Weight loss is the overall drop in weight due to any body component, including fat, muscle, water, and more. Fat, muscle, and water can play a role in weight loss. However, it can also occur due to other factors, such as bone mineral or glycogen stores.

Glycogen stores may be particularly relevant for people following low-carb diets. Sometimes, people use the terms weight loss and fat loss interchangeably. However, they have different effects on the body and health.

When people are trying to lose weight, they might typically weigh themselves on a scale. However, this only tells them how much weight they have lost — not how much fat. Losing fat is more beneficial than losing water or muscle, so it is helpful to be aware of body composition and how it affects health.

This article explains the difference between weight loss and fat loss and their effects on health. It explains how to measure fat loss and gives tips to maintain muscle and lean body mass. Read on to find out how to lose weight and fat safely without compromising health.

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When someone loses weight, they may lose water and muscle, not just fat. Fat loss refers to losing only excess fat from the body.

To understand this concept further, here is an explanation of body composition:

Body composition explained

  • Fat mass is the weight of all the fat molecules in a person’s body.
  • Lean body mass and fat-free mass are terms that people may use interchangeably to refer to the non-fat molecules in the body. This includes most of the mass of internal organs, bones, muscle, and more, as well as all the water in the body.

On average, water can account for 50-60% of a person’s total body weight. The term “water weight” refers to any extra water the body is holding.

However, drinking less water will not cause a person to lose water weight safely. Conversely, drinking more water can help a person lose weight more effectively.

Water also helps transport carbohydrates and proteins in the bloodstream so the body can metabolize them.

The first step to losing water weight involves reducing sodium intake. Excess sodium can make the body hold on to too much water in order to keep the correct salt-water ratio.

Learn more ways to reduce water weight here.

Sometimes when people lose weight, they decrease their muscle and fluid density as well as fat levels. This could result in a reduction in lean body mass and adverse health implications.

According to a 2018 review, the negative health implications of a loss of lean body mass are as follows:

  • lowered metabolism
  • fatigue
  • declines in neuromuscular function
  • potential effects on emotion and psychological states
  • increased risk of injury

Moreover, the authors note that the metabolic decline that occurs following a loss of lean body mass can regain fat mass and cause unfavorable changes in body composition.

The researchers advise that sustainably losing fat mass while maintaining lean body mass is even more important than overall weight loss.

Health professionals can measure someone’s body fat using anthropometric devices. Still, a 2021 review indicates that no single method is sufficiently adequate, and many measuring methods are either expensive, complicated, or inaccurate.

There are several ways to measure fat loss:

  • Body fat scales use bio-impedance to tell someone what their body fat percentage is, and a person can use the scales to track their fat loss.
  • Callipers measure fat in specific areas by pinching the skin, such as the abdomen. However, they can be challenging to use accurately.
  • A tape measure can track where someone is losing weight. However, it does not specifically show if the inches lost are fat.
  • Body mass index (BMI) is an anthropometric measurement that health professionals recognize to classify someone’s weight. If BMI reduces, a person could be losing body fat and lean body mass.
  • Waist-to-hip ratio or waist circumference are measurements that a person can obtain with a tape measure and may help monitor fat around the middle.

Learn more about different ways to measure body fat.

Losing weight and fat can help a person to avoid obesity and its related adverse health effects. However, it is essential to maintain lean body mass and muscle mass for the body to function correctly.

According to a 2018 review, popular diets such as low carbohydrate, ketogenic, and high-fiber diets result in weight loss — as well as a reduction in lean body mass. However, a high-protein diet resulted in more fat loss and less lean mass loss.

The same review indicated that some dietary supplements, including chromium picolinate and green tea catechin, might preserve lean mass while losing fat.

However, the authors concluded that the best approach includes a comprehensive strategy of evidence-guided calorie and macronutrient intake and resistance exercise.

The bottom line

A person should include adequate protein, and do strength and resistance training, to maintain muscle mass while losing weight.

More on fat loss and muscle growth

In older adults

Losing fat and maintaining muscle can be particularly challenging as a person ages.

Research suggests that as we get older, body fat increases, and lean mass and bone density decrease. In addition, older adults may develop sarcopenia, which is muscle loss due to aging.

Moreover, these changes in body composition put someone at more risk of chronic diseases, such as cardiovascular disease, diabetes, and osteoporosis.

The following factors can help a person reduce muscle loss as they age:

  • Exercise: Older adults should participate in muscle-strengthening activities 2 or more days a week. The activities should work the legs, hips, back, abdomen, chest, shoulders, and arms.
  • Nutrition: Eating more protein can help maintain good levels of muscle. Research shows that adults should eat 30-35% of their total calories as protein.

Losing weight can help someone avoid obesity and the risk of chronic diseases. However, losing fat can also mean losing fluid and muscle, and reducing lean body mass.

People must maintain their lean body mass for health, strength, and overall vitality. This can be particularly challenging for older adults, who are more at risk of sarcopenia or muscle loss.

Eating adequate amounts of protein, paying attention to macronutrients and calories, and strength training can help lose fat and maintain muscle. People can also consult a nutritionist or exercise professional for individual advice and recommendations.