Cancer and Obesity

Disclaimer: I support the body positive community, as in I don’t think people should be made to feel bad about how they look or be treated poorly based on their size or appearance (why can’t we all be nice to each other). I also want to stress that when I say “fat people,” I’m using ‘fat’ merely as a descriptor and am not using it to shame or make fun of anyone.

A few weeks ago, Cancer Research UK (CRUK) debuted what I thought was a cleverly designed campaign to raise awareness about obesity and increased cancer risk. I think I was in the minority in thinking it was clever. To put it lightly, it was not well received, particularly amongst body positivity advocates. As of writing this article, over 13,000 people have signed a petition to ask CRUK to remove the advertisements and end the campaign.

The issue with this campaign is everything involved here is very nuanced. What I mean is we know the causes of obesity are varied, and we also know the causes of cancer are varied. There are no clear-cut answers of which side has the “correct” opinion, because there are good arguments to be made for and against the campaign. Let’s break it down objectively, and I’ll give my final opinion at the end, so stay tuned! Or jump to the end if you want to, I can’t control your life.

Obesity

The number one cause of obesity is an unhealthy lifestyle – eating too much, not getting enough exercise, etc. For some, this is due to an intentional choice. But for a lot of people, it arises from elements beyond their controls such as mental illness, eating disorders, socioeconomic status and/or the unavailability of inexpensive healthy options/general lack of healthy options.

More minor causes of obesity include certain medications that cause weight gain or make it difficult to lose weight, genetics, and certain diseases such as Cushing’s disease. However, lifestyle by far outweighs medication, genetics, and diseases as causes of obesity.

Before getting into the research, I want to make a quick note that the current standard of obesity diagnosis (or being diagnosed as simply overweight) relies on Body Mass Index (BMI). On the population level, BMI does correlate well with diseases such as diabetes, arthritis, and sleep apnea. However, in the past few years BMI has gotten a lot of attention, as it is not as accurate a measure of health and body composition as it’s sometimes made out to be. For example, it doesn’t take into consideration muscle mass versus actual body fat mass, so if you have a lot of muscle, you could be categorized as an “overweight” BMI, even though you’re obviously healthy. This has brought up many conversations surrounding the idea that “health comes in many different sizes,” because you can be clinically overweight but have a healthy lifestyle. This is something to keep in mind as we get to the research behind obesity and cancer, as most studies rely on BMI as a measurement of obesity.

The Research

I follow a prominent body positive Instagrammer. I’ve followed her for a while now because I like her message and she generally posts uplifting content. When this whole scandal broke loose, she had a series of stories in which she shared her opinions on the issue. It almost caused be to unfollow her, because she was stating there was “no science to back the claims,” insisting that “correlation does not prove causation.”

Excuse me, but no.

There is a ton of literature out there supporting obesity as a risk factor for cancer (rather than link them all here I’ve included a few at the end). There are also causational studies – yes, they’re done in mice, but that’s because you can’t ethically force a group of humans to gain excessive amounts of weight purely for the science. It was disheartening to see such an influential body positive presence straight out denying the science. Sure, she has a right to have a negative opinion about the campaign, but she does not have a right to be a science denier.

(Okay, she does have the right to deny science, but it doesn’t mean she’s correct about it).

Inflammation

Here’s what we know: chronic inflammation is pro-cancer. The inflammatory response occurs naturally in our bodies in response to trauma – things like cuts and infections. It’s a necessity to keep our bodies healthy. However, chronic inflammation – that is, when the inflammatory signals are constantly on – is bad for us. Cancer cells can use this inflammation in their favor. Since the inflammatory pathway is designed to help heal us, is signals for new growth to happen. This helps cancer cells grow larger, faster, and escape detection from other parts of our immune system. Chronic inflammation can also allow for the build-up what’s known as reactive oxygen species – natural bi-products of our daily metabolism. These ROS’s can cause DNA damage, which can then lead to cancer-causing mutations. Essentially, chronic inflammation prepares a pro-cancer environment in our tissues.

Other impacts of obesity on cancer include higher levels of insulin, upregulated growth factors (also related to inflammation), and excessive hormone production (this is mainly important in post-menopausal women). All of these can factors can cause cells to divide more rapidly, increasing the chances of developing and accumulating cancer-causing mutations.

The majority of obese individuals exhibit chronic inflammation. This varies a bit (as everything does in human health), but it’s common enough to be a generalized fact. Therefore, it should come as no surprise that obese people have increased risk for certain cancers – especially gastrointestinal, breast, liver – and chronic inflammation is generally accepted as the reason. This has not been proven in clinical trials, because it should come as no surprise that forcing people to gain enormous amounts of fat to see if they get cancer is considered unethical.

