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Lean Body Mass (LBM) for Women Over 40: What It Is and Why It Beats Scale Weight

During the 40s, women experience a decline in the reproductive hormone estrogen that results in menopause symptoms and physiological changes. During this time, fat storage shifts from the thighs and hips toward the abdomen, while there is a decrease in muscle, bone, and organ mass, which impacts energy expenditure.

Research shows that energy expenditure is divided into the following categories:

• Resting metabolic rate: 60–80%
• Thermic effect of meals: 10%
• Non-exercise activity thermogenesis (NEAT)/Exercise: 20–50%

Studies highlight that a greater lean body mass, which means greater energy expenditure, as it requires more energy to maintain.

However, when this declines, it can have a major impact on your resting metabolic rate, with sources indicating a 1–2% decline in resting energy expenditure (resting metabolic rate) per decade.

From the outside, this can appear simply as unwanted weight gain, leading many women to focus on the scales, leading many to adopt unhealthy weight loss practices, which deprive the body of vital nutrients, worsening health concerns.

Monitoring lean body mass, on the other hand, provides a deeper understanding of how the decline of hormones affects the body. When these areas are addressed, they can not only improve weight loss but also bone mass, strength, and metabolic health.

LBM Calculator for Women: Required Inputs and Outputs

The LBM calculator for women provides valuable insights to help you achieve your goals. Below, we highlight the required inputs and the results to expect when using this calculator.

Inputs

The LBM calculator uses weight, body fat % (or unknown), age, and activity levels to determine your LBM and basal metabolic rate (BMR).

• Weight: Identifies total body weight
• Body Fat % (Or “Unknown”): Used to determine fat to muscle ratio
• Age: Influences energy expenditure
• Activity (Female Preset): Influences energy expenditure:

Outputs

The calculator will provide you with the following outputs, including:

• LBM (kg/lb)
• Protein/day from LBM
• BMR via Katch–McArdle
• Optional goal-based macros

The Math Behind the Tool (Explained Simply)

Using the information you provide, the LBM calculator determines LBM, Basal metabolic rate, and protein targets. Below, we provide a brief explanation of how these are calculated.

LBM

Lean body mass is calculated using the following formula:

• Body Weight (kg) × (1 − Body Fat %) = LBM

Here is an example for an 80 kg woman with 35% body fat:

• 80 kg x (1 - 0.35) =
• 80 kg x 0.65 = 52 kg

This person has 52 kg of lean mass (muscle, bone, organs, fluids) and 28 kg of fat mass.

BMR (Katch–McArdle)

The Katch-McArdle method is used to determine a person's basal metabolic rate (BMR), which is the number of calories (kcal) your body burns at rest.

• 370 + (21.6 × LBM (kg)) = BMR

Here is an example using the results from above

• 370 + (21.6 x 52 kg) = BMR
• 370 + 1123.2 = 1493.2 kcal/day

Using this calculation, we have determined that an 85 kg woman with 35% body fat has a BMR of 1493.2 kcal/day

Protein Target

The calculator will use this data to determine your protein target using the following formula.

• 1.6–2.2 g × LBM (kg) (favor upper range for training in midlife)

Here is an example using the results above.

• 2.0 x 52 kg (LBM) = 104 g/day

This means that the women will require 104 grams of protein per day.

Estimating Body Fat % When You Don’t Know It (Women 40+)

Estimating your body fat percentage can be done using several methods, including the BIA scale, tape/circumference, skinfold calipers, and DEXA scan. Below, we describe how each works, the pros, and cons of each method.

BIA Scale (Bioelectric Impedance Analysis)

The BIA scale is a scale with two handles that sends a harmless electrical current through the body. Lean mass conducts better than fat. The scale analyzes the current to determine the total body fat.

• Pros: Quick, easy, and non-invasive like a set of scales.
• Cons: Does not account for hydration and food intake, which can alter results
• Tips: Improve accuracy by measuring under the same conditions each time, such as morning, before food or drink.

Tape/circumference

Measures the circumference of the waist, neck, hips, and thigh, and using a formula, estimates a fat percentage.

• Pros: Inexpensive, requiring only a tape measure.
• Cons: Requires precision and can be less accurate for individuals with atypical fat distribution.
• Tips: Measure the same spots, with the same posture, at the same time of day.

Skinfold Calipers

Measure the thickness of skinfolds at specific sites, including the triceps, hip, and thigh.

• Pros: Accurate when performed by a trained professional.
• Cons: Requires a skilled professional; pinch technique errors can affect results.
• Tips: Use the same professional, caliper sites, and precise technique each time.

DEXA (Dual-Energy X-ray Absorptiometry)

Measure body fat using X-rays to distinguish fat, muscle, and bone.

