If you’re using body composition tools like calipers to measure your body fat percentage to assess your health, then you’re already ahead of most (like those
who are still using BMI).

But be aware that body fat percentage doesn’t always paint a complete picture when it comes to body composition. A drop in body fat percentage doesn’t always mean you’ve lost fat. Sometimes, weight loss comes from muscle mass and water, not fat. That’s because body fat percentage is a simple equation of your fat mass divided by your total weight.

Body Fat Percentage = Fat Mass / Total Weight

A study found that up to 25% of weight lost during dieting can come from fat-free mass, including muscle and water, rather than fat. Therefore, simply tracking body fat percentage may not accurately reflect the true changes in fat versus muscle during weight loss.

The good news? Once you identify the cause of this issue, you can make targeted changes to focus on sustainable fat loss while preserving your hard-earned muscle mass. Here are a few examples:

1. You’re Working Out, But Body Fat % Doesn’t Change (or increases)

This situation can occur when you are working out to gain muscle in order to improve your physique, but you aren’t seeing the changes in the mirror that you hoped to see as quickly as you’d like. When you check your body fat percentage, you don’t see any change despite a month of hard workouts. What’s going on?

Check for Changes in Your Weight

The first thing to check is to see if your weight has changed. It probably has. If your weight has increased but your body fat percentage remains unchanged, this likely means that your SMM (Skeletal Muscle Mass) is increasing at the same time as your Fat Mass.

As you build muscle, fat gain can occur because of the caloric surplus needed to support muscle growth. This is a common occurrence in bodybuilding and is often referred to as “bulking.”
Research shows that during caloric surplus for muscle growth, fat mass often increases alongside lean mass gains. Specifically, those in the higher energy surplus group saw increased fat without a proportional gain in muscle, reinforcing the idea that bulking can lead to both muscle and fat gain.

The Anabolic State and Increased Caloric Needs

If your body fat percentage rises again after a couple of months, it’s likely because your body has entered an anabolic state. In this state, your body is focused on increasing muscle production, which requires more calories than usual to build muscle mass.

However, not all of these extra calories go toward muscle development. Being in a calorie surplus can also lead to fat gain, which in turn causes an increase in body fat percentage.

The Cardio-Only Exercise Trap

Excessive cardiovascular exercise without resistance training creates a metabolic environment that favors muscle loss over fat loss. Your body adapts to prolonged cardio sessions by becoming more efficient at using muscle protein as fuel. In a controlled trial, individuals performing only steady-state cardio for 12 weeks lost significantly more muscle than those combining cardio with resistance training.

Low-intensity steady-state cardio sessions lasting longer than 60 minutes trigger cortisol release. Elevated cortisol levels promote muscle breakdown while encouraging fat storage, particularly around your midsection. This hormonal response explains why marathon runners often maintain higher body fat percentages despite burning thousands of calories weekly – in other words, they may be losing fat but not weight, especially if their muscle mass remains unchanged while fat levels decrease gradually.

Exercise Program Design Flaws

Your workout structure might emphasize volume over intensity, limiting fat loss effectiveness. Programs consisting of multiple 30-45 minute moderate-intensity sessions weekly don’t create sufficient metabolic stress to trigger significant fat loss adaptations. Your body quickly adapts to predictable exercise patterns, reducing caloric expenditure over time.

Training programs lacking progressive overload fail to stimulate muscle growth and maintenance. Your muscles adapt to consistent workloads within 2-3 weeks, requiring increased resistance or complexity to continue developing. Static exercise routines that don’t evolve prevent the metabolic adaptations necessary for sustained fat loss while maintaining muscle mass.

2. You’re Losing Weight, But Your Body Fat % Doesn’t Change (or increases)

Similar to #1, this situation also involves little or no change in body fat percentage but instead of occurring due to anabolism, this time, catabolism is the driving force behind the change – a common frustration for people wondering, “why am I losing weight but not fat?”

In catabolism, the body focuses on reducing tissue rather than building it. To lose weight, especially fat, the body needs to be in a catabolic state, which occurs when you’re in a caloric deficit (taking in fewer calories than needed). In gym terminology, this is referred to as “cutting.”

If you observe that you’re losing weight, but you don’t see the results in the mirror that you’d like to see and notice that your body fat percentage is unchanged, this is because your SMM and Fat Mass are actually decreasing together.

Why would Skeletal Muscle Mass decrease when you’re trying to target body fat only?  Although there isn’t a singular cause, the majority of the time, this is caused by improper training and diet.

Weight loss typically involves reductions in both body fat and skeletal muscle, though targeted training and nutrition can help preserve lean mass. For this reason, preserving or even increasing muscle becomes a priority when encouraging the body to enter a catabolic state. This means ensuring your nutrient intake is balanced while engaging in some kind of resistance or weight training.

