Short-term fasting and chemotherapy­—where the science stands

A version of this originally appeared on Today’s Dietitian RD Lounge here.

Sickness often turns us to comfort foods like chicken noodle soup, but maybe it’s not ideal for everyone. In the field of oncology, fasting for disease treatment has become a popular subject. As research of calorie restriction though short-term fasting just before chemotherapy, generally defined as a complete lack of food with non-caloric beverages, has demonstrated a wide range of beneficial effects. It has helped to reduce tumor growth by aiding in the efficacy of chemotherapies to reducing damaging side effects from these treatments. Research continues as initial studies in mice and dogs yielded positive outcomes looking at fasting a few days before chemotherapy. Scientists have since moved to small human studies of only approximately 10-20 cancer patients in each, investigating fasting therapy prior to receiving chemotherapy. These studies also yielded positive results and additional clinical research trials are now underway.

Proposed mechanism of short-term fasting

Generally healthy cells are growing and reproducing, but during fasting their energy shifts towards repairing and protecting instead. Researchers postulate the external stress of energy restriction causes rapidly reproducing cancer cells to not respond and protect themselves as quickly—known as differential stress resistance. It’s likely in extreme environments that cancer cells are unable to quickly adjust to metabolic pathways. As a result, chemotherapy agents hit cancer cells harder since they target rapidly dividing cells. So with energy restriction, normal cells metabolically slow down and are protected from chemotherapy’s toxic effects when in self-maintenance mode.

A dive into the latest research

A 2017 systematic reviewof 22 studies investigated short-term fasting and its role in cancer treatment as this was evaluated in previous studies with inconsistent results. In this review, 18 studies were conducted with mice and dogs and 4 were with humans. Animal studies were randomized controlled trials and adopted 24-72 hour periods of complete food deprivation prior to chemotherapy. 10 of these studies identified chemoprotective effects and 15 showed tumor suppression effects.

Other studies also find benefit only after 48-72 hours of fasting, such as Dorffet al, which looked at cancer patients and similarly included three cohorts of fasting for periods of 24 hours, 48 hours, or 72 hours before chemotherapy. This study did allow for <200 calories per day however. The study suggested patients in the 48 and 72-hour fasting groups had significantly reduced rates of chemotherapy toxicities and reduced DNA damage compared to the 24-hour fasting group. Another study conducted by Chenget al investigated blood work in mice and found there were normal lymphocyte counts and normal white blood cell counts with the 72-hour fasting group, but not for those in the 24 hour fasting group. Although species differ between mice, dogs, and humans, these studies still reveal the 24-hour fasting period maybe insufficient for potential fasting benefits.

Overall findings

Overall studies indicate that fasting substantially decreases chemotherapy side effects, such as organ damage, toxicity, immunosuppression, chemo induced death, suppressing tumor progression and improves survival. It also helped to restore cardiac function, and relieved bone marrow suppression in some. Fasting longer than 48 hours and up to 72 hours was found to be crucial for exerting the positive effects of fasting therapy.

When fasting therapy was paired with chemotherapy, the anti-tumor effect of chemotherapy drugs was increased. A synergistic effect appears to result by combining these therapies as this achieved better outcomes than using either of the treatment methods alone. All studies did not limit the food intake during the period of re-introducing food. Overfeeding is common in this period and study subjects would typically regain the weight that was lost during the short-term fasting period relatively quickly, which is generally desirable in order to reduce the risk of malnutrition.

Future directions for research

Areas for further investigation continue to be uncovered. For example, fasting therapy could also be influenced by the tumor types and applied to chemotherapy drugs. Also, whether the sufficient calorie supply in the entire fasting therapy cycle is required still remains a question and needs to be resolved in future studies. This would help to further understand fasting therapy in cancer patients. Additionally, if fasting enables higher tolerances to chemo regimens, this could raise the upper limits of tolerable chemo doses. It could also determine whether the methods could achieve a higher tumor control rate and may be promising directions for future researchers.

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Considerations and precautions

Fasting is NOT ideal for everyone!! If you have any chronic diseases such as diabetes, kidney disease, liver disease, heart disease, low blood sugar, low blood pressure, or an autoimmune disease, then fasting may not be advised. Also use caution if you have a history of an eating disorder, since this can trigger a relapse. People who are in a severe wasting state called cachexia or are otherwise malnourished should avoid fasting therapy to prevent further weight loss. Some cancer types and treatments can make your body hypermetabolic, where your metabolism runs very rapidly, and are more prone to unintentional significant weight and muscle loss. Fasting might only be advised for certain types of cancers since head and neck, lung, pancreatic, stomach, liver, ovarian, or metastatic cancers often cause hypermetabolism, resulting in unintentional weight and muscle loss. It may be best reserved for those with breast and prostate cancers, but it is just speculation at this time. Additionally, some drug therapies have a better response to treatments if people gain weight and not lose it. Most people who are otherwise healthy may consider fasting if your oncologist approves.

If you are taking oral chemotherapy, do NOT fast if pills cannot be taken on an empty stomach. Some oral chemo drugs must be taken with food for best absorption. Some even have very specific recommendations for the amount of carbohydrates, fats, and proteins to eat in order for the medication to be absorbed properly.

The application of fasting therapy with cancer patients should be used very cautiously and the science needs to be more firmly established. A long fasting duration should be avoided to prevent severe calorie insufficiency and weakening of the body. The effects are a cost to benefit ratio.

Take home message

First, I’d like to say always ask your oncologist before fasting first!!I cannot stress this enough. This is an exciting area of research with a lot of potential, but it is not safe for everyone. The role of fasting in cancer patients should be a very guarded approach, as the risk of malnutrition and muscle loss may occur. This can result in treatment delays, chemotherapy dose reductions, or other side effects.

If short-term fasting is appropriate for you, it may potentially be an effective and extremely inexpensive option to decrease side effects, suppress tumor progression, and further improve prognosis when used with chemotherapy. Additional clinical trials with more patients are still needed before short-term fasting could be used in standard practice. The studies conducted reveal that short-term fasting prior to chemotherapy appears to be more effective than intermittent fasting.

If you are able to fast, continue to drink water! You do not want to show up to your treatments dehydrated. You want to protect your kidneys from some of the drugs. This could delay your treatment or you may need fluid infusions first. Fasting does not mean skipping out on fluids.

This potential intervention requires further validation by evidence based clinical data to determine which cancers, at which stage, and in what combinations of fasting show to be effective. If you do it too long you can do more harm than good as it may weaken the immune system, cause unwanted weight loss, and delay treatments. Everything has to be timed so it maximizes damage to the cancer. Despite some of the limitations and unknowns, I’m still quite excited to see where the research ends up taking us.

For more updates, you can follow Survivors’ Table on Facebook. Thanks for joining me on this journey! – Danielle

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