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Diet soda: good or bad?

Diet soda has never been more controversial in the wake of the wars on both sugar and non-nutritive sweeteners. Here’s a good review of the evidence by a reporter who understands the difference in quality of data from observational studies vs clinical trials.

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 is essentially a mixture of carbonated water, artificial or natural sweetener, colours, flavours 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 (1).

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 (2).

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 (3, 4).
  • 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 (4, 5).
  • 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 (4).
  • Colours: The most commonly used colors are carotenoids, anthocyanins and caramels (4).
  • Flavours: Many different kinds of natural juices or artificial flavors are used in diet soda, including fruits, berries, herbs and cola (4).
  • Preservatives: These help diet sodas last longer on the supermarket shelf. A commonly used preservative is potassium benzoate (4).
  • Vitamins and minerals: Some diet soft drinks add vitamins and minerals to market themselves as healthier no-calorie alternatives (4).
  • 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 (1, 6).
Summary: Diet soda is a mixture of carbonated water, artificial or natural sweeteners, colours, flavours and extra components like vitamins or caffeine. Most varieties contain zero or very few calories and no significant nutrition.

Effects on Weight Loss Are Conflicting

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 (7, 8, 9, 10).

Scientists have suggested that diet soda may increase appetite by stimulating hunger hormones, altering sweet taste receptors and triggering dopamine responses in the brain (11, 12, 13, 14).

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 (5, 11, 15).

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 (16, 17).

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 (18, 19).

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 (20).

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 (21).

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.
Some Studies Link Diet Soda to Diabetes and Heart Disease

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 (22, 23).

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 (24, 25, 26, 27).

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 (28, 29).

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 (30, 31, 32).

Additionally, one study has linked diet sodas to a small increase in the risk of stroke, but this was only based on observational data (33).

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 (24, 34, 35).

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….
Healthline.com: Read the full article here

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