Fatcalc.com

Weight Loss Calculator and Planner to Reach Your Goal Weight

Use this weight loss calculator and planner to help you reach your goal weight within a realistic time frame and maintain it. The calculator is based on formulas developed by the National Institute of Health. It can determine the calories you would need to consume daily, over a specified period of time, to reach your goal weight.

Alternatively, you can specify a daily dietary calorie intake that's workable for you and it will calculate how long it would take to reach your goal weight.

The results of the calculations will show your projected weight loss or gain over time.

Weight Loss Calculator

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Enter your body parameters and your goal weight. If you don't know your activity level, click the Estimate button for an estimation.

Select the Energy option and enter a start date and end date if your want to calculate the average daily energy intake you would need to reach your goal weight within that time frame.

Select the Time option and enter a start date and your planned daily energy intake to calculate an estimation of when your goal weight will be reached with that dietary intake.

Click Calculate and the results will be presented in tabular and graphic formats. If your goal weight is less than your current weight, the graphics view will also include a chart series of your weight projections at starvation level (0 Calories) and at 1,000 Calories per day. Consult a doctor for guidance and support if you are considering a diet of less than 1,000 Calories (4,200 kilojoules) per day. Food group targets and nutrient recommendations will not be met below that level.

What is the science behind weight loss?

A change in body weight results from the difference between your food energy intake and the amount of energy expended by your body. Energy is burned in maintaining your body functions and in performing physical activities. For successful weight loss to occur, there must be an energy imbalance such that your energy expenditure is greater than your energy intake.

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Can I lose a pound a week if I eat 3500 fewer calories?

It is a myth that by reducing your weekly energy intake by 3500 calories, you will lose 1 lb of weight a week. This is sometimes referred to as the 3500 calories per pound rule. It does not take into account the physiological changes that occur during weight loss, your sex, age and initial weight. The amounts of body fat and muscle tissue both change with an energy imbalance. When you reduce your energy intake, muscle mass is lost along with fat mass and muscle burns more energy than fat. In general, as you lose weight, so does your body's ability to burn calories.

As an example, if you were to take in 500 less calories a day (3,500 calories a week), you would lose 1 lb a week according to the rule. So if you were planning on losing say 25 lbs, it would take you 25 weeks to do so. This is clearly wrong. According to the Hall's model, it would actually take over 37 weeks if you were a 34 year old, 6 foot sedentary male initially weighing 250 lbs. Actual times would vary somewhat depending on sex, age, height and initial weight.

About the Calculations

Calculations incorporated into this app are based on the model developed by Kevin Hall, Ph. D., and a team of researchers at the National Institute of Health. It is much more accurate in determining energy expenditure and energy requirements for the purpose of weight management. It challenges the 3,500 calories per pound rule by taking into consideration the physiological changes that take place during weight loss. This includes changes in body fat, muscle mass, the thermic effects of feeding, glycogen levels and sodium intake.

Along with your sex, age and basic body measurements, the model requires your body fat percentage. The calculator roughly estimates it through a formula derived from research by Jackson et al on estimating percentage body fat from body mass index.

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Your resting metabolic rate (RMR) or resting energy expenditure (REE) value is also required. The terms RMR and REE are generally used interchangeably and is a measurement of the energy burned by your body to keep it functioning while at rest. Both RMR and REE are usually measured by means of indirect calorimetry gas analysis. Such measurements can be taken at health clubs and some medical clinics but can be expensive and inconvenient. This calculator roughly estimates it for you through a predictive Mifflin-St Jeor formula based on your height, weight, age and sex.

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References

  1. Quantification of the effect of energy imbalance on bodyweight.
    Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA.
    Lancet (2011 Aug 27) 27;378(9793):826-37.
  2. The effect of sex, age and race on estimating percentage body fat from body mass index.
    Jackson et al
    International Journal of Obesity (2002) 26, 789–796
  3. A new predictive equation for resting energy expenditure in healthy individuals.
    M D Mifflin, S T St Jeor, L A Hill, B J Scott, S A Daugherty, Y O Koh
    The American Journal of Clinical Nutrition, Volume 51, Issue 2, February 1990, Pages 241–247