Body fat can be found within muscle tissue (intramuscular), under the skin (subcutaneous fat), or around organs (visceral fat), and is necessary for overall health. Certain levels of "essential fat" help protect internal organs, store fuel for energy, and regulate temperature and important body hormones.
If a person’s body fat percentage is too high, they may want to decrease it to improve their health, athletic performance, or wellbeing, or to decrease their risk of obesity-related disease. Conversely, if their body fat percentage is below the level of essential fat, they may also want to make changes to bring it up to a level that reduces their health risks.
To change body composition for improved health and fitness, individuals should aim to increase lean body mass and decrease excess fat mass. Changes to diet, activity, or a combination of both will help achieve this.
The graphic below is an adaptation from Am J Clin Nutr. 2000 Sep;72(3):694-701.
Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index.
Gallagher D1, Heymsfield SB, Heo M, Jebb SA, Murgatroyd PR, Sakamoto Y.
This study is well-regarded in clinical practice to indicate ranges of body fat percentage tabulated by gender, ethnicity and age.