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Diet and Fasting during chemo?
Hi, wondering if anyone has explored or has practiced fasting during their chemo regimen? I have been reading up on intermittent fasting and there is a body of knowledge around the benefits of fasting on metabolic processes within the body and specifically the growth and impacts on cancer. One good source is a study published in the NEJM (New England Journal of Medicine) titled "Effects of Intermittent Fasting on Health, Aging, and Disease" first published in Dec. 2019 (381;26).

The study summarizes intermittent fasting effects on the body and the switch from 1) energy repletion (utilization of glucose for cell growth/plasticity) when consuming food and sleeping to 2) periods of systematic and cellular adaptation (body goes into ketogenesis to build resistance of cells/organs during periods of stress) when fasting.

For cancer, there are studies dating back a century and the underlying mechanisms (during fasting) are thought to involve the activation of transcription factors and enhancing cellular protection against cancer and bolstering the stress resistance of cells. An excerpt of the study on clinic trials:

"Clinical trials of intermittent fasting in patients with cancer have been completed or are in progress. Most of the initial trials have focused on compliance, side effects, and characterization of biomarkers. For example, a trial of daily caloric restriction in men with prostate cancer showed excellent adherence (95%) and no adverse events. Several case studies involving patients with glioblastoma suggest that intermittent fasting can suppress tumor growth and extend survival. Ongoing trials listed on ClinicalTrials.gov focus on intermittent fasting in patients with breast, ovarian, prostate, endometrial, and colorectal cancers and glioblastoma (see Supplementary Table S1). Specific intermittent-fasting regimens vary among studies, but all involve imposition of intermittent fasting during chemotherapy. No studies have yet determined whether intermittent fasting affects cancer recurrence in humans."

The study notes challenges in adopting such an approach based on the cultural practice of consuming 3 meals a day (plus snacks) and a switch from this cultural norm will not normally be contemplated by a doctor.

Anyway, if anyone has any experience with fasting, I would love to hear from you....

And no need to reply back with advice on eating 3 square meals a day...LOL.


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6271 Posts
TravelBugMick‍ hi there! !! I don't have any experience with this but it would be best to check with your your oncologist first. My fiance's oncologist wanted him to consume as many calories as he could get (he had esophgeal cancer and couldn't eat) and was dangerously underweight. he had his shakes via feeding tube. He needed the calories to have strength for treatment and surgery. That was a different situation of course. You can also check with the cancer info line and see what they have to say. 1 888 939 3333. Hope you get the information you are looking for.
22 Posts
Hi Mike,

The benefits of intermittent fasting are extensive and I have been doing it for many years. However, researchers have reported opposing views about its benefits for cancer so, since my cancer diagnosis last year, I do only 14-16 hour fasts to avoid autophagy. Autophagy is believed to be protective against cancer in someone who does not have cancer, but in someone who already has cancer, research has shown that autophagy may also protect cancer cells from treatment.

It’s similar to the research that reports the benefits of antioxidants for cancer. Again, antioxidants may be protective against cancer in someone who does not have cancer, but researchers have discovered that antioxidants also protect cancer cells so cancer patients are advised to avoid vitamin C supplements and other antioxidants in the form of supplements while receiving chemotherapy. (Nutrients from food are considered safe.)

As for ketosis from a ketogenic diet, in theory it sounds beneficial to reduce carb intake to starve cancer cells because of their uptake of glucose. However, some cancer cells-not all-have shown maladaptive behaviour in which they resort to thriving on fats in the absence of glucose. Research on this topic is more in favour of a ketogenic diet, but there is increasingly more research coming out to support avoiding it. Personally, I enjoyed a plant-based ketogenic diet with some fish, but I stopped it after the cancer diagnosis.

I would say diet and nutrition, and what counts as a healthy diet for a cancer patient has the most opposing views of any topic related to cancer. Everyone agrees on the benefits of exercise, but no one agrees on what counts as a healthy diet for people who already have cancer. I will return with a link that supports intermittent fasting for decreasing the risks of breast cancer recurrence. Edited to add link:


As for fasting during chemotherapy, are you planning to do it? The research on this topic is very interesting.
Hello Everyone,

Great discussion! Eating well during treatment is so important. Treatment centres often have Dietitians you can speak with to come up with the best plan for you!

