What is a calorie?
A calorie is a unit of energy, more precisely, a calorie is the amount of heat energy needed to raise the temperature of one gram of water by one degree centigrade, from 14.5 to 15.5 degrees at one unit of atmospheric pressure. You can think of calories as the energy needed to fuel our bodies – maintain our body temperature, digest our food, move our muscles, and make our brains function.
How are the calories in food measured?
Calories are determined by the use of an instrument, a calorimeter. The food is completely burned in the presence of oxygen and carbon dioxide and water to determine the gross energy of the food. How much of the gross energy that is used by your body is called the metabolizable energy. Energy in food comes from carbohydrates, protein, fats, and alcohol; vitamins, minerals, and trace elements do not contain energy or calories.
What is BMR?
Although BMR varies from person to person, using prediction equations, we can calculate BMR based on a few factors – sex, age, height and weight. BMR stands for basal metabolic rate and it is the calories your body requires to sustain metabolic activities of the body, such as blood circulation, breathing, digesting and absorption, and urinating. BMR is a large part, about 70%, of what your body expends each day. BMR is affected by age – when we are young, we have a higher BMR and as we age, our BMR declines; women have a lower BMR than men because men have more metabolically active muscle than women.
By factoring in your daily activity to your BMR, you can determine how many calories you need each day to maintain your current weight, or your daily calorie needs.
How many calories do I need to lose weight?
You have already calculated your daily calorie needs (question above) – those are the calories that will maintain your weight. To lose weight, you will need to eat fewer calories than your daily calorie needs and/or increasing your physical activity and exercise. A suggestion is to cut your calorie intake by 250 to 500 calories a day, which should result in about a ½ to 1 pound weight loss per week, at least initially. Even a small deficit of 50 to 100 calories a day will lead to weight loss over time.