• Pros: Highly accurate and regarded as the gold standard, and provides bone density reading.
• Cons: Performed in a clinic or lab, which can be expensive.
• Tips: Complete occasionally for baseline reading.

Turn Your LBM Into Daily Protein and Simple Macro Targets

Now that we have determined your lean body mass, you can use it to create protein and macronutrient targets to meet your goals. Below, we discuss goals including fat loss, recomposition, and muscle gain, including calorie and macronutrient recommendations.

Fat Loss

Fat loss requires a calorie deficit (consuming fewer calories than your BMR) and a greater focus on protein intake to improve fullness and preserve muscle mass.

During fat loss, intake needs to be around 2.0–2.3 g of protein per kilogram of LBM. To compensate, carbohydrate intake is lowered, while fat intake is maintained for hormone regulation. Alongside this, we suggest walking 7,000 steps/day to increase energy expenditure.

Calorie and Macro Recommendations

• Calories: Calorie deficit
• Carbohydrates: 40% of daily calorie intake
• Protein: 30–35% of daily calorie intake
• Fats: 25–30% of daily calorie intake

Professional Tips

If you experience plateaus with weight loss, BMR may be altered due to the decrease in body mass. We recommend recalculating your BMR and establishing a calorie deficit to continue fat loss.

Recomposition

Body recomposition refers to the process of simultaneously building muscle and losing fat. Like fat loss, recomposition requires a calorie deficit, an increase of protein of 2.0 g/day, and a lowering of carbohydrates while maintaining fat intake.

However, the difference here is that it requires resistance training 2–3 times per week to build muscle, and 7,000 steps/day to increase energy expenditure.

Calorie and Marco Recommendations

• Calories: Calorie deficit (200–400 kcal)
• Carbohydrates: 40% of daily calorie intake
• Protein: 30% of daily calorie intake
• Fats: 30% of daily calorie intake

Professional Tips

If progress begins to stall, consider adjusting calorie intake, increasing daily steps, and changing your resistance program.

Muscle Gain

Building muscle requires a calorie surplus (consuming more calories than your BMR). However, unlike fat loss and recomposition, it requires a higher carbohydrate intake to fuel resistance training sessions.

Alongside this, resistance training sessions should be performed 2–4 times per week to progressively overload muscle tissue to promote muscle growth.

Calorie and Macro Recommendations

• Calories: Calorie surplus
• Carbohydrates: 45–50% of daily calorie intake
• Protein: 25% of daily calorie intake
• Fats: 25–30% of daily calorie intake

Professional Tips

During hypertrophy training, mass and strength can plateau. If this happens, consider modifying your existing training program, nutrition, and training schedule. We recommend trying split programming to increase training volume, which research shows enhances growth.

Worked Examples You Can Follow Today

Begin using the lean body mass calculator today. Below, we discuss the steps for beginners, intermediate, and advanced users to start achieving their goals.

Beginner – (Estimated Body Fat %)

Beginners can start by estimating their body fat percentage by using a mirror or by using online comparison charts. This method is convenient, non-invasive, and can be done instantly.

While it may not be 100% accurate, it will provide a ballpark figure, and you can take the following steps to start:

Example

• Estimate: 80 kg woman, approx. 35% body fat.
• LBM: 80 x (1-0.35) = 52 kg.
• Protein Requirements: 2.0 x 52 = 104 g/day.
• Goal: Fat Loss. Begin at 1,800 kcal.
• Macronutrient Ratios:
  • Carbohydrates: 40% (180 g)
  • Protein: 30% (135 g)
  • Fat: 30% (60g)

Intermediate – (BIA or Skinfold Calipers)

For intermediate users who want more accurate body fat measurement, we recommend using BIA or skinfold calipers. These are accessible and affordable options:

Example

• Example: 75 kg woman, BIA displays 25% body fat.
• LBM: 75 x (1-0.25%) = 56.25 kg
• Protein Requirements: 2.0 x 56.25 = 112.5 g/day
• Goal: Body Recomposition. Begin at 1,900 kcal.
• Macronutrient Ratios:
  • Carbohydrates: 40% (190 g)
  • Protein: 30% (142 g)
  • Fat: 30% (63 g)

Advanced – (DEXA-verified)

Advanced users wanting a precise body fat percentage reading may want to try the DEXA scan. As mentioned, this is the gold standard for measuring body fat percentage while recording bone density.

Example

• Estimate: 68 kg woman. 22% body fat.
• LBM: 68 x (1-0.22) = 53.04 kg
• Protein Requirements: 1.8 x 53.04 = 95.47 g/day
• Goal: Muscle Gain. Begin 2,200 kcal
• Macronutrient Ratios:
  • Carbohydrates: 50% (220 g)
  • Protein: 25% (165 g)
  • Fat: 25% (73 g)

Accuracy, Re-Testing, and What to Track Besides Weight

When tracking LBM and measuring body fat percentages requires precision, and will require re-testing as you progress.

