, upregulation of GLUT-4, UCP-3, Hexokinase II along with other metabolic and mitochondrial enzymes despite decreases in AMPK activity with training. Questions also arise because skeletal muscle cells which express these decreases in AMPK activity in response to endurance training also seem to be maintaining an oxidative dependent approach to metabolism, which is likewise thought to be regulated to some extent by AMPK activity.
   The theory presents simple mechanistic rules that describe the uptake and allocation of energy (and nutrients) and the consequences for physiological organization throughout an organism's life cycle, including the relationships of energetics with aging and effects of toxicants. Assumptions of the DEB theory are delineated in an explicit way, the approach clearly distinguishes mechanisms associated with intra‐ and interspecific variation in metabolic rates, and equations for energy flows are mathematically derived following the principles of physics and simplicity.
  
  Cornerstones of the theory are:
  
  BULLET::::- conservation of mass, energy and time,
  
  BULLET::::- relationships between surface area and volume
   Acetylcholine stimulates muscle to raise metabolic rate.
  
  The low demands of thermogenesis mean that free fatty acids draw, for the most part, on lipolysis as the method of energy production.
  
  A comprehensive list of human and mouse genes regulating cold-induced thermogenesis (CIT) in living animals ("in vivo") or tissue samples ("ex vivo") has been assembled and is available in CITGeneDB.
  
  Section::::Regulation.
  