The expression "low will power" is negatively charged. Using it
might cause a person with an eating disorder to feel guilty. He or she
won't benefit from feeling guilty. It doesn't improve the condition in any
way and only produces feelings of failure and worthlessness.
However, if an overweight person is going to get thinner, then a diet with
a low amount of fat must be used. If the person concerned is fond of a fat
diet, the change will, of course, require considerable personal effort.