LONDON: Body fat is often treated as something to eliminate, particularly on social media, where extremely lean and highly defined physiques are frequently promoted as the ideal. But health experts say having too little body fat can be harmful because fat plays several essential roles in the body.
While excess body fat can increase the risk of conditions including cardiovascular disease, type 2 diabetes and some cancers, the body also needs a certain amount of fat to function properly.
“Fat is an important biological function,” Elif Oral, an endocrinologist and professor of medicine at the University of Michigan, told the BBC.
Body fat is different from dietary fat. Dietary fat comes from food, while body fat stores excess energy for later use. When the body consumes more energy than it needs, fat cells called adipocytes store the excess nutrients as lipids.
Researchers now understand that body fat is not simply an energy reserve. It acts as an active endocrine organ that communicates with other parts of the body and helps regulate several biological processes.
One important function is hormone production. Fat cells produce hormones including leptin, which helps signal to the brain that the body has sufficient energy reserves.
When energy availability becomes too low, the body can respond by reducing or deprioritising certain functions. This can affect reproduction, immunity and other processes that require adequate energy.
Body fat also helps regulate temperature. White fat provides insulation, while brown and beige fat contain specialised cells that can generate heat by using stored energy.
What happens when body fat falls too low?
Severe calorie restriction can cause body fat levels to fall to unhealthy levels. Researchers say the body may then begin conserving energy and breaking down other tissues, including muscle.
Low body fat can contribute to reduced bone formation and repair, increasing the risk of fractures and frailty. It can also leave the body with fewer energy reserves to cope with infections or other serious medical problems.
Hormonal and reproductive health can also be affected. Men who chronically under-fuel themselves may experience lower testosterone levels, reduced energy and poorer physical performance. Female athletes with very low energy availability can develop irregular or absent menstrual periods.
In extreme cases, severe loss of body fat can be associated with serious illness and organ damage. Eating disorders such as anorexia nervosa can become life-threatening without appropriate treatment.
How much body fat is healthy?
There is no single body-fat percentage that is considered ideal for everyone. Age, sex, genetics, physical activity and other individual factors can affect healthy body composition.
As a broad guide, healthy adult men often have around 10% to 20% body fat, while healthy adult women tend to have around 20% to 29%. People living with obesity generally have substantially higher body-fat levels.
Athletes may have lower body-fat levels, but extremely low percentages are not necessarily healthier. Research involving more than 700 athletes found the lowest measured body-fat levels at around 10% for a male athlete and 16% for a female athlete.
The location of body fat also matters. Visceral fat, which accumulates around internal organs, is associated with inflammation, impaired insulin regulation and a higher risk of metabolic disease.
How can body fat be measured?
A DEXA scan can provide a detailed assessment of body composition, including fat, muscle and bone. However, the technology requires specialist equipment and may be expensive.
Skinfold measurements are another option, but they estimate fat based on measurements at selected areas of the body and cannot directly assess visceral fat.
Smart scales that use bioelectrical impedance can estimate body-fat levels, but their readings can be affected by hydration and other factors. They are therefore not considered highly accurate for determining overall body-fat levels.
For most people, detailed body-fat measurements are not necessary for maintaining good health.
Simple measurements such as waist circumference and waist-to-height ratio can provide useful information about central fat levels. A waist-to-height ratio of around 0.4 to 0.49 is generally considered a healthy range.
BMI can provide a broad measure of body size but cannot distinguish between fat and muscle. As a result, people with substantial muscle mass may have a high BMI despite having relatively little body fat.
As people age, maintaining healthy body composition becomes increasingly important because muscle and bone mass tend to decline while fat mass can increase.
Rather than pursuing extreme levels of leanness, experts recommend focusing on balanced nutrition, regular physical activity and strength training.
Body fat can pose health risks when present in excess, but eliminating as much of it as possible is not a healthy goal. The body needs an appropriate amount of fat to store energy, regulate hormones, maintain temperature and support essential biological functions.
