Improve Immunity with Food, Not Probiotic Supplements

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In the world of dietary supplements, probiotics are a big deal. After vitamins and minerals, probiotics are the third most popular supplement purchased. 

From improving digestion to immunity, people take probiotics for various reasons. However, a new diet habit survey among individuals with cancer suggests that high-fiber foods may be more powerful for immune function than pills.

Food Over Pills:

The observational study, published in late December in the journal Science, found that -- in 293 people receiving skin cancer treatment and taking probiotics -- none had a significant boost in immunity from taking a probiotic. Eating a diet high in fiber, however, was linked to better survival rates.

In addition, a rodent study done using probiotics versus a high-fiber diet had similar results. Diet was helpful in warding off cancer, while probiotics were associated with tumor growth. 

Carrie Daniel-MacDougall, director of the MD Anderson Bionutrition Research Core at the University of Texas MD Anderson Cancer Center, suggests the results of the study should make us think about probiotics more carefully and not simply consider them harmless. 

The Study:

Let's go back to the results from Science.

A lifestyle survey completed by 293 patients with skin cancer (melanoma) was compiled. It examined food records and probiotic use. Eighty-seven percent of subjects had immune checkpoint blockade therapy, a type of medicine that helps the immune system find and attack cancer cells. 

Within the group, 31 percent had used a probiotic in the previous month, while roughly 29 percent had adequate fiber in their diets (20 grams or more daily).

The investigators did not find a big difference in outcomes in progression-free survival for patients that took probiotics compared to those who didn’t. Those with adequate fiber in their diets had better chances at cancer-free survival when compared to the participants with limited fiber consumption.

“As expected, dietary fiber intake was highly correlated with fruit, vegetable, legume, and whole grain intake and, to a lesser extent, with calcium intake,” the study states. The best results were seen in those with high-fiber diets without supplement use.

The Effects of Probiotics Compared to Fiber:

Now let's explore the rodent portion in more depth.

This study utilized mice to confirm the effect of probiotics or adequate fiber intake in the human subjects. All mice were given skin cancer tumors and then received treatment with a compound that was similar to the human immune checkpoint blockade therapy.

In part of the study, mice were separated into two different groups: one was divided into two subgroups -- one subgroup took a commercially-purchased probiotic and the other took a placebo. The second group also had two subgroups -- one subgroup ate a high-fiber diet while the other subgroup ate a fiber-poor diet. A high-fiber diet seemed to help the mice combat cancer better than those in the other groups.

“Mice receiving a fiber-rich diet demonstrated delayed tumor outgrowth compared with mice who received a fiber-poor diet,” the study reports.

The mice receiving probiotics did worse than those not receiving them. Investigators noted, “they had significantly larger tumors compared with control mice”.

What All This Means and Why It Matters: 

With the increasing interest in probiotics, “good bacteria,” and the gut microbiome, probiotics are becoming staples in our kitchen cupboards. However, they haven’t been well-studied.

Most people consider probiotics harmless, particularly those that have the most reason to consider using them, like individuals with chronic illnesses. 

“However, we know from other fields, like nutrition, that specific and high-dose supplements can have unintended effects or consequences under various conditions,” states Daniel-McDougall.

While they are highly-publicized in the general population, results in clinical trials are contradictory, particularly in cancer patients. The use of probiotics while receiving cancer therapy needs more attention and research. 

On the other hand, only 5% of Americans obtain the National Academy of Medicine’s advised daily dose of fiber, which is 20 grams per day. This equates to a cup of beans and a few servings of berries. 

What Can Your Clients (With or Without Cancer) Do?

  1. Obtain more overall fiber in their diet. Focus on whole grains, whole fruits and vegetables, and more beans and legumes to obtain 20 grams of fiber per day or more.
  2. Discuss the use and safety of probiotics and other supplements with their health care provider, pharmacist, or dietitian.
  3. Avoid restrictive diets that eliminate high-fiber food groups such as low carb, keto, or paleo type diets.
  4. Limit highly-processed and refined grains which are low in fiber.
  5. Reduce alcohol, processed meat, and sugar intake, which negatively impacts the gut microbiome.

By Lisa Andrews, MEd, RD, LD


Dietary fiber and probiotics influence the gut microbiome and melanoma immunotherapy response (

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