Is Diet Soda Bad For You?

Is Diet Soda Bad For You?

Last week on “The Faces of RxFIT” podcast, I interviewed metabolic scientist, Dr. Jeffery Tessem. We discussed the pros and cons of four diets, specifically: keto, intermittent fasting, vegan, and macros (with a cheat meal). You can listen to the episode here.

During that conversation, the topic of diet soda came up. In answer to the question, Dr. Tessem referenced this first-of-a-kind study performed in 2014: Artificial Sweeteners Induce Glucose Intolerance.

But in order to look forward and answer the question, “Is diet soda bad for you?”, we must first look back.


The Deadly Quartet


Dr. Norman Kaplan published a paper in 1989 claiming to find the culprit for four chronic diseases that were rapidly taking over the human population, especially the United States.

Kaplan’s hypothesis was that obesity, hypertension (high blood pressure), glucose intolerance (leads to Type II Diabetes), and hypertriglyceridemia (leads to Heart Disease) were tied to the same root problem: hyperinsulinemia.

“Hyperinsulinemia” means that the body is becoming insulin resistant.


Insulin Resistance


When you eat a carbohydrate, glucose enters the bloodstream. Insulin is a hormone that essentially grabs that glucose and uses it for energy (or stores it later for energy). If insulin weren’t released, you would have high blood sugar and diagnosed as a Type I Diabetic. If you didn’t constantly monitor your blood sugar, a host of problems would follow; the worst of them being death.

The more glucose there is in your blood, the more insulin your body has to produce. Insulin resistance then occurs when you begin to release so much insulin that your body stops recognizing it. It’s no different than sun light. The sun shine is good, but too much of it is a bad thing.

Therefore, if your body loses its ability to recognize insulin, you will be diagnosed as a Type II Diabetic. One of the most effective ways to reverse this disease is to significantly reduce your consumption of carbohydrates (the keto diet).

The interesting thing that we didn’t know until Kaplan’s research was that insulin resistance doesn’t just lead to diabetes, but also to the other three grim reapers: obesity, high blood pressure, and heart disease.




Diets like Keto and Intermittent Fasting are becoming more and more popular because of this understanding of insulin resistance. These diets either limit the total consumption of carbohydrates (Keto) or limit their constant consumption throughout the day (Intermittent Fasting).

I recognize that not all carbohydrates are created equal and that there are other sugars outside of glucose. However, in an effort to keep this article simple and specific, we can conclude that carbohydrates, glucose, and sugar are synonyms for each other.

The common belief was that sugar only enters the bloodstream when you eat sugar. This is why soda has received so much criticism over the years because instead of chewing carbohydrates, you could now drink it – and you could do it in much higher quantities.

But what about diet soda? Diet means it doesn’t include any calories; and if there are no calories, there are no carbohydrates. So, thanks to diet soda, now we can drink as much soda as we want!

Well, not really…


Diet Soda


2014’s study introduced to me by Dr. Tessem is a pioneer of its kind. It looked at the body’s response to “Non-caloric Artificial Sweeteners” (NAS). Diet soda and energy drinks are the most popular NAS. The researchers write this on page 5 of the hyperlinked pdf:

Artificial sweeteners were extensively introduced into our diets with the intention of reducing caloric intake and normalizing blood glucose levels without compromising the human ‘sweet tooth’.

The study, which looked at short- and long-term diet soda drinkers (and other artificial sweeteners), concluded that “human individuals feature a personalized response to NAS, possibly stemming from differences in their microbiota composition and function.”

In other words, for many individuals diet soda prevents your body from processing insulin properly. Those individuals and their genes are outlined in the study.

Of this conclusion, the researchers said, “Our findings suggest that [diet sodas] may have directly contributed to enhancing the exact epidemic that they themselves were intended to fight.”




There is an obvious limitation with this finding, which is that this is the first study of its kind. One study is insignificant until it can be replicated. I asked Dr. Tessem if he has seen anything replicated to date and he said he hasn’t.

However, scientific data around the topic of diet soda has been weak and controversial since it was first introduced. This is the first study (that we’re aware of) that meets scientific rigor. The findings of which are fascinating.


Looking Forward


So what should you do?

As your coach, I would simply say to limit your consumption of diet soda.

For example, you already know that eating candy is bad; but you’re not going to stop eating it all together. Clearly there are days and occasions when you will willingly choose to eat candy (Easter, Halloween, Christmas, etc.).

I would imagine that diet soda now is no different.

For me, my plan is to simply limit my diet soda consumption. I’m a personal fan of these drinks because of its ability to “trick the sweet tooth.”

But moderation must be had.

I invite you to join me.


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