Correlation, causation

But we’re forgetting that not all of this is correlational research, because we have a handy tool in science called model organisms that we can use when human subjects are unethical. Many labs have taken to feeding mice traditional “Western diets” or other obesity-promoting diets to see how it impacts cancer development. This has been done on a variety of cancer types, including breast, colon, and liver cancers. Each one has delivered similar results – obese mice developed cancer at increased rates. Not only this, mice who were once obese and went back to a healthy weight, still had increased rates of cancer. These findings lend more support in favor of obesity as a factor in cancer development.

Yes you can say the research is purely correlational in humans. But the scientific principles guiding the correlation are difficult to dismiss, especially in the wake of mouse obesity studies. We’re not trying to say that obese people are a disease, we’re trying to educate people about the potential dangers of being obese and the diseases they could be at greater risk for.

Body Positive, Health Negative

Does anyone remember the movie that Will Smith starred in about the physician (Bennet Omalu) who discovered the link between professional football and potential brain damage? This is what I equate this argument with. When the National Football League caught wind of this research, they tried to bury it. In the process, they were letting the players continue to play, unaware of the possible risks to their long-term health. Dr. Omalu wasn’t trying to stop people from playing football – he said he loved the sport even – but he wanted the players to be aware of the risks and choose to continue to play or not from an informed standpoint.

CRUK is not trying to vilify fat people. They are not trying to shame them for their bodies or tell them they’re a walking disease. Like Omalu, they simply want to inform, let obese individuals know what risks they are living with, so they can make informed health decisions. The body positivity community is behaving like the NFL – thinking they are protecting their community but are actually just further endangering people for the benefit of their own image. And it really rubs me the wrong way, because the truth may hurt but it’s better to know than live in uncertainty.

Final Thoughts

There is one main issue I take with the campaign – CRUK is outright stating that obesity is a cause of cancer. We know diseases like cancer aren’t often caused by one singular point, and as I pointed out, the research done in humans has been correlational. Yes, it’s a pretty convincing correlation especially if you understand the science behind it (and the added causational mouse studies), but correlational nonetheless. And if there’s one thing about research that most people know, it’s that correlation does not equal causation.

(Though I do want to point out that no causational studies have been done on smoking and cancer, but everyone knows smoking is a cause of cancer…there’s actually an interesting paper about “proving” causality in instances like this.)

I’ve been careful to only say that obesity is a risk factor for cancer. That’s a huge difference, defining it as a cause versus a risk. I think if the campaign was identifying obesity as a risk (or even a potential cause), people would feel less like CRUK is equating a group of people as a “walking disease,” and more like CRUK is just trying to spread a message about health.

In the end, I find myself to be relatively neutral on this issue. I see the logic (or maybe emotion…ahem body positive community) in both sides of the argument. I won’t be signing the petition to cease the campaign, but I won’t be upset if the campaign does end – or is at least redone. If I was absolutely forced to choose a side, it should be unsurprising that I would go with the science. While the billboards themselves may be a bit extreme, I think the underlying message is what’s truly important.

Here’s the thing, though – the controversy is now outshining the message. Therefore, it might be best for everyone to rethink the campaign into something a little less…striking. And change the phrasing to more accurately represent the science. And then not have people deny the science. I don’t think that’s too much to ask…right?

Further Reading

BMI and Alternatives

• Relative Fat Mass to measure body fat percentage
• Misclassification of cardiometabolic health by BMI

Inflammation and Cancer

• Comprehensive review (Nature)
• More review
• Identification of specific mechanism linking inflammation and cancer
• Inflammation and the microenvironment

Obesity and Cancer in Humans

• Summary of emerging evidence
• National Cancer Institute fact sheet on obesity and cancer
• Review of obesity and cancer hypotheses
• CDC fact sheet on obesity and cancer
• US longitudinal study on obesity and cancer in women
• BMI and cancer screening – note that there was no connection between BMI and breast cancer, but was with colorectal cancer
• Longitudinal study of diet and colorectal cancer
• Young adult risk factors for cancer – note that this study takes into account socioeconomic status as well

Obesity and Cancer in Mice

• Colon cancer, obesity, and exercise
• Obesity and breast cancer metastasis
• Diet-induced obesity and ovarian hormones in cancer development
• Obesity and breast cancer recurrence