There have been a lot of ominous news stories over the last few days raising the alarm about the artificial sweetener aspartame. I remember people saying aspartame caused cancer all the way back to the 90’s, but the renewed interest comes from a recent press release by the World Health Organization identifying aspartame as a “possible human carcinogen”. So, how worried should we be?
The different types of artificial sweeteners
There are many types of sweeteners on the market and they all differ in their chemistry. The most common artificial ones that you may have heard of:
Aspartame (Equal, NutriSweet and present in hundreds of products like Diet Coke, Coke Zero, Crystal Light, Sugar-Free Jell-O, etc.)
Sucralose (Splenda and present in products like Diet Lipton Tea, Gatorade G2 and Propel, etc.)
Saccharine (Sweet N’Low and in products like Tab, chewing gum and some other processed food, although its fallen out of use due to some bad publicity in the 70’s and 80’s and replacement by better tasting artifical sweeteners).
While the chemical make up of each of these sweeteners differ, the thing they have in common is that they trigger the sweet taste receptors on your tongue which registers as “sweet” by our brains but they aren’t metabolized by our bodies as “food” so they are not an energy source like carbohydrate, fat or protein.
What did the recent WHO statement say about aspartame?
The WHO released the results of a review performed by The International Agency for Research on Cancer (IARC), the WHO, and the Food and Agricultural Organization (FAO)’s Joint Expert Committee on Food Additives (JECFA). It stated that there is “limited evidence” that aspartame is carcinogenic to humans and placed aspartame on the IARC’s list of carcinogenic compounds in the category 2B.
Here are the IARC’s categories:
1: Carcinogenic to humans (either there is sufficient evidence of direct carcinogenesis to humans, or sufficient evidence in animals PLUS strong evidence in humans). There are 121 substances in this group. Notable inclusions you’ve heard of: HIV, Hepatitis B and C viruses, Alcohol, Formaldehyde, sunlight, air pollution, engine exhaust, processed meat, tobacco, tanning beds.
2a: Probably carcinogenic to humans (either limited evidence of carcinogenesis in humans PLUS sufficient evidence in animals, or a variety of other considerations). There are 89 inclusions in this group. Notable inclusions you’ve heard of: Malaria, consumption of red meat, drinking “very hot” beverages, being a hairdresser or barber, night shift work.
2b: Possibly carcinogenic to humans (either limited evidence of carcinogenesis in humans PLUS less than sufficient evidence in animals, or a variety of other metrics). There are 318 inclusions in this group, including: Chloroform, Gingko biloba extract, Kava extract, Aloe vera, gasoline, diesel, specific applications of Talc, being a firefighter or dry cleaner. And now, aspartame.
3: Not carcinogenic (evidence of carcinogenesis in humans is inadequate PLUS inadequate or limited in animals, or other considerations; things that don’t fall into the other groups). There are 499 substances in this group and its pretty much everything else.
So, category 2B is the third out of four categories of cancer risk. Now let’s look at the data they were considering in their analysis.
The human studies
First, let me start off by saying that doing studies of food in humans is …… complicated at best. Because these studies often go on for years (cancer being a disease that has a long course and often results from years of exposure to a substance) you can’t do controlled studies. No one would consent to being locked in a lab for years and fed a scientist-controlled diet. So, they are all “observational” or you ask people what they ate, they tell you, then you compare people who ate the thing to people who didn’t. So, these studies are relying on large groups of people keeping accurate food diaries. For years.
People are notoriously bad at reporting what they ate, both on purpose and by accident. Some scientists think that with proper controls and taking account of confounders (non-food variables that might also affect the results like cigarette smoking, BMI, gender, age, etc) these observational studies can be useful. Other scientists think that observational nutritional studies border on pseudoscience.
That being said, here are some of the studies they looked at:
The Nutri-Net Sante study: A study of 102,865 French people (78% women) across 7.8 years. Those who ate artificial sweeteners had a cancer risk 13% higher than those who didn’t (aspartame in particular was 15% higher). The highest risk was in breast cancer.
The Cancer Prevention Study-II: 934,777 Americans were studied since the 1990s. They found drinking 2+ sugar sweetened beverages a day was associated with a slight risk in colorectal and kidney cancer (but none others) by 9% and 17%, respectively. Artificially sweeteened beverages were associated with an 11% increase in pancreatic cancer.
