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Are you prone to gaining weight around the belly? Are you worried about high cholesterol or high blood pressure? Do heart attacks or diabetes run in your family?

Then steer clear of a “Western pattern” diet, which puts you at risk of a condition known as metabolic syndrome, according to a new study at the University of Minnesota. The syndrome—characterized by abdominal fat, high blood pressure, and high cholesterol—doubles a person’s chances of heart disease and increases the risk of diabetes five-fold.

What is this so-called Western diet? It might be dubbed a “fast-food diet”—with at least two daily helpings of red or processed meat (the equivalent of two burger patties) and plenty of deep-fried food. That’s not surprising, perhaps. We’ve heard for years that fried foods and heaping portions of red meat aren’t good for us.

But here’s the kicker—the other component of a Western diet, the item more strongly associated with metabolic syndrome than either fried foods or red meat? Diet soda.

Yes, the carbonated, artificially sweetened beverages many of us drink to lose weight have actually been associated with weight gain and the development of metabolic syndrome. Diet soda, recommended by the American Diabetes Association to avoid high-calorie sugar, actually corresponded with the onset of diabetes.

“Isn’t that interesting?” remarks Lyn Steffen, associate professor of epidemiology at the University of Minnesota and lead author of the study published this January in Circulation, the journal of the American Heart Association. “Is it the artificial sweetener that’s causing it? Or is it a behavioral kind of mechanism where people will say—and women are great at this—‘I’ll drink my diet soda and then I can eat my chocolate chip cookie’?”

Early warnings
As early as the 1920s, researchers began to notice that certain troublesome symptoms appeared in concert. More recently, this cluster of risk factors for heart disease and diabetes was dubbed “syndrome X” and then “metabolic syndrome.” Generally, the condition applies if a person has at least three of the following: fat around the waist (more than 40 inches for men or 35 inches for women), high blood pressure, cholesterol problems (high bad cholesterol, low good cholesterol, or high triglycerides), insulin resistance, proinflammatory state (elevated C-reactive protein in the blood), or prothrombotic state (predisposition to a blood clot).

More of us are developing metabolic syndrome. More than 50 million Americans have the condition. (It’s especially prevalent among Hispanics; more than a third of Hispanic adults have it.) Soon it will surpass cigarette smoking as the leading risk factor for heart disease in the United States. More than anything, according to experts, the rise in metabolic syndrome follows the increase in obesity.

The trend is worrisome. Overall, patients with metabolic syndrome have a significantly higher risk of death (53 percent) over the course of an 11-year study than those without the syndrome. The first line of attack in battling metabolic syndrome: Losing weight.

While excess weight is key to metabolic syndrome, the role of diet isn’t entirely clear. Is it certain foods or patterns of eating that are at work? To find out, Steffen and her co-investigators analyzed the diets of more than 9,500 participants ages 45 to 65 in the Atherosclerosis Risk in Communities (ARIC) study, funded by the National Heart, Lung, and Blood Institute.

At the beginning of the study and then six years into the study the participants were asked to characterize their diets during the previous year on a 66-item food frequency questionnaire. “Self-reporting is a problem,” Steffen admits. “This questionnaire is notorious for underestimating food intake.” For one thing, it can’t list everything people would eat. Second, normal-weight people routinely overestimate what they eat while overweight people underreport.

Nonetheless, the survey was sufficiently clear and detailed to allow Steffen to divide participants into two groups according to the character of their diet. The Western-pattern diet was big on refined grains, red meat, processed meat (such as bacon and sausage), fried food, eggs, and carbonated drinks. Fish, fruit, vegetables, and whole grains mostly went missing. The “prudent diet” included plenty of vegetables, especially cruciferous vegetables (such as cabbage, radishes, and broccoli) and carotenoid veggies (carrots, pumpkins, peppers, and spinach), as well as seafood, poultry, whole grains, and low-fat dairy. In addition to these broad patterns, researchers examined the relationship between metabolic syndrome and individual foods.

