I’ve long looked for an iron-clad reason to remove diet soda permanently and completely from my diet.
I rarely drink it these days, and there are stretches where I completely shun it, either because I’m avoiding caffeine or because I’m avoiding highly acidic beverages.
But, while I’ve succeeded in shunning sugary beverages (those that actually contain sugar, rather than artificial sweeteners), sugary desserts, white flour (including white bread, white pasta and many processed foods) and white almost completely from my diet, diet soda has a way of sneaking back in, albeit in relatively small quantities, from time to time.
And the main reason is, even though I have a nagging feeling that diet soda is terrible for me, I have yet to find all that dramatically compelling a reason to keep it out. After all, it has zero calories, doesn’t get my highly intoxicated, and doesn’t seem to have any other immediately nasty health consequence.
But there are worrying studies out there about diet soda. The main one is that diet soda consumption is very strongly correlated with obesity. People who drink two or more diet sodas per day see 5 times the increase in waist circumference over a 10 year period than people who don’t drink diet soda. And waist circumference is heavily correlated with a slew of health problems, ranging from diabetes to heart disease to certain cancers.
Now, correlation doesn’t prove causation, and it’s hard to imagine how diet soda, a zero-calorie beverage, could lead to long-term weight gain. Maybe it’s just that people who drink diet soda are often drinking it as part of a fast food meal that’s otherwise unhealthy, or tend to have other bad habits that tend toward long-term increases in the waistline. Maybe people who exercise tend not to do things like drink diet soda. Who knows. So maybe the weight gain has nothing to do with the diet soda itself.
But there are a couple reasons I’m hesitant to write off the connection between diet soda and weight gain. The biggest one until now has been that soda is heavily acidic, and tends to have a heavily acidic effect on the body. (Some acidic foods, like lemons, actually have an alkalizing effect on the body. Soda doesn’t.) And when your body consumes a heavily acidifying food, it needs to do something to balance out its pH. It tends to do this by drawing calcium and magnesium from your bones and other tissues (perhaps among other changes). Higher quantities of these minerals show up in our urine after consuming acidifying food or drink. This depletion of calcium may contribute to osteoporosis.
And it may also contribute to weight gain. It’s possible that, when we draw nutrients from our bodies, our bodies want us to replace those nutrients, and make us hungry. So we eat more. Just because we had that diet soda. So, even though the diet soda itself has no calories, it causes us to eat more of other foods that do have calories, in order to replace the nutrients it leeches from our bodies, and we put on weight.
But this weight gain seems temporary, and harmless, assuming we only have a diet soda now and then (and not the two diet sodas per day that the people in the study consumed). So it’s not compelling enough evidence to cause me to never drink diet soda. And when I’m running 50 to 60 miles per day in the heat as I’ve done this summer for marathon training, it’s very tempting after my longer runs (one every week or two extends as far as 18 to 23 miles) to reward myself with diet soda. It’s so cold, and so refreshing. It may be bad for my body, but at least it’s a short-term effect that reverses when I go back to a good diet. Right?
Maybe not. The far scarier effect diet soda may have on our bodies is on insulin resistance.
Insulin resistance is still imperfectly understood, but it’s a major hallmark of diabetes, and is heavily correlated with obesity, heart disease and other “diseases of civilization.” What tends to happen is that when we pour sugar into our body, our body responds with the release of an enormous amount of insulin, which tells our body’s cells to take in that sugar either as energy to be burned up immediately (the “sugar high”) or deposited as fat.
If we keep pouring sugar into our bodies, our bodies keep getting this rush of insulin, and our muscle cells start dulling their reaction to it. So, over time, you need more and more insulin for your body muscle cells to react to it and to take in the sugar and burn it as energy. They become “insulin resistant.” So your body has to produce more and more of it for your muscle cells to do their thing.
But your fat cells apparently never become insulin resistant. So, when your body produces more and more insulin in order to get your muscle cells to react and take in energy from your blood sugar, those higher insulin levels merely tell your fat cells to take in more and more fat. And, unlike muscle cells, they won’t learn to stop taking in so much in response to insulin; the more insulin you throw at them, the more fat they’ll store.
And this effect may be permanent. So, forever afterwards, your body needs you to take in more and more food in order to generate enough insulin to get your muscle cells to take an appropriate amount of energy. But that extra food also goes into our fat cells in correspondingly greater amounts. So, we tend to gain more and more weight over time, and it becomes harder and harder for us to ever lose the weight, because our body keeps telling us to eat more and more because it’s more and more resistant to insulin and needs more and more blood sugar to get it to do its job.
So what does this have to do with diet soda? Artificial sweeteners, though they have zero calories, seem to have a similar effect on our insulin system that sugar has. Our bodies seem to recognize its sweetness, not its caloric content, and give us that sharp burst of insulin that we’d get if we’d consumed a regular, sugar-packed soda.
In the near term, this doesn’t do a whole lot to pack on the pounds, because the diet soda doesn’t itself contain calories. It may cause us to get hungrier because it depletes our body’s stored nutrients in the way described above; but that should be easily reversible if it’s not done over and over again. But the surge of insulin may encourage insulin resistance, and that insulin resistance may not reverse so quickly, if ever. This could explain why, though diet soda doesn’t necessarily lead to sharp, immediate weight gain, it does contribute slowly but surely to significant long-term weight gain that’s tough to stop and very hard (maybe impossible?) to reverse.
Now, I don’t know for a fact that this is what happens to our bodies after consuming diet soda. Insulin resistance may not work in this clear-cut a manner. (Many natural foods like bananas and carrots also have a high “glycemic index,” meaning they cause a spike in blood sugar; and yet I don’t think fresh fruits and vegetables lead to long-term insulin resistance or weight gain, or these metabolic syndromes would have been just as common decades ago. This suggests our understanding of insulin resistance and its contribution to obesity may be highly imperfect.) It may be that insulin resistance doesn’t actually cause obesity, heart disease or diabetes but instead is simply correlated with it. And it may not be permanent after all; it may be that if we stop eating foods that cause insulin spikes, our muscle cells will become less insulin resistant over time. Any of these factors could make diet soda AOK.
But it’s also possible that diet soda does have these frightening effects, and that it does do long-term harm. And this is a powerful incentive to not give in and have just that diet soda next time you feel hot, tired and in need of a quick shot of cold, sweet, caffeinated, carbonated refreshment. It may have an impact for a long time to come.