Last week fellow Plogster Steve Silberman forwarded me a link to this interesting article on the health effects of aspartame (the sweetener used in Diet Coke, among other things). It discusses the evidence, or rather the lack of evidence linking aspartame with various types of cancer. The article was well-outside of my area of expertise (I’m hoping that my PLoGs colleagues David and Melinda may share their 2 cents on the aspartame-cancer issue), but it did remind me of an issue that’s been coming up for some time in obesity research:
Is aspartame a cause or a cure for obesity?
Aspartame itself has no calories, so it couldn’t possibly result in increased body weight, right? This is where things get interesting. You see, some evidence suggests that aspartame may somehow increase hunger/energy intake, resulting in greater caloric intake and increased risk of obesity. Here is what I had to say about the topic in a post back in January of 2009:
An article published last summer by Sharon Fowler in the journal Obesity suggests that individuals who consume diet soft drinks are at dramatically increased risk of overweight and obesity than those who do not consume diet soft drinks. For example, over an 8-year period, individuals who consumed just 3 diet soft drinks a week were 40% more likely to be overweight or obese than those who consumed none. The risk of overweight and obesity continued to increase dramatically with increased diet soft drink intake, and was independent of other factors like exercise, smoking, and socioeconomic status.
The Fowler study doesn’t prove that diet soft drinks cause obesity (people who drink more diet soft drinks may also have other behaviors that put them at increased risk for weight gain), but they are still pretty surprising. While diet soft drinks may themselves be free of calories, recent evidence suggests that they may increase caloric intake at future meals. For example, when rats are given access to unlimited amounts of food, those who are used to consuming calorie-free drinks eat dramatically more than those who are used to consuming drinks flavoured with sucrose. It may be that calorie-free drinks impair the body’s ability to anticipate the caloric content of a given meal, eventually resulting in increased caloric intake and weight gain. Others have suggested that calorie-free sweeteners like aspartame may also increase appetite at future meals.
Our friend Yoni Freedhoff of Weighty Matters (who works with patients with obesity on a daily basis) is unconvinced (emphasis mine).
Researchers in New Zealand studied folks who had successfully lost weight and their dietary consumption patterns. More specifically they looked at folks who had maintained a weight loss of greater than 10% of their weight for 11.5 years and they compared these folks’ dietary strategies to folks of similar weights who had never been overweight.
What unshocking yet valuable results did they find?
They found that folks who lost the weight had to work harder at their dietary strategies to help keep that weight off than folks who never had weight to lose. Their strategies included consuming fewer calories from fat (though the importance of this one’s debatable as the 90s were the low-fat decade and more recent data from the National Weight Control Registry suggest that low-calorie is of course more important than low-fat and can be accomplished many different ways), consuming more of sugar and fat modified foods (reduced fat, reduced sugar), consuming more water, less pop and three times more daily servings of artificially sweetened soft drinks.
So what gives? Does aspartame make you gain weight, or is it a useful weight loss tool? And more importantly, who is right – me or Yoni? I honestly have no idea, although I’m guessing that the answer is somewhere in the middle. A new review in the Yale Journal of Biology and Medicine looks at the evidence linking artificial sweeteners (aspartame, sucralose, etc) and body weight, and it’s not terribly conclusive one way or the other:
…consensus from interventional studies suggests that artificial sweeteners do not help reduce weight when used alone [2,25]. BMI did not decrease after 25 weeks of substituting diet beverages for sugar-sweetened beverages in 103 adolescents in a randomized controlled trial, except among the heaviest participants . Adouble blind study subjected 55 overweight youth to 13 weeks of a 1,000 Kcal diet accompanied by daily capsules of aspartame or lactose placebo. Both groups lost weight, and the difference was not significant. Weight loss was attributed to caloric restriction . Similar results were reported for a 12-week, 1,500 Kcal program using either regular or diet soda . Interestingly, when sugar was covertly switched to aspartame in a metabolic ward, a 25 percent immediate reduction in energy intake was achieved . Conversely, knowingly ingesting aspartame was associated with increased overall energy intake, suggesting overcompensation for the expected caloric reduction .
