Why losing all body fat is not a healthy goal

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Body fat is often viewed as something people should reduce as much as possible when trying to lose weight, but experts say having some body fat is essential for maintaining good health.

Body fat is not simply excess weight stored by the body. It serves several important functions, including storing energy, producing hormones, helping regulate body temperature and supporting other biological processes.

While excess body fat can increase the risk of several health problems, having too little can also affect the body's normal functioning. The goal, therefore, should not be to eliminate body fat but to maintain a healthy body composition.

What does body fat do?

Dietary fat and body fat are not the same thing. Dietary fat comes from food, while body fat is part of the body's natural energy-storage system.

When the body receives more energy than it needs, some of the excess is stored in fat cells. These cells are not simply passive storage units but play an active role in regulating several bodily functions.

Stored fat can provide energy when food intake is limited, helping the body meet its energy needs during periods of reduced calorie intake.

Fat also plays a role in hormones

Fat cells produce hormones and other signalling molecules that help regulate energy balance and other functions.

One important hormone is leptin, which helps signal to the brain that the body has sufficient energy reserves. When energy availability becomes too low, the body can begin reducing or altering certain functions that are not immediately essential for survival.

Very low energy availability can therefore affect processes including reproductive health and immune function.

Body fat helps regulate temperature

Fat also helps the body maintain its temperature.

White fat primarily stores energy and provides insulation, while brown and beige fat contain specialised cells that can convert energy into heat.

This means that body fat contributes to the body's ability to maintain a stable temperature, particularly in cold conditions.

What happens when body fat becomes too low?

The health risks associated with excessive body fat are widely recognised, including increased risks of heart disease, type 2 diabetes, some cancers and joint problems.

However, severe calorie restriction and prolonged inadequate food intake can also cause serious health consequences.

When the body does not receive enough energy, it may begin conserving resources and reducing certain functions. If energy stores become severely depleted, the body can also break down muscle tissue for energy.

This can contribute to muscle weakness, reduced bone health, physical fatigue and an increased risk of fractures.

Hormonal and reproductive health can be affected

Very low body fat and inadequate energy intake can also affect hormone levels and reproductive health.

Men who remain in a prolonged state of low energy availability may experience changes in testosterone levels, energy and physical performance.

In women, particularly athletes with very low energy availability, menstrual cycles can become irregular or stop altogether.

These changes can be signs that the body does not have enough available energy to support normal physiological functions.

Is some extra fat ever beneficial?

Researchers have observed that, in some older adults and people with certain serious illnesses, higher body weight has sometimes been associated with different survival outcomes.

During severe illness, the body's stored energy reserves may provide additional fuel when food intake is reduced.

This has contributed to discussion around the so-called “obesity paradox”, in which some studies have found different outcomes among people with higher body weight during certain medical conditions.

However, this does not mean obesity is beneficial or that people should deliberately gain excess weight. Obesity remains associated with numerous serious health conditions.

Extremely low body fat and prolonged severe undernutrition can also become life-threatening. Eating disorders that result in prolonged starvation, for example, can damage vital organs and may be fatal.

How much body fat is healthy?

There is no single ideal body-fat percentage that applies to everyone. Healthy levels can vary according to age, sex, body composition and other factors.

As a broad guideline, body fat in healthy adult men may fall around 10% to 20%, while women may typically have around 20% to 29%. Higher levels can indicate excess body fat, although individual assessment is more useful than relying on a single number.

Athletes can have lower body-fat levels, but extremely low levels are not necessarily healthier.

A study examining body composition in more than 700 athletes found the lowest recorded body-fat levels were around 10% in a male athlete and 16% in a female athlete.

Where fat is stored also matters

The amount of body fat is not the only consideration. Where the fat is stored can also affect health.

Visceral fat, which accumulates around internal organs in the abdomen, is particularly associated with health risks when present in excess.

It can contribute to inflammation and affect blood pressure and insulin function, potentially increasing the risk of conditions such as type 2 diabetes.

Can you measure body fat at home?

Accurately measuring body fat is more difficult than simply stepping on a weighing scale.

A DEXA scan can provide a detailed assessment of fat, muscle and bone, but it requires specialised equipment and can be expensive.

Skinfold callipers can estimate subcutaneous fat, but the results depend on where and how the measurements are taken and they cannot directly measure visceral fat.

Smart scales that use bioelectrical impedance can also estimate body-fat percentage. However, hydration levels can affect their readings, meaning they should not be treated as a highly precise measurement of body fat.

These devices also cannot reliably determine how much fat is stored around internal organs.

Waist measurement can provide another clue

People do not necessarily need to measure their body-fat percentage in detail to monitor their health.

Waist measurements and waist-to-height ratio can provide useful indicators of abdominal fat. Waist-to-hip ratio can also offer information about where fat is distributed.

BMI, meanwhile, has limitations because it does not distinguish between muscle and fat. A muscular person, for example, may have a high BMI despite having relatively little body fat.

Body composition changes with age

As people age, body-fat levels can increase while muscle and bone mass may decline.

Maintaining a balanced diet, staying physically active and doing strength-training exercises can help support muscle and bone health as the body changes with age.

The key message is that healthy body composition is about balance rather than eliminating fat completely.

Courtesy: BBC, SAMAA