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If you work as a nutritionist or a registered dietitian, you’re probably very familiar with the importance of knowing your clients’ weights. After all, their body weight is likely one of the first metrics you obtain on your quest to help them achieve their health and fitness goals. 

However, your clients’ body weight alone is not enough to tell the full story. 

Just as any good nutritionist knows that calorie counts aren’t enough to determine the quality of your clients’ dietary patterns, you should also know that a number on a scale simply isn’t informative enough to determine your clients’ wellness. Body composition analysis has the potential to take your practice to the next level by providing tangible, specific information about your clients’ body fat and muscle percentages that helps you create actionable plans for them. 

Why nutritionists and registered dietitians should be using body composition measurements 

A nutritionist measures a client's waist.

Body weight needs context in order to be a useful number. So, many nutritionists typically evaluate their clients’ health by using their weight to find their Body Mass Index (BMI), a value that is determined using one’s height as well. 

BMI is useful in some contexts, as it can help generally categorize whether or not someone is overweight or obese. Unfortunately, BMI does not take into account all the differences between individuals, nor does it fully indicate health risks on its own. For example, BMI doesn’t tell you how much body fat someone has, and it doesn’t take into account individual differences based on age, culture, and location. This is important, because all of these factors and more can make a huge difference in what a person’s weight says about their health.   

Ultimately, this means that only using weight and BMI to determine the wellness of an individual can cause you to miss the “big picture,” which may negatively impact your ability to help your clients achieve their goals in a healthy manner. If you want to design a targeted nutrition plan, these metrics alone may not provide sufficient information about a client’s overall health and fitness levels.

You may already take this into consideration at your own practice, since many nutritionists and dietitians use measuring tape to take their clients’ physical measurements at different points throughout their wellness journeys, which can reveal how their body composition is changing beyond the scale. But taking this idea one step further, body composition metrics may be able to give you a more accurate understanding of how your client’s body is transforming in reaction to your program. These insights can assist you with mapping out the best steps to take next. 

What body composition data can tell you about your clients

A nutritionist consults with a client.

Body composition data can help nutritionists to evaluate their clients’ nutritional status through a more holistic lens. 

It’s especially important to keep your clients’ body composition in mind when making a nutrition plan because, just as with weight, their body composition metrics can change based on genetics, environment, lifestyle, and age. When used in conjunction with other tools of the practice, such as medical history and reported food intake, body composition data provides detailed info that gives you a better understanding of your clients’ current nutritional status, which may help you to create a more targeted action plan to address their specific health and nutrition needs as individuals.

Common issues that body composition metrics may help nutritionists to pinpoint include: 

  • Declines in bone density 
  • Declines in muscle mass 
  • High percent body fat

Doctors can also use body composition data to help them assess the risk of chronic conditions, such as cardiovascular disease, Type 2 diabetes, and cancer.

Ultimately, body composition data provides an analysis not just of weight gained or weight lost, but of multiple factors, which can help you understand how their weight is correlated to your clients’ overall health

Muscle Mass 

One of the most important health factors that can get overlooked when using weight and BMI is one’s muscle mass, which is the amount of lean muscle tissue that you have in your body. This metric can be used to evaluate progress in a weight management sense, since muscle tends to weigh significantly more than fat tissue, meaning that a client may be making plenty of progress gaining muscle but not have their progress show on the scale (or vice-versa).  

Knowing your clients’ muscle mass can also help dieticians to identify issues like sarcopenia (muscle wasting) in older adults, so that you can decide whether a more targeted nutrition intervention would be appropriate.

Body Fat Mass 

Another piece of body composition data that you can use as a nutritionist is your client’s body fat mass, or the amount of fat tissue in their body. 

Body composition analysis show you how much fat (or adipose) tissue your client is holding, and it can also differentiate between types of fat (i.e. the visceral fat that surrounds the organs in your abdomen versus the subcutaneous fat that lies close beneath your skin). 

This is extremely important because these two different kinds of fat tissue are both linked to a variety of outcomes, but visceral fat is much harder to detect than subcutaneous fat without body composition analysis technology.

