- Skinny fat means having an increased amount of adipose tissue even at a normal body weight.
- This problem may not be detected during a routine examination associated with a BMI calculation.
- A greater number of controllable and uncontrollable factors are likely to be involved in the development of obesity at a normal weight.
What is skinny fat?
Skinny fat can be found in the literature under many names, including normal weight obesity, metabolic obesity, sarcopenic obesity and lean obesity. In 2006, "normal weight obesity" was described as a condition where an individual has a high amount of body fat even though they do not fall into a high‑risk category by weight (i.e., overweight or obese). This problem is being addressed particularly in Asia, where research suggests that the incidence is significantly higher.
Obesity can be overlooked in the long term, especially if the person relies on BMI to diagnose, which does not detect the condition. In the case of petite figures with apparently normal weight and no visible fat, even a doctor or other health professional may overlook it.
The "boundaries" of overweight and obesity
Overweight and obesity refer to an increase in body weight and body fat above the normal range, which has numerous negative consequences for overall health. Typical examples are an increased risk of damage to heart and blood vessel function, the development of an inflammatory environment in the body, damage to the musculoskeletal system or excessive secretion of certain substances derived from fat mass.
And how do you actually find out about these conditions? There are two assessments used:
- BMI assessment: a value above 25 points is considered overweight, and a value above 30 points is considered obese.
- Fat mass assessment:
- Men: overweight when exceeding 20%, obese when exceeding 25%
- Women: overweight when crossing 30 % body fat, obese after 35 %
While you need to take measurements (most often using the InBody method) to determine the amount of body fat, a simple equation is all you need to find your BMI. BMI assessment is therefore used much more frequently in prevention due to its simplicity, speed and low cost. But as you can already guess, with such an assessment, "skinny fat" can go undetected for a long time, which can cause health complications (see below).
The Asian population has a much higher incidence of missing skinny fat than the European population, where the prevalence of normal‑weight obesity is low. For this reason, especially in the South Asian region, these values have been reduced, as shown in the table from Dr Kapoor's paper. The phenomenon of skinny fat has been the subject of intense study in these countries, as the proportion of people with type 2 diabetes and excessive body fat has increased considerably in recent years, even though the weight appears, at first sight, to be within normal limits.
What can lead to the development of skinny fat?
Most likely, it is a combination of lots of factors.
- Genetic predisposition: Some people have a genetic predisposition to accumulate fat tissue, and genes may also influence its distribution (i.e., location on the body). There is a hypothesis called the "thinning phenotype", which suggests that if a child has not been adequately nourished before birth, he or she will develop mechanisms to help conserve energy and store it for a rainy day. Skinny fat can occur in females and males, and according to research, it is impossible to say with certainty which gender is more often affected.
- Low birth weight: Somewhat related to the previous point, it has been shown that such babies are actually more prone to being overweight and developing obesity and type 2 diabetes.
- Diet: Accumulation of adipose tissue is mainly related to a positive energy balance. Thus, another risk factor is excessive energy intake, overeating or a diet with a high energy density, which are typically processed or high‑fat foods.
- Lack of physical activity: Lack of physical activity can promote a positive energy balance through low energy expenditure. People with minimal exercise also have little incentive to build and maintain muscle mass, which can further exacerbate the problem of skinny fat.
How can undetected lean obesity affect your health?
- Cardiovascular health: A large‑scale analysis from 2022 shows that people who are obese or of a normal weight have a significantly higher prevalence of so‑called cardiometabolic risk factors. These include the presence of diabetes mellitus, dyslipidaemia (e.g., elevated total cholesterol, LDL cholesterol or triacylglycerols), elevated glucose levels and high blood pressure). The authors of the study, therefore, point out that, particularly in populations with an increased prevalence of skinny fat status, it is appropriate to use not only BMI but also body fat measurement to assess overall risk.
- Inflammatory markers: Higher concentrations of inflammatory markers have been identified in people with skinny fat than in their counterparts with normal body fat. Chronic inflammation can then lead to further damage to the heart's health and blood vessels or affect the immune system.
- Reproductive disorders: A 2024 study suggests that reproductive health may also be affected in skinny fat women; for example, they noted a lower number of antral follicles as well as high‑quality embryos. No such investigation has yet been carried out in men in relation to obesity at a normal weight. Still, the effect can be expected to be similar to that of "classic" obesity, where sperm quality and reproductive ability are also negatively affected.
What to do about it?
Due to differences in genetic makeup, the state of skinny fat can only be influenced to a certain extent in some individuals. However, there are effective strategies that can lead to, for example, increased muscle mass, improved overall performance and enhanced cardiometabolic function. In general, it is recommended to follow the principles of a healthy lifestyle:
- Eat a balanced diet with a predominance of unprocessed foods, plenty of good quality protein, complex carbohydrates, unsaturated fatty acids, fruit, vegetables, fibre and omega‑3 fatty acids.
- Exercise regularly, bothaerobic and strength training. Cardio will support your performance and cardiovascular health, while strength training will help you build muscle mass.
- Sleep 7‑9 hours a day, and pay attention to the quality of your sleep, too.
- Don't smoke, and limit your alcohol intake. These substances further exacerbate risk factors and increase the risk of negatively affecting your body.
- Working effectively with stress. Excessive stress can be another risk factor for many diseases.
Bottom line
Although the phenomenon of skinny fat has a higher prevalence in Asian countries, it should not be ignored in other regions because it can have a hidden negative effect on your health for many years. A combination of genetic predispositions, low birth weight and environmental and lifestyle factors such as poor diet or low levels of physical activity are likely to be the cause of the development of this condition. Obesity can also have a negative impact on cardiovascular health, the immune system and fertility — similar to 'classic' obesity.
