The Diet Soda Dilemma
We've developed a national sweet tooth problem. Enjoying sweet foods is the most natural, inborn tendency - it used to get us excited about mother's milk and ripe fruit -- but our level of added sugar consumption has reached such absurd heights that it's clear that these mountains of sugar are fueling the obesity epidemic.
To our alleged rescue came non-caloric sweeteners, offering the same intense sweetness without the caloric price tag.
Alas, diet drinks may not assist with weight loss. A few long-term studies surprisingly showed a dose-response correlation between consuming diet drinks and the development of obesity.
What was even more alarming was the emergence of studies showing a connection between the consumption of diet drinks and chronic disease: diet drinks were linked with the metabolic syndrome* and type 2 diabetes, and a recent study published in the Journal of General Internal Medicine showed that people who drink diet soft drinks on a daily basis may be at increased risk of stroke, heart attack, and vascular death.
The study of nutrition is a very tricky thing, as people don't eat at researchers' will, and the effects of many lifestyle choices - not limited to food - over a lifetime affect the measured health outcome. That's why a good study looking at nutrition and heart health, for instance, controls for obvious confounders such as obesity, smoking, exercise and lipid profile.
The question always remains: Is it possible that the metabolic and heart problems experienced by diet soda drinkers come from some other behavior they share, one that has nothing to do with diet soda? Specifically, could diet soda drinkers have a tendency for a less healthy diet, which is the real (and already known) cause for the increased risk of disease observed?
Do those eating a less healthy diet prefer diet soda?
A new study, published online ahead of press in the American Journal of Clinical Nutrition tries to tease out the specific role that diet beverages play on metabolic health when the general healthfulness of the diet is considered at the same time.
The researchers, led by Kiyah Duffey, looked at the data of more than 4000 young adults, who were followed for 20 years for signs of heart disease, and analysis showed that their dietary practice can be broadly defined as fitting a "Prudent Diet" - emphasizing more fish, fruit, nuts and whole grains -- and "Western Diet" - highlighting meat, poultry, fast foods, refined grains, snacks and sugar sweetened drinks. Diet beverages consumption was considered separately, and the study population was classified as "Consumers" vs. "Nonconsumers". The study looked for development of the components of the metabolic syndrome: abdominal obesity (measured by weight circumference), elevated blood glucose, high blood pressure and high cholesterol.
Here are the main findings:
People who ate a Prudent diet had a lower incidence of the metabolic syndrome and each of its components, compared with those who eat a Western diet.
People who didn't drink diet beverages (Non-consumers) had 19% lower risk of the metabolic syndrome compared with those who drank diet beverages, although the effect was not on all components of the metabolic syndrome: being a non-consumer lowered the risk of abdominal obesity the most.
People on a Prudent diet were more likely to consume diet beverages than people on a Western diet; in other words, drinking diet soda is mainly a habit of those eating healthier diets.
Eating a Prudent diet and not consuming diet drinks put people at the lowest risk.
The combination of a Western diet and diet drinks put people at the highest risk for cardiometabolic outcomes.
So at least by the findings of this study, diet beverages aren't the typical drink paired with a Western diet -- quite the opposite -- and they're associated with greater risk independently of diet quality.
Why would diet drinks lead to obesity?
The authors conclude that both dietary pattern and diet beverage intake are independently associated with the development of the metabolic syndrome and the development of abdominal obesity.
On the other hand, the study suggests that being a consumer of diet beverages in the context of a Western diet increases the risk of a metabolic outcome even more, so it very well may be that there's an interaction between these two things.
This study didn't go into proposed mechanisms that may explain how diet beverages might affect obesity or metabolic outcomes. Artificially sweetened beverages may habituate our taste receptors to prefer intense sweetness, leading us to reject less-sweet foods (such as veggies and fruit) and seek intensely sweetened foods. Diet drinks may also trick our hormonal and neurobehavioral pathways -- sweetness signifies to our body that energy and nutritious food are on the way, enacting a cascade of reactions, yet with diet drinks no calories are actually consumed. The outcome of this disconnect isn't yet clear.
I'd still pick a diet drink over a full calorie one, but is seems like the more we study diet drinks the more we realize that they're not an effective way to improve heart and metabolic health, or even lose weight.
Dr. Ayala
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Full disclosure: I'm vice president of product development for Herbal Water, where we make organic herb-infused waters that have zero calories and no sugar or artificial ingredients. I'm also a pediatrician and have been promoting good nutrition and healthy lifestyle for many years.
*The metabolic syndrome is a group of risk factors including abdominal obesity, high blood pressure, elevated triglycerides, low levels of high-density lipoprotein (HDL or "good") cholesterol and high fasting glucose levels. The presence of three or more of the factors increases a person's risk of developing diabetes and cardiovascular disease. The metabolic syndrome has become increasingly common in the United States. It is estimated that over 50 million Americans have it.