Many people neglect these important precautions and cause their body to metabolize muscle as well as fat. Depending on how much muscle is lost, body fat percentages can drop extremely slowly, stay the same, or in extreme circumstances, increase.

3. Your Body Fat Percentage is Acceptable, But You’re Underweight

At first, this doesn’t seem like it makes sense – how can you be at a healthy body fat percentage, but not be healthy overall? Simple: you’re underweight.

While underweight individuals may have enviable body fat percentages, this can create the illusion of good health. However, being underweight typically means that you lack adequate muscle mass.

Chronic underweight status can increase the risk of osteoporosis, immune dysfunction, and hormonal imbalances.

The Risk of Muscle Loss When Sick

Not having enough muscle mass will also become problematic if you get sick. When you become sick, the body’s need for amino acids to power its immune and recovery processes increases, and it will look to your muscle mass for those amino acids. Essentially, your body will start to break down muscle in order to fight and recover from disease, and if you’re underweight with a healthy body fat percentage, you won’t have enough muscle to easily fight off illness.

Metabolic Consequences of Being Underweight

Chronic calorie restriction without adequate protein intake triggers muscle catabolism while preserving fat stores for survival. Your basal metabolic rate drops by 200-400 calories per day when you lose substantial muscle mass. This metabolic adaptation makes future fat loss increasingly difficult and often leads to rapid weight regain once normal eating patterns resume.

Hormonal disruptions accompany this underweight state. Testosterone levels in men can decrease by 20-40% while women may experience menstrual irregularities or amenorrhea. Thyroid hormone production (T3) reduces by approximately 6% to conserve energy, further slowing your metabolism and making fat loss more challenging.

4. Your Body Fat Percentage is Acceptable, But You Have Muscle Imbalances

Even with a healthy body fat percentage, muscle imbalances can significantly impact overall health and performance. While body composition analyses provide valuable insights into fat and fat-free mass, they often overlook the distribution and development of muscle across different body segments.

Specifically, people can have well-developed Lean Body Mass areas in some parts of their bodies but not in others. Some people prefer developing upper body muscle while neglecting lower body muscle development. Others may have what’s referred to as a bilateral imbalance, which occurs when one side of the body is stronger than the other.

Here’s what that looks like from a body composition analysis viewpoint:

In this example, this person has almost one pound of muscle difference between their right and left arms. Although this might seem more of an aesthetic problem, significant muscle imbalances such as the one shown above can also contribute to injury. In athletes, muscle imbalances, such as in the shoulders, are linked to higher rates of pain and injury.

It’s Just One Number

Although your body fat percentage is a very significant and useful number, relying on any one number, even an important number like body fat percentage, will never provide you with a complete picture about your overall health. While body fat percentage is a very good way to assess your weight, it only takes Body Fat (and by extension Fat-Free) Mass and Weight into account.

In order to maintain your weight and understand the changes that your body experiences over time, including your change in body fat percentage, you will need more specific values than just Fat and Fat-Free Mass. If you don’t compare your body fat percentage to Skeletal Muscle Mass, you won’t be able to:

• Understand increases and decreases in body fat percentage

• Maintain a healthy body fat percentage in respect to a healthy weight and muscle mass level

• Determine if your muscles are balanced

Your body is a very complex system of many components all working together. That is why it is very important to get as much information as possible in order to understand your weight and your health properly.

Skinfold calipers provide a basic estimate of body fat, but advanced tools like Direct Segmental Multi-frequency Bioelectrical Impedance Analysis (DSM-BIA) offer more complete insights into muscle mass, fat mass, and body water.

FAQ

Why am I losing weight but not losing body fat?

This occurs when you’re losing muscle mass and water weight instead of fat tissue. Common causes include excessive cardio without strength training, inadequate protein intake, insufficient recovery time, and poor exercise programming. This type of weight loss can actually increase your body fat percentage even as the scale goes down.

Can doing too much cardio prevent fat loss?

Yes, excessive low-intensity cardio without strength training can lead to muscle loss while preserving fat tissue. This creates a metabolic environment that favors muscle breakdown, especially when combined with calorie restriction. The body may adapt by slowing metabolism and preferentially burning muscle for energy instead of fat.

What’s the best exercise approach for fat loss?

Combining cardiovascular exercise with resistance training yields the best results for fat loss and muscle preservation. This approach maintains metabolic rate, preserves lean muscle mass, and creates optimal conditions for burning fat. Progressive overload and adequate recovery are also essential components.

How can I tell if I’m losing muscle instead of fat?

Monitor body composition using DEXA scans, bioelectrical impedance, or circumference measurements. Visual signs include maintaining the same body fat appearance despite weight loss, feeling weaker, and developing a “skinny fat” look. Progress photos and strength performance tracking can also indicate muscle loss versus fat loss.