Hi Annie,
Keeping fit & eating healthy can be a struggle during your treatment that's for sure. At the time i was diagnosed with breast cancer in july last year, I was fit, active & healthy. By the time my treatments (chemo + radio) finished mid April 2012 I had lost all muscle tone, gained about 10kg in weight (blew up like a puffer fish), & felt quite lethargic for it. One of the reasons i put on my weight was due to being on steroids as part of my treatment - this meant that at times i ate like a horse!
I was lucky enough to only have the metallic taste in my mouth for a relatively short period of time, & the only mouth ulcers i had were the ones i had prior to any treatment - probably stress related!
Ideally, try to do things that boost your immune system, cleanse the liver/kidneys, improve circulation, & keep your body active (without overdoing it!).
Some of the things i did to try & keep fit & eat healthy were:
1) made regular fresh juices with fruit & veg (eg "detox type drink" - green apple, celery, carrot, ginger, broccoli, & i often added orange, blueberries & other berries). This helps with liver cleansing & gives you energy. I was advised not to eat much citrus as its important to avoid acidic foods, & helps reduce chance of mouth ulcers.
2) go for walks with friends & relatives - walking with others gave me more incentive to get out & do more rather than doing it on my own - youll be amazed how long you walk for & how far you get just by having another person with you.
3) I started out doing some tai chi (a free weekly class at my local hospital - run by Community Health). Nice & light exercise that helps give you back some coordination, & you also meet new people. Also taught me some patience!
4) I also did some light yoga - again, light exercise that helped me with flexibility & core strength, & met some great new people (some who have had breast cancer in the past).
5) YWCA Encore Program - this was a free 8 week program run one night per week specifically for people who have been diagnosed with breast cancer, which involved light floor exercises, hydrotherapy (which i didnt do because i was still having chemo at the time & didnt want to risk an infection), & guest speakers (which were often oriented around healthy eating/maintaining fitness etc which gave you some good tips & advice). Also met some great people here too.
Other things included pilates (targeting my recovery - good for correct breathing techniques, circulation, flexibility & improve core strength). I even played field hockey whilst i was having chemo! Mind you, my brain was where the ball was but my body was way behind! But i didnt care because i was at least out of the house doing something, doing something i enjoy, getting fresh air, amongst some people i knew already & met even more new people.
I'm still carrying alot of the weight i gained during my treatment, but gradually getting back into more exercise now my treatments finished - hard to get motivated in winter, i became REALLY lethargic during radio, & i've had to move towns twice for work, move house twice, & will have to move house again soon. Doh! Once im settled again i'll definitely be able to get involved in alot more - looking forward to that.
It really is a very individual thing trying to keep fit & eat as healthy as possible during our treatments, as you often dont know what you're going to feel like from one day to the next. The main thing i would encourage is to try & do things you liked to do before your diagnosis as you're more likely to continue doing it, & perhaps doing things that involves other people to keep up your incentive. It's easy to talk yourself out of exercise but alot harder to say no to friends & family.
Other possible ways to help you could be to contact your nearest Breast Care Nurse - they can provide great advice on this sort of thing & may refer you to other specialists eg Community Health often have access to dieticians, exercise physiologists, living well programs etc. It's amazing what assistance is out there once you know where to start looking, but depends on where you live & access to that assistance; NSW Cancer Council has a booklet about Food & Cancer - you should be able to call them & get a copy sent to you for free through their info line.
All the best & i hope you find lots of interesting things that keep you as healthy as possible during your treatment :)