What This Functional MD Wants You To Know About Intermittent Fasting & Cancer
In our society, many believe getting cancer is a predestined fate. An uncontrollable genetic destiny. However, according to nephrologist Jason Fung, M.D., fasting expert and author of The Cancer Code, lifestyle and environmental factors do play a role: When it comes to cancer, "genetics are not the only thing that's important," he explains on this episode of the mindbodygreen podcast. Genetics are key, yes, but there are lifestyle factors at stake that may encourage certain cancers to manifest and grow.
Which raises the question: What are the lifestyle factors that can potentially raise your risk of getting cancer? Well, says Fung, "Sugar and processed foods are probably the biggest contributors, as well as eating constantly." Let's unpack that last one: Here, Fung breaks down the link between fasting and cancer.
Cancer loves to grow.
"If you're going to tip the scales in favor of growth, then you're going to tip the scales in favor of cancer because cancer loves to grow," notes Fung. That's because when your cells constantly grow, without a proper cleanup process to clear out any damaged proteins and organelles, those damaged particles can accumulate in your cells. When this happens, your cells cannot divide and function normally, which can cause cell death, contribute to age-related diseases, and, yes, have the potential to become cancerous.
So, where does fasting come into play? Well, says Fung, "Every time you eat, you're telling your body you should grow. And the one thing that's going to grow more than anything else is those cancer cells."
Intermittent fasting can halt your body's growth mode.
Since your cells grow with more fuel, intermittent fasting "turns off the engine," so to speak, so damaged cells aren't constantly building up. "Once your body recognizes that there are no nutrients coming in, it goes into this repair maintenance mode. It starts to break down all of your old cellular parts and organelles," says Fung (aka, that necessary cleanup process we mentioned above). "It's actually the first step in the rejuvenation process because you've got to get rid of the old stuff first before you can bring in and rebuild that new stuff."
It's a process known as autophagy, and its primary trigger is, in fact, intermittent fasting. It's important to note, though, that autophagy remains a bit controversial when it comes to cancer: Research has shown that autophagy may help stop cancer before it starts but that if tumors are in the late stage, autophagy may actually contribute to their growth. (Read more about autophagy and cancer in our full explainer here.)
So how long should you fast?
Of course, much more research is necessary to demonstrate a clear link between the two, but intermittent fasting is a great tool nonetheless (see more of its benefits here). But there are more than a few time-restricted eating plans out there—how long do you need to fast to reap those autophagy-related benefits?
Here's what Fung suggests: "I think in order to get into autophagy, you have to be up into the 16-plus-hour range." You may need more or less, depending on your exact eating habits and weight, but a 16-hour fast is what he generally recommends.
However, Fung also encourages an occasional longer fast, if you can handle it. "I think it's always beneficial once in a while to get into a longer state, which is sort of 24 hours plus because then, you're really gonna activate [autophagy]," he says. "You can store sugar in the form of glycogen in your liver, and that will last about 24 hours. [After 24 hours], you can start to break down some of these other proteins you don't need."
That's not to say you have to complete a super-long fast (shorter 16-hour fasts are A-OK), but Fung says you may experience greater autophagy if you do it occasionally—think once or twice a year.
There's so much more we need to learn about the connection between intermittent fasting and cancer (in fact, there's so much more to learn about cancer in general), but the research is interesting nonetheless. Plus, intermittent fasting is a free and relatively easy tool to incorporate into your lifestyle. As Fung notes, "Maintain a good weight, don't eat too much sugar, and maybe throw a bit of intermittent fasting in there. You never know; that could really benefit you."
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