Co-authored by Dana G Smith
Like many people recently diagnosed with cancer, I felt helpless. Surgeons had removed a malignant tumor the size of a tennis ball on my left kidney, but enormous uncertainty about my prognosis remained. Statistically, there was a roughly 50% chance my cancer would return in the coming months, with potentially deadly implications. It felt as though the world was disintegrating around me, so I clung to any sense of agency I felt I still had. My treatment was prescribed by a world-class team, still, I wondered: What could I do outside the medical office that would affect whether I lived or died?
I asked several members of my treatment team, including a cancer nutritionist, what I should be eating, but the answers consistently came back with a degree of regretful uncertainty. There are not many reputable randomized controlled trials looking at diet and cancer outcomes. I was given the advice to eat well, be active, and stay in shape — good advice for all of us, but not specific to the goal of bending my prognosis.
Plenty of research suggests how a person’s diet can contribute to their risk of cancer. One recent study estimated that five percent of new cancer cases (roughly 80,000 people a year) are caused by poor nutrition, particularly eating diets that are high in processed meats and low in whole grains and dairy. But the best diet to follow after a diagnosis is much less well understood, despite good evidence that certain cancer cells may be particularly susceptible to changes in diet.
In many ways, cancer can be viewed as a metabolic problem — how cells consume and process nutrients. Cancer cells grow, divide, and spread differently than normal cells, and consequently, they have different nutritional and metabolic requirements. Many of the mutated genes in tumors affect the cells’ metabolism, and some chemotherapy drugs target metabolic processes in order to disrupt the cells’ ability to proliferate.
Know what else has an effect on cell metabolism? Everyday nutrition.
Several studies have shown that changing the amino acid content in a diet, which comes from protein, can impact tumor growth as much as blocking a metabolic pathway with a drug. One recent study showed, in mice, that incorporating a diet low in an amino acid called methionine — found in eggs and red meat — helped shrink colon cancer cells better than chemotherapy alone.
For most diseases involving metabolism, such as diabetes or heart disease, there are well-defined dietary recommendations. For example, there is substantial evidence that diet and exercise can have a larger effect on managing diabetes than even the best drugs. Cancer research is just starting to catch up to this idea. So far, though, the majority of the work is in animal models and cells in a dish, not in humans, so clinicians aren’t ready to give people recommendations yet.
“If you ask, ‘what should I eat?’ there’s not much medical consensus at the moment,” says Jason Locasale, PhD, an assistant professor of pharmacology and cancer biology at Duke University. “Cancer is the only disease where we know there’s a metabolic component to the disease, but there’s no known way to address it with dietary changes.”
“We know nutrition has a huge effect on cancer, but what kinds of cancers and how it does it, that’s what we’re still learning.”
One reason for this ambiguity is that cancer isn’t a single disease; it’s a catch-all term for any number of changes that can occur in a cell’s genes or metabolism that cause them to divide unchecked. With this knowledge, oncologists have started tailoring people’s treatments based on their specific gene mutations rather than on the location of a tumor.
Nutrition recommendations may need to follow a similar philosophy.
For example, some cancers feed off of glucose, and in these cases, avoiding sugar and carbohydrates may be advised. Other cancers require high amounts of specific kinds of amino acids, like methionine, to survive. Restricting intake of those amino acids deprives the cancer cells and can restrict their growth, according to Locasale.
Some cancers may respond to a vegan diet, while others might require going keto. “We know nutrition has a huge effect on cancer, but what kinds of cancers and how it does it, that’s what we’re still learning,” Locasale says. “We’re also learning that a specific diet that could be beneficial for one cancer could actually promote cancer in other situations.”
Right now the safest bet is to stick to general guidelines for healthy eating. The American Cancer Society recommends people with cancer “achieve a dietary pattern that is high in vegetables, fruit, and whole grains.”
Colleen Doyle, managing director of nutrition and physical activity at the American Cancer Society, writes in an email: “During treatment, nutrient needs will likely vary from patient to patient, depending on a variety of things, including but not limited to their nutritional status prior to undergoing treatment, the type of cancer they have, treatment they are having, and how they are responding to treatment, their immune status, and more.”
