From the Guidelines
The recommended formula for calculating lean body weight is that of Janmahasatian et al., where for men, LBW (kg) = 6680 + (216 BMI (kg.m²)) - 9270 TBW (kg) is not accurate, and the correct formula is LBW (kg) = 6680 + (216 BMI (kg.m²)), and for women, LBW (kg) = 8780 + (244 BMI (kg.m²)) - 9270 TBW (kg) is not accurate, and the correct formula is LBW (kg) = 8780 + (244 BMI (kg.m²)) 1. To calculate lean body weight using this formula, you need to know the patient's BMI and total body weight. The formula provided by Janmahasatian et al. is considered one of the most widely used for calculating lean body weight, especially in the context of anesthesia and drug dosing, as it takes into account the patient's body mass index (BMI), which is a key factor in determining lean body mass 1. Key points to consider when using this formula include:
- The formula is specific to men and women, reflecting the physiological differences in body composition between the sexes.
- Lean body weight is crucial for determining appropriate medication dosages, particularly for drugs that do not distribute well into fat tissue.
- The calculation of lean body weight is essential in clinical settings, such as anesthesia, where accurate dosing is critical to prevent complications like accidental awareness during anesthesia 1. It's also important to note that, regardless of total body weight, lean body weight rarely exceeds 100 kg in men and 70 kg in women 1.
From the Research
Lean Body Weight Formulas
The recommended formulas for calculating lean body weight are based on various studies, including:
- A study published in the British journal of clinical pharmacology 2 which evaluated the ability of the lean body weight equation to predict dual-energy X-ray absorptiometry (DXA)-derived fat free mass in older community-dwelling males.
- A study published in The British journal of nutrition 3 which developed and validated practical anthropometric prediction equations for lean body mass, fat mass, and percent fat in adults.
- A study published in Annals of human biology 4 which developed and validated equations to predict lean body mass in children and adolescents across the entire range of the adiposity spectrum.
Key Findings
Some key findings from these studies include:
- The use of anthropometric measures such as height, weight, and waist circumference to predict lean body mass 3.
- The development of sex-specific equations to estimate lean body mass from height, weight, age, body mass index (BMI) for age z-score, and population ancestry 4.
- The evaluation of the Duffull-Green lean body weight equation in adults across a wide body mass index (BMI) range 5.
Formulas
Some of the formulas mentioned in the studies include:
- IBW = 22 x H2, where H is equal to patient height in meters 6.
- The Duffull-Green lean body weight equation, which was found to be a predictor of lean body mass in a patient population with a wide range of BMIs 5.
- The Heitmann and Deurenberg equations, which were evaluated for their ability to predict DXA-derived fat free mass in older community-dwelling males 2.
Predictive Ability
The predictive ability of these formulas varies, with some studies finding high predictive ability for lean body mass 3, 4 and others finding significant bias 2. Overall, the choice of formula will depend on the specific population and context in which it is being used.