Yes, it is ok to do less than that. Some people do bread and water fasts, some do only one meal, etc.
BUT:
If you are under doctor’s care or have any medical conditions/ill health your advise your doctor what you intend to do regarding fasting and get it cleared with the doctor. Those who are ill are not required to fast and the doctor may advise against any severe fast.
A severe fast should also be done under spiritual direction. Self-mortification should never be taken to an extreme and a spiritual director can help you assess whether what you are proposing to undertake is within a healthy range.