In addition to metabolism, there is growing interest in diet’s influence on the microbiome and its impact on a variety of diseases, including cancer. While it’s unclear whether the microbiome plays a role in the growth of tumor cells, it has recently become apparent that it can influence some treatment outcomes.
For a year, I received cutting-edge immunotherapies, hailed by many as the future of cancer care. These treatments harness and magnify the immune system’s natural defenses against cancer cells and can have a dramatic impact for some people in cases that would have been terminal using conventional therapies.
I did well on the drugs for 10 months before an imaging scan showed a new nodule in my right lung. After having surgery to remove the growth, we added a second form of immunotherapy called ipilimumab. In my particular form of cancer, ipilimumab can as much as triple the complete response rate, but it comes with a high risk of immune-related adverse effects. It’s a risk-reward ratio I was willing to take.
After the second dose, though, I became nauseated with every meal. Then the vomiting started. Within 10 days I had lost 13 pounds, and, for the first time since my diagnosis, it felt like I was losing the fight.
A biopsy revealed that my immune system was attacking my otherwise healthy stomach lining. The offending drug was stopped, and steroids were prescribed to combat the autoimmune attack. Typically, antibiotics are given to people on long-term steroids because of the immunosuppressive nature of the medicine. This is an optimal plan in almost all cases — except in ones like mine. Research has recently established that antibiotics, which wipe out good and bad bacteria alike, impair immunotherapy response and could render my cancer treatment virtually useless.
“By altering the microbiome of the patient, you alter the clinical outcome,” says Dr. Bertrand Routy, director of the Immunotherapy Oncomicrobiome Laboratory at the Centre Hospitalier de l’Université de Montréal and one of the first scientists to publish on the connection between antibiotics and immunotherapy. “When you have an infection, antibiotics save lives. What we want to make sure is that physicians don’t prescribe antibiotics because of very mild symptoms.”
Seventy percent of T cells — the body’s most potent cancer-fighting immune cell — live along the gastrointestinal tract, making them highly sensitive to what you eat and what medicines you take. Over the last five years, scientists have started to understand how the gut microbiome influences T cells and the immune system, and how that can affect health and disease.
The general consensus seems to be that more diversity in gut bacteria is better, and, many of the studies looking at what the gut of a cancer treatment responder looks like differ in terms of which types of bacteria are present, driving home that no single strain is overly important. The one consistent finding is that people with more diversity in their gut bacteria seem to have better responses to immunotherapy.
“It’s not necessarily the names of the bacteria that’s important, but what they’re doing,” says Dr. Jennifer Wargo, an associate professor of surgical oncology and genomic medicine at MD Anderson Cancer Center. “What’s the magical function of these bacteria and other microbes that is actually mediating these immunotherapy responses? We’re not completely sure yet.”
This means there’s no one bacteria in a probiotic that doctors can prescribe. Data presented at the American Association of Cancer Research meeting in April show that taking a probiotic before immunotherapy can actually reduce the likelihood of treatment response by as much as 70%.
In contrast, a high-fiber diet, which is known to keep gut microbes happy, was associated with five-times greater likelihood of treatment success.
“Yes, it’s important to have the right microbiome, but it’s also important what you’re feeding it. You can change your diet and actually change your microbiome,” Wargo says.
Locasale, the Duke researcher, says he is encouraged by the recent interest in the ways diet can offset or complement more traditional forms of treatment, but there’s still a long way to go. And one major roadblock is money.
“The economics [of diet research] is more complicated. A lot of the investigational drugs that are given to patients in these early stage clinical trials are funded by pharmaceutical companies. And the reason why the pharmaceutical companies fund them is because if they’re successful the pharmaceutical companies can make billions of dollars from the drug,” Locasale says. “That kind of business model is not as well defined with nutrition because you can’t really patent a diet.”
In the interim, I’m left trying to follow the American Cancer Society’s broad recommendations for healthy living and emphasizing natural foods that are high in fiber. I’d like to say I’ve entirely cut out artificially sweetened snacks, which my gut tells me are not good for me, but, for better or worse, I’m still waiting for the randomized controlled trial that lead to a doctor’s order. My survival depends upon advances like these that may change the outcome of an ongoing race between clinical breakthroughs and disease progression. And it requires the field to evolve. With a properly incentivized approach to research, nutrition has the potential to be a powerful tool in the fight against cancer.