David Ludwig, MD, PhD, director of Children’s Optimal Weight for Life Program, just published a commentary in JAMA expressing concern about the widespread use of artificial sweeteners in soft drinks. Below, he offers some insight about why humans naturally crave sweetness, and the potential danger of confusing our ancient biological pathways of hunger and satiation with fake sugars.
Ever since our distant ancestors crawled out of the ocean, animals have been trying to eat plants. In this conflict, animals would seem to have a distinct advantage: we can move about, they can’t. But plants are by no means defenseless against our predations. They protect themselves with thorns, bark and tough fibers; stash their starches in tubers that are difficult to digest (at least when uncooked); encase their most prized possessions, high energy nuts and seeds, in impervious shells; and lace their leaves with bitter, toxic chemicals.
In fact, plants have long taken advantage of animals to help them reproduce. To entice us to serve them, plants have created seed-bearing fruits and infused them with sugar, the gold standard of energy metabolism. Sugars constitute the building blocks of all carbohydrates, rich in available energy and used by every cell in the body. Plants have also loaded fruits with other vital nutrients, including vitamins, minerals and water, to keep helpful animals alive and well. In contrast to most other parts of the plant, fruit is highly nutritious, safe and easy to eat. For this reason, plant-eating animals (including humans) have come to associate sweetness with goodness and evolved an innate preference for all things sweet.
Consumption of sugars in their natural forms tends not to cause health problems because plants dispense with the minimum amount of calories necessary to keep seed-spreading animals coming back for more, but not enough to cause obesity. An 8-oz apple contains fewer calories than a 2-oz pretzel. Problems arise when sugars are refined, concentrated and added to the food supply in massive amounts. Sugar-sweetened beverages merit special mention, because sugar in liquid form seems to escape notice by the body’s calorie-detecting apparatus.
Modern science, which gave us refined sugars like high fructose corn syrup, has proposed a novel solution to the obesity epidemic: artificial sweeteners. These compounds stimulate taste receptors at hundreds to thousands of times the potency of natural sugars, producing intense sweetness at trace concentrations. (Curiously, the artificial sweetener sucralose was discovered after a young Indian chemist in London was told to test a potential insecticide; due to the language barrier, he misunderstood and proceeded to taste the newly synthesized compound, finding it overwhelmingly sweet.)
With growing attention to the adverse effects of sugar-sweetened beverages, consumption of artificial-sweetened beverages has increased dramatically. Indeed, some industry analysts predict that sales of these “diet” drinks could eventually exceed those of sugar-sweetened beverages. Clinical trials show that artificial-sweetened beverages may produce short-term weight loss when substituted for their calorie-containing counterparts, but these effects have never been tested for more than a few months. One reason for concern is that consumption of artificial-sweetened beverages produces an evolutionarily unprecedented dissociation between sweet taste and calorie intake that might confound the regulatory system designed to control hunger and body weight.
In support of this possibility, a recent study found that rodents fed the artificial sweetener saccharin lost the ability to accurately regulate calorie intake and gained weight. Another concern is that habitual consumption of artificial-sweetened beverages may “infantilize” taste preferences, especially among children. Compared to the hyper-intense sweetness of these beverages, fruit may seem bland and vegetables may seem inedible, adversely affecting overall diet quality. Indeed, two observational studies have linked artificially sweetened beverage consumption to higher risk for obesity, cardiovascular disease and type 2 diabetes.
Humans have always savored sweetness, and until recently, our sweet tooth caused limited harm. However, high consumption of sugar-sweetened beverages throughout the last three decades has almost certainly fueled the obesity epidemic. The recent trend to substitute artificially-sweetened beverages for sugar-sweetened beverages–an attempt to have our cake and eat it too–-represents a public health experiment of unprecedented scale. Never before have synthetic compounds that potently interact with ancient biological pathways been added to the food supply in such large amounts. Until long-term trials are available, traditionally consumed beverages such as water, effervescent mineral water and coffee or tea (perhaps with just one teaspoon of sugar) may be our safest choice.