Hi and warm welcome to the Macmillan Online Community although sorry that you had to find us and especially sorry to hear about your BC diagnosis.
Over my many years and over 750hrs of chemo I have tried everything and what happens happens. A group of 10 people doing exactly the same prep going through exactly the same chemo will have 10 different reactions.
The one thing I would say is you need as much ‘fuel’ to keep your energy going as this is one of the casualties during treatment, so not sure that fasting would be helpful as you are not getting your fuel tank topped up 
I was continually told eat a balanced diet but think ‘pregnant mum’ 
I had a blood cancer and the treatment for this is completely different from BC treatment but you may find talking with others who are walking the same type of cancer treatment journey will help you navigate this difficult time.
The Community is organised into cancer specific support groups so can I recommend you join our supportive Breast cancer group as this will be a good place to connect with patients and families navigating the same type of cancer treatment journey.
To join a group just click on the link above then choose 'click to join' or 'join' (depending on the device you're using) on the page that opens.
You can then introduce yourself by putting up a ‘New Thread’ or hit the box with the X on the top right (phones), you could just copy and paste the text from this your first post. You can also join in with existing ‘Discussions’ by clicking on 'reply'.
It’s always good to talk and the Macmillan Support Services provides lots of information, support, financial guidance or just a listening ear.
Most services are open 8am to 8pm, 7 days a week and it's free to call on 0808 808 00 00 have a look by Clicking here to see what is available and we also have our Ask an Expert section, but do allow two working days for replies from our expert team.
To find information covering diagnosis, treatments and pages covering most types of cancers can be found on our Online Information and Support Section.
((hugs))