What possible mechanisms are involved in whatever is going on with these non-caloric sweeteners? They cite a number of studies which suggest that real and artificial sweeteners have different effects on the brain:
Sweetness decoupled from caloric content offers partial, but not complete, activation of the food reward pathways. Activation of the hedonic component may contribute to increased appetite. Animals seek food to satisfy the inherent craving for sweetness, even in the absence of energy need. Lack of complete satisfaction, likely because of the failure to activate the postingestive component, further fuels the food seeking behavior. Reduction in reward response may contribute to obesity. Impaired activation of the mesolimbic pathways following milkshake ingestion was observed in obese adolescent girls .
The full text of the paper is available in Pubmed Central, so I’d strongly urge everyone to go check it out by clicking here. Unfortunately there have yet to be any truly systematic reviews on the topic, so it’s going to be a while before we have a clear answer as to the role of artificial sweeteners in obesity and weight management (the above review doesn’t cite the paper that Yoni discussed – probably because it came out just before the review was written, but it makes me wonder what else a systematic review might find).
Others have also discussed the issue of aspartame and obesity of late. Stephen Novella of Science-Based Medicine covered the topic briefly in his recent post on all things aspartame, and is taking a cautiously optimistic approach to aspartame and body weight:
The question of aspartame and weight control is a complex one, and can be approached from many research angles. Here is a recent review of research [Travis’ Note: this is the Yale review I mentioned above]. At present the question is very much unsettled. It seems that there is no significant metabolic and no demonstrated neuronal effect from artificial sweeteners. However, people who knowingly consume diet drinks do tend to overcompensate by consuming greater calories overall. While studies of substituting aspartame for sugar in a blinded fashion show that calories are reduced, contributing to weight loss.
By my reading, the current summary of available research is that consuming calories in drinks contributes to weight gain and obesity, substituting calorie-free drinks (whether water or diet drinks containing artificial sweeteners) does help reduce caloric intake and aid in weight control, but there is a tendency to overcompensate by increasing other caloric intake. Therefore it seems reasonable to use artificial sweeteners to reduce caloric intake from drinks, but to be careful to control overall caloric intake (so no, putting aspartame in your coffee does not mean you can eat the cheesecake).
While I have not seen any papers demonstrating a neuronal effect of artificial sweeteners, some studies do seem to suggest that artificial sweeteners result in different patterns of brain activation than their full-calorie counterparts (examples here and here). But whether those differences are meaningful in terms of weight maintenance, and in what direction, is up for debate (for example, this study suggests that aspartame results in beneficial changes in brain peptides related to satiety in rats), and I think that the approach Stephen is advocating is a pretty reasonable one given the current state of the evidence.
One thing that I haven’t seen any study address is how diet soft-drinks with and without caffeine differ in their physiological effects – caffeine inhibits the appetite and increases energy expenditure, so it’s possible that diet drinks with caffeine aren’t as obesogenic as diet sodas without caffeine. In other words, this situation could get even more confusing than it already is…
So, what’s the take-home message? I really don’t know, although people may find it interesting to note that we obesity researchers tend to consume an enormous quantity of diet soft drinks (I’d estimate that I personally I drink 2-3 diet cola’s a week, but I know many researchers who have at least one a day, often before noon). Until the dust settles and the evidence is a bit more clear, I’ll stick with a slightly updated version of my conclusion from back in 2009:
So, while it is not yet completely clear what role diet soft drinks play in weight management, there are some good reasons to limit their intake to a moderate level, and to be careful that you don’t compensate for diet drinks by increasing your consumption of other high-calorie foods. Plain water is always a great choice, and if you find that too boring, consider adding a few slices of lemon or cucumber to add some fresh flavour. And as always, a little physical activity is always a good decision
I’m looking forward to some good discussion in the comments section!
Yang Q (2010). Gain weight by “going diet?” Artificial sweeteners and the neurobiology of sugar cravings: Neuroscience 2010. The Yale journal of biology and medicine, 83 (2), 101-8 PMID: 20589192