Health / Nutrition / Sweeteners / Weight Loss

Diet Soda: A Real Weight Loss Tool?

Diet Coke a real weight loss tool

When Diet Coke was introduced in 1982 it was targeted at women wanting to lose weight. How fantastic it was that you could still enjoy “the same great taste” but with none of the associated calories. Rather than embroil ourselves with the subsequent sweetener safety debate (see my other article) in this article I’ll explore whether Diet Soda can really help you lose weight or not.

Several studies have been done in response to claims that the extremely sweet taste of artificial sweeteners such as aspartame, saccharin, and acesulfame-K increased ratings of hunger and, particularly after saccharin consumption, to increase actual food intake. This needed establishing, as if you want to lose weight you’re hardly going to drink an appetite stimulant!

So do the artificial sweeteners in diet soda whet your appetite?

A 1991 review delved into the effects of intense sweeteners, present in diet soda, on hunger, food intake, and body weight. However, most investigators found that aspartame consumption (used to sweeten Diet Coke) was actually associated with decreased or unchanged hunger. Crucially, even in the rarer cases when aspartame did make people hungrier, it apparently failed to impact the control of food intake and hence body weight. Indeed, both short-term and long-term studies showed that consumption of aspartame-sweetened foods or drinks was associated with either no change, or a reduction in food intake. Such trials suggested that aspartame may therefore be a useful aid in body fat reduction or weight maintenance.

This study showed that aspartame sweetened diet soda (just the sweetener) decreased calorie intake in both male and female groups. In the men, it even caused weight loss over the duration of the study.

Further to the aforementioned studies, this May 2012 review explains that low calorie sweeteners had never been found to cause weight gain in humans. Equally however, it explains that their role in weight management has not been thoroughly established, so we can’t yet claim that they’re actually an aid in dieting for fat loss. So can we put another nail in the coffin of the idea that satiety signal hormones are being trampled by the sweeteners?

So some studies suggest diet soda consumption doesn’t stimulate appetite, but does it make you fat regardless?

This 2010 study suggested that sweeteners by themselves are acutally capable of increasing body weight even when food intake was kept constant. The main problem with the experiment? It was conducted with mice. To try to explain the observations it has been speculated that the sweeteners had a hormonal effect on the mice’s bodies whereby calories were partitioned to fat storage rather than energy expenditure. Does this mean that artificial sweeteners stimulated insulin secretion, and that leads to fat storage? We’re still disentangling the exact physiological effects of diet soda, which is in itself a rather heterogenous group of drinks. The hugely interesting thing about this particular study is that food intake remained constant but body weight increased only in the artificially sweetened group. Were all the mice eating all their food all the time? It seems unlikely, but it’s possible. We’ll have to keep looking for an explanation.

In another study published in 2011 at the University of Texas Health Science Center at San Antonio, researchers found that diet soda drinkers (humans this time) experienced 70 percent greater increases in waist circumference than non-drinkers. They recorded the height, weight, waist circumference, and diet soda intakes of 474 initially, and again in three follow-up exams over two decades. Those who said they were frequent drinkers, defined as consuming two or more diet sodas a day, experienced waist circumference increases that were 500 percent greater than those who didn’t drink diet soda at all. To someone unfamiliar with epidemiology, and laissez-faire studies like this, the results here might seem quite convincing: apparently diet soda does make you fat?!

Careful… here’s why that study is a load of rubbish. Whilst the results were adjusted for waist circumference, diabetes status, leisure-time physical activity level, neighborhood of residence, age, smoking status, sex, ethnicity and years of education, you’ll notice that they weren’t adjusted, nor was the data taken for dietary parameters. Critical flaw? How can you say diet soda is fattening when you don’t know what your participants are actually eating, and when during your study national obesity rates are climbing? “It must be the zero-calorie beverage that’s making them fat, not the Big Mac and fries that normally accompany it!”

Continuing with the criticism, is it not possible to think that people consuming diet sodas are concerned about their weight, but not necessarily their health? Sodas in general including diet sodas are hardly health promoting beverages, and those who choose to drink them seldom do so as they think it will improve their health in some way. Could it be that the kind of person drinking diet sodas has less healthy general dietary habits? Might a diet soda consuming person eat fewer healthy snacks in favour of that occasional donut, or opt for pasta at lunch rather than a salad? Psychologically, if you think you’ve saved a few calories from drinking a diet soda rather than a sugar-laden drink, you might think you could consume a little more of calorie rich food to compensate; after all it’s human nature to seek to reward oneself. Granted my objections are speculation but I’m obviously not alone in my skepticism, and the point is that the study we’re discussing is inherently incapable of confirming anything, so cannot be taken as de facto proof. This is important because when you’re claiming two things are linked you have to be sure there is no doubt, but there obviously is much doubt, many flaws, and ubiquitous confounders. This is why I hate it when the press get hold of studies like this, because they sensationalize the study to attract a readership, meanwhile the real science becomes clouded with irrationality, and subtle qualifying words like “could”, “might” and “suggests”.

Essentially, epidemiology is all too pseudo-scientific. These observational trials were never meant to be rigorous, indeed they’re almost worthless. They continue to be done because it was noted in the year 2000 that overall Randomised Controlled Trials (RCTs) and Observational Trials produce similar results, and the latter are often much cheaper to implement. Saying the two studies produce similar results is dangerous, because although true in the majority of cases it has the potential to cloud true science by devaluing the much better results and superior methodology of RCTs.

Let’s try to summarise…

Essentially, at this point in time we’re seemingly no closer to the truth than we were in 1986 when this study was published. We still don’t know the ins and outs of diet soda consumption and more specifically how it affects your weight long term. It could well affect different people in quite different ways, being a weight loss tool for some, but halting progress for others.

If indeed it is the diet soda that was the cause of the weight gain seen in various studies, could it be that there is a problematic ingredient in the diet soda other than the sweeteners, perhaps even working in combination with them? Such other ingredients (caramel colour? phosphoric acid?) haven’t been studied thoroughly enough, and could work solo or in combination with the artificial sweeteners by negatively affecting satiety hormones leading to increased eating, or by stimulating energy storage through some unknown mechanism.

As usual the gold standard in scientific enquiry, Randomised Controlled Trials, are needed to establish that actual facts surrounding low calorie sweeteners. Until the relevant, correctly administered studies are done, all we can do is speculate wildly and inaccurately.

Whilst diet soda is certainly a better alternative to its sugar-laden partners, the debate continues as to whether it helps or hinders with fat loss.

In the meantime, call me mad but I certainly won’t be blaming obesity on zero calorie drinks like Diet Coke. So long as the majority of your fluid intake is water, as it should be you’ll find it hard to dangerously over-consume diet soda. But because we don’t know exactly how good or bad it is for us, further study is always needed. The more cautious amongst us might max out at half a litre a day.

Share your opinion.


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