The Dark Side of Diet Soda
One of our nutrition policies at Kenzai is to steer clear of drinking your calories when you’re in the process of getting in shape.
This means things like soda, juice, milkshakes and their twins, fancy café drinks, and yes, alcohol, are best avoided. This causes a lot of disruption for our clients who are used to enjoying liquid calories, but it’s a sacrifice that’s worth it.
What is it about drinking calories that’s so unhelpful? It comes down to satiation. You might not think about it, but eating solid food is a kind of ritual. You place the food in your mouth, cut and grind it into a mash with your teeth, then use your tongue to shape the mash into a ball that slides down your esophagus with the help of your swallowing muscles. From there the stomach starts pulsing and churning to prepare the food for its journey through your intestines, where the nutrients will be extracted. Each of these steps sends biofeedback to your brain. It tells the brain “I’m eating something. I’m receiving sustenance. My stomach is filling with matter. I am satisfied.”
Compare this with drinking a caloric liquid such as a soda. There’s no chewing. The tongue is passive. There’s no solid matter working down the throat. The stomach doesn’t pulse. The brain never gets the “I’m satisfied” message.
As a simple experiment, compare how full you feel eating two entire large apples vs a 20 oz soda.
These items have an equal amount of calories, but are they really the same?
After two apples, most people are completely stuffed, and the thought of more food is unappealing. But after a 20 oz soda, they barely feel like they’ve “eaten” anything, and can happily move on to the next food input as if nothing has happened. In fact, people will often drink one of these bottles of soda while washing down their “real” food, in essence eating two meals at once.
In a nutshell, liquid calories make it much more likely that you’ll overshoot your caloric budget. It’s vastly easier to make a simple rule to cut them out in favor of non-caloric drinks like water, coffee, and tea as your go-to beverages. Whether you’re in a fitness program or not, avoiding liquid calories is a great rule to follow. If you think of caloric beverages as a rare treat, you’ll be much more likely to stay trim as the years go by. Believe it!
However, it doesn’t take long for most people to find a loophole to the “no caloric drinks” guideline:
Surely diet colas and other zero calorie beverages must be fine, right? Instead of sugar, they use molecules like aspartame, saccharin, or sucralose to approximate the taste of sugar without any corresponding caloric hit. Are these ok to drink when you’re trying to lose body fat and get in shape?
To answer this question, we'll first break down how these drinks pull off the magic trick of tasting sweet without using sugar.
Let’s talk about the tongue. If you look at your tongue closely, you’ll see that it’s covered in various kinds of bumps and ridges. These are called papilla, and they come in many shapes and sizes based on the taste they’ve evolved to sense.
Contrary to what you might have learned in school, the tongue does not have different regions that perceive the different tastes (sweet, salty, sour, bitter, umami). Instead these thousands of papilla are scattered fairly evenly across the tongue. Your nose also has its own set of cell receptors, and together these two sensor-arrays create the sensation of taste.
Inside each papilla are between 40 and 100 cells with a small, flower-bud-like appearance. This is why they're called taste buds. These buds have an array of cellular triggers which send information about what’s on your tongue directly to your brain.
The yellow lines in the picture represent the nerve cells that run straight to the insular cortex deep in the middle of your head. In a sense, your tongue is just a bit of your brain sticking out into the world!
These taste cells have structures and mechanisms which only unlock when the right “key” is inserted. The key is the different molecular shapes of the different foods you eat.
For example, when you taste sour, what you’re actually experiencing is a food that contains the molecular structure of an acid, which triggers the acid-oriented receptor to shoot a message to your brain that's translated as “sour”. It’s strange to think about, but taste happens in your brain, not on your tongue.
The sweet receptor has evolved to be unlocked by the presence of simple molecules of carbon, hydrogen, and oxygen called saccharides.
The blue sucrose molecule fits into its counterpart cell receptor, sending a signal to the brain that the tongue has encountered a molecule from the saccharide family.
When you connect saccharides in various ways you get the “-oses” —most famously sucrose, fructose, lactose, and dextrose. The body is able to take these sugars and convert them to its preferred molecular structure — glucose. Glucose in the blood (blood sugar) is the energy source that keeps you moving and living.
