Diet sodas are popular beverages all over the world, especially among people who want to reduce their sugar or calorie intake.

Instead of sugar, they are sweetened with artificial sweeteners like aspartame, cyclamate, saccharin, acesulfame-k or sucralose.

Almost every popular sugar-sweetened beverage on the market has a "light" or a "diet" version -- Diet Coke, Coke Zero, Pepsi Max, Sprite Zero, etc.

Diet sodas were first introduced in the 1950s for people with diabetes, though they were later marketed to people trying to control their weight or reduce their sugar intake.

Despite being free of sugar and calories, the health effects of diet drinks and artificial sweeteners are controversial.

Diet Soda: Good or Bad?

Diet soda is essentially a mixture of carbonated water, artificial or natural sweetener, colors, flavors and other food additives.

It usually has very few to no calories and no significant nutrition. For example, one 12-ounce (354-ml) can of Diet Coke contains no calories, sugar, fat or protein and 40 mg of sodium ().

However, not all sodas that use artificial sweeteners are low in calories or sugar-free. Some use sugar and sweetener together. For example, one can of Coca-Cola Life, which contains the natural sweetener Stevia, contains 90 calories and 24 grams of sugar ().

While recipes differ from brand to brand, some common ingredients in diet soda include:

  • Carbonated water: While sparkling water can occur in nature, most sodas are made by dissolving carbon dioxide into water under pressure (, ).
  • Sweeteners: These include common artificial sweeteners, such as aspartame, saccharin, sucralose or an herbal sweetener like Stevia, which are 200–13,000 times sweeter than regular sugar (, ).
  • Acids: Certain acids, such as citric, malic and phosphoric acid, are used to add tartness to soda drinks. They are also linked to tooth enamel erosion ().
  • Colors: The most commonly used colors are carotenoids, anthocyanins and caramels ().
  • Flavors: Many different kinds of natural juices or artificial flavors are used in diet soda, including fruits, berries, herbs and cola ().
  • Preservatives: These help diet sodas last longer on the supermarket shelf. A commonly used preservative is potassium benzoate ().
  • Vitamins and minerals: Some diet soft drinks add vitamins and minerals to market themselves as healthier no-calorie alternatives ().
  • Caffeine: Just like regular soda, many diet sodas contain caffeine. A can of Diet Coke contains 46 mg of caffeine, and Diet Pepsi contains 34 mg (, ).
Summary Diet soda is a mixture of carbonated water, artificial or natural sweeteners, colors, flavors and extra components like vitamins or caffeine. Most varieties contain zero or very few calories and no significant nutrition.

Because diet soda is usually calorie-free, it would be natural to assume it could aid weight loss. However, research suggests this solution may not be so straightforward.

Several observational studies have found that using artificial sweeteners and drinking high amounts of diet soda is associated with an increased risk of obesity and metabolic syndrome (, , , ).

Scientists have suggested that diet soda may increase appetite by stimulating hunger hormones, altering sweet taste receptors and triggering dopamine responses in the brain (, , , ).

Because diet soft drinks have no calories, these responses may cause a higher intake of sweet or calorie-dense foods, resulting in weight gain. However, evidence of this is not consistent in human studies (, , ).

Another theory suggests that diet soda’s correlation to weight gain may be explained by people with bad dietary habits drinking more of it. The weight gain they experience may be caused by these existing dietary habits, not diet soda (, ).

Experimental studies do not support the claim that diet soda causes weight gain. In fact, these studies have found that replacing sugar-sweetened drinks with diet soda can result in weight loss (, ).

One study had overweight participants drink 24 ounces of diet soda or water per day for a year. At the end of the study, the diet soda group had experienced an average weight loss of 13.7 pounds (6.21 kg), compared to 5.5 pounds (2.5 kg) in the water group ().

However, to add to the confusion, there is evidence of bias in the scientific literature. Studies funded by the artificial sweetener industry have been found to have more favorable outcomes than non-industry studies, which may undermine the validity of their results ().

Overall, more high-quality research is needed to determine the true effects of diet soda on weight loss.

Summary Observational studies link diet soda with obesity. However, it’s not clear whether diet soda is a cause of this. Experimental studies show positive effects for weight loss, but these might be influenced by industry funding.

Although diet soda has no calories, sugar or fat, it has been linked to the development of type 2 diabetes and heart disease in several studies.

Research has found that just one serving of an artificially sweetened drink per day is associated with an 8–13% higher risk of type 2 diabetes (, ).

An observational study in 64,850 women found that artificially sweetened drinks were associated with a 21% higher risk of developing type 2 diabetes. However, the risk was still half that of regular sugary drinks. Other studies have found similar results (, , , ).

Conversely, a recent review found that diet soda is not associated with an increased risk of diabetes. Also, another study concluded that any association could be explained by the existing health status, weight changes and body mass index of participants (, ).

Diet soda has also been linked to increased risks of high blood pressure and heart disease.

A review of four studies including 227,254 people found that for each serving of artificially sweetened beverage per day, there is a 9% increased risk of high blood pressure. Other studies have found similar results (, , ).

Additionally, one study has linked diet sodas to a small increase in the risk of stroke, but this was only based on observational data ().

