Two weeks ago in part 1, we explored the history of artificial sweeteners (AS) and debunked the claim that they have been proven to cause weight gain, the most infamous accusation against synthetic sweeteners. This week, we take a look at the next three allegations, that AS:
- Cause diabetes,
- Disrupt gut bacteria, and
- Cause cancer.
If we search PubMed, we’ll find studies that support these claims. We’ll also find studies that contradict them. This makes our job more fun, although significantly more difficult – instead of simply reading titles and abstracts, we have to assess the strength of the evidence to develop an informed opinion. Lucky for you, I’m going to take care of all of it. Additionally, we’ll discuss the acceptable daily intake (ADI) of the most common AS. Sit back, relax, and let’s dive in.
Artificial sweeteners cause diabetes
Now that we know that AS have not been shown to cause fat gain, it’s time to answer another question about its metabolic effects; do AS cause diabetes? Similar to the relationship between AS and obesity, researchers have found an observational link between AS intake and diabetes (1, 2, 3, 4).
Once again, these are observational studies and not well-controlled experimental trials – yet another example of correlation vs. causation and reverse causality leading to a misinterpretation of research. This being the case, the research only conveys that people with metabolic syndrome and diabetes are more likely to consume AS (possibly in an effort to decrease sugar intake) and not that AS cause these diseases. In contrast, high quality studies have found that diet beverage consumption has no effect on metabolic disease risk (5, 6, 7).
To better understand the directionality of the link between AS intake and metabolic disease risk, let’s take a look at the studies on the impact of AS on hormones and blood sugar response. A few studies have found that AS negatively impact satiety hormones and increase blood sugar levels. This study in mice supports that AS consumption may increase energy intake by suppressing GLP-1, a hormone that makes us feel full after a meal and plays an important role in glucose homeostasis (8). And this small study of seventeen obese women found that those who drank an artificially sweetened beverage before consuming a sugary drink had 14% higher blood sugar levels and 20% higher insulin levels, compared with those that drank water before the sugary drink (9). With this study in particular, as these women had not previously consumed artificially sweetened beverages, it is important to note that AS may have different physiological effects depending on one’s age, genes, and history.
If I was trying to demonize AS – as many nutrition “experts” will do – I would end this section here and you would probably be convinced that your weight loss plateau is being caused by the Splenda in your coffee. But, in the interest of painting a comprehensive picture, we must consider the opposing argument. In fact, the majority of human studies have found that AS intake does not increase blood sugar, insulin levels, or other satiety hormones (10-21).
For instance, this randomized controlled trial of 50 people found that an intake of 2 diet sodas/day for twelve weeks had no effect on insulin response, as well as no effect on bodyweight or food intake (23). And in contrast to the previously mentioned rat study on GLP-1, this study of healthy human subjects found that AS had no effect on GLP-1 release (24).
In conclusion: There is no doubt that consumption of artificially sweetened beverages are better for acute glycemic response and short-term metabolic health than fully sugar-sweetened beverages, and there is no human evidence that shows AS consumption increases one’s risk of developing metabolic syndrome or diabetes.
Artificial sweeteners disrupt gut bacteria
The study of the gut microbiota is a relatively new science with far-reaching implications. It appears likely that the types and number of bacteria that reside in the gut affect many facets of health, from body composition to mood to heart and brain health.
While it is becoming increasingly apparent that the condition of our gut plays an integral part in the maintenance of our health and wellbeing, the impact of AS intake on gut bacteria is not as clear-cut. First, we know that the food we consume does have an impact on the number, structure, and activity of the bacteria in our gut (25, 26). It follows, then, that AS intake would have some effect on the gut microbiota. The question at hand is whether that effect is positive, negative, or inconsequential. Holding strong to the common theme with AS, it’s complicated.
In mouse studies, the effect of AS intake on the gut microbiota looks grim. In general, mice that are given AS experience negative changes to their microbiome, resulting in more fat gain and an impaired metabolic response to glucose, compared to their counterparts given water or sugar sweetened beverages. In some studies, it is suspected that the metabolically damaging effects are due to increased hunger and caloric intake, while in others it is speculated that the negative effects are caused directly by altered gut microbiota resulting in decreased glucose tolerance and insulin sensitivity (27-32).
Fascinatingly enough, some studies even found that AS resulted in adverse metabolic effects despite positive changes in body composition. For instance, a 2014 study found that mice fed artificial sweeteners had increased fasting glucose levels and more insulin resistance than the mice fed sugar, despite having a lower bodyweight and improved body composition (33). For people that consider their physique a reliable indicator of health, this finding is especially concerning – this particular study indicates that artificial sweeteners may have an insignificant effect on our physical appearance but, nevertheless, may cause metabolic damage. As we know from “metabolically obese, normal weight people“, it is certainly possible to look “good” on the outside but be in poor physical health (34).
