Is low body fat bad for your health?

Low Body Fat
The risks of high body fat are well known. Common obesity-related diseases include diabetes, strokes, sleep apnea, certain cancers, and more. Most doctors will recommend that all else being equal, it's best to try and keep your body fat within normal or at least lower "overfat" range.
Does that mean that low body fat is inherently healthy? Not necessarily!
Bodybuilding is a competitive sport that we can use as an illustrative example. In this sport, contestants are judged subjectively on their physical appearance (as opposed to how much strength they have, as done in sports like powerlifting).
Because bodybuilders strive for extremely low body fat in the lead-up to a competition, they are a good subject of study to see how low body fat can affect your body! Typical preparation for a contest involves years of strength training to build up muscle size, and a period of "preparation" before a competition, where the contestant focuses on drastically reducing body fat to enhance muscle appearance.
In this study published in the International Journal of Sports Physiology and Performance, researchers tracked a male bodybuilder for 6 months before and 6 months after a competition. In addition to the expected decline in body fat percentage, they also observed other physiological changes, including:
"Of note, many of the physiological changes observed included an elevation in cortisol, reduction in testosterone, reduction in immune function, alterations in mood status, and decreases in physical performance and maximal heart rate" .
It's important to note that a few months after competition, the contestant was able to return many indicators to normal (including body fat) as they stopped their intense pre-competition diet control, returning to a more sustainable diet. However, it is also important to note that strength did not fully recover to pre-preparation levels, although fat-free mass remained relatively stable. This indicates that despite retaining a relatively stable level of muscle mass throughout the process, strength decreased during preparation, reaching a low point at the time of competition (though unlike most other sports, physical performance isn't directly relevant for bodybuilding).
Female athletes with very low body fat can also experience less than ideal physiological changes/effects, such as athletic amenorrhea - temporary stop of the menstrual cycle, possibly caused by insufficient energy availability.
So if body fat that is either too high or too low may be bad for your health, what is the ideal body fat range? There is in fact no simple answer for this. While Charder's devices provide a general range of body fat that is associated with "normal" bodies (taking into account normal body functions), your ideal body composition is determined based on your personal goals and needs, whether aesthetic, performance, or just general functionality. Having a lean appearance is perfectly fine, and you can function fairly well on a relatively low body fat!  It's just important to keep in mind that there is in fact such a thing as "too low", where insufficient body fat is affecting your body's ability to function normally!

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