Percent Body Fat

Body composition analysis also yields information about the amount of muscle versus fat tissue your clients carry, which can be used to evaluate exactly how much progress your clients are making in their health — not just in their weight — goals. It’s a more in-depth analysis than the use of body weight measurements alone, especially considering how muscle and fat impact your weight differently

Other useful information you can get from body composition measurements

Finally, body composition metrics can also be used in a variety of other ways to address a client’s overarching health needs. For example, using DEXA scans, dietitians can take a look at their clients’ bone density, which can help you to assess them for undernutrition and, if necessary, set up the appropriate nutrition interventions, which are especially important for older adults suffering from osteoporosis. 

Nutritionists and dietitians can also use body composition measurements to see how much of their client’s total mass is made up of water, otherwise known as their Total Body Water percentage. This tool can offer clues to the amount of sodium a client is consuming, as salt consumption can cause your body water percentage to change

How nutritionists can use body composition measurements to improve their services 

A nutritionist shows a client an informational hand-out on healthy eating.

Putting it all together, here are some concrete examples of how your nutrition practice (and your clients!) can benefit from the implementation of body composition measurements. 

Identifying specific areas that clients want to improve 

Having information on someone’s weight is a good start for helping them get to their goals, but knowing their body composition can give you more specific guidance on how to approach their program. Even better: having someone’s body composition metrics also gives you the opportunity to better educate your clients about how the nutrients they eat contribute to their body composition, ultimately allowing them to take a more hands-on approach with their own health

For example, many of your clients may come in wanting to lose weight, but knowing their ratio of fat tissue to muscle tissue can reveal whether more specific goals are more appropriate. If a client wants to get fitter but is already at a healthy weight, you may choose instead to work on body recomposition goals, such as losing fat and gaining muscle, rather than focusing solely on weight alone, which could put your client in danger of becoming underweight.  

You can use body composition data to help guide your nutrition plan (i.e., recommending more protein to combat muscle loss and fewer carbohydrates for fat loss, rather than focusing on total calorie intake alone). Your clients can also use that information to approach their own health through a more balanced, health-first lens. 

Adjusting total caloric needs

Knowing your clients’ body composition metrics can provide you both with a better understanding of their Basal Metabolic Rate (BMR), which is the number of calories that your clients burn on a daily basis. This is imperative data for determining the number of calories they should be eating for their goals without over- or underestimating their unique needs

BMR can be estimated using many different calculations, but these calculations are not always completely accurate. For example, relying only on calculations based on weight and height can skew results and lead to inaccurate numbers, especially since many of these population-based calculations do not take into account differences in physical activity level, body composition, or sex. In other words, these calculations may be relevant to the populations that they were based on, but it doesn’t mean that they’ll be accurate for your client. 

Instead, nutritionists may do better to use calculations that take body composition into account, since differences in body fat tissue and lean muscle tissue can alter the number of calories you burn on a daily basis.  In fact, there’s evidence to suggest that lean body mass is the strongest determinant of BMR, since muscle requires more energy to maintain, and that body fat mass, physical activity level, and nutrition play their roles on a smaller scale. So, using your client’s body composition metrics to calculate BMR may assist you in creating a more accurate estimation of your client’s needs.

Identifying over- and under-nutrition for goals and for health 

Knowing someone’s body composition metrics can also help nutritionists and dietitians get a better “big picture” view of someone’s nutrition status, which can be applied to both their fitness and health goals. 

For example, someone who is not eating as many calories as they need may experience a loss of muscle mass that could be masked if you’re only looking at the number on a body weight scale. Malnutrition is linked to various health risks, such as muscle loss, which are relevant in a broader health sense, so it’s important to screen for it when possible. 

Tracking client history 

Finally, keeping track of a client’s body composition changes over time can give you in-depth insights into your clients’ progress. Knowing how someone’s muscle mass and body fat percentage have changed over time can:

  • Give you a more accurate understanding of how well your program is working
  • Help you identify areas that could be improved


Helping your clients to achieve their nutrition and fitness goals requires a distinct combination of lifestyle improvements on their part and careful monitoring of key metrics on your part. By implementing the use of body composition measurements in your nutrition practice, you may be able to give yourself and your clients better information about their bodies. 

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