Because most of the studies were observational, it may be that the association could be explained another way. It’s possible that people who were already at risk of diabetes and high blood pressure chose to drink more diet soda (, , ).

More direct experimental research is needed to determine if there is any true causal relationship between diet soda and increased blood sugar or blood pressure.

Summary Observational studies have linked diet soda to type 2 diabetes, high blood pressure and an increased risk of stroke. However, there’s a lack of research on possible causes for these results. They may be due to preexisting risk factors such as obesity.

Intake of diet soda has been linked to an increased risk of chronic kidney disease.

A recent study analyzed the diets of 15,368 people and found that the risk of developing end-stage kidney disease increased with the number of glasses of diet soda consumed per week.

Compared to those who consumed less than one glass, people who drank more than seven glasses of diet soda per week had nearly double the risk of developing kidney disease ().

A suggested cause for the kidney damage is the high phosphorus content of sodas, which may increase the acid load on the kidneys (, ).

However, it has also been suggested that people consuming high amounts of diet soda may do so to compensate for other poor dietary and lifestyle factors that may independently contribute to the development of kidney disease (, ).

Interestingly, studies investigating the effects of diet soda on the development of kidney stones have found mixed results.

One observational study found that diet soda drinkers have a slightly increased risk of kidney stone development, but the risk was much smaller than for regular soda. In addition, this study has not been supported by other research ().

Another study reported that the high citrate and malate content of some diet sodas may help treat kidney stones, particularly in people with low urine pH and uric acid stones. However, more research and human studies are needed ().

Summary Observational studies have found an association between drinking a lot of diet soda and the development of kidney disease. If diet soda does cause this, a potential reason could be increased acid load on the kidneys due to its high phosphorus content.

Drinking diet soda while pregnant has been linked to some negative outcomes, including preterm delivery and childhood obesity.

A Norwegian study in 60,761 pregnant women found that intake of artificially sweetened and sugar-containing drinks was associated with an 11% higher risk of preterm delivery ().

Earlier Danish research supports these findings. A study in almost 60,000 women found that women who consumed one serving of diet soda per day were 1.4 times more likely to deliver preterm than those who did not ().

However, recent research in 8,914 women in England did not find any association between diet cola and preterm delivery. However, the authors admitted that the study may not have been big enough and had been limited to diet cola ().

It’s important to note that these studies were only observational and offer no explanation of exactly how diet soda may contribute to preterm birth.

Another troubling finding is that consuming artificially sweetened drinks while pregnant is significantly associated with an increased risk of childhood obesity ().

One study found that the daily consumption of diet drinks during pregnancy resulted in a doubled risk of a baby being overweight at one year of age ().

Further research is needed to analyze the potential biological causes and long-term health risks for children exposed to artificially sweetened sodas in the womb.

Summary Large studies have found associations linking diet soda to preterm delivery. However, a causal link has not been found. Additionally, infants of mothers who drank diet soda while pregnant are at an increased risk of being overweight.

There are several other documented health effects of diet sodas, including:

  • May reduce fatty liver: Some studies have shown that replacing regular soda with diet soda can reduce fat around the liver. Other studies have found no effect (, ).
  • No increase in reflux: Despite anecdotal reports, carbonated drinks have not been found to make reflux or heartburn worse. However, the research is mixed, and more experimental studies are needed (, ).
  • No strong links to cancer: Most of the research on artificial sweeteners and diet soda has found no evidence it causes cancer. A slight increase in lymphoma and multiple myeloma in men was reported, but the results were weak (, ).
  • Changes to the gut microbiome: Artificial sweeteners alter the gut flora, leading to reduced blood sugar control. This may be one way diet soda increases the risk of type 2 diabetes, but more research is needed (, ).
  • Increased risk of osteoporosis: Diet and regular cola is associated with bone mineral density loss in women, but not in men. The caffeine and phosphorus in cola might interfere with normal calcium absorption ().
  • Tooth decay: Like regular soda, diet soda is associated with dental erosion due to its acidic pH level. This comes from the addition of acids, such as malic, citric or phosphoric acid, for flavor (, ).
  • Linked to depression: Observational studies have found higher rates of depression among those who drank four or more diet or regular sodas per day. However, experiments are needed to determine if diet soda is a cause ().

While some of these results are interesting, more experimental research is needed to determine whether diet soda causes these issues, or if the findings are due to chance or other factors.

Summary Diet soda may improve fatty liver and does not appear to increase heartburn or the risk of cancer. However, it may reduce blood sugar control and increase the risks of depression, osteoporosis and tooth decay. However, more research is needed.

Research on diet soda has produced a lot of conflicting evidence.

One explanation for this conflicting information is that most of the research is observational. This means it observes trends, but there is a lack of information about whether diet soda intake is a cause or simply associated with the real cause.

Therefore, while some of the research sounds quite alarming, more high-quality experimental studies are needed before concrete conclusions can be drawn about the health effects of diet soda.

Regardless, one thing is certain: diet soda does not add any nutritional value to your diet.

So, if you’re looking to replace regular soda in your diet, other options may be better than diet soda. Next time, try an alternative like milk, coffee, black or herbal tea, or water infused with fruits.