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The Sweet Tease:

Can artificial sweeteners actually promote weight gain?

 

Katherine Bruton

October 10, 2008

http://timesonline.typepad.com/comment/food_and_drink/index.html

 

Introduction:

With the obesity epidemic on the rise and a plethora of evidence correlating excess weight with serious illness, such as heart disease and diabetes, Americans are becoming increasingly more calorie-conscious (Blackburn et al., 1997).  Consequently, food producers strive to provide alternatives for dieters and those who simply want to avoid excess calorie consumption. The most widely used, and possibly most highly debated, of these alternatives are non-nutritive sweeteners.  These sugar substitutes allow one to indulge without the guilty repercussions.  For example, by drinking a can of Diet Coke, one avoids the extra 155 empty calories from a can of regular Coke (http://www.annecollins.com/calories/calories-coca-cola.htm). But are these substitutes really a dieting sweet tooth’s dreams come true? Or are our bodies being teased by experiencing a sugary taste without a subsequent intake of extra energy? These questions have struck a recent debate and onset of research to solve whether sugar substitution is a safe and viable method of reducing caloric intake.

Background Information:

            Nonnutritive sweeteners, also termed intense sweeteners, artificial sweeteners, and alternative sweeteners have been utilized since the 1950s in attempt to reduce calorie consumption in a variety of beverages and sugary foods.  Those approved by the FDA include saccharin, aspartame, acesulfame-K, sucralose, and neotame, with aspartame being the most common as well as the most thoroughly researched http://www.fda.gov/fdac/features/2006/406_sweeteners.html.  Although each subtype has some varied uniqueness, for clarity I will focus on aspartame, the one most likely to be found in common food products, such as diet soda.

           FDA approved since 1981, aspartame has been incorporated into a variety of consumer goods including soda, chewing gum, cereal, and desserts.  Although it has the same caloric value as regular sugar (sucrose), it is 200 times sweeter.  So, its caloric content is negligible with typical use.  Chemically speaking, when digested, it converts into methanol and two amino acids, aspartic acid and phenylalanine.  These three compounds are actually consumed daily in greater volumes via other common foods like meat and vegetables.

Methanol

 

 Aspartic Acid

 
                                                      

http://www.chemistrydaily.com/chemistry/Methanol                     http://www.3dchem.com/molecules.asp?ID=51

Also, the body processes these constituents the same way, whether they are taken in by aspartame or a typical food (http://www.caloriecontrol.org/aspartame.html).  Yet, because of significant criticism over its proposed link to a variety of illnesses such as cancer, it has been heavily investigated.  Despite suspicions, over 200 studies have given evidence to negate such claims and support its safety (http://www.medicinenet.com/artificial_sweeteners/page4.htm#nonnutritive).

http://www.aspartametruth.net/ramazzini/news_005.html

Why opt for sugar free?

            The rise in aspartame usage can be directly equated to its many benefits as a substitute for sucrose.  Many are enticed by its intense sweetening capacity, which proves much greater regular sugar.  Any coffee or tea drinker can attest to the convenience of one packet of Equal versus five packets of table sugar to sweeten one’s beverage.  Others use it to avoid tooth decay caused by sucrose rotting enamel.  Or, many with diabetes benefit from its use to help manage blood sugar levels.  But mostly, consumers use artificial sweeteners to decrease calorie intake.  The sweetness without the calories allows them to have a more manageable weight loss or weight maintenance plan, without so many sacrifices. One must understand, however, that there are no claims about sugar substitutes as appetite suppressants.  In order to be effective in weight management, one must couple sugar-free with a balanced diet, exercise, and behavior modifications. Regardless, the use of aspartame-substituted foods has proven to be an integral method of managing today’s obesity epidemic (http://www.caloriecontrol.org/aspartame.html). 

A Whole New Issue…

            Despite benefits, non-nutritive sweeteners are artificial substances.  Consequently, controversies surrounding their safety for consumption continually arise. Although time-and-again researchers deem them unassociated with adverse health effects, they seem to have failed to recognize increasing evidence that they may actually be perpetuating over-eating habits, thereby counteracting the calorie-free benefits. A comparison of the trends alone poses a substantial argument.  Over the time period from 1987 to 2000, obesity rates doubled from 15% to 30% of the U.S. population (Flegal, 2005).  Intriguingly, during about the same time frame, rates of consumption of sugar substitutes also doubled from 70 million Americans to around 160 million (http://www.caloriecontrol.org/lowcalqa.html).  While this correlation could be coincidental, it certainly gives reason for further investigation. 

