Comparing Studies on Kidney Safety

By Keith Ayoob
Comparing Studies on Kidney Safety
With previous studies showing the safety of sweeteners with kidney function, how does this latest study compare? And is any new information brought forward?
January 6, 2010

With previous studies showing the safety of sweeteners with kidney function, how does this latest study compare? And is any new information brought forward?

This latest study, presented at the American Society of Nephrology, suggested an "association" between the decline in kidney function and the consumption of diet sodas. This kind of study points out however, that just because research gets published, doesn't mean it is useful. Here's why:

  • They used food questionnaires that were received in 1984, 1986, and 1990. While kidney decline can take a while to develop, this study gives no clues as to how these people were eating for the past 20 years, so some very important information was omitted. If the researchers had access to this data, they decided not to include it in this study.
  • This study mentioned an "association" between diet soda consumption and kidney function decline, but an "association" is not the same as "cause and effect" and here's an example of why: Say there's an "association" between the incidence of obesity and people who have cable television. That doesn't mean that having cable television "causes" your body to gain weight. It's likely due to another factor. Perhaps it's that having cable television makes you less likely to exercise. Less exercise COULD cause you to gain weight, even if you don't have cable television.
  • The researchers avoided claiming a causal effect for good reason: they don't have the evidence for that. Indeed, well-done recent research - 3 studies in the past year, in fact - found good evidence for the exact opposite of what this study said.
    That is, these latest studies found:
    - No link between consumption of diet soda and kidney disease.
    - No link between consumption of diet soda and a sensitive marker of kidney disease.
    - No difference between diet soda and water on the formation of kidney stones.

Studies that draw "associations" can irritate those of us who try to help the public make sense of the mind-numbing amount of research that is thrown at consumers on a daily basis. Sometimes research can be less about giving consumers useful information and more about just trying to publish another paper.

The bottom line is, there's probably a reason that well-done research finds no connection between consumption of diet sodas and kidney disease: diet soda is really just flavored, fizzy water. No calories, no sugar, no sodium, and many don't even have any color. Sodas sweetened with aspartame have a very tiny amount of extra protein, the aspartame, which provides the sweetness. That protein is broken down into it's two amino acids - phenylalanine, which is essential to us, and aspartic acid, which our body makes on its own in larger amounts. Apart from that, the only other byproduct is a little methanol, which we also make ourselves. Some healthy foods, like tomato juice and red grape juice, have far more ethanol than an aspartame-sweetened soda, and they're perfectly safe for people.

Water is an excellent beverage and we should drink it daily. As an alternative sometimes, having a sugar-free soda on occasion certainly counts towards your daily fluid intake, just like water does.

"Keith Ayoob is a registered dietitian and associate professor at Albert Einstein College of Medicine. He provides expert counsel to the Aspartame Resource Center."

Comparing Studies on Kidney Safety

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