How many calories do I burn every day?
The energy in food and beverages is the only contributor to the “energy in” side of the energy balance equation. Now when you’re familiar with calculating the energy value of foods (daily energy or caloric intake) it’s time to look at the “energy out” side of the energy balance equation. This article discusses about the components of energy expenditure. Some components (factors) of energy consumption contribute more to total energy consumption than others. It is, therefore, crucial to identify such components as well as the ways to manipulate with them in our favour. Figuring out how many calories you burn every day is a must if you want to get a clear picture of whether you’re approaching toward or moving away from your goals. Only after comparing these two values (calories in; calories out) you’ll know exactly where you stand.
Components of energy expenditure
Factors that affect energy consumption (calorie burning) are as follows:
- Basal metabolic needs (basal metabolic rate: BMR);
- Food intake effect (thermic effect of food: TEF);
- Energy expenditure of physical activity (activity thermogenesis: AT);
TOTAL ENERGY EXPENDITURE (CALORIES BURNED) = BMR + TEF + AT
Basal metabolic needs
The concept is really simple. Basal metabolism is measured in terms of basal metabolic rate (BMR). Basal metabolic rate is the energy expended when an individual is lying at complete rest (but awake), in the morning, after sleep, in a room at a comfortable temperature and in the postabsorptive state.
In a nutshell, it is the rate at which the body expends energy for life sustaining activities that take place all the time without the person’s conscious awareness. These activities include: inhaling and exhaling of air, beating of the heart, maintenance of body temperature, work all of the organs in our body, etc.
We express this rate in kcalories per kilogram of body weight per hour.
Basal metabolism in normally the largest part of a person’s daily energy expenditure. In individuals with sedentary occupations basal metabolic rate accounts for ~ 60% (about two-thirds) of total daily energy expenditure.
The table below summarizes the factors that affect (raise and lower) the BMR.
|Factor||Effect on BMR|
|Age||Lean body mass diminishes with age, slowing the BMR.|
|Height||In tall, thin people, the BMR is higher.|
|Growth||In children, adolescents, and pregnant women, the BMR is higher.|
|Body composition (gender)||The more lean tissue, the higher the BMR (which is why males usually have a higher BMR than females). The more fat tissue, the lower the BMR.|
|Fever||Fever raises the BMR|
|Stresses||Stresses (including many diseases and certain drugs) raise the BMR.|
|Environmental temperature||Both heat and cold raise the BMR.|
|Fasting/starvation||Fasting/starvation lowers the BMR.|
|Malnutrition||Malnutrition lowers the BMR.|
|Hormones (gender)||The thyroid hormone thyroxin, for example, can speed up or slow down Ihe BMR. Premenstrual hormones slightly raise the BMR.|
|Smoking||Nicotine increases energy expenditure.|
|Caffeine||Caffeine increases energy expenditure.|
|Sleep||BMR is lowest when sleeping.|
Calculating basal metabolic rate:
You can obtain very good estimation of your basal metabolic needs on the following way:
BMR for men: 1 kcal x kg body weight x 24 = kcal/day
BMR for women: 0.9 kcal x kg body weight x 24 = kcal/day
To convert pounds (lb) to kilograms (kg), divide pounds by 2.2.
The Harris-Benedict equation provides a more precise, although still imperfect, approximation.
Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)
Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)
In these two equations weight is measured in kilograms, height in centimeters, and age in years. The result is in kcal/day.
For instance, for a 45-year-old woman who is 5 foot 4 (or 64 inches) and 150 pounds the BMR would work out to 1.386,83 calories. For a man of the same age, with the same height and weight, the BMR would work out to 1.526,45 calories, a difference equal to about one small chocolate chip cookie.
This calculation tells you the amount of energy you’d burn without eating and exercising. It, therefore, reveals your basic calorie needs – the caloric cost of being you.
Food intake effect (thermic effect of food)
The second component of energy expenditure is the thermic effect of food (energy to manage food). The muscles that move the food through the intestinal tract speed up their rhythmic contractions. The cells that manufacture and secrete digestive juices begin their tasks. All these and other cells need extra energy. After eating, food stimulates the metabolism and requires extra energy for the digestion, absorption, transportation, and storage of nutrients to the cells. This effect varies with the kind and amounts of food you eat and your metabolic needs. The use of nutrients to build new tissue requires more energy than the breakdown of nutrients to provide energy. The thermic effect of food varies from about 10 to 15% of total energy needs.
