Saturday, October 8, 2011

Sweet Nothings? Sugar Substitutes and Weight Gain

     The only source of sweet for 99.9% of human existence has been glucose and fructose. Not surprisingly we developed a physiology where feeding behavior is largely controlled by the ebb and flow of blood levels of these sugars and their metabolites which reflect our energy status. In other words, a part of the brain watches our gas tank and sends messages accordingly, directing us toward or away from the kitchen. The obesity epidemic strongly suggests that we have lost this signal.

      The sources of sweet started to change after World War II. The combination of a sugar shortage and a changing esthetic that favored a thin figure encouraged women to try a sugar substitute. Saccharin (Sweet N' Low), the oldest nonnutritive sweetener was discovered in 1879 at Johns Hopkins during experimentation with coal tar derivatives. Saccharin had been used to replace sugar in soda marketed to diabetics until after the war when soda bottle labels were changed from "for use only in people who must limit sugar intake" to "for use in people who desire to limit sugar intake." Saccharin, which is 300 times sweeter than sucrose (table sugar, a disaccharide composed of 50% glucose and 50% fructose) was followed by cyclamate in 1937. Concern over cyclamate's capacity to cause cancer took it off the market in 1969. Similar concerns resulted in the FDA's plan to pull saccharin in 1977, but consumer protest reversed the decision. A warning label accompanied all saccharine products until 2000 when subsequent studies demonstrated that it is not carcinogenic. These investigations essentially silenced concerns over the safety of artificial sweeteners. Cyclamate continues to be available in 50 countries including Canada.      

     The next generation of sugar substitutes gave us aspartame (NutraSweet, Equal, 200 times sweeter than sucrose), sucralose (Splenda, 600 times sweeter than sucrose), and Neotame, the sweetest, weighing in at 7,000 times the sweetness of sucrose. These sweeteners have been well received. Between 1999 and 2004 6,000 food products containing these agents went to market. According to, an ingredient search engine, there are now no fewer than 3,648 foods containing these chemicals in the U.S.. A sizable majority of americans consume artificial sweeteners, usually believing that they are making the healthy choice. In fact diet soda drinkers diets contain more whole grains and low-fat dairy, and less processed meat and refined sugar, than the general population. The idea that diet soda is a health food has accelerated with the recent "low-carb" diet fad.

     Unfortunately, what was supposed to provide the perfect solution to caloric overload and weight gain by eliminating the need for sugar failed miserably. In fact, many large epidemiological studies have demonstrated a positive correlation between artificial sweeteners and weight gain. How could this happen? Ironically, exactly what seemed to make nonnutritive sweeteners ideal, the capacity to provide unlimited sweetness with zero caloric load, opened the door to overeating on a scale our species has never witnessed.

     Human taste provides sensations of sweet, sour, salty, bitter, savory and possibly fat and metallic. While the identification and tracking of food relied upon the visual and olfactory systems, animals developed the capacity for taste in order to recognize potential nutrients and poisons. A keen sense of taste was enormously adaptive because it provided a guide to what was full of energy/calories (sweet), a source of electrolytes (salty), rich in protein (savory) and a potential toxin (bitter).

     Because life ceases without an energy source, our capacity to discern small differences in sweetness and our preference for the sweeter, is innate, not learned. We come into the world fully loaded with a genius for choosing the sweeter option, the product of about two and half million years of evolution. Newborns will invariably prefer a sweetened nipple. Numerous experiments have documented infants' pleasure response to sweetened water including a slowed heart beat, relaxed face, hedonic brain pattern and endorphin release. Infants also learn to associate thicker fluids with greater sweetness because the viscosity and caloric density of human breast milk vary together.

     Experiments in a variety of animals including humans have repeatedly demonstrated that artificial sweeteners increase hunger and total energy intake while sugar seems to trigger a mechanism that keeps energy consumption fairly constant. Functional MRI studies, where they take pictures of the brain while someone ingests something and see what areas are active, indicate that the food reward system responds differently to sugar versus artificial sweetener. This reward system is not only what drives appetite, but also when turned off, allows us to push away from the table before loosening our belts.

     When man tampered with nature and uncoupled the sensory signal (sweetness) from caloric load, a pairing that we adjusted to for over 100,000 generation, our capacity to know when we had enough was eradicated.  Failure to activate the full food reward response fuels increased consumption.

     There is another unanticipated side-effect of these sugar impostors. In 2005 Americans ate 24 pounds of sugar substitutes per person, double the 1980 rates. Surprisingly, sugar consumption increased by 25% between 1980 and 2005. Our sweet receptors evolved in environments with so little sugar they seem to have no shut off point. By exposure to compounds that are hundreds to thousands of times sweeter than sugar, our taste for sweetness is being up-regulated. This has translated into consuming more sugar while using sugar substitutes.

     Once again what seemed like a no-brainer proved to be a disaster because of a disregard for our evolutionary history. It is not unreasonable to suggest that sugar substitutes have significantly contributed to the obesity and type 2 diabetes epidemics. Completely change something as basic as the fuel we've survived on since the beginning? What could possibly go wrong?


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