After nine years, when the study ended, nearly 3,800—about 40 percent—of the participants had developed metabolic syndrome. If you count the 5,000 ARIC participants Steffen excluded from her study who already had metabolic syndrome, 60.5 percent of the group had the condition by the end of the study.

Steffen found that a Western dietary pattern increased the incidence of metabolic syndrome. Two daily servings of red and processed meat increased risk by about 25 percent, compared with people who ate only two servings a week. Eating plenty of fried foods also increased risk about 25 percent. Simply eating an average of one serving of french fries each day boosted risk 10 percent.

Dairy products, especially yogurt and low-fat milk, actually seemed to ward off metabolic syndrome. Not contributing one way or the other were whole grains, refined grains, fruits and vegetables, nuts, coffee, and beverages sweetened with sucrose or fructose.

The strongest and most startling correlation was diet soda. Diet pop drinkers—those who drank at least one diet soda a day—were 35 percent more likely to develop metabolic syndrome than those who drank little or none. By comparison, regular soft drinks didn’t boost risk by a statistically significant amount. Steffen says her study doesn’t reveal why red meat, fried foods, and diet soda might cause metabolic syndrome. Or even that they do—a point emphasized by the American Beverage Association: “This study merely shows that diet soda consumption and certain markers for metabolic syndrome occur simultaneously— not that one causes the other.”

Indeed, these foods may simply correlate with unhealthy lifestyles or behaviors. “After working many years with dietary intake,” Steffen says, “I’ve noticed that people who consume a more Western-pattern diet, their lifestyle habits aren’t really quite as healthy as people who eat a lot of fruit and vegetables or a lot of whole grains. People who eat a lot of red meat, refined grain, or candy or fried foods—they’re not very physically active.”

Something similar may be at work with diet soda in particular, she says. Perhaps diet soda drinkers generally lack concern about proper nutrition. Or perhaps they choose it because they are already overweight and at risk for more serious health problems and believe diet drinks will help shed pounds. Or maybe drinking diet soda sets up the psychological bargaining that excuses the extra chocolate chip cookie.

Or perhaps it is something more.

Sweet nothings
Soda (known as “pop” in Minnesota and much of the Midwest) has been around for two centuries, but it wasn’t until 1952 that the first diet soft drink went on sale. Since then, our consumption of carbonated beverages has climbed from about 10 gallons per person each year to more than 50. For years, diet soda has made up nearly 30 percent of the total volume of sales. So as soda sales have climbed, so has our consumption of diet pop.

There’s little in diet drinks to raise suspicions of a connection to metabolic syndrome. Water makes up 99 percent of most diet sodas. Carbon dioxide gas, responsible for the fizz, is added by a “carbonator machine” at the bottling plant. Bottlers also add natural and artificial flavors and colors. Acidulants such as phosphoric acid and citric acid make soda slightly tart—both to enhance taste and to retard spoilage. Some drinks also contain small amounts of preservatives to protect flavor. Many of the additives in soda contain potassium and tiny amounts of sodium.

The most notable ingredient is the sweetener. Regular soft drinks contain sucrose (from sugarcane or sugar beets) or high-fructose corn syrup. Low-calorie drinks most often contain aspartame or sucralose. Though aspartame has been blamed for everything from brain tumors to cancer, it has been approved by the Food and Drug Administration and other health agencies. Neither artificial sweetener—or anything else in soda—has been shown to cause metabolic syndrome directly. “No, no, no, no,” says Barry Popkin, a professor of nutrition at the University of North Carolina specializing in beverages. “Not that we know from all the research that has been done on beverages.”

Some research has shown, not surprisingly, that people lose weight when they actually replace the regular soda in their diets with artificially sweetened soda. But other investigations indicate that often people eat foods and beverages containing artificial sweeteners in addition to all the sugar they normally eat. And still other studies indicate that without careful supervision artificial sweeteners lead to even greater sugar consumption and weight gain.

