When it comes to sugar-free sodas, Diet Coke and Coke Zero often take center stage. To many, they appear almost identical, offering zero sugar, zero calories, and a guilt-free alternative to regular Coke. However, subtle differences in taste, formulation, and health impact exist, especially for those focused on weight loss.
Diet Coke: A Long-Standing Alternative
Launched in 1982, Diet Coke quickly became the go-to option for soda lovers wanting the Coke brand without the sugar and calories. Its formula replaces sugar with aspartame, an artificial sweetener that provides sweetness without energy intake. Diet Coke has a distinct flavor that doesn’t exactly mimic classic Coca-Cola, which is why many drinkers consider it a unique beverage rather than a substitute. The Food and Drug Administration (FDA) has deemed it safe for the general population, only necessary to avoid it if you have the rare genetic condition, PKU (FDA, 2023).
Coke Zero: Mimicking the Original Taste
Coke Zero, officially branded as Coca-Cola Zero Sugar, was introduced in 2005 to appeal to a new generation of soda drinkers. Its formula was designed to taste closer to the original Coca-Cola than Diet Coke does. Unlike Diet Coke, Coke Zero uses a combination of aspartame and acesulfame potassium, a sweetener blend that delivers a flavor profile more similar to regular soda.
Marketing also positioned Coke Zero differently, using terms like “zero sugar” rather than "diet" to avoid the stigma associated with dieting. While both sodas contain no calories or sugar, the difference lies in their sweeteners and flavor. Diet Coke uses only aspartame, while Coke Zero uses both aspartame and acesulfame potassium (a.k.a. Equal or the blue packet) for a bolder taste. According to consumer taste studies, many people find Coke Zero tastes closer to the original Coca-Cola, while Diet Coke stands apart with a lighter flavor.
Nutritional Value: A Closer Look
From a nutritional standpoint, neither soda offers added vitamins, minerals, or hydration benefits-they are neutral in calories but not a source of nutrition. Both also contain caffeine, which can provide a temporary energy boost but may disrupt sleep or contribute to dehydration if consumed in excess.
Read also: Zero-Calorie Cherry Soda Review
Artificial Sweeteners: Safety and Impact
Artificial sweeteners have long been studied for their safety and impact on health. The National Institutes of Health (NIH) notes that while sweeteners like aspartame and acesulfame potassium are generally recognized as safe, research on their long-term effects continues (NIH, 2024).
Potential Downsides of Artificial Sweeteners
Some studies suggest that diet soda consumption may increase cravings for sweet foods, making it harder for some people to manage their diets. Emerging research also points to potential effects on gut bacteria and metabolism, though evidence remains mixed.
Coke Zero and Weight Loss: What the Research Says
While some believe diet soda controls hunger and can suppress appetite, or help prevent weight gain, this is not necessarily true. Despite containing virtually no calories, Coke Zero and other types of diet soda have been associated with weight gain. One study has found that people who drank artificially sweetened beverages had an increased risk of being overweight or obese [9], and another systemic review found a "significant association" between non-nutritive sweeteners and obesity [10]. Another study found diet soda may be linked with both having a higher waist circumference and metabolic syndrome [11]. There have also been concerns that consuming diet sodas and artificially sweetened food can actually lead to hunger, more cravings for sweet things, and increased food consumption.
Artificial and zero-calorie sweeteners often have a sweeter taste than sugar, and some researchers have suggested this could impact food preferences and increase the desire for sweet food [12]. Researchers have even found carbonated beverages could impact the body's production of the hunger hormone ghrelin, which can also impact how much you eat [13].However, other research has found that diet soda has a positive association with weight loss, so again, more research may need to be done in the area [14].
The Gut Microbiome and Artificial Sweeteners
There have also been concerns about aspartame and other zero-calorie sweeteners causing gut health issues [4]. Research suggests that it does seem to impact the gut microbiome to some degree, but more investigation needs to be done [5].
