Part 2: Nutritional Considerations for Cancer

Jul 16, 2025

a woman sitting at a desk in front of a laptop — Photo by Beyza Yılmaz on Unsplash

Last week, we looked at some nutritional recommendations for someone who has been diagnosed with cancer.

Of course, there are many different types and sites of cancer, and even if a cancer is identified in every way imaginable, it’s important to remember that cancer is heterogenous, like snowflakes, that no two types are alike. Moreover, nutritional requirements will change from pre-diagnosis, to treatment, to recovery and post-treatment.

Still, what I’m doing is looking at the best nutritional guidelines across the board. The American Institute on Cancer Research and the World Cancer Research Fund are among the best organizations to refer to regarding nutrition and cancer, as well as activity and other lifestyle habits.

As quick recap, in last week’s article, I did a quick take on antioxidants (referring to earlier articles). Dietary antioxidants (that is, those obtained from whole foods and not supplements) neutralize and buffer cellular damage as well as metabolic waste products and are therefore anti-cancer molecules regardless of a diagnosis. Additionally, “a high intake of anti-oxidant-rich foods is inversely related to cancer risk” and “Cancer treatment by radiation and anticancer drugs reduces inherent antioxidants and induces oxidative stress, which increases with disease progression.”1 As I said in the last article, we acutely deplete antioxidants with exercise--even stress can do the same. With active cancer and cancer treatment, imagine just how much we deplete antioxidants.

Another consideration from the last article was saturated fat, which is positively associated with cancer-specific and all-cause mortality. One review we looked at noted that cancer patients who continued to eat high-saturated fat diets had the highest mortality rates, and those who limited their saturated fat intake were more likely to survive. Unfortunately, the greatest amounts of saturated fats are found in red and processed meats, followed by full-fat dairy products.

In the vein of fat, the omega-3 fats are also positively associated with better outcomes in the context of cancer. One systematic review of nutrition and cancer outcomes noted that consumption and intake of specifically marine omega-3 fats “improves DFS [disease-free survival (that is, once cancer is cured)] and OS [overall survival--that is, irrespective of the state or stage of the disease]. Indeed, in vitro, studies showed that ω3 PUFAs have antiproliferative and apoptotic effects on human colorectal cancer stem-like cells.”2

On to the new stuff: All about fiber.

Fiber may not sound like the most exciting topic on the surface, but bear with me, and hopefully you’ll see it differently in a bit.

Fiber is probably more studied regarding its relationship to colorectal cancer than to any other cancer. In terms of prevention, fiber intake is negatively associated with incidences of colorectal cancer.3 That is, the more you tend to consistently consume fiber, the less likely you are to develop it, but the benefits don’t end there.

One study AND meta-analysis looked at and evaluated the available evidence of fiber intake and its relationship with colorectal cancer (CRC), titled “Association between Dietary Fiber Intake and Mortality Among Colorectal Cancer Survivors”4: The authors looked specifically at four prospective (forward-looking/going) cohort studies that included about 500 people with CRC, diagnosed between 1999 and 2003, who were enrolled in the Newfoundland Familial Colorectal Cancer Study. Their follow-up period went through 2010.

From the Newfoundland study, the authors found that “CRC patients with the second quartile of dietary fiber intake had a 42% lower risk of all-cause mortality… and 58% lower risk of CRC-specific mortality… compared with those with the lowest quartile.”

To put some hard numbers on it, the authors explained that “For each 5 g/day increase in fiber intake, the risk of all-cause mortality and CRC-specific mortality decreased by 14%.” (The CRC-specific mortality relates to people succumbing specifically to CRC, as opposed to something else while they were dealing with it.)

The interesting thing is that the authors found that the benefits of fiber seemed to plateau at about 22 grams a day. A measly 22 grams. To put that in perspective, the Dietary Guidelines for Americans recommends fiber intake for people two years and up (yes, two-years-old)--excluding, of course, infants and pregnant or lactating women (who have different nutritional needs and requirements)--of 14 grams for every 1,000 calories consumed.5 If you eat 2,000 calories a day, that would equal 28 grams. So, for a person with CRC were to simply get this recommendation, they’d likely be more than good.