The Animal Studies
Another word of caution. While animal studies are valuable, humans are not mice. Plus, these animals are almost always genetically engineered or bred for certain characteristics and live in such controlled environments that they are almost not comparable to a “normal life”.
Mice study 1: 6 groups of ~100 Swiss mice were exposed to different doses of aspartame (0ppm, 2,000ppm, 6,000ppm, 8,000ppm, 16,000ppm or 32,000ppm) every day of their life including 12 days of gestation (like when their mouse mom was still pregnant with them). They saw an increase in liver cancer in only the male mice at the two highest concentrations of aspartame: the 16,000ppm group had a ~10% increase, and the 32,000ppm group had a 13% increase. They found an increase in lung cancer in only the male mice, again at the highest exposure groups: 6% increase at the 16,000ppm exposure and 7% in the 32,000ppm exposure.
Reality check: what does 16,000ppm and 32,000ppm asparatame look like for humans? The authors state that 16,000ppm is equivalent to 2,000mg/kg of body weight and 32,000ppm is equivalent to 4,000mg/kg body weight.
To give you perspective, the recommended maximum aspartame consumption for a human is 40-50mg/kg per day. This is equivalent to 9-14 cans of diet soda a day.
The mice in this study were being given 40-80 times more than that, or the equivalent of 360-1,120 cans of diet soda (for a human) a day. Talk about the Pepsi generation.
Mice study 2: A lower dose aspartame study on 3 groups of ~80 Sprauge-Dawley rats (0ppm, 400ppm or 2,000ppm per day for their whole lives, including 12 days of gestation). There was a 16% increase in male rats that had tumors in the 2,000ppm group. This included lymphomas/leukemias and mammary carcinomas.
2,000ppm is equivalent to a daily intake of 250mg/kg of aspartame or 5 times the recommended daily amount for humans.
This reminds me of the old adage in medicine “the poison is in the dose”. Meaning that something can be harmless at a normal dose, but dangerous or even fatal at an elevated dose. Kind of how moderate amounts of salt is absolutely essential to human life, but eating a pound of salt will kill you.
What are the pros and cons of artificial sweetners?
At this point, I am unconvinced that moderate consumption of aspartame causes cancer. But that doesn’t mean there aren’t other considerations!
Pros: Artificial sweeteners (all of them, not just aspartame) can help lower the amount of glucose that a person consumes daily. This can be really helpful for diabetics or those with pre-diabetes. It may also prevent tooth decay by lowering the amounts of sugar in the mouth.
Cons: While artificial sweeteners may not increase blood sugar levels (there is a bit of disagreement about this with sucralose and saccharine) they MAY increase insulin levels. When your taste buds register “sweet”, the brain thinks that “food is coming!” and turns on insulin production to help process that sugar. Then, no food comes, and the insulin is raised for no reason. You can mitigate this effect by eating artificial sweeteners only when you are eating actual food too.
Another issue is that artificial sweeteners may dysregulate our gut bacteria, which may even lead to glucose intolerance (what we worry about with pre-diabetes and diabetes). There is still some disagreement about this in the scientific community, but it’s ironic that artificial sweeteners may end up contributing to diabetes in some anyway.
The Hot Take:
Despite recent news articles that are scaring people into thinking aspartame causes cancer, the human studies are limited at best. In animals, aspartame only causes cancer when taken in extreme amounts, way above normal daily consumption. While artificial sweeteners may have other issues (insulin production, changes in gut bacteria) moderate amounts of them are probably safe in relation to cancer risk. As always, everything in moderation!
If you are worried about aspartame, ask yourself… do I drink alcohol? Eat red or processed meat? Am I exposed to sunlight, engine exhaust or air pollution? These have much higher risks than aspartame. Know your risk and keep everything in perspective.
Stay happy, healthy and informed,
Jessica at TCA
WHO. Aspartame hazard and risk assessment results released
The American Cancer Society. Aspartame and Cancer Risk.
Riboli, et al. Carcinogenicity of aspartame, methyleugenol, and isoeugenol. The Lancet Oncology.
Cancer Council Australia. IARC Classifications.
Wikipedia: List of IARC group 1 carcinogens. Group 2a, Group 2b. Group 3.
Wade, G. Some artificial sweeteners can raise your blood sugar. New Scientist