Is Diet Soda Better Than Regular Soda?

Diet soda versus regular soda: Is one better?

This is a question I am often asked as a registered dietitian. Regular soda has sugar and calories and diet soda achieves a similar taste using low and no calorie sweeteners and is calorie-free. 

People often fear diet soda because of the artificial sweeteners but regular pop has sugar, which we know is not good for us in excess. 

Neither one of these is considered physically nourishing. They don’t add any nutrition to our diets. Dietary guidelines around the world suggest making water our drink of choice, which I agree with.

But if you want a soda, is there a difference health-wise between diet and regular?

Let’s take a look.

Diet soda and regular soda are made with similar ingredients including carbonated water, caramel color, caffeine, and phosphoric acid. The main difference is the type of sweetener used. Diet soda uses artificial sweeteners including aspartame and acesulfame K and regular soda uses high fructose corn syrup. 

One can of regular Coke provides 140 calories and 39 grams of sugar. One can of Diet Coke, has 0 calories and 0 grams of sugar. 

The World Health Organization recommends we consume no more than 10% of our calories from added sugar per day. The American Heart Association recommends a lower limit of six percent each day. For women, that’s no more than 100 calories per day or about six teaspoons. For men, it’s 150 calories per day, or about nine teaspoons. One 12oz can of Coke has almost 10 teaspoons of sugar. 

Studies have shown that one of the top sources of added sugar in Americans’ diets is sweetened beverages.

Consuming too much sugar has been associated with weight gain and obesity, diabetes, impaired cardiovascular health, dental caries, and many other health concerns. Overconsuming sugar-sweetened beverages, such as regular soda and juice, is thought to be a major culprit in obesity and weight gain.

Dietary guidelines and clinical practice guidelines recommend <5-10% energy from free/added sugars, which admittedly, many of us exceed. The US guidelines in 2015-2020 recommended against low calorie no calorie sweeteners, but have changed their tune. The 2020-2025 guidelines do recommend them, because there is now sufficient evidence to support the recommendation to replace added sugars.

What are Low And No Calorie sweeteners?

These sweeteners include artificial sweeteners and sugar alcohols. Diet soda typically contains aspartame and acesulfame K. Aspartame is 200 times sweeter than regular sugar so you need much less of it to achieve a sweet flavor. Because you use so little of it, the calories are negligible. I’ve written a lot about artificial sweeteners and their safety here. 

In July 2023, there was a media frenzy when the WHO updated its guidelines on artificial sweeteners and declared aspartame as “possibly carcinogenic to humans”. This was blown out of proportion and I’ll explain why. 

The classification which was made by the WHO International Agency for Research on Cancer (IARC) was based on “limited or insufficient evidence” that aspartame might cause cancer in people. The evidence was based on animal studies that used a dose of aspartame that humans would likely never reach. 

This classification is also based on the evidence of whether something can cause cancer in humans however it does not say how likely it is to cause cancer.

Other things that have been categorized as the same level of carcinogen as aspartame are aloe vera, pickled vegetables, and cell phones.

There’s often the issue of reverse causality in research around sweeteners. People who are more likely to have risk factors for diseases, may also be more likely to consume these ingredients.

Interestingly, at the exact same time as the IARC conclusions were released, the Joint FAO/WHO Expert Committee on Food Additives (JECFA) released their evaluation around aspartame safety, declaring that there is “no convincing evidence from experimental animal or human data that aspartame has adverse effects after ingestion…there is no reason to change the previously established ADI of 0–40 milligrams per kilogram of body weight per day for aspartame.“

To add weight to the JECFA conclusion, the FDA has disagreed with the IARC’s assessment while throwing its support behind JECFA, saying “We believe that JECFA is better suited (than IARC) to assess risk associated with aspartame consumption.”

The FDA has set upper limits on how much artificial sweeteners someone would have to consume before they could be harmful. The levels are set much higher than people would typically consume.  For example, one 12oz can of diet soda has 200mg of aspartame. The FDA has set the limit for aspartame at 50mg/kg/day. This means that a person weighing 60kg (132lbs) would have to drink 15 cans of diet soda a day to reach the limit. 

Diet soda is considered an ultra-processed food. A little bit is okay but you don’t want a diet full of them. The same goes for regular soda. 

I’ve written about diet soda and whether it is unhealthy here.  

Is high fructose corn syrup worse than regular sugar?

