An interesting piece in a recent issue of the Journal of the American Medical Association raises one of the concerns that I’ve long had about artificial sweeteners: that calories alone are not the only problem with sweet tastes. For one thing, we appear to have sweet taste receptors not only in the mouth but the gut. For another, I believe (and folks like wine tasters would no doubt agree) that the palate and food preferences can be trained. If we constantly hammer our taste buds with simplistic, blunt-instrument flavours, we don’t develop the ability to appreciate the subtler flavours that occur in the natural world.
The sad irony, of course, is that the natural-world flavours are infinitely more interesting. Developing sensitivity to real-world flavours actually makes you a more careful, nuanced eater who focuses on food quality, and ultimately enjoys food more. After all, be honest: have you really savoured the bouquet of cheezies? If you really focused on the scent and taste notes of Rock Star drink, or Twizzlers, you wouldn’t touch the shit because you’d start to notice the waxy mouth feel or the chemical aftertaste. But if I handed you a $10 Godiva truffle, you’d certainly spend a little quality time with that bad boy before snarfing it down.
Interestingly, however, other studies have shown that athletes who simply swished glucose in their mouths — without swallowing — experienced the restorative effects of glucose without actually ingesting it. Control samples that were equivalently sweet didn’t have the same effect, suggesting that the brain somehow recognizes both sweet taste and the presence of sweet calories.
Anyhoo, this commentary points out that aside from the safety concerns about artificial sweeteners, we should also be concerned about the relationship that the taste has to our consumption habits and potential secretion of fat-deposition hormones. As I mentioned recently, we start to secrete hormones in advance of actually eating a sweet taste, so it stands to reason that experiencing a sweet taste would affect our hormonal environment as well.
Conversely, also note the author’s points that (a) in nature, sweet foods are normally nutritious; and (b) liquid sweet foods are less satiating. Think about that next time you’re drinking a “diet” strawberry shake… maybe you should have the actual strawberries, instead of a soy-oil-based, high-fructose-corn-syrup-sweetened, chemically flavoured concoction.
Ludwig, David S. Artificially sweetened beverages: Cause for concern. JAMA. 2009;302(22):2477-2478.
The taste receptor for sweetness, T1R2/R1R3,1 can detect sugar at a concentration as low as about 1 part in 200, whereas some bitter substances can be detected in the range of a few parts per million, perhaps explaining why most individuals prefer foods with high sugar content but little bitterness. However, this innate preference for sweetness does not necessarily lead to obesity or other diet-related diseases because sugar-containing foods in their natural form tend to be highly nutritious. For instance, an 8-oz apple contains beneficial vitamins, minerals, and phytochemicals but fewer calories than a 2-oz portion of bread. Most fruits elicit a high level of satiety relative to calories ingested due to their low-energy density, high-fiber content, and low glycemic index.2
Problems occur when sugars—chiefly sucrose and the chemically similar product, high-fructose corn syrup—are refined, concentrated, and consumed in large amounts. Without the protection conferred by an intact, natural food containing fiber and antioxidants, these refined sugars increase blood glucose and insulin levels rapidly after consumption, increasing concentrations of triglycerides, inflammatory mediators, and reactive oxygen radicals.2 In contrast to whole fruit, intake of refined carbohydrate increases risk for diabetes, cardiovascular disease, and other chronic illness.3 Sugar-sweetened beverages may have an especially adverse effect on body weight because of the exceptionally low-satiety value of sugars in liquid form.
One proposed solution to the problems caused by overconsumption of these fattening, empty calories is artificial sweeteners. Presently, 5 such products have US Food and Drug Administration (FDA) approval: saccharin, acesulfame, aspartame, neotame, and sucralose. (Stevia, a natural extract from the plant Stevia rebaudiana, received FDA approval in 2008.) These synthetic substances are hundreds to thousands of times more potent than sucrose and elicit an intense sensation of sweetness in trace concentrations.
As suggested by the term diet with which these products are marketed, foods and beverages with artificial sweeteners are intended to produce a sweet taste comparable with their sugar-containing counterparts but with fewer calories, thereby promoting weight loss when substituted for calorie-containing products. Short-term clinical trials provide some evidence for this effect. For example, obese adults who consumed an average of 600 kcal/d of sucrose, mostly in the form of beverages, for 10 weeks showed increased body weight, blood pressure, and inflammatory markers compared with a control group given artificial sweeteners.4-5
However, body weight is regulated by complex and redundant biological and behavioral pathways. Calories displaced by artificial sweeteners may be replaced over time from other sources; the nature and completeness of this compensation would therefore determine the ultimate effects on body weight and other health outcomes. In addition, overstimulation of sugar receptors by frequent consumption of hyper-intense sweeteners may cause taste preferences to remain in, or revert to, an infantile state (ie, with limited tolerance for more complex tastes). Individuals who habitually consume artificial sweeteners may find more satiating but less intensely sweet foods (eg, fruit) less appealing and unsweet foods (eg, vegetables, legumes) less palatable, reducing overall diet quality in ways that might contribute to excessive weight gain.
Diet drinks may comprise a special and particularly concerning case. Diet drinks have essentially no calories, unlike most artificially sweetened solid foods that typically contain other nutrients. Moreover, diet drinks are often consumed in the absence of other foods, producing a dissociation between sweet taste and calorie intake. One concern is that the dissociation of these physiological events might disrupt the hormonal and neurobehavioral pathways regulating hunger and satiety.
Examining this hypothesis, researchers gave rats, including rats with previous cocaine habits, sweet tastes in the form of saccharin. Findings? “Rodents fed saccharin compared with those fed glucose showed diminished calorie compensation ability, increased calorie intake, and increased body weight,” and even the cokehead rats preferred sweet taste over more coke. “[T]he absolute preference for taste sweetness may lead to a re-ordering in the hierarchy of potentially addictive stimuli, with sweetened diets. . . taking precedence over cocaine and possibly other drugs of abuse.”
Digest that for a moment. Sweetness beats out coke.
In humans, there are no long-term studies yet. However, in observational studies, diet drinks are associated with overweight/obesity in a dose-dependent way — in other words, the more diet drinks you consume, the heavier/fatter you’re likely to be (and the more likely you are to have metabolic syndrome and/or full-blown type 2 diabetes). Authors caution, however, that “excessive weight gain may prompt some individuals to increase diet drink consumption, producing reverse causation.”
Per capita diet drink intake has increased from less than 1 oz per day in the 1960s to about 4 oz per day this decade. Among regular consumers of diet drinks, intake now totals more than three 8-oz servings per day. If trends in consumption continue, the nation will, in effect, have embarked on a massive, uncontrolled, and inadvertent public health experiment. Although many synthetic chemicals have been added to the food supply in recent years, artificial sweeteners in beverages stand out in their ability to interact with evolutionarily ancient sensorineural pathways at remarkably high affinity.