Basic Calorimeter Design
To lose weight, most people think they have to start counting calories. It’s true that losing weight is essentially about burning more calories than you take in. To do that, of course you need to know just how many calories you’re eating. However, the amounts of calories in food, as listed on food labels and in virtually every available reference, are determined using a calorimeter, a device invented over a century ago.
Tracking food intake
Today we know that the results obtained with a calorimeter are often overestimated. This is because the total calories a person gets from food are affected by many variables, including the degree to which a food is processed, the degree to which food is chewed, the energy required for digestion and an individual’s ability to utilize the calories that are absorbed, rather than excreted.
Understanding that calorimeters are fallible, the Department of Agriculture (USDA), which regulates the content of nutrition facts on food labels, allows calorie counts a plus or minus 20 percent margin of error. But even though calorie counts are flawed, they’re still useful for keeping track of your food intake. Counting calories makes you aware of the quality of your diet and helps you be accountable for your food choices.
How many calories do you need?
The first thing you need to know about counting calories is how many calories you need, or your Total Energy Expenditure (TEE). Your Resting Energy Expenditure (REE) is about 70 percent of your TEE. The Thermic Effect of Food (TEF) you eat accounts for about 10 percent. Physical activity accounts for about 20 percent of TEE.
Resting Energy Expenditure
One of the most accurate tools most often used by dietitians to calculate REE is called the Mifflin/St. Jeor equation:
Men: (10 x weight in kg) + (6.25 x height in cm) – (4.92 x age) + 5
Women: (10 x weight in kg) + (6.25 x height in cm) – (4.92 x age) – 161
Physical Activity Factor
The calories burned from physical activity can be accounted for by applying a multiplier to the result of the Mifflin/St. Jeor equation:
REE x 1.2 – Sedentary (little or no exercise, desk job).
REE x 1.3-1.4 – Lightly Active (light exercise 3-5 days/week).
REE x 1.5-1.6 – Moderately Active (moderate exercise 3-5 days/week).
REE x 1.7-1.8 – Very Active (rigorous exercise 6-7 days/week).
Thermic Effect of Food
Accounting for TEF results in an estimation of TEE:
REE x Activity Score x 1.1 (TEF) = TEE
Total Energy Expenditure
Our hypothetical 38 year-old female weighs 170 pounds (72.7 kg) and is 5’-7” (170 cm). She has a desk job and is sedentary.
REE = (10 x 77 kg) + (6.25 x 170 cm) – (4.92 x 38 years) – 161 1,485 calories
TEE = 1351 x 1.2 x 1.1 1,960 calories
Our hypothetical person requires about 2,000 calories to maintain her current weight. To lose weight she would need to increase her level of physical activity, as well as decrease her amount of daily calories. The good news is that cutting calories doesn’t necessarily mean eating less. The trick is to choose more foods that are nutrient dense—such as fruits and vegetables—instead of calorie dense (fast foods, processed foods).
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