High fructose corn syrup (HFCS) is the main sweetener used in regular soda. It is commonly used in foods and beverages. It has been demonized in the scientific community and the media. It has been said to be a direct cause of obesity because its increased use between 1960 and 2000 correlates with increasing obesity rates in that same period.

HFCS accounts for 50% of the caloric sweeteners used in the United States and 8% used worldwide, sucrose (table sugar) accounts for the rest. The hypothesis that HFCS is a direct cause of obesity is no longer supported. If HFCS was substituted for a different sweetener, such as sucrose, calorie intake wouldn’t change as it has similar calories to other caloric sweeteners. 

One particular food isn’t the cause of obesity. Overall calorie intake went up since the 70s, especially from fats, flours, and cereals. We also saw a rise in women working and increasing convenience foods being served at home during this time. As technology became more popular, people also became more sedentary which can lead to weight gain.

If any particular food is consumed in excess, including added sugars, it can lead to weight gain. Around the world, HFCS does not account for a huge percentage of sweeteners used. 

Obesity is multifactorial and can’t all be blamed on HFCS.

Diet soda versus regular soda and weight:

While it might be expected that substituting diet soda for regular could help reduce calorie intake and weight, this topic has been debated over the years and some people say that drinking diet soda may lead to weight gain.

In a systematic review and meta-analysis, substituting low/no calorie beverages for sugar sweetened beverages was associated with reduced weight (a small amount, only ~1kg) and BMI and lower body fat percentage. Water as a substitute for sugar-sweetened beverages was not associated with significant improvements. 

Further, studies looking at people in the National Weight Control Registry, which is a research study that tracks people who have lost at least 30lbs and kept it off for at least one year, have found that 26% of participants consume diet soda regularly (defined as at least once per day). Of those who consumed it at least once a week, the majority felt that it helped them control or reduce their calorie intake. Many of them also felt that making changes to their beverage consumption was important for helping them lose weight. Other studies have also found higher rates of low-calorie beverage consumption in people who have successfully lost weight and kept it off. 

For people who routinely drink regular soda and are looking to lose weight, the evidence suggests that changing to diet versions may have a slight advantage and they also appear to help people maintain their weight.  

The thought around diet soda and weight gain, is that the sweet taste makes people crave sweets even more, and leads to higher calorie intake and thus weight gain. This however has never been proven.

Clinical practice guidelines for obesity, diabetes, and heart disease in Canada, the US, UK, and Australia are universal in recommending low calorie sweeteners as a strategy for sugar reduction.

Is soda bad for our bones?

The sugars, phosphoric acid, caffeine, and acidity of soda may impact bone metabolism by decreasing calcium absorption and increasing calcium excretion through urine. Adding acids to drinks gives them the tangy flavor people enjoy. 

It is also thought that if someone is drinking a lot of soda or other sweetened beverages, these are displacing milk, which has calcium in a highly absorbable form and consumption has a positive impact on bone health. Drinking sweetened beverages is also thought to be associated with an overall lower diet quality, for example more fast-food intake and less fruits and vegetables.

In a systematic review and meta-analysis, researchers found an inverse association between consumption of sugar sweetened beverages (SSBs) and bone health. The articles included in the review varied with the drinks included, some included only carbonated drinks whereas others looked at SSBs in general (juice, soda, sweetened coffee beverages). The effects of SSB on bone health appeared to be more pronounced in women and girls than in men and boys, even though boys/men had higher consumption. Women have smaller bones than men and are more susceptible to fractures in general. 

Caffeine consumption in high amounts may negatively impact calcium absorption. The effect of this is more pronounced when someone doesn’t get enough calcium in their diet. So, if you are drinking a lot of coffee or caffeinated sodas, make sure you are getting enough calcium.

Not much literature exists on diet sodas and bone health however diet soda contains phosphoric acid so it may have the same effect on bone health as regular soda, especially if it is displacing other healthier beverage options, such as milk. People choosing diet soda may also be restricting their calories to lose or maintain weight and may be having lower overall intakes of calcium and other nutrients. 

Diet soda vs regular Soda: Bottom line

When it comes to choosing between diet and regular soda, there is no “healthy” choice. Both of these offer no nutrition to our diets however there is no reason they can’t be enjoyed occasionally, if you enjoy them. 

When it comes to weight, diet soda offers an advantage for people who want to lose weight and for people who are trying to maintain weight loss. 

Whether it is sugar as well as artificial sweeteners that you are having, choose as little as possible. Most of us could do with cutting down on our sugar intake overall.