However, (shocking!) not all of the research is consistent. Another study found that AS intake actually improved glucose tolerance in insulin-resistant mice and yet another study found that Stevia intake had no impact on bodyweight or glucose tolerance (35, 36).
Once again, let’s break down the two sides of the evidence. As we now know, there is a mountain of evidence showing that high intakes of AS in mice wreaks havoc on gut bacteria and results in serious adverse metabolic consequences. On the other hand, humans are not mice and most people do not consume even close to the amount of AS used in these studies. For instance, another rodent study found harmful effects on the gut microbiome, except it was with doses of AS equivalent to humans eating 165 packets of Splenda or 36 cans of diet coke per day, for 6 months! (37).
If you know anyone that consumes 6,500 cans of diet soda over the course of 6 months, he/she may have cause for concern. Otherwise, I am skeptical that AS intake in moderation, i.e. not 36 cans of diet soda a day, as a component of an otherwise well-balanced, primarily whole foods diet, will have significant harmful effects on the gut microbiota (38).
In conclusion: The gut microbiota is a complex realm of human physiology. For this reason, it is the effect of AS on gut bacteria that gives me greatest pause with my personal AS consumption. Most of the information regarding the effect of AS consumption on the gut microbiota is speculation derived from observational research and studies performed on rodents or petri dishes. There is a significant need for more well-designed studies in humans to assess this topic and, until that time, it is advised to proceed with caution. Consume AS in moderation or not at all if you have concerns about the health of your gut microbiota (39).
Artificial sweeteners cause cancer
Do AS really cause cancer? Despite all of the evidence that supports the contrary, the scary myth that diet soda is a carcinogen can still be heard today at water coolers around the world. After a study was published in 70s that showed saccharin caused increased rates of bladder cancer in rats, it was claimed that AS caused cancer (40). As a result, in the 80s the FDA required that artificial sweeteners come with a warning label and saccharin was even banned in the U.S. until 2000. In Canada, it was banned until just a few years ago! (41, 42)
Not so fast, Canada. The bad news – a lot of innocent rats were killed in that study. The good news – the dosage of AS given to the rats was outrageously high, rats are not humans (in case there’s still confusion), and the carcinogenic effects, as it turns out, do not translate to humans (43). A subsequent study found no association between saccharin intake and bladder cancer in humans (44). Future studies on sucralose and stevia have concluded that they are also not carcinogenic to humans (45, 46).
In conclusion: You can rest assured that artificial sweetener intake has NOT been shown to cause cancer. If I haven’t yet convinced you, here are some more resources that explain the history of the relationship between artificial sweeteners and cancer.
Artificial sweetener acceptable daily intake
Acceptable daily intake (ADI) is the maximum amount of a compound that can be consumed daily over a lifetime that is deemed to not cause appreciable adverse health effects (50). The ADI for the most common artificial sweeteners is very high. This is important to note because many of the studies I cited, especially those that showed harmful health effects, used doses of artificial sweeteners that were near or at the ADI.
- Aspartame 50 mg/kg/d (21 cans of diet soda)
- Sucralose. 5 mg/kg/d (31 Splenda packets)
- ACE-K 15 mg/kg/d (30 cans of diet soda)
- Saccharin 5 mg/kg/d (10 Sweet n Low packets)
- Stevia 40 mg/kg/d (40 Stevia packets)
From Additional Information about High-Intensity Sweeteners Permitted for Use in Food in the United States (United States Food and Drug Administration webpage) (51).
Although I’m sure they exist in some dark corner of the universe, nobody I have ever met consumes 20+ cans of diet soda per day. It is not a stretch to believe that while occasional AS intake may be more or less harmless, 20 cans of diet soda daily may have some negative health effects.
Conclusion: I’ve made my decision, you have to make yours
Human nutrition is complex. Every food decision is influenced by, just to name a few, biological, psychological, physical, societal, and economic cues. The specific choice to consume artificial sweeteners is made even more complicated by mixed research, conflicting expert opinions, headline-grabbing fear mongering, and logical fallacies. It’s not a black and white concept, and there is no correct answer that applies to everyone. That being said, it becomes our responsibility to consider the strength of the available evidence and our individual circumstance to make the best possible decision for our health and wellbeing. After performing a thorough cost benefit analysis, I have made my decision.
For me, the pros of artificial sweeteners:
- increased adherence to my macronutrient/calorie goals
- increased enjoyment of my food
- increased diet satisfaction while limiting my intake of hyper palatable “junk foods” such as donuts, cookies, and ice cream,
outweigh the potential cons:
- increased appetite
- decreased sensitivity to sweetness
- negative effects of very high doses on the gut microbiome resulting in decreased glucose tolerance
Sure, a diet without AS may technically be “healthier”, but if their intake facilitates better overall health through lower caloric intake and decreased stress and feelings of restriction, it may very well be more optimal to include them your diet. Although at this point it does not appear that artificial sweeteners are a 100% risk-free biological free lunch, they are a useful tool that, when used in a reasonable way, can help us achieve our health and body composition goals.