This is why we find sweet things so pleasing. Getting enough sugar is so important that the tongue and brain have evolved to release a burst of feel-good reward hormones when we get lucky enough to find a sugary food in the wild.
Finding sugar in the wild is a wildly rewarding experience for the brain.
Our brains find sweet-tasting things so pleasurable that it’s easy to overeat (or overdrink) sugar. The body dutifully converts this excess glucose to fatty acids just in case we need that energy later. But later never comes, our fat stores fill up across our bodies, and we notice our clothes are getting tight.
This is where artificial sweeteners come in. Through modern chemistry, novel types of molecular structures can be made in the lab. Over the decades, mostly through accident, we found that some of these structures taste sweet, usually because some part of their structure mimics what our tongues have learned is a saccharide molecule.
For example, let’s compare sucrose (table sugar) to the novel molecule sucralose (Splenda), invented in the mid-70’s.
You can see the molecules are nearly identical, the only difference being that a few hydroxides have been replaced with chlorine atoms. This means that sucralose will fit in the same taste receptors as sugar. The power of artificial sweeteners is that their unique molecular structures are able to not only fit, but to overwhelm the sweet receptors of the tongue and open the sweetness floodgates to your brain.
Aspartame, for example, is 200 times sweeter than sugar. Sucralose is 600 to 1000 times sweeter (the reason these molecules taste sweeter is complicated, but it has to do with how the substances are able to sit on the taste bud and soak into the receptor cells).
In this case, the purple artificial sweetener is able to fill many more cell receptors than normal sugar, hugely amplifying how sweet the brain perceives the molecule.
This is the magic that makes artificial sweeteners work. The net effect of this hyper-sweetness is that when included in a product, you need 200 to 1000 times less artificial sweeteners than sugar.
A can of soda has about 40 grams of sugar (yikes!). If you’re using aspartame instead (as in Diet Coke or Coke Zero) you’d only need 0.2 grams of the artificial sweetener to achieve the same sweetness level. At that low amount, any calories are a write-off and the drink can legally be called “zero calorie.”
The tongue has evolved to be incredibly sensitive, and it’s remarkable that despite so much R&D artificial sweeteners don’t fool anyone. They always have a taste that’s somehow “off” when compared to real sugar sources. But most people find with repeated exposure the palate gets accustomed to the artificial taste and it can be consumed happily. But is it safe?
Over the decades there's been a lot of concern over potential side-effects of artificial sweeteners. One of the problems studying this topic is that mice, the favorite subject of lab studies, seem to have a much harder time with artificial sweeteners than humans do. There will often be an alarming result in a mouse study that doesn’t bear out with human subjects.
After 40 years of research and billions of people consuming artificial sweeteners, it’s clear that there are no clinical side-effects from artificial sweeteners and the diet sodas that contain them. These two extensive reviews of the scientific literature both come to the same conclusion that low calorie sweeteners are safe (PMID: 25842566 [behind paywall] and PMID: 28558975 which is free to read).
These studies represent long term, peer reviewed, clinical study on a large number of humans. Research doesn’t get better than this. Artificial sweeteners appear to be generally safe. There are still a few lingering areas of concern, notably how artificial sugars affect the gut biome, and how children's brains respond to these products confusing stimuli. We'll keep an eye on the continuing research, but at this point it's unlikely that a hidden danger of artificial sweeteners will come out of nowhere and surprise us. So does this mean you should stock up your fridge with diet soda?
Remember, our original question was, "Does diet soda help you stay trim on your fitness journey?" A lot of research has been done into this as well, and the result is a confusing data set. When we look at observational studies, we see that drinking diet sodas does not result in fat loss, and often is accompanied by fat gain (PMID: 25780952, PMID: 27358413, PMID: 25984744, PMID: 28074617).
But when we look at controlled studies, where the subjects are in a monitored program actively working to get in shape, we see that diet soda doesn’t interfere with fat loss and is, as promised, a zero-calorie addition to the diet with no ill-effects (PMID: 2349932, AJCN 95-3). What should we make of these confusing results?
