accounting for 15 percent of body heat loss); 3) Radiation (the transfer of heat through radiation to the environment, accounting for 60 percent of body heat loss); 4) Evaporation (the transfer of heat through the evaporation of water or sweat, accounting for 20 percent of body heat lost). The basal metabolic rate or BMR is the daily energy expenditure by humans at rest in the postabsorptive state and in a neutrally temperate environment. About 70 percent of all daily energy expenditure comes in the form of basal metabolic functions, 20 percent comes from physical activity, and 10 percent comes from body thermoregulatory processes. The BMR goes down when lean muscle mass is lost and with age.
NUTRITION AND METABOLISM The energy used and needed by the body involves what’s called the “nutritional calorie.” This is the amount of heat necessary to raise a kilogram of water by 1 degree Celsius. Approximately 1500-2000 calories per day are necessary to sustain daily activities—but it depends on body mass, gender, height, age, and activity level. More calories are required in situations of more activity. An extra 3500 calories per day are required to gain a pound of weight. The reverse is true when one wants to lose weight. Surprisingly, very little calories are burned in exercise. An example is jogging. One full mile of jogging will burn just 100 calories. Carbohydrates require the least amount of energy to process, while the processing of proteins requires the most energy. The balance of weight depends on what is taken in, how many calories are taken in, and how much energy is expended. The body mass index or BMI is a measure of the weight-to-height ratio and is a calculation used to determine a person’s level of obesity. A normal BMI is between 18 and 24.9 kg/m2. Being overweight involves a BMI of between 25 and 29.9 kg/m2, and being obese is a BMI of greater than 30 kg/m2. Being overweight or obese is associated with an increase in many types of diseases, ranging from type 2 diabetes to heart disease and certain cancers. Vitamins are a variety of organic molecules needed in biochemical processes but that are generally not synthesized de novo by the body. When it comes to metabolism, the B vitamins
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