For most of us, losing weight in an inexact science.  Weigh yourself on any two consecutive days, and you'll find your reported weight bounces around like the price of a share on the stock market.

Surprisingly, however, scientists do understand the mechanism of weight loss rather well, and in fact, this detailed understanding which science now has allows us to predict the pattern of your weight loss with some degree of relative accuracy.

Daily fluctuations

To begin with, for the most consistent results possible it is best to weigh yourself at a similar time of day.  Establish for yourself a pattern.  Certainly our bodies do, and it is this pattern we are trying to tap into in order to reap the most meaningful results.  We're lightest first thing in the morning, and "put on weight" progressively throughout the day.  Hence, by weighing yourself, say, first thing of a morning, you immediately remove the effect of fluctuations caused by weight changes throughout the day.  In fact, first thing in the morning will generally give you the most consistent results.

So why are we lightest in the mornings, and why does our weight fluctuate so wildly between daily weigh in?  Well, it all related to the amount we consume in food and liquid, primarily water.  What you eat and drink has a very measurable mass.  Eight glasses of water weighs two kilograms, or approx 4.4 pounds.  Add to that several pounds of food a day, and you can see that it's virtually impossible to remain at a constant weight for any length of time.  You can expect a daily weight fluctuation in the order of about 3 kilos or around 6 pounds.  These fluctuations shouldn't bother you and have no bearing on your overall long term weigh loss or gain.

Doing the math

Other than natural daily weight fluctuations caused by the consumption and expulsion of food and liquid, weight loss is a function of the amount of Calories or kilojoules you consume minus the amount your body uses in exercise and in maintaining functions like heating itself and keeping your brain and other body organs working efficiently.  Surprisingly, we can actually fairly accurately predict what this base rate of energy consumption will be.  Your basal metabolic rate is the amount of energy your body will burn if you lay about on the couch with your remote watching TV soaps all day long.

We then add to that the amount of energy you would typically consume catching the train, walking up the stairs to work, walking out to a cafe at lunch time, and finally arriving home to put up your feet for the 6 o'clock news.  A typical daily energy usage for a normally active person comes in around 2000 Calories or 8360 kilojoules.

Of course, being someone concerned about your body image, you may well add some specific exercise to your daily routine, perhaps walking the dog, or taking in a quick hit of tennis. 

The equation now becomes the amount of energy eaten minus the amount of energy expended in normal living minus the amount of energy used in exercise.  The resulting surplus or deficit (we hope) measured in Calories will tell you fairly accurately the amount of body weight you are likely to gain or lose over the period of a week or several months.

To simplify all of this, a tool such as the one found in the Weight Loss International Slim for Life Program can do the math for you, and give you a prediction of how much weight you will lose, and what you will weigh next week, this time next month, or on a certain date in six months time.

All this can be fairly handy if you're planning to squeeze into that bridesmaid's dress or new suit, or merely have to look fit when the old school chum comes over to visit to reminisce about the good old days.