Body fat percentages vary from person to person and athlete to athlete. A swimmer may have a different body fat percentage to a runner and this is due to the different demands of the sports. Water supports the weight of the swimmer, but extra body mass is inactive weight for the runner to carry.
While it’s a fact that lower body fat means faster run times, you need to be sensible – and there’s generally considered to be a minimum level of body fat required for healthy living. Going below the recommended lower levels (5% for men and 12% for women) will dramatically increase the risks of colds and injuries. Staying below these levels for a long period will increase the risk of other issues, such as inadequate muscle repair after heavy training, bone breaks and, for women, cessation of menstruation. So it’s actually okay to have that piece of cake every now and then!
If you feel you need to lose weight, it’s best to approach it from two directions; a well-balanced diet with lots of fresh whole foods, fruit, vegetables, combined with a training routine that hits all exercise intensities. Short high-intensity sessions will help build quality muscle tissue, while longer steady sessions will make sure the muscle tissue knows how to use fat as fuel.
Any change in bodyweight best occurs slowly, as this means it’s come through a gradual change in lifestyle, which is more likely to be sustainable long-term. Permanent habit changes are better the short-term fads.