For purposes of rough estimates, though, the thermic etfect of food is not always included. We’re also not going to include this component when calculating total daily energy expenditure. Why? For most purposes, you can simply ignore this effect when estimating energy expenditure. Its contribution to total energy output is smaller than the probable errors involved in estimating overall energy intake and output. Therefore, in most cases, the TEF of your diet is small enough that it’s not even worth counting.
Energy expenditure of physical activity
The third component of energy expenditure is the energy expenditure of physical activity, ”activity thermogenesis.”
To determine your energy needs for physical activity, you can keep records of every activity you perform during the day and the time spent engaging in each activity. This is for sure not very practical. This table (energy expenditure per pound per hour during various activities) will be of great help if you decide to use this approach. You will have to multiply the activity factor by the weight in pounds by the fraction of hour spent performing the activity. You will have to repeat the process for each activity you perform during the day and then add all these numbers together.
An easier, but less precise way to estimate your energy expenditures for physical activity is to use the following “rule of thumb.” Choose the category of physical activity in table below that best describes your usual physical activity level. For example, if you spend most of your day sitting while taking classes, studying, and watching TV, you probably have a sedentary level of activity. If you sit some of the time but move around while working, you might rate your level of physical activity as light. If you are on your feet most of the time and engage in strenuous work such as lifting heavy
objects, you are probably expending energy at the heavy level of intensity.
Physical activity factor (PA):
|Intensity||Physical activity||Activity factor for men||Activity factor for women|
|Very light||Standing; sitting, driving, typing, sewing, cooking, playing cards or a musical instrument||1.3||1.3|
|Light||Walking on a level surface at 2.5 to 3.0 mph, carpentry, child care, golf, sailing, table tennis||1.6||1.5|
|Moderate||Walking 3.5 to 4.0 mph, gardening, carrying a load, cycling, skiing, tennis, dancing, walking and exercise 2-3x weekly||1.7||1.6|
|Heavy||Walking uphill carrying a load; digging by hand; playing basketball, football, or soccer; climbing; exercise hard more than 3x weekly||2.1||1.9|
|Exceptionally heavy||Athlete training or participation in professional or world-class events; exercise hard daily||2.4||2.2|
In this final step we simply have to add together all the components of energy expenditure. Therefore, your estimated energy requirement (in kcal) per day is the sum of your body’s three uses of energy, which are as follows: basal metabolic rate, thermic effect of food, and physical activity.
- Calculate your basal metabolic rate (BMR);
- Determine your physical activity factor (PA);
- Multiply your basal metabolic rate by your physical activity factor
The resulting number is the approximate daily kilocalorie intake to maintain current body weight.
A 29-year-old man weights 180 lb (82 kg), is 6 feet tall (183 cm), and eats an average of 3.700 kcal/day while maintaining moderate active lifestyle (he exercises 2-3x weekly). Calculate his daily energy expenditure (energy output).
BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years) = 88.362 + (13.397 x 82) + (4.799 x 183) – (5.677 x 29) = 1.901 kcal/day
Total energy expenditure = BMR x physical activity factor = 1.901 kcal/day x 1,7 = 3.232 kcal/day.
Result: this men will tend to gain weight with his current exercise and meal plan, because he is consuming 468 kcal more than he is expending. Because 1 lb (0,45 kg) of body weight equals approximately 3.500 kcal, he will gain approximately 1 lb (0,45 kg) every 7 days with the preceding eating and exercise routine.
Summing up: Components of energy expenditure
There are three principal components to energy expenditure in humans: (1) basal metabolic rate, (2) thermic effect of food, and (3) and the energy expenditure of physical activity.
The amount of energy spent in a day differs for each individual, but in general, basal metabolism is the largest component of energy expenditure, and the thermic effect of food is the smallest. The amount spent in voluntary physical activities has the greatest variability, depending on a person’s activity patterns. For a sedentary person, physical activities may account for less than half as much energy as basal metabolism, whereas an extremely active person may expend as much on activity as for basal metabolism.
Estimating calories burned is not so easy do. Most people overestimate their calorie burn – often by a lot. If you don’t see the desired results over some reasonable time period, it’s probably time to check your calculations.