            As a result of recent evidence, the media has taken a foothold in this possible counter-effect of sugar-free substitutes.  TIME magazine reported in February of this year,” your body may actually be keeping better count than you are.”  This proposition reflects new data (see below) claiming that our bodies expect sweet taste to be coupled with high calorie consumption.  Thus, when something ingested that tastes sweet is void of calories, we are motivated to compensate by eating more (http://www.time.com/health/article/0,8599,1711763,00.html).  Similarly, Sharon P. Fowler, MPH and colleagues of the University of Texas Health Science Center, San Antonio reported findings that reveal a 41% increase in risk of obesity for every 12oz. can of diet soda consumed each day.  However, she does recognize that this observation does not validate a causal relationship between diet soda intake and obesity.  She merely poses the correlation (http://www.webmd.com/diet/news/20050613/drink-more-diet-soda-gain-more-weight).  While ample discussion of this research exists on the Web, I was unable to locate the scientific literature.  As a result, one cannot take these statistics too seriously. 

Evidence from Scientific Literature

 
            A newly published study analyzing the effects of artificial sweeteners on consumption in lab rats has recently drawn significant attention to this question.  Researchers from Purdue University use the idea of Pavolovian conditioning to illustrate their hypothesis that interfering with the predictive relationship between sweet taste and caloric intake disrupts the “conditioned cephalic-phase reflexes” responsible for “tight physiological control of energy regulation.”   To make this claim, they performed a series of experiments.  In the first, separately caged lab rats received alternating servings of sweetened and unsweetened yogurt along with lab chow over a period of 5 weeks. The sweetened yogurt for one group was predictive of increased caloric content (i.e. sweetened with glucose), while the other was not (i.e. sweetened with a sugar substitute).  External variables such as feeding times and amounts were accounted for and a control group was used.  After each week the amount consumed was recorded and weights were measured.  At the end of the testing period, 27 rats overall were analyzed for body composition using x-ray absorptiometry.  Statistical analysis demonstrated that the rats consuming non-predictive yogurt ate the most, gained the most weight, and had significantly greater adiposity.                  

            In the subsequent part of the study, researchers analyzed whether artificial sweetener consumption over time impaired the rats’ abilities to compensate for a high calorie intake by eating less at the next opportunity.  For 14 days two groups of adult male rats of similar weight were fed either predictive or non-predictive sweetened yogurt in a similar fashion to the first experiment. Then, all the rats were given a premeal of thickened Chocolate Ensure Plus for 30 minutes followed by regular chow for 3 days.  The results showed that the rats in the nonpredictive group consumed more chow after a high calorie premeal than those of the predictive group, thereby supporting the hypothesis: the rats did not demonstrate an ability to reduce consequent calorie intake after a rich premeal (Swithers & Davidson, 2008). 

In sum, this study demonstrates the counterintuitive correlation between sugar substitute use and increased overall caloric intake.  However, one must take into consideration that while these results prove strong, the experiment was conducted on rats, so we cannot automatically assume that one would obtain the results on human subjects.  Yet, it is possible that the apparent physiological responses to a sweet taste, sans energy intake, are indicative of the simultaneous increase in obesity rates and aspartame consumption.

Thus, observation of other arguments proves necessary.  A much older experiment by Blundell and Hill (1986) supports the findings of the aforementioned study. These researchers measured level of appetite for 95 male and female volunteers aged 18-22 after ingesting a) a 50g glucose in 200ml solution b) an equivalent sweetness of aspartame solution (162mg in 200ml), and c) 200ml of unsweetened water.  Participants in the aspartame group recorded significantly more increases in “pleasantness” (or desire for) food after consumption of their beverages in comparison to those in both the sucrose and the water groups. Ergo, this research actually demonstrates an appetite stimulating effect of aspartame.  Specifically, participants reported a “residual hunger” following an aspartame-sweetened drink, as opposed to the suppressed motivation to consume more reported by the glucose drink group. In other words, this data illustrates the disparity between artificial sweetener consumption and satisfaction of appetite. Like Swithers & Davidson (2008), Blundell and Hill (1986) argue the perilous effects of deregulating the body’s conditioned response to sweet taste coupled with high-energy intake.  Despite the evidence of this study, however, no one else has been able to show that sugar substitute consumption causes increased appetite. Thus, this study has not yet since been replicable (Bellisle and Drenowski, 2007).

            Counterarguments also exist that belittle the credibility of the previous evidence.  A study on body weight management of 163 obese women shows that aspartame is an effective weight loss tool when coupled with behavioral modification within a weight loss program.  The woman participated in a 19-week weight-reduction program; followed by a 1-year maintenance program and a 2-year follow up.  The women were randomly assigned to either avoid or consume aspartame-sweetened products for 14 of the first 19 weeks while maintaining a strict 1500kcal/day diet.  Both groups showed an equivalent 10% loss of body weight initially.  However, the aspartame-consuming group regained less than 5% of the body weight during the first year, while the other group regained almost 10% of the body weight during the same time frame (Blackburn et al., 1997).  In this way, this data supports the claim that sugar substitutes are, in fact, effective in promoting decreased calorie intake.  However, it fails to provide adequate information about the role of sugar substitutes independent of confounding variables, such as regulated diet and exercise.  Additionally, since only obese women were studied, this research lacks generalizability.  Yet, one can conclude that when calorie intake is minimized and exercising takes place, aspartame flavored foods and drinks can be help to facilitate weight management for obese women.

