Calories and Weight Loss

Fat textureHow calories work?

I have briefly talked about how calories work and what’s the chemistry behind losing weight, but some of you asked me to try to explain it in another way.

This is simply mathematics. One kilogram (2 pounds) of fat is 7000 calories and according to the First Law of Thermodynamics, energy cannot be created nor destroyed, only converted from one form to another. This means that you have to find a way to transform the 7000 calories into energy. What that means for you is that in order to lose 1 kilogram of fat, you have to metabolize as energy 7000 calories more than you eat or drink.

This difference between energy used and your intake is called caloric deficit.

How to really lose weight?

To lose weight can be very simple if you focus on deficit from sports and eating. It’s not enough to just exercise and let your calorie intake get out of control or just diet (which in some unfortunate cases diet means to throw yourself into a fasting state to overcome the lack of sport). The goal is to create well-controlled caloric deficit between the energy you take in and the energy that you burn.

Your daily “caloric deficit” depends on all sorts of factors:

  • your height,
  • weight,
  • lean mass,
  • gender,
  • workout intensity,
  • portion sizes.

If you’re following the workouts and watch your diet you can have a target fat loss of as much as 0,5-1 kg (1 to 2 lbs) a week for women, and as much as 1-1,5 kg (2 – 3 lbs) a week for men. If you are not working out for 8h/day than don’t expect to lose more than 1,5-2 kg per week. If you do lose more, than watch your diet as you may be eating less than necessary. Most of the cases with great weight loss during one week are due to the lost of water and muscle, not fat.

How much caloric deficit?

This is the tricky part, which makes the difference between people that successfully lose weight and the ones that are always on a diet. Severe caloric restriction (less than 1000 calories) increase the level of “fat storing” enzymes (lipoprotein lipase) in the body, slows your metabolism down and causes muscle loss. The caloric deficit should be between 500-100, but be careful about severe caloric restriction.

I’m not losing weight as fast as I should

Studies show that when an increase in physical activity occurs, fat loss is generally smaller than expected, because people usually counter the extra activity by increasing their food intake (“Great workout. Let’s get a beer”). This is also the case with the people that turned to light Coke instead of regular.

What is the perfect number of calories?

There is no such thing. No matter how good you plan your exercises and your meals, your body will adapt. It’s not something you can control, it’s just “survival skills”. You should change your training routine at least every two weeks and your meals every day.

How to calculate your “Base Metabolic Rate” or BMR

Your body needs a certain number of calories to support your “Base Metabolic Rate” or BMR. A normal BMR is rarely less than 1100 calories a day, but as the caloric deficit, the BMR depends on the same factors.

Let’s try to estimate your BMR using the Harris Benedict Calorie Needs Formula

For Women

1. First, calculate your BMR according to this formula:

655 + (9.6 x weight in kilos) + (1.8 x height in centimeters) – (4.7 x age in years)

For Men

1.First, calculate your BMI according to this formula:

66 + (13.7 x weight in kilos) + (5 x height in centimetres) – (6.8 x age in years)

2. No matter if you are a woman or a man, in order to calculate your total calorie needs, multiply your BMR by the appropriate activity multiplier:

Activity Multiplier:

  • If you are sedentary (little or no exercise, desk job) multiply BMR by 1.2
  • If you are lightly active (light exercise/sports 1-3 days per week) multiply your BMR by 1.375
  • If you are mod. active (moderate exercise/sports 3-5 days per week) multiply your BMR by 1.55
  • If you take heavy exercise (hard exercise/sports 6-7 days per week) multiply your BMR by 1.725


  • eat small and frequent portions for fat loss
  • eat larger and frequent meals with a lot of activities for muscle gain
  • the choices you make about foods (lean meats and unprocessed fruits and vegetables) are playing a major role in your weight also.

RSS Trackback URL 9. August 2007 (15:24)
Filed under: Body, Diets, Fitness, Motivation, Nutrition, Weight loss by


  1. Ahd Akhtar

    8. July 2008 | 22:49 h

    again, the appropriate information for a training person. and I would like to say thanx, as i just calculated my base metabolic rate. because I don’t really think that most of the gym instructors wud be able to provide the formula for it . haha

  2. To Count Or Not To Count? | DietMotion

    8. September 2011 | 15:33 h

    [...] is an ongoing debate whether it is good to count calories or not during a diet, but also in [...]

Write a Comment

© 2007 - 2017 DietMotion | Entries RSS | Comments RSS