Still, this fiber-intake recommendation is kind of a minimum target, and Americans have a hard time getting there. According to NHANES data--National Health and Nutrition Examination Survey--the average US adult eats 16 grams of fiber a day.6 This is the average, and not unsurprisingly, women tend to eat a little more fiber than men, which may partly explain why CRC tends to occur more in men.

Although it was outside of the scope of cancer, another review--“The Health Benefits of Fibre”--examined European and North American fiber intake and looked at the associations of health outcomes. Based on their analyses of the available literature, the authors state:

Comparison with data from the National Health and Nutrition Examination Survey (NHANES) showed that on average, dietary fibre intake in European countries was higher than in North America. Based on these data, it appears that within Europe and the US, dietary fibre intake is around one third below the recommended level. Stated differently, within the Western world, most of us should increase our dietary fibre intake by around 50% compared to our current intake.7

Let’s sing it again: they recommend we double our fiber intake.

So, what is it about fiber that’s so beneficial?

First, not all fiber is the same. There are insoluble and soluble types.

Soluble fiber (SF) generally comes from whole grains and legumes and binds with molecules and escorts them out. The mechanism of soluble fiber is that it “dissolves in water and forms a gel-like substance,” and “In this process, short-chain fatty acids, such as butyrate, acetate, and propionate, are produced. They act as energy source for colonocytes [colon cells] and the microbiome, offering anti-inflammatory and immunoregulatory effects. Butyrate is also proposed to be protective against CRC by attenuating its cell proliferation.”8

By contrast, insoluble fiber (IF) generally comes from fruits and veggies and is straight roughage that plows through our digestive tract. “IF do not dissolve in but are able to hold onto water,” and “unlike SF, IF is not fermentable by the colonic microbiota. IF’s beneficial functions include adding bulk to stool and promoting gut motility. By reducing transit time of stool in the colorectum, it is proposed that IF helps to prevent CRC by shortening contact time of carcinogen with the mucosal cells.”

Going a little deeper into the short-chain fatty acids (SCFAs), echoing a previous point, some of them, “such as butyrate and propionate, may help induce apoptosis [programmed cell death] in tumor cells” (footnote 4). We can obtain some SCFAs through our food, but much of them are used, absorbed, and metabolized early in digestion, way before they get to our colon, so the gut bacteria that produce the SCFAs allow these beneficial molecules to be present at a time and place where the nutrients from food just can’t get to in the numbers we need.

And “Dietary fiber intake could affect mortality through several mechanisms. Dietary fiber may influence CRC survival by increasing fecal bulk, absorbing fecal carcinogens, binding secondary bile acids that might otherwise act as tumor promoters, taking them out of the digestive tract, and thereby decreasing interactions between colorectal tissue and carcinogens” (footnote 4).

Even though we started with nutritional considerations in the context of cancer, healthy eating is healthy eating, and healthy eating will lower your risk of developing chronic diseases, and in this case, specifically eating fiber will reduce your risk of developing colorectal cancer, and if you happen to have it or have had it, eating a diet that is dense in fiber-rich foods should be a priority.

The great thing is that the foods that bring the fiber also bring tidal waves of other nutrients, nutrients that are essential for health and staving off disease. One recurrent and consistent theme I kept seeing in these papers--the ones cited and the other two dozen I didn’t--was the Mediterranean Diet--a diet that is low in saturated fat (as discussed in the previous article), rich in unsaturated fat, omega-3 fats, and antioxidants. It limits red and processed meats, is plant-predominant but includes plenty of fatty fish, olive oil, and low-fat dairy. It’s an easy dietary pattern to follow and to adhere to.

And the Mediterranean Diet is not only recommended in a lot of recommendations as a nutritional therapeutic approach to cancer. It’s also recommended in just about every reputable corner of nutrition.

Whether you’re well or ill and if you want to improve your diet, your health, and likely your longevity, a great place to start is with this dietary pattern.9

But we’re not done yet. Next time, we’ll wrap up this mini-series with a couple of more nutritional considerations for cancer.

The Flexitorium by Joseph Anthony

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