Adding a link from www.cancer.ca on healthy eating: Eat well - Canadian Cancer Society and the booklet Eating Well When You Have Cancer.

3 Posts
My naturopath had recommended that I fast 13 hours between supper and breakfast as well as fast the evening before a chemo IV to after the chemo IV.
I have followed his advice. My first IV went quite well and I plan to do the same for the one coming tomorrow.
1 Posts
HI Mick

Interesting discussion. Diet is obviously important at any time ... and I know fasting can be a good routine for clearing out toxins and your system generally. If this works for you, it would be great. But I would support Brighty's suggestion to talk with your consultant beforehand.

I completed R-CHOP chemo for follicular lymphoma three months ago. Fortunately I didn't have too many adverse effects, but nausea (not actual sickness) was a big factor. The chemo chemistry affected my tastebuds and olfactory senses such that for the first 11 days (of each 3-week cycle) after treatment it was a challenge to eat anything. My focus was to get enough calories into me to keep my weight up. For the first couple of days each cycle, I really had to make myself eat despite the weird taste. Not terrible, but sort of a slow, psychological coaxing process. What I found pleasant to eat throughout my chemo were: cornflakes with lots of blueberries, strawberries, raspberries; yoghurt and fruit; and vegetable soup. What I couldn't face was complex dinners with sauces -- even things that I normally love. The plainer the better.

A couple of weeks after chemo my appetite returned to normal and I am now enjoying all the stuff I did previously. Everyone reacts differently with different types of treatments.

Good luck with your chemo. Keep that positive spirit. Don't be too hard on yourself!

Cynthia Mac
2927 Posts
TravelBugMick‍ , you mention "studies dating back a century," and I would think that many such studies would be quite out of date now. It's been my general practice to discount information older than several years to a decade, because mindsets and practices and research changes so quickly. Goodness, I'm sure if we were to go back a century, we'd find plenty of studies advocating that people consume tobacco and laudanum!

As for choosing to fast or not, I'm in the "check with your oncologist" camp.
Cynthia Mac‍, I am more partial to leeches. They help to get the bad mojo out of the blood....LOL

Not to be contrarian, but I shall, there are immense bodies of knowledge in countless disciplines that have been handed down to generations for millennia. These studies in particular were cited by doctors as the foundation for the understanding of fasting and the evolutionary survival role it has played for humans (and extends to other mammals). We have an abundance of food available at all times so the work is looking at "reactivating" metabolic pathways that are usable by the body to change gears for cellular restoration when in food deprived states. An important "built in" genetic tool that should not be ignored in my opinion. And preliminary clinical study work in last 5 years supports benefits so not voodoo science.....

I spoke to my med oncologist, to get the expert advice, and while he felt there may be some good benefit, the significant hurdle now is the specific recommendations for fasting given over 200 drugs and different treatment regimens (curative vs palliative). His issue was providing a specific recommendation given the myriad of drugs and complimentary drugs that often should be taken with food to ensure the patient is maintaining nutrition during treatment. No easy fix here as I see this as a long term issue that involves both considerable effort for clinical trials and involvement by drug companies to look a slow release options to allow fasting periods when only consuming water.

While I see good support from naturopathic doctors, pharmacological recommendations are based on clinical trials and there are pretty serious complications that could be encountered if drugs are not taken as recommended. So, I decided against winging it with the naturopathic approach.

So, no definitive outcome here for my fasting and I appreciate everyone weighing in on the topic.... :)

Cynthia Mac
2927 Posts
You make a really good point, TravelBugMick‍, that many drugs (and some vitamins) need to be taken with food, and if you’re fasting from 6 at night til 8 the next morning, you’re going to have a challenge taking that medication that needs to be taken with food at 10 p.m.!

