Measuring Energy in Food For Losing Weight While Pregnancy
Humans obtain energy from foods and beverages. Measuring the exact caloric, or energy, value of food can be achieved through direct calorimetry. In this method, a food sample is burned in a bomb calorimeter that measures the heat produced by measuring the change in temperature in the chamber. The heat is directly measured; therefore, this is considered a direct measure. The three macronutrients, carbohydrate, protein, and fat, have all been analyzed for their energy content using direct calorimetry, as have many combinations of macronutrients in common foods. In the late 1890s and early 1900s, W.O. Atwater and colleagues developed the Atwater general factor system, which was later modified in the 1950s to the Atwater specific factor system. Both Atwater factor systems provide estimates of metabolizable energy (ME), or the amount of energy that remains available to the body after accounting for losses attributable to incomplete digestion of food resulting in fecal and urinary losses, and small amounts lost from the body surface. Carbohydrate and protein have an energy or kcal value of 4.2 kcal/g, alcohol has 7.0 kcal/g, and fat has 9.4 kcal/g. Using the precise kilocalorie value for each macronutrient makes for tedious calculations, so they are rounded to the nearest whole number.
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• Carbohydrates = 4 kcal/g
• Protein = 4 kcal/g
• Alcohol = 7 kcal/g
• Fat = 9 kcal/g
Since these values are rounded, when they are multiplied by several factors, such as in the case of determining the caloric value of a meal, this could result in under- or overestimation of total calorie content. Food labels should also be viewed as estimates because, although the most accurate calorie value of a food would be measured via direct calorimetry, this is rarely the case. Few packaged and processed foods have been measured directly for their caloric content for many reasons, including cost of direct calorimetry, needed equipment, time constraints, and the impractical-ity of burning every manufactured food item. Instead, food processing software with comprehensive databases is used as a proxy to estimate the calorie value. This is considered an indirect measure because the actual food item is not being measured.
Even if direct calorimetry was used to measure every food product available, only the heat produced from food samples is being measured. Direct (or indirect) calorimetry cannot measure the amount of energy that is actually transferred to the body through the process of digestion, metabolism, and absorption; this amount cannot be directly measured. Given these limitations, calories should only be viewed as estimates. “Calorie counting” as a method to change body composition may result in over- or underestimation of actual caloric intake. People who try and count every calorie that they consume must realize they are only estimating their energy intake and are not getting an exact measurement. For example, packaged food items are allowed to be 10 percent higher or lower in kcal content than the value indicated on the nutrition facts; so even if you were able to count every calorie consumed, you may have over- or underestimated your caloric intake by more than 10 percent.
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