Diet Coke and Coke Zero are both the global biggest-selling soft drinks in the world.
Over the years there has been a huge debate online on what the difference is between the two popular drinks.
According to the Coca-Cola Company's official results, sales of Coke Zero grew by 14% in 2025, while sales of Diet Coke remained flat with the year before. The company made $47.9 billion in revenue in 2025.
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Diet Coke was the company's first sugar-free cola, which it launched in 1983. This was followed by Coca‑Cola Zero in 2006, which was then replaced by Coca‑Cola Zero Sugar in 2016.
Low-sugar and no-sugar drinks have surged in popularity in recent years, with some believing that they can aid weight loss, though scientists and researchers question whether this is the case.
Does drinking Diet Coke or Coca-Cola Zero lead to weight loss?
If you looked at the nutrition information on a can of Coca-Cola Zero or Diet Coke, you might think it can't possibly be making you put on weight.
Both drinks list 0g of fat, 0g of carbohydrates and 0g of sugar. Coca-Cola Original Taste, on the other hand, contains 10.6g of sugar in a 330ml can.
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The Coca-Cola Company's states that "both drinks are sugar-free and calorie-free", which means millions drink it in the belief that it is not contributing in any way to weight gain.
However, Robert H Shmerling from Harvard University Medical School said: "Research suggests that none of these choices may actually help with weight loss. Worse, they might even lead to weight gain.
"One worry is that artificially sweetened diet sodas may create a craving for sweet, high-calorie foods. So, even as calorie counts drop from zero-calorie sodas, consumption of other foods and drinks might add back even more.
"In rodent studies, at least one artificial sweetener (aspartame) has been found to damage a part of the brain that tells the animal when to stop eating.
"And a number of studies in humans... have actually found a tendency toward weight gain among people drinking artificially sweetened beverages."
Although he did acknowledge that research has been mixed and that "other studies have found that artificially sweetened low-calorie beverages can help with weight loss."
He adds that the study of zero-calorie beverages and weight loss is "reverse causation".
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This means people at risk of obesity tend to choose these beverages, making it appear that these drinks are to blame.
Difference in Coke Zero and Diet Coke
The Coca-Cola Company says the difference between Coca Cola Zero and Diet Coke is "the taste".
It says: "Both drinks are sugar free and calorie free. Coca‑Cola Zero Sugar looks and tastes more like Coca‑Cola original taste, while Diet Coke has a different blend of flavours which gives it