            A review article (Bellisle and Drewnowski, 2007) summarizes the seemingly insufficient and inconclusive literature surrounding this topic.  It examines the same questions of whether intense sweeteners promote over consumption by elevating desires for sweet foods, by focusing on the responses and interactions of our physiological systems related to digestion.  While it acknowledges the evidence suggesting “that sweetness, when not accompanied by calories, results in ambiguous psychobiological signals that confuse the body’s regulatory mechanisms,” it concludes that studies suggesting subsequent loss of appetite control are not replicable.  A mention of  the Blundell and Hill (1986) study is made along with a supporting study by Black et al. (1993).  In this case, appetites showed no immediate increase after aspartame ingestion, yet “a transient increase in the desire to eat” ensued.

            Secondly, it makes the criticism that the available research from long-term studies supporting sugar substitutes as a weight loss tool is inconclusive.  One longitudinal study on 46 obese women reflected findings from the Blackburn et al. (1997) data. The women in the aspartame group lost about 1.6kg more than those not consuming aspartame. In contrast, in the case of 11 males, researchers found the opposite (Kanders et al., 1988).

A new perspective from this review also proves applicable in analyzing the available research. It explains that the human body seems to lack the ability to achieve exact “energy homeostasis,” the notion in which ingestion is regulated in order to supply for its needs and a balanced internal environment.  This claim may well account for the contradicting evidence in attempt to answer the sugar-substitute and over-consumption correlation.  In all, this review concludes that non-nutritive sweeteners are beneficial in that thy do eliminate many calories from sweet foods, but must be utilized within a controlled setting in order to be absolutely effective in weight loss or management.

Coincidence or correlation?

            So is there a relationship between America’s overweight trends and rates of sugar substitute consumption?  At this point, data proves inconclusive. However, fascinating observations and statistics urge us to explore this question further.  Some evidence strongly suggests that non-nutritive sweeteners disrupt the body’s natural capacity to measure caloric content based on how sweet it tastes.  Other studies suggest that sugar substitutes are an integral and effective component of weight management when behavioral modifications are simultaneously employed.

When reviewing the available literature, it is important to recognize the vast amount of dependent measures involved in such experiments.  Unlike rats, humans are much more susceptible to variable behavior due to environment.  Because they are aware, experience emotions, and alter moods, changes in consumption behavior may be due to an innumerable amount of interplaying factors that prevent researchers from arriving at conclusive evidence.  Regardless however, these new findings serve as first steps on the way to unraveling this perplexing mystery.  In the meantime, in my opinion, anything attracting such volumes of controversy about its health effects should be treated with caution.  Ideally, practices of moderation ought to be adopted, as with any nutritionally balanced lifestyle.  When teamed with a diet control strategy, sugar substitutes may serve helpful in an effort to limit calorie intake.  But, they cannot be relied upon as primary weight-loss tools, and one should recognize the possibility that they may actually serve to encourage over-eating habits.

References

Bellisle, F. and Drewnowski, A. (2007). Intense sweeteners, energy intake and the control

            of body weight. European Journal of Clinical Nutrition, 61, 691-700.

Black, R.M., Leiter, L.A. Anderson, G.H. (1993). Consuming aspartame with and

            without taste: differential effects on appetite and food intake of young adult males.

            Physiological Behavior, 53, 559-466.

Blackburn, G.L., Kanders, B.S., Lavin, P.T., Keller, S.D., and Whatley, J. (1997). The

Effect of aspartame as part of a multidisciplinary weight-control program on

short- and long-term control of body weight. American Journal of Clinical

Nutrition, 65(2),409-418.       

Blundell, J.E. and Hill, A.J. (1986).  Paradoxical effects of an intense sweetener    (aspartame) on appetite. The Lancet, 327 (8489), 1092-1093.

Flegal, K. M. (2005). Epidemiologic aspects of overweight and obesity in the United

States. Physiology & Behavior, 86, 599-602.

Kanders, B.S., Lavin, P.T., Kowalchuk, M.B., Greeenberg, I., Blackburn, G.L. (1988).

            An evaluation of the effect of aspartame on weight loss. Appetite, 11(1), 73-84.

Swithers, S.E. and Davidson, T.L. (2008). A role for sweet taste: calorie predictive

            Relations in energy regulation by rats. American Psychological Association,

            122(1), 161-173.

Additional Reading

Although I used fairly neutral and unbiased Web information in this review, many articles can be found online that pose strong opinions.  Here are a few examples:

 

 

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