Re-testing using BAI and skinfolds can be done every 4–6 weeks. Meanwhile, the DEXA scan can be completed every 2–3 years for healthy individuals.

Re-testing logs your progress and helps you identify changes in LBM that will alter your calorie and protein intake. As mentioned, the key is to retest under the same conditions for accurate readings.

Tracking doesn’t stop there. We also recommend tracking other areas, including:

• Energy Levels: Modifying calorie and macro intake can affect your energy levels. If you experience low energy, consider increasing calorie or carbohydrate intake.

• Sleep: Intense training, changing hormones, and unhealthy, heavy meals can disrupt sleep. Modifying these areas can help improve sleep, hormone regulation, and weight management.

• Mood: Reduced calories, lower energy levels, and poor sleep can negatively impact mood. Making adjustments can help improve mood.

• Before and After Photos: Before and after photos provide visual data.

• Menopause Symptoms: Monitoring changes to symptoms can highlight whether you are on track with your nutrition and training.

Re-check Monthly (Waist/Hip and Key Strength Lifts)

Recording baseline measurements of waist/hip, key strength lifts, and re-checking monthly is also vital when maintaining LBM.

Studies show that muscle mass declines by 3–8% per decade after 30. Unchecked, this can lead to age-related muscle loss (sarcopenia), which research which results in muscle loss that is so significant that it leads to loss of strength and function, leading to a greater risk of falls.

Performing resistance training, re-checking girth measurements, and key lifts ensure that strength and mass are maintained.

Here is a list of key strength movements that should be considered:

• Squat — Strengthen, and monitor lower body strength
• Lunge — Used to strengthen and monitor the lower body and improve balance
• Kettlebell Deadlift — Strengthen the posterior chain (hamstrings, glutes, back) and lifting ability
• Push-up — Used to improve and gauge upper body strength
• Plank — Assess core strength and improve stability
• Dumbbell Overhead Press — Improves and gauges overhead strength and function

These movements challenge different planes of movement that are necessary for daily function. Being key exercises, they contain fundamental movement patterns that are present across different resistance training exercises.

This means that while they may not always be programmed into your routine, they will strengthen similar muscle groups and functions, making them great for re-checking.

Sources

1. Slater GJ, Dieter BP, Marsh DJ, Helms ER, Shaw G, Iraki J. Is an Energy Surplus Required to Maximize Skeletal Muscle Hypertrophy Associated With Resistance Training. Front Nutr. 2019 Aug 20;6:131. doi: 10.3389/fnut.2019.00131. PMID: 31482093; PMCID: PMC6710320. http://pmc.ncbi.nlm.nih.gov/articles/PMC6710320/
2. Manini TM. Energy expenditure and aging. Ageing Res Rev. 2010 Jan;9(1):1-11. doi: 10.1016/j.arr.2009.08.002. Epub 2009 Aug 19. PMID: 19698803; PMCID: PMC2818133. https://pmc.ncbi.nlm.nih.gov/articles/PMC2818133/
3. Siervo, M., Oggioni, C., Lara, J., Celis-Morales, C., Mathers, J.C., Battezzati, A., Leone, A., Tagliabue, A., Spadafranca, A. & Bertoli, S. (2015). Age-related changes in resting energy expenditure in normal weight, overweight and obese men and women. Maturitas, 80(4), 406–413. https://doi.org/10.1016/j.maturitas.2015.01.016. https://www.sciencedirect.com/science/article/abs/pii/S037851221500002X
4. Schoenfeld BJ, Contreras B, Krieger J, Grgic J, Delcastillo K, Belliard R, Alto A. Resistance Training Volume Enhances Muscle Hypertrophy but Not Strength in Trained Men. Med Sci Sports Exerc. 2019 Jan;51(1):94-103. doi: 10.1249/MSS.0000000000001764. PMID: 30153194; PMCID: PMC6303131. https://pmc.ncbi.nlm.nih.gov/articles/PMC6303131/
5. Volpi E, Nazemi R, Fujita S. Muscle tissue changes with aging. Curr Opin Clin Nutr Metab Care. 2004 Jul;7(4):405-10. doi: 10.1097/01.mco.0000134362.76653.b2. PMID: 15192443; PMCID: PMC2804956. https://pmc.ncbi.nlm.nih.gov/articles/PMC2804956/
6. Walston JD. Sarcopenia in older adults. Curr Opin Rheumatol. 2012 Nov;24(6):623-7. doi: 10.1097/BOR.0b013e328358d59b. PMID: 22955023; PMCID: PMC4066461. https://pmc.ncbi.nlm.nih.gov/articles/PMC4066461/

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