Diet soda beats water for weight loss? Hang on a minute

A new study suggests diet soda may be healthier than water

Pexels/Robbins Flores

A new study suggests diet soda may be healthier than water

Pexels/Robbins Flores

What are you going to believe—the methodology or the results?

Research. It’s the reason the full professors have abandoned the classroom, leaving your kids to be taught by grad students. It’s a leading cause of cancer in mice. Worst of all, it costs money to conduct. And that’s a problem, because many of the folks with full pockets have reasons to want the results of scientific research to go their way.

And so you have situations like the one Marion Nestle describes in her blog: She’s recently reviewed at 114 industry-sponsored studies of food. Only nine produced results that went against the sponsors’ interests. That should give us all pause.

You didn’t need to know who the sponsor was to know that it was flawed.

Of course, you have to be cautious in looking at a number like that. Corporations have learned to be smart about the research they sponsor. By the time they write a check, they ought to have a pretty good idea of what the research will find. (In the world of pharmaceuticals, many people are scandalized by how low the success rate is in late-stage clinical trials. Why, they ask, are companies wasting time and money on things that they don’t already understand thoroughly?) For example, a recent study out of the University of Granada found that vegetables fried in extra-virgin olive oil had higher concentrations of phenols than boiled vegetables. But consider two facts: (a) there are phenols in extra virgin oil, and (b) when you fry food it loses moisture, automatically increasing the concentration of what’s left. Do we think anyone was yelling eureka! around that lab?

On the other hand, there are studies that stink to high heaven, like that University of Maryland study in which concussed athletes who drank a particular brand of chocolate milk did better on cognitive tests. (New York magazine has posted a hilarious account of one reporter’s efforts to find out what, if anything, was behind the press release that started the whole flap.) Sponsorship was undoubtedly a problem, but the way it played out was in bad methodology. You didn’t need to know who the sponsor was to know that it was flawed.

Which brings us to this week’s big food-science scandal. The Independent in England blew the whistle on a study that found that diet soda could lead to weight loss. The study, it revealed, was sponsored by the International Life Sciences Institute, an organization that included Coca Cola and Pepsico as members. One of the researchers actually belonged to an ILSI task force, and others had worked with sweetener-related companies and organizations. Worst of all, though the researchers had reviewed 5,000 previous papers, they used only three in reaching their conclusion—though only one actually agreed with them.

Sounds awful, right?

But before we tweet our condemnations to the world, let’s take a minute and look at the study itself, which appeared in the International Journal of Obesity. It’s slow reading but interesting for showing what people are studying in the field and what the issues are for scientists. Here’s what it covers:

  • First the researchers review studies in animals, which are important, because they are the ones likely to turn up evidence that low energy sweeteners (LES) can cause weight gain. They look at a variety of approaches, and the only one that seems to cause cause consistent weight gain is when experimenters made the animals’ feed more palatable by making it sweeter.
  • Then it’s on to human observational studies, a dozen of them, all including at least 500 subjects. The results are mixed: About half show weight gain and half weight loss, but the changes are tiny. When the results of all the studies were folded together, they showed a change of body mass index of just -0.01 percent over a year.
  • Short-term human experiments with humans show that swapping out sugar for LES over the course of a day reduced the number of calories they took in. That seems to eliminate the idea that LES stimulate appetite directly. (There was even one interesting study that showed that people taking capsules of aspartame ate less, perhaps because of some sort of sweetness detector in the gut.) But the real concern is for the long run.
  • Here’s the part the Independent was incensed about: long-term experiments involving humans. There weren’t just three studies. There were a dozen, though a majority either failed to achieve statistical significance or didn’t report statistical significance. The three the Independent is talking about were the ones that included a comparison between LES and water. (This may be the real outrage: How can it be that only three studies have asked that question?) The three taken together included 541 subjects, and they showed a statistically significant level of weight loss, or slowed weight gain, for people consuming LES versus those consuming water.

A couple of thoughts:

  1. Three studies with 541 people is not much. Am I persuaded? Kinda sorta. Should you be? Your call.
  2.  The science of obesity is much more complicated than we civilians know. For example, look at this review article from the International Journal of Obesity, which reviews what science does and doesn’t understand about the mechanisms by which drinking sugar-sweetened drinks leads to obesity. You’d think we would know by now. But we don’t.
  3. Science is the process through which we gradually discover that all is not as it seems. The basic criticism of the LES study seems to be that the results are outrageous, therefore the science is bad. A cardiologist named Aseem Malhotra, who’s an advisor to the National Obesity Forum in the UK, told the Independent: “To suggest that diet drinks are more healthy than drinking water is laughable unscientific nonsense.” OK, but judging science on its conclusions rather than its methods, while not laughable, is unscientific nonsense too. It seems that at least sometimes LES might be better for weight loss (not “more healthy”) than water. It would be nice to know the circumstances under which that happens.

Bottom line: Let me just say what the researchers always say. More study is needed. And results we can trust.

Patrick Clinton is The Counter's contributing editor. He's also a long-time journalist and educator. He edited the Chicago Reader during the politically exciting years that surrounded the election of the city’s first black mayor, Harold Washington; University Business during the early days of for-profit universities and online instruction; and Pharmaceutical Executive during a period that saw the Vioxx scandal and the ascendancy of biotech. He has written and worked as a staff editor for a variety of publications, including Chicago, Men’s Journal, and Outside (for which he ran down the answer to everyone’s most burning question about porcupines). For seven years, he taught magazine writing and editing at Northwestern University's Medill School of Journalism.