Popcorn Science: Hunger and Artificial Sweetener

I hear a lot of interesting things when I play the “fly-on-the-wall scientist.” Most statements uttered casually between friends can be tested scientifically; at the very least, research has already been done and one only needs to dig a little to find out whether the statement is true. There are many things in life that can be demonstrated true and false. Grab a bowl; let’s pop a serving of buttery science!

Consuming artificially sweetened beverages causes you to gain weight because artificial sweeteners increase your hunger.

Photo by Becky Stern, 2009. This and other photos by Becky are available from http://www.flickr.com/photos/bekathwia/3286606272/

I heard this statement uttered recently at a party where people were downing lots of chips, cake, soda, fatty meats, and other assorted party foods. A casual conversation about weight and losing weight arose nearby  in the living room. The above statement was uttered fairly casually, as if fact. But is it true? Do people who consume artificially sweetened foods gain weight over people who don’t? If so, is this because such sweeteners increase your hunger (appetite), and thus make you consume more food?

First of all, a statement about science. Science is the process of understanding the natural world by forming a hypothesis, designing an experiment to gather data to test the hypothesis, and understanding the data to see if the hypothesis is correct. Science can be messy; things don’t usually happen in an orderly way. But we need guiding principles, and these are a few.

We also need some guiding principles. What will constitute a “good study” of this question? Here are a few things:

  • test subjects must have nearly identical characteristics – weight, eating and exercise habits, etc.
  • test subjects should be divides into “control” and “test” groups; the control group gets sugar, the “test” group gets artificial sweetener. Ideally, the study should be double-blind: the researchers shouldn’t know who is getting sugar and sweetener, and subjects should also not know this.
  • the food industry does pump a lot of money into such studies; while scientists always have external funding, we should at least consider the possible effects of different funding sources.

I took a look on scholar.google.com for some studies matching the search terms “artificial sweetener and hunger.” I found a review article by Qing Yang, from the Department of Molecular, Cellular and Developmental Biology at Yale University. It referenced a large number of articles that contain the actual research. Based on a readinf of several of the referenced articles, this review is a pretty coherent summary of the current state of understanding of the effects that artificial sweeteners have on human weight changes. Here are some relevant excerpts from the review article:

Surprisingly, epidemiologic data suggest [artificial sweeteners do not help you lose weight]. Several large scale prospective cohort studies found positive correlation between artificial sweetener use and weight gain [3]. The San Antonio Heart Study examined 3,682 adults over a seven- to eight-year period in the 1980s. When matched for initial body mass index (BMI), gender, ethnicity, and diet, drinkers of artificially sweetened beverages consistently had higher BMIs at the follow-up, with dose dependence on the amount of consumption. Average BMI gain was +1.01 kg/m2 for control and 1.78 kg/m2 for people in the third quartile for artificially sweetened beverage consumption. The American Cancer Society study conducted in early 1980s included 78,694 women who were highly homogenous with regard to age, ethnicity, socioeconomic status, and lack of preexisting conditions. At one-year follow-up, 2.7 percent to 7.1 percent more regular artificial sweetener users gained weight compared to non-users matched by initial weight. The difference in the amount gained between the two groups was less than two pounds, albeit statistically significant. Saccharin use was also associated with eight-year weight gain in 31,940 women from the Nurses’ Health Study conducted in the 1970s.

The review goes on to talk about data from youth studies; while the review author claims that those youth studies suggest more obese children show weight gain when using artificially sweetened beverages, a closer look at the reference [4] reveals a non-significant result, suggesting that there is no measurable effect on weight in this study.

But, overall, the studies seem to suggest that there is a trend, in populations that consume significant quantities of artificial sweetener, toward increased body-mass index (BMI). That trend is not extreme, but the data supports its existence. The study in [3] offers several hypotheses, ranging from correlation but not causation (people who overeat tend to adopt artificial beverages and so that population naturally demonstrates an increase in weight) to causation (people who consume artificial sweetener then tend to overcompensate by eating more).

Is there any clarity on whether this is correlation or causation?

The review article in [2] goes on to note other studies that suggest that people that experience a stronger sweet taste report increased appetite; since most artificial sweeteners are much sweeter in taste than sucrose or glucose, this might suggest causation due to the extreme sweetness triggering a more enhanced hunger response.  The article then explores the neuronal connection between sugar and satisfaction, between the response of taste receptors and the brain’s mechanisms for sending the “all satisfied” signal.

The paper ends with a very nice point, based on these recent pilot studies of the neurological sweetness connection:

Lastly, artificial sweeteners, precisely because they are sweet, encourage sugar craving and sugar dependence. Repeated exposure trains flavor preference. A strong correlation exists between a person’s customary intake of a flavor and his preferred intensity for that flavor. Systematic reduction of dietary salt  or fat  without any flavorful substitution over the course of several weeks led to a preference for lower levels of those nutrients in the research subjects. In light of these findings, a similar approach might be used to reduce sugar intake. Unsweetening the world’s diet may be the key to reversing the obesity epidemic. [emphasis is mine]

Our modern American diet is swimming in fat, salt, and sugar. We have been conditioned by the kinds of products commonly available in restaurants to expect fatty texture, savory and sweet foods. Artificial sweeter only appears to exaggerate an underlying problem; our expectation for sweetness leads us to greater consumption of high-energy-content foods. Altering our preferred tastes is more important than slashing artificial sweetener, because the problem may be our preferences and not what’s in the can of diet cola.

[1] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2771213/

[2] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892765/

[3] http://www.nature.com/oby/journal/v16/n8/full/oby2008284a.html

[4] http://www.ncbi.nlm.nih.gov/pubmed/16510646

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