I also find that with this “intermittent fasting buzz” the terms “fasting” and “intermittent” are sometimes “fuzzy” with respect to definition. I saw a comment somewhere recently that there should be 13 - 16 hours between dinner and breakfast. Well, if you have dinner at 6:00 and breakfast the next morning at 8:00, you pretty much fasted for about 13 1/2 hours, and I was always taught that we got the word breakfast from “breaking the fast.” A friend of mine said she was going on an intermittent fasting meal plan, and she said it boiled down to eating only when she was hungry. So, maybe this intermittent fasting thing is just over my head.
4 Posts
Hi TravelBugMick!

I've been doing research and practiced fasting to different degrees as part of managing my long-lived type 2 diabetes. Some of it I've looked at in the context of my wife's stage 4 inflammatory breast cancer care. Fasting is a hot topic these days, with a lot of differing professional and pseudo-expert views indeed. The base knowledge I collected along the way was useful to understand some of the advice you hear as it relates to her cancer treatment - like the idea of limiting anti-oxidants while undergoing chemo, how fasting can trigger cell-level improvements, and how it can be a double-edged sword with trying to fight cancer. It's a complicated topic all right.

My wife and I have embraced forms of fasting, but I make no claims to what it did for her cancer. All I can mention are my experiences. I've had positive results with rebalancing my sugars through fasting, but I've had also some setbacks with it. I lost my GP when he had to leave Canada to look after his mom in England when COVID hit. In my opinion, not being medically supervised during fasting is a bad idea if you aren't healthy to start with or you take a potpurri of drugs for health reasons.

What could go wrong? Well let me tell you how I learned one way, the hard way. One of the drugs I had been taking did not do well with resuming fasting after binge-eating this past Christmas, and it triggered an euglycemic diabetic ketoacidosis episode that caught me by surprise with a visit to the ER and a week in the hospital. I knew something was up before it went critical, but I had no GP to check in with. I wanted to get my blood and urine checked, and I couldn't get anyone to check while COVID locked down visits to walk-in clinics and the hospital. The GP the clinic assigned to check on me after the hospital visit was right on the ball with the latest research, and that was a breath of fresh air. I went too far off-balance with that drug in the mix (and all the home baked goodies family kept dropping off for Christmas), and it would take months of not fasting to rebalance before I can go back to using any form of fasting again. Oops!

Unfortunately, having someone to talk to that could relate didn't last, as they assigned me a new doctor fresh out of school at the clinic after that. She is a great doctor, but not comfortable with the idea of fasting at all. That's not what she was taught to communicate to her patients, and I get that. I got the lecture about eating 3 square meals a day, add snacks, and I'm sure you know the drill with the expected standard of care.

Have I found some interesting resources on fasting out there? Well I'm a layman in the field, so my opinion of the resources is worth squat, but there were two Canadian doctors that helped add context and thought by offering free information based on what feels like evidence based practice/research.

Dr. Peter Attia's podcasts are great mind snacks. Watched him on a TED talk, where he was really passionate about the idea of helping people live better and longer by bringing knowledge to the masses. Fasting was one of those areas he brings up a lot, as it keeps coming up in the context of cancer and diabetes from the researchers he talks to. Dr. Attia interviews a lot of true researchers in the field of living longer - but the level of detail in some of those podcasts is over the average layman's comfort level. I hesitate to recommend his podcasts to people that aren't comfortable with the science. I had to use a lot of circular learning with some of the metabolic topics - but - there are also some really interesting topics and people he interviews where you don't have to dig deep to follow what is going on. For instance, his talk with Matthew Walker about why sleep is important to rebuilding your mind and body was an eye opener for many I've recommended it to.

I also found out about Dr Jason Fung on one of those podcasts, and he has been preaching to the diabetic world for a while now about fasting. He has a lot of compelling arguments pro-fasting as a general concept and a lot of public media published to tell people about the evidence he has collected. He's been expanding that concept into the context of cancer recently. He starts with telling people to have a physician onboard to watch your body's response while you go down that path, if it's something you can explore, and I agree.

I don't take either resource as authoritative, but I do respect their data and their arguments that there is more we can do to improve our health. I get a lot of access to knowledge without spending a dime, and that works for me.

It sounds like you have done a lot of research on your own, so those resources might be too simplistic for your needs, but I thought I'd share my experience and two resources that have been interesting.

Best regards and luck with the research,

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