Read also: 2 Liter Diet Coke Analysis
Dental Health Considerations
The phosphoric acid in diet soda (and regular soda) can also be bad for your teeth [6], and some research has found artificial sweeteners can contribute to an increased risk of issues with obesity and heart-related conditions [7].Similarly to regular soda, drinking diet sodas like Coke Zero is associated with an increased risk of tooth erosion. One of the main ingredients in Coke Zero is phosphoric acid. One 2002 study on human teeth noted phosphoric acid causes mild enamel and tooth erosion.
An older study from 2015 observed that Coca-Cola Light (Diet Coke), which differs from Coke Zero only in that it contains both phosphoric and citric acid, caused enamel and tooth erosion in freshly extracted cow’s teeth in just 3 minutes. Still, the same 2002 study suggests that citric acid erodes teeth more than phosphoric acid, which suggests that Coke Zero may affect tooth enamel slightly less than Diet Coke.
Diet Coke had less erosive effects than other beverages, such as Sprite, orange juice, and apple juice.
Diabetes Risk and Artificial Sweeteners
Coke Zero is sugar-free. However, the sugar substitutes it contains may not necessarily be a better option for people looking to reduce their risk of diabetes. A large 2023 study involving 105,588 participants with a follow-up of 9.1 years suggests that consuming non-nutritive sweeteners is associated with an increased risk of developing type 2 diabetes.
A 2024 review of research suggests non-nutritive sweeteners may negatively affect the gut microbiome, or the helpful bacteria that live in your gut and aid digestion, potentially affecting metabolic health and contributing to diabetes risk and worse outcomes for people with diabetes. The results from these studies don’t provide an exact explanation of how artificially sweetened beverages increase your risk of diabetes. Therefore, more research is needed.
Read also: Investigating Diet Coke and headache connection
Other Potential Health Issues
Artificially sweetened beverages like Coke Zero have been linked to other health issues, including:
- Increased risk of heart disease: An observational study found a link between artificially sweetened beverages and an increased risk of heart disease among women with no prior history of heart disease.
- Increased risk of kidney disease: Soda’s high phosphorus content may damage kidneys. A 2017 study noted that those who drink more than 7 glasses of diet soda per week nearly double their risk of kidney disease.
- Could alter your gut microbiome: Artificially sweetened beverages may alter your gut microbiome, potentially negatively affecting blood sugar management.
Further research is needed to determine the exact effects of Coke Zero and other diet beverages on your health.
The WHO's Advice on Artificial Sweeteners
The WHO has also advised against using artificial sweeteners for weight loss and says there is not sufficient evidence that there are any real benefits compared with the negative effects [8].
Coke Zero: Is It Actually 0 Calories?
According to the nutritional label on Coke Zero, a 375ml can contains 4.5 kilojoules, which is equivalent to about 1 calorie. The label says 1 drink contains 0.09 grams of protein, 0 grams of fat, 0.1 grams of carbohydrates, and 0 grams of sugar. A 375ml can of regular Coca-Cola contains 161 calories, with 0 grams of fat and 0 grams of protein. It contains 40 grams of carbohydrates, all of which are sugar. This is virtually your entire recommended daily intake of sugar in 1 drink [1]. So a person who drinks multiple cans of Coca-Cola (or other sweet carbonated beverages) is certainly going over the recommended daily sugar intake.
Ingredients in Coke Zero
The ingredient label on cans of Coke Zero sold in Australia says the drink contains carbonated water, colour 150d (this gives the drink its caramel-brown colouring), food acids 338 (phosphoric acid) and 331 (sodium citrate), sweetener 951 (aspartame) and 950 (acesulfame potassium), flavour, and caffeine. As we can see, Coke Zero does indeed have zero calories and no sugar, so it will not contribute to your calorie intake. However, it also does not offer any nutritional value.
Can You Drink Coke Zero Every Day?
While Coke Zero does not contain the high levels of sugar or calories that regular Coke does, it is not necessarily a healthy option, and it does not offer any nutritional benefits. There are a number of reported side effects to Coke Zero, and drinking it every day could put you at risk. More studies need to be done to fully determine the effects of Coke Zero on the body, but what we know so far indicates that while the odd drink is probably ok, it may be best to avoid drinking every day.
Why Limit Diet Soda Intake?
