Science Fact: Diet drinks are consumed to help us diet. They are misnamed, because they don’t help us diet at all: diet drinks don’t reduce our weight, and they aren’t even very satisfying! Scientists are finding out why.
Diet drinks are reduced sugar or sugar-free beverages, usually artificially sweetened. A CDC study of 2009-2010 data found that on an average day, 20% of the U.S. population consumed a diet beverage, a number that had been increasing year by year. That’s 61 million people. More than half of those people consumed more than 16 ounces a day.
Although consumption in the last few years has been decreasing, diet sodas still make up a $7 billion business in the US. And most people consume diet drinks with the belief or hope that they will reduce their calorie input and as a result not gain weight.
Let’s consider a few numbers. In 2010 the Coca-Cola Company sold 927 million cases of Diet Coke, where a “case” (“unit case”) means 192 fluid ounces. Looking at relative market share this means 1,788 million cases of diet soda. At 11 calories per ounce for cola (more for other flavors), this adds up to 3.8 trillion calories. That’s sort of a hard number to think about. But for those 61 million people, that’s 1,190 calories per person per week. Given the conversion 3500 calories = 1 pound, in the course of a year that means each person avoided gaining 18 pounds in body weight compared with drinking sugared soda.
Wow, I just avoided gaining 18 pounds last year! And 180 pounds during the last 10 years! I’m slim as a model, right?
Not quite. We still have an obesity epidemic in the U.S. And diet sodas appear to have been making it worse, not better: one study found that over a ten-year period, the waist sizes of diet soda drinkers actually grew 70 percent more than the waists of non-diet drinkers.
So diet drinks don’t seem to work as a dieting strategy. This is a puzzle, and wherever there’s a puzzle you will find scientists trying to unravel it.
The understanding of diet drinks got a boost from research on runners. Long-distance runners, who run for two or more hours at a time, typically perform “carbohydrate loading.” The athlete eats extra carbohydrates during several days prior to a race in order to store extra glycogen in the muscles and liver to serve as a source of energy.
However, the glycogen explanation doesn’t seem sufficient: eating carbs also seems to enhance performance over shorter intervals such as an hour, which is not long enough to exhaust the body’s glycogen supplies. In a 2009 study, researchers tested sixteen cyclists, fourteen men and two women. The scientists tested their cycling endurance on four different days. On the third and fourth tests, their mouths were rinsed with glucose, with maltodextrin or with a non-carb saccharin mixture of similar sweetness. Both glucose and maltodextrin are carbohydrates that are used by the body for energy, but maltodextrin is a starch, a “non-sweet” carb. In addition, the cyclists’ brain activity in response to the mouth rinse was measured using functional MRI.
The researchers showed that not only did endurance improve significantly with a carb mouth rinse, but the carbs also activated parts of the brain associated with reward and with motor control. Thus even without digesting any carbs, the cyclists’ brains recognized carbs in their mouth, then amped up their performance and their feelings of satisfaction.
Similar results were found by other researchers in 2011 when testing thirteen “non-athletic” men. Cycling endurance was significantly improved when their mouths were periodically rinsed with maltodextrin, whether or not they had previously eaten a carbohydrate-rich breakfast. This year a third study by Turner, Byblow, Stinear and Gant at the University of Auckland, New Zealand showed that rinsing the mouth with a tasteless carbohydrate solution improves visual perception and ability to grip a sensor in response to a visible signal. Since you can’t (yet) strap an MRI machine to a cyclist while exercising, this last study made an important addition because it measured brain function and physical performance simultaneously.
Perhaps science journalists are unusually on the ball, or perhaps the University of Auckland has an unusually savvy media department. Either way, the recent study stimulated some great headlines:
– You Cannot Fake Out Your Brain with Artificial Sweeteners
– Tongue Has a Sixth Sense
– You can’t fool the human body when it comes to carbs
– Sixth Taste on Our Tongues May Unleash Our Energy Reserves
– Does the human tongue have a SIXTH sense? Researchers claim people have ‘sense of carbs’ – and it triggers the brain’s pleasure centre
Thus thanks to the research on athletes, we can now understand why diet drinks don’t seem to help people diet: your body can tell the difference. It can “taste” genuine carbohydrates that provide it with energy, and is not fooled by artificial sweeteners.
Drinking diet soda does not reduce your weight by 18 pounds a year, because it doesn’t satisfy your body’s hunger for food. In fact, some doctors assert that artificial sweeteners may upset the body’s regulatory system that normally restrains our caloric intake.
Science Speculation: Researchers in this area are beginning to talk in terms of an extra sense, separate from the normal sensations of taste, that can distinguish carbohydrates. We’re all familiar with the standard basic tastes: sweet, sour, salt, bitter and umami (“brothiness” or “meatiness”). Does it seem reasonable that humans developed an independent sense for carbohydrates?
Perhaps so. Early humans, like us, were omnivorous. At times when familiar food was scarce, people needed a way to tell what was safe to eat and what was not. It’s reasonable to believe that food safety would have had a strong influence on our evolving ability to taste and smell. However, it’s not enough just to avoid toxic mushrooms and poisonous hemlock: we also need foods that will provide energy, and necessary vitamins and minerals.
That suggests that we may have evolved senses that would guide us toward a healthy diet, a diet that not only provides enough energy but also the other nutritional components. That’s the implication of a famous study by Clara Davis in the 1930s, in which fifteen infants were allowed to eat exactly what they wanted for a several year period, choosing from 33 available foods. There are many reasons such a study would not and could not be conducted today. Nevertheless, it is fascinating that although the children could have managed to develop one or more serious nutritional deficiencies, none of them did. And this is true although their diets varied tremendously from child to child and from day to day.
So our bodies are very smart about what they are eating. We cannot use “diet” foods to trick them into eating less. If anything, the artificial sweeteners used in such foods may confuse our bodies and interfere with our normal appetite regulation (e.g., if I’m hungry I’ll eat, if I’m full I won’t).
Weight control is a puzzle that science may yet unravel. However, diet drinks, and artificially sweetened foods in general, don’t appear to provide an answer.
Are diet drinks a part of your diet? If so, do you feel that they actually decrease your calorie intake?
Drawing Credit: Gerald_G, on openclipart.org