How Many Calories Should I Eat?

The number of calories people should eat each day depends on several factors, including their age, size, height, sex, lifestyle, and overall general health. A physically active male, aged 22 years, requires considerably more calories than a sedentary woman in her 70s.

Each country in the world have different measure to calculate how many calories we should eat each day. For the human body to remain alive, it requires energy. Approximately 20% of the energy we use is for brain metabolism. The majority of the rest of the body's energy requirements are taken up for the basal metabolic requirements - the energy we need when in a resting state, for functions such as the circulation of the blood and breathing.

If our environment is cold, our metabolism increases to produce more heat to maintain a constant body temperature. When we are in a warm environment, we require less energy. We also require mechanical energy for our skeletal muscles for posture and moving around.

Respiration, or specifically cellular respiration refers to the metabolic process by which an organism gets energy by reacting oxygen with glucose to produce carbon dioxide, water and ATP energy. How efficiently energy from respiration converts into physical (mechanical) power depends on the type of food eaten, as well as what type of physical energy is used - whether muscles are used aerobically or anaerobically.

As with how many calories you should consume each day, your ideal body weight depends on several factors, including your age, sex, bone density, muscle-fat ratio, and height.

• BMI (Body Mass Index) - some say BMI is a good way of working out what you should weigh. However, BMI does not take into account muscle mass. A 100-metre Olympic champion weighing 200 pounds (about 91 kilograms), who is 6 feet (about 1mt 83cm) tall, who has the same BMI as a couch potato of the same height, is not overweight, while the couch potato is overweight.

• Waist-hip ratio - this measurement is said to be more accurate at determining what your ideal weight should be, compared to BMI. However, waist-hip ratio does not properly measure an individual's total body fat percentage (muscle-to-fat ratio), and is also limited.

• Waist-to-height ratio - this new way of determining ideal body weight is probably the most accurate one available today. It was presented by Dr. Margaret Ashwell, ex-science director of the British Nutrition Foundation, and team at the 19th Congress on Obesity in Lyon, France, on 12th May, 2012. It is also a very simple calculation; easy for lay people to work out.