Weight loss is a multifaceted journey, and tracking progress effectively is crucial for motivation and success. While the number on the scale provides a basic measure, understanding weight loss in terms of percentages, particularly the percentage of excess weight loss (%EWL), offers a more insightful perspective. This article delves into the concept of %EWL, its calculation, and its significance in assessing weight loss, especially in the context of bariatric surgery.
Introduction to Weight Loss Metrics
When individuals embark on a weight loss journey, various metrics can be used to track their progress. These include:
- Pounds or Kilograms Lost: The simplest measure, indicating the absolute amount of weight reduction.
- Body Mass Index (BMI): A ratio of weight to height, providing an estimate of body fat.
- Percent Weight Loss (%WL): The percentage of total body weight lost.
- Percent Excess Weight Loss (%EWL): The percentage of weight loss relative to an "ideal" BMI.
What is Percent Excess Weight Loss (%EWL)?
Percent Excess Weight Loss (%EWL) is a metric primarily used in bariatric surgery to describe the percentage of weight lost relative to achieving an "ideal" BMI. It essentially quantifies how much of the weight exceeding a healthy range has been shed. A BMI of 25 kg/m2, the upper limit of a "normal" BMI, is frequently used as the target, but other standards, including race-specific BMI standards or other “ideal weights” according to the Metropolitan Life Insurance Company life tables, may also be used to represent “normal.”
How to Calculate %EWL
To calculate %EWL, you need the following information:
- Starting Weight: The patient's weight before the weight loss intervention.
- Current Weight: The patient's weight after the weight loss intervention.
- Ideal Weight: The weight corresponding to a BMI of 25 kg/m2 (or another chosen "normal" BMI) for the patient's height.
The formula for %EWL is:
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%EWL = ((Starting Weight - Current Weight) / (Starting Weight - Ideal Weight)) x 100## Step-by-Step Example:
- Determine the patient's starting weight: Let's say it's 120 kg.
- Determine the patient's current weight: Let's say it's 90 kg.
- Calculate the ideal weight: If the patient's height is 1.7 meters, the ideal weight (BMI of 25) would be 25 x (1.7)^2 = 72.25 kg.
- Apply the formula: %EWL = ((120 - 90) / (120 - 72.25)) x 100 = (30 / 47.75) x 100 = 62.8%.
In this example, the patient has lost 62.8% of their excess weight.
Significance of %EWL
- Assessing Bariatric Surgery Success: %EWL is a key indicator of success after bariatric surgery. It provides a standardized way to evaluate the effectiveness of the procedure in helping patients achieve a healthier weight. The commonly cited minimum 50% EBWL for “success” after bariatric surgery is thus a reinterpretation of the method proposed by Reinhold, and remains a somewhat arbitrary target for “success.”
- Comparison Across Individuals: %EWL allows for a more meaningful comparison of weight loss outcomes between individuals with different starting weights and heights.
- Clinical Relevance: It represents the extent of a patient’s travel from their baseline weight to a “normal” weight.
Limitations of %EWL
- Arbitrary "Ideal" Weight: The concept of an "ideal" weight based on a fixed BMI can be somewhat arbitrary, as individual health and body composition vary.
- Doesn't Account for Body Composition: %EWL, like BMI, doesn't differentiate between fat mass and muscle mass.
- Potential for Misinterpretation: Focusing solely on %EWL may not provide a complete picture of a patient's overall health and well-being.
Alternatives to %EWL
While %EWL is a valuable metric, it's essential to consider other measures of weight loss and health improvement, including:
- Percent Total Body Weight Loss (%TBWL): This is how much of your overall body weight you’ve lost. Most modern research now prefers %TBWL because it is easier to compare across patients, regardless of their starting BMI. It’s also a better predictor of long-term health benefits.
- Improvements in Metabolic Health: Changes in blood pressure, cholesterol levels, blood sugar control, and other health markers.
- Increased Physical Activity: Improvements in fitness, strength, and endurance.
- Enhanced Quality of Life: Subjective improvements in mood, energy levels, and overall well-being.
The Role of Preoperative BMI (pBMI)
Preoperative BMI (pBMI) is one of the strongest known predictors of WL after RYGB when weight is characterized as pounds/BMI lost, final weight or BMI, or %EBWL. Despite these associations, however, pBMI is not a sufficiently powerful predictor to drive most clinical decision-making, as patients with higher initial BMIs lose less %EBWL yet benefit immensely from RYGB and thus would not be strongly contraindicated for surgery.
%WL: An Alternative Metric
Percent weight loss (%WL) was calculated by dividing the absolute pounds lost by the patient’s initial weight and is statistically interchangeable with percent BMI change. In this study we found that percent weight loss (%WL) has substantial advantages as a metric for characterizing weight loss after RYGB. Relative to other WL parameterizations, including pounds or BMI units lost, attained weight or BMI, and %EBWL, %WL is least associated with baseline BMI.
Practical ways to track improvements in your health
More practical ways to track improvements in your health include:
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- measuring how much your strength has increased if you’ve been exercising
- checking how clothes fit you (perhaps you’ve changed the notch on your belt)
- thinking about whether you feel fitter or have more energy
- looking at how much you’ve improved your diet
Weight Loss and BMI Calculator
Dr. Belsley uses this calculator during his office consultation to help provide information regarding diet, nutrition and estimates for surgical weight loss. Although these estimates are consistent with accepted norms in the surgical literature, nothing is guaranteed nor implied with you using this calculator. A small part of the equation is the actual operation. You must be committed to diet, exercise and life-change if you wish to have a lasting result. Body mass index (BMI) is an estimate of unhealthy body weight based on height and weight that applies to both men and women. Your doctor can talk to you about your BMI, waist measurement, and risk factors.
Benefits of Weight Loss
According to the CDC, even a modest weight loss of 5-10% of your total body weight can be good for your health and lead to benefits, such as lower blood pressure, cholesterol, and blood sugar. They recommend aiming to lose 1-2 pounds per week. This approach, they say, is more likely to lead to success than trying to lose weight quickly. How much of your body weight percentage this is equal to depends on your current weight.
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