Anecdote is no replacement for data, but I can use an anecdotal experience I had over the summer to illustrate what researchers think is going on here.
A few months ago I was doing my usual supermarket shopping and noticed that the store had a “buy one get one free” deal on Coke Zero. I don’t drink Coke Zero, but I thought it might be a nice thing to offer to guests at barbecues. So I took advantage of the deal and thus randomly had 24 Coke Zeroes spread across my pantry and refrigerator.
The next hot day I cracked one open, and, like most people, found the taste to be odd — sickly sweet with a metallic aftertaste. I wouldn’t describe it as “good”, but after half a can my tongue had gotten used to it. If I didn’t dwell on it and just chugged it down, I could imagine I was drinking a real Coca-cola. It wasn’t great, but it was more fun than water. Over the next few days I kept drinking the Coke Zeroes, mostly due to what we call Everest Eating (“Why’d you just eat that?” - “Because it was there.”) The more exposure to the aspartame I had, the more normal it tasted. And all for zero calories. Was it too good to be true?
The problem was that during these Coke Zero weeks, I noticed that I was getting strong, primal cravings for sweets. Not for the usual savory sweets I prefer, but simple, blunt sugars like candy and processed cookies. My daughter had some Oreo snack packs, and I’d find myself reaching for them after meals, because I wanted "just a taste" of something sweet. After the Oreos were gone I broke into a container of jelly beans that had been sitting in the cabinet for months.
Before the Coke Zero I had no inclination to eat these things. But the exposure to hyper sweet stimulation had gotten my brain into a habit loop where every few hours it wanted a hit of concentrated sweetness in order to find homeostasis. I could fill this with more Coke Zero, but a person can only drink so much of that stuff, and so it didn’t take long for my brain to start casting a wider net to feed this sweet craving. And when that net was cast, it brought in a lot of food which was very much not zero calories.
Zero-calorie soda is fine on its own, but it provokes the consumption of other super-sweet, high-calorie choices.
THIS is why you shouldn’t drink diet sodas when looking to get fit. The most important piece of the fitness puzzle is your nutrition. A healthy diet that gets results is full of vegetables, fruits, lean meats, sensible amounts of dietary fat and clean carbohydrates, without extra “riders” like heavy sauces and excess condiments. But when you’re blowing out your taste receptors with the lab-made hyper-sweetness of diet sodas, your palate can’t appreciate the subtle tastes of vegetables, fruits, simply prepared meats and whole grain carb sources.
A good test of this is the humble apple. When you’re eating clean and sticking with fresh foods, you’ll find an apple is deliciously sweet and satisfying. But if you’re coming off a more processed diet with big bold artificial flavors, your palate won’t be able to pick up the low-key sweetness of an apple. All you’ll perceive are the bitter, sour undertones.
In other words, diet sodas make apples taste bad, and that’s a HUGE problem when you’re trying to eat right. All your attempts to eat fresh vegetables and fruits will run into a stumbling block, and your likely to find yourself covering your otherwise healthy food in sugary dressings, dips, and sauces to compensate.
This is probably why the human studies that tracked people in very controlled situations showed that diet sodas weren’t a problem for fat loss. When a person has researchers tracking their meals and checking their weight frequently, they have an extra layer of willpower to resist the cravings that diet sodas bring on. Not only do they want a good result for themselves, they don’t want to “mess up” the experiment.
But when studied in real life situations, where it’s easy enough to grab that Oreo or jelly bean, diet sodas go hand in hand with gaining fat. The reason isn’t because of the diet soda itself, but because of the brain getting stuck in a sweetness reward tornado which sucks in non-helpful food while ejecting “bland”, “sour” and “bitter” choices that have real nutritional value.
This is why we advise people to stay far, far away from diet sodas when getting in shape. Throw them in the same trash bin as the sugary drinks they strive so hard to replace. If you’re really craving the experience of cracking open a cold can of something tasty, make it a sparkling water in the flavor of your choice. As long as there’s no artificial sweetener or sugar, you won’t be falling into the diet-drink trap.
Water, tea, and coffee are your allies when you want to get trim. Diet soda works against you! Let your palate stay clean and you'll see your body stay lean.
