Nutrition also affects skill gain. When nutrition is higher than 50%, you get a bonus of 1% increased skill gain per 10% nutrition. For example, 65% nutrition would result in 1.5% extra skill gain, and 99% nutrition would result in 4.9% extra skill gain.
Loss of some amount of some skills at death is unavoidable aside from skills that have reached a level of 99+. However, fighting and skill characteristics will suffer losses in the event of any death, regardless of skill levels previously attained.