Could diet soda be worsening your mood?

Depressed and irritable? It could be your diet.

A 2014 study at the University of North Dakota found that students placed on a diet that included high levels of aspartame via diet soda, yogurt, gelatin, ice cream and other foods became irritable, showed signs of depression and had worsened  spatial skills, compared with when they ate lesser helpings of aspartame.

The “high aspartame diet,” which the students consumed for 8 days, delivered 25?milligrams per kilogram of body weight per day. That amount is half of what the Food and Drug Administration (FDA) has deemed to be a safe level of consumption of aspartame, which is sold as “Nutrasweet” and used as a sweetener in a host of diet foods and drinks.

For perspective, there are 180 milligrams of aspartame in a can of diet Coke. So in the study,  someone weighing 81 kilograms (180 pounds) would have consumed 2025 milligrams of aspartame (25 mg per kg of body weight). That equates to about 11 cans of  diet Coke, though they would have been given the sweetener in some combination of several diet sodas and an array of other sweet treats sweetened with aspartame.

(The FDA threshold of 50 mg per kg of body weight holds that 21 cans of diet soda would be a safe amount to drink per day.)

The researchers put another group of students on a “low aspartame” diet of 10 mg per kg of body weight. Each group later switched places, after an interim two-week “washout” period to flush the chemicals.

The researchers found that when the students were on the “high aspartame” diet they were noticeably more irritable and showed signs of depression, with three of the students testing as mild or moderately clinically depressed. When on the “low aspartame” diet, these symptoms disappeared.

Aspartame has long been villified as a dangerous food additive by natural food advocates. They point out that aspartame breaks down into methanol, phenylalanine and aspartic acid, which can all be toxic at high doses.

Another factor that casts suspicion on aspartame is the fact that some people report it causes immediate symptoms, such as headaches or cognitive fogginess. This has lent credence to concerns that it could be contributing to worse outcomes, such as brain tumors and cancer.

Those who say aspartame is safe, however, note that the very small amount of aspartame in diet drinks, gum and other foods does not generate enough methanol or phenylalanine in the human body to cause serious health issues. The US and European governments have not banned the additive and believe it’s largely safe at reasonable consumption levels.

And so, as the North Dakota researchers point out, “the artificial sweetener aspartame remains one of the most controversial food additives, due to mixed evidence on its neurobehavioral effects.”

Their research did not explore long-term toxicity, but did conclude, after charting the behavioral and cognitive changes in the “high aspartame” group, that the sweetener had obvious negative neurological effects.

“When consuming high-aspartame diets, participants had more irritable mood, exhibited more depression, and performed worse on spatial orientation tests. Aspartame consumption did not influence working memory. Given that the higher intake level tested here was well below the maximum acceptable daily intake level of 40-50?mg/kg body weight/day, careful consideration is warranted when consuming food products that may affect neurobehavioral health.”

Does this make sugar superior as a sweetener? Probably not. There are plenty of studies warning of the link between high sugar consumption and diabetes, and more recently, heart disease.

Researchers and natural food advocates recommend that people replace sugar with stevia, a natural sweetener that, like aspartame, packs a lot more sweet into a smaller package but without the controversy. Other low-glycemic sweeteners suitable for those watching their sugar intake include agave syrup, molasses or brown rice syrup.

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