There are a number of factors as to why regularly drinking Coke Zero can be harmful, and it's not all about weight gain. One thing to be aware of is the artificial sweetener aspartame, which is a key ingredient in Coke Zero and other artificially sweetened diet sodas. It also appears in many low-calorie snacks and diet foods, so you may already be consuming it without even realising it. The problem is, there have been health concerns about frequent consumption of artificial sweeteners [2][3].
The Fitness World and Diet Drinks
Zero calorie a.k.a diet drinks are among the most commonly consumed products in the world of fitness. From zero-calorie energy drinks to all-time classics like Diet Coke, diet drinks come with all the positives of their sugar-filled originals, but without the excess calories from sugar. The fitness world aside, the increasing prevalence of obesity and its associated health risks have prompted widespread efforts to identify effective weight management strategies, with a pivotal aspect of these efforts revolving around the role of beverage consumption, particularly the impact of sugar-sweetened beverages on weight gain and related health outcomes. Recognizing the adverse effects of excessive sugar intake, dietary guidelines advocate for alternatives such as water or non-nutritive sweetened drinks, meaning drinks with no nutritional value, which we will refer to as “diet drinks” in this review. However, randomized controlled trials have yielded divergent findings, showing that indeed, diet drinks can be a great tool to aid in weight loss, with some studies even showing that diet drinks can be superior to water for weight loss 3. But, here comes the study by Harrold et al to clear things up.
The Harrold et al Study
The study we’re reviewing was “inspired” by a previous study conducted by Peters et al 3. Peters et al 3 specifically compared the effects of diet drinks and water on weight loss and maintenance. The study included 12 weeks of active weight loss, where participants took part in a weekly behavioral weight management program, followed by 40 weeks of assisted weight maintenance, where participants were provided monthly lifestyle intervention sessions. As briefly mentioned above, the participants consuming diet drinks managed to lose more weight and do better at maintaining their post-weight-loss weights versus the group that consumed water. This study used a very similar design to the Peters et al 3 study, but also added a voluntary 52-week unassisted study extension after the 40-week assisted weight-maintenance phase. This means that participants were invited to continue being part of the study after finishing the 52 “assisted” period, although that part of the study has not yet been completed. You may be wondering “what’s the point of doing a very similar study if we already have one showing that diet drinks are better than water for weight loss?”.
A 12-Week Study on Diet Drinks vs. Water
In a short but controlled trial of beverages and weight loss, diet soda linked to slightly greater loss compared to other beverages, according to a new study published in the journal Obesity. The study adds to the limited, but growing body of human research on diet beverages. With obesity being a cause of eight cancers, understanding how our food and beverages affect weight gain or loss is important to cancer prevention.
For the trial, one-half of the 300 overweight participants were instructed to drink at least 24 ounces of water daily and not to consume any diet beverages. The other half were told to drink at least 24 ounces of diet drinks, but they could also drink water. All participants also attended weekly group meetings as part of their behavioral weight loss program, to help with weight loss strategies, including learning about portion sizes, self-monitoring and physical activity. They all received the same information, except for instructions on drinking water or diet drinks.
After 12 weeks, those consuming the diet beverages lost more weight than the group consuming water. The difference was small, but significant, with the diet drink group losing an average of 13 pounds and the water group, 9 pounds.
Although it isn’t clear why the diet drink group would lose more weight than the water group, one finding that could be a factor was that the water group reported more hunger than the diet beverage group. The authors note too, that all participants came into the study drinking diet beverages, so the water group had to make the greatest behavior change - switching from diet drinks to water. This 12-week study was part of a larger 1-year trial also looking at weight loss maintenance. At the end of the year, researchers will determine how successful participants were at keeping the lost weight off.
What to Drink Instead of Coke Zero
Despite these health risks, the occasional Coke Zero is ok. But as we have discussed, it is probably not something you should be drinking every day. For a healthier refreshing drink, you could try fruit-infused water, unsweetened tea, kombucha, or carbonated water without artificial sweetener or flavour added. You can also opt for fruit juice, but make sure to check the ingredients and sugar content as these can often be very sweet and have a high amount of added sugar.