An analysis of more than 6,000 participants in the famed ongoing Framingham heart study showed that individuals consuming more than one soda a day had a higher incidence of metabolic syndrome (including obesity) than those drinking less. The association held true with both diet and regular sodas. Soda drinkers ate more calories, more saturated fat and trans fat, and less fiber than people who didn’t drink soda. They also exercised less.

A weakness of many of these studies is that they involved humans—humans who cannot be controlled and supervised for months or years, humans who fib about and continually stray from their diets.

So a Purdue study published early this year created a lot of excitement because its participants were carefully controlled and monitored. The investigators demonstrated a link between use of artificial sweeteners and eating more, gaining weight, and growing fatter. Only the subjects weren’t humans; they were rats.

But the authors, Susan Swithers and Terry Davidson of Purdue’s department of psychological sciences, suspected that what was true for rats might also hold true for the “millions of people . . . being exposed to sweet tastes that are not associated with caloric or nutritive consequences.” That is, artificial sweeteners. And they do mean millions. The number of U.S. adults consuming artificially sweetened products of all kinds increased from 68 million in 1984 to 180 million in 2004. During the same period, the incidence of obesity has doubled.

Swithers and Davidson divided their rats into groups that were fed yogurt sweetened with high-calorie glucose or with the low-cal artificial sweetener saccharine. All the rats also ate meals of unsweetened yogurt and all the rat chow they wanted.

The rats on artificial sweeteners gobbled more rat chow than their counterparts did. When both groups of rats were fed a rich meal of high-energy, high-protein milkshake, the rats conditioned to real sugar compensated by eating less rat chow, but the rats on diet sweeteners went on eating as before. In another test, when the sugar-conditioned rats ate their milkshake, their metabolisms kicked into high gear, burning calories. But the rats on diet sweeteners showed much less of a metabolism boost.

As a result, Swithers says, after five weeks “animals that had experience with the artificially sweetened yogurt were heavier, they were fatter, and they had decreases in core body temperature responses to sweet-tasting foods.

“We think that in our rats that the experience or learning between the sweet taste and the calories that follow is one of the mechanisms that are producing these changes in body weight and body composition,” she says.

An animal, goes her theory, is conditioned from birth to expect that a sweet taste precedes a wallop of calories. Its body compensates by reining in the appetite. Diet sweeteners break the link between sweetness and calories. The body loses its conditioned response. With no signal to stop, the animal keeps eating.

“We also think the same kinds of processes could be happening in people,” Swithers says. “If the same thing is happening, then we would predict that you would see increased body weight and other sorts of physiological complications by consuming artificially sweetened products.”

As Swithers notes in her study, “Such an outcome may seem counterintuitive, if not an anathema, to human clinical researchers and health-care practitioners who have long recommended the use of low- and no-calorie sweeteners as a means of weight control.”

Finding the sweet spot
Minnesota’s Lyn Steffen wonders if the results of Purdue’s rat study can be duplicated with more popular sweeteners. “We need to get other investigators to replicate the saccharine study but also to test aspartame and sucrolose,” Steffen says. “And those are rats. Now we also need to conduct the same study in humans.” She would also like to see additional human studies parse the results of her own research.

Until then, the jury is out on diet soda, she says. Despite the implications of recent studies, “the evidence just is not there yet to say don’t drink it.”

That doesn’t mean she doesn’t have recommendations for dieters with concerns about weight gain, heart health, and diabetes. Go easy on red and processed meat, avoid deep-fried foods. In place of diet sodas, drink coffee, tea, and especially low-fat milk, which provides calcium for bones and teeth and seems to protect against weight gain.

And one thing more. “I think that people in this country do not drink enough water,” Steffen says. “Just regular old water.”

Greg Breining is a freelance writer based in St. Paul.