Why Am I Losing Weight But Not Body Fat?

Weight loss can be confusing and frustrating, which is why many people end up giving up. Don't let that be you — losing weight but not fat is common but can be easily fixed. Once you learn about body composition and how the body burns fat, you'll understand how it affects the number on the scale. You'll also learn that the number on the scale isn't the best way to assess fat loss.

Don't assess your progress only by the number on the scale. (Image: Zinkevych/iStock/GettyImages)

Tip

You may be losing weight but not fat because you're losing muscle mass.

Losing Weight but Not Fat

The term "weight loss" is often misused. What people want to lose is body fat, not necessarily weight — and these are two distinct concepts.

The number you see on the scale is the combined weight of your muscles, bones, organs and fat. And a lot of your body weight is water that you need to survive. Do you want to lose water, muscle, bones and organs? No — you just want to lose fat!

Based on that explanation, the most likely reason you're losing weight but not inches is that you're losing muscle mass. If you're not doing weight-bearing exercise to counteract this, you're going to lose weight in pounds, but not necessarily fat.

You're Eating Too Few Calories

The fewer calories you eat, the more fat you burn, right? Wrong. Eating too few calories can actually hinder fat loss. There are several reasons for this. The first is that without enough calories, your body goes into survival mode and begins breaking down even more muscle mass for energy, according to Caroline Kaufman, MS, RDN.

Second, an excessive calorie deficit causes changes in your metabolic function. According to Laura Schoenfeld, MPH, RD, these changes affect your hormones, reducing thyroid hormone, which can slow fat loss. At the same time, they increase cortisol levels, which will further affect your body's ability to burn fat.

Additionally, since it's conserving energy, the body stops building muscle to save calories for other more important physiological functions. Building muscle isn't a priority in survival mode. So even if you're exercising, if you're not eating enough calories, you won't be gaining muscle.

You're Losing Weight Too Quickly

According to a study presented at the 12th annual European Congress on Obesity in Bulgaria in 2014, rate of weight loss is associated with loss of fat-free mass (everything that makes up your body weight besides fat). Very rapid weight loss results in a greater loss of fat-free mass than gradual weight loss.

In the study, overweight and obese participants were put on either a very low-calorie diet (VLCD) lasting five weeks or a low-calorie diet (LCD) lasting 12 weeks. At the end of the diet in both groups, weight loss was similar. However, the VLCD group that dropped weight quickly lost more fat-free mass, while the LCD group that lost weight more slowly experienced a greater reduction in fat mass.

You're Not Strength Training

The best way to lose fat is to eat a calorie-appropriate diet and strength train to maintain or build muscle. This will lead to a decrease in your body fat percentage but not your weight.

There's another big reason to strength train: building muscle actually helps you lose fat faster. Muscle tissue is metabolically active, meaning your body expends energy to maintain and build it. This increases your resting metabolism, the calories you burn even when you're not exercising.

According to Paige Kinucan and Len Kravitz, Ph.D., of the University of New Mexico, muscle mass accounts for as much as 20 percent of total daily energy expenditure, while fat mass only accounts for 5 percent or less. If you're not strength training, you're hindering your fat loss efforts in more ways than one.

Reading the Scale

Once you start strength training —and eating enough calories — you will start to see the scale level out. In the beginning of a strength-training program, people typically gain muscle more quickly as the body is adapting to the stressor. You might gain 10 pounds of muscle and lose 10 pounds of fat at the same time, in which case the number on the scale won't budge.

After a time, your rate of muscle gain — and of fat loss — will start to slow down, which is normal. According to registered dietitian Densie Webb, the body also adapts to a lower calorie intake, even if it's a conservative deficit, which can slow weight loss over time.

Whether or not the weight on the scale goes up, down or stays the same depends on how your rates of muscle gain and fat loss change over time.

Assessing Your Progress

A better way to judge your progress is to keep an eye on the way you look and the way your clothes fit. You can also take measurements of your upper arms, thighs and waist to see changes in fat mass.

Having your body fat tested is another way to keep track of your progress. This can be done through any number of procedures, from a simple skin caliper test administered by a personal trainer at your gym to hydrostatic underwater weighing in a laboratory setting.

Eat and Train Smart

It's important to note that being more active and lifting weights increases your calorie needs. Depending on the intensity and frequency of your program, it could increase them quite a bit. Depending on your calorie intake before training, you may not need to decrease your calories but increase them.

The most important thing is that these calories come from nutritious foods. Eating more lean protein supports the growth of lean muscle mass, and both protein and dietary fiber can help you control your calorie intake and encourage fat loss, according to a study published in 2018 in Nutrition. Nutritious sources of protein include chicken, fish, eggs and legumes, while fruits, vegetables and whole grains are rich sources of fiber.

Aim to get at least 0.8 grams of protein per kilogram of body weight each day. However, according to the American College of Sports Medicine, people who strength train regularly should eat more protein — 1.2 to 1.7 grams per kilogram of bodyweight.

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