Fasting: it's a thing these days. Lots of talk about fasting.
First: Fasting isn't for everyone. People who have had a journey with disordered eating probably should keep eating on a regular basis and have some support. Medical conditions can affect how well you tolerate any diet, including one that is limited. Be aware, informed, and keep your medical team in the loop.
Second: What do we even mean by the word? I can see the eye rolls from folks with lots of experience with water fasts (consuming only water for a period of hours or days) with all this talk about "fasting" when really we are eating food. I get it and wish we had better words.
Fasting: not eating, not consuming calories, typically water only or non-caloric teas
Intermittent Fasting (Time Limited Eating): Confining eating to specific times during the day. For example, eating between noon and 6PM and not consuming anything but water the rest of the day.
Juice Fasting/Cleansing: Consuming only water, teas, juices.
Fasting Mimicking Diet: Can you see the irony? It's a fast AND a diet, which means eating and fasting at the same time. Yep. It's about trying to achieve the health benefits of fasting and avoid the downsides that limit the tolerability and safety of fasting in some circumstances.
All of these ways of eating or not eating have health benefits and risks. Some have been embraced for cultural or spiritual reasons as well.
There is a rabbit warren that of articles and information and opinions about fasting and chemotherapy that can occupy many hours. I know. My footprints are there. Some references are at the end of this post.
Here is my best summary of what I found helpful.
Regarding use with chemotherapy, the most researched approach is the Fasting Mimicking Diet (FMD) which is typically:
2. 25% of the recommended calorie intake for the height and weight of the person
3. Mostly vegetables with some nuts and olives.
FMD likely decreases side effects of chemo, allows people to avoid use of steroids, and increases the effectiveness of chemo. Very preliminary studies, small numbers, and mostly by the same team of researchers. Not definitive, but I had to decide what I was going to do during my chemo which was October 2021 through February 2022. I used what we knew at the time. Very little downside to fasting: safe, cheap, likely effective.
FMD was developed to be safe to use in medical conditions in which benefits are likely if a person fasts for several days and repeatedly. Complete fasting in situations like cancer treatment, autoimmune disease, chronic illness is challenging since many people experience hunger, headache, and weakness at the beginning of the fast. In addition, fasting completely from food or caloric beverages results in weight loss which can be undermining. Specifically in cancer treatment, loss of weight can limit the ability to tolerate treatment, and can be extreme enough to be life threatening.
The researchers are asking if there is a way to get the benefits of Fasting (lower blood sugar, lower insulin levels, lower Insulin-like Growth Factors (IGF), without the extreme weight loss. How much of which kinds of food can be eaten and keep weight stable and also get the metabolic benefits?
What did my FMD look like? Well, it evolved as I learned. I personally did better when I avoided high histamine foods during my fast and for the few days after chemo, so the prescribed FMD used in the studies wouldn't work for me. I also really don't like olives and found that eating olives during a fasting day just made me feel really sad. So, I made soups from vegetables that I roasted with some olive oil, seasoned with salt and herbs, and pureed with water. I ate 2-3 cups of this soup each day. I also ate limited amounts of nuts, and some crackers I made from nuts and seeds. I found that my hunger was much stronger once I started to eat for the day, so I ate at 2PM, at 4PM, and at 6PM.
Impact of modified short-term fasting and its combination with a fasting supportive diet during chemotherapy on the incidence and severity of chemotherapy-induced toxicities in cancer patients - a controlled cross-over pilot study
Randomised controlled trial of intermittent vs continuous energy restriction during chemotherapy for early breast cancer
Fasting-mimicking diet plus chemotherapy in breast cancer treatment
Fasting mimicking diet as an adjunct to neoadjuvant chemotherapy for breast cancer in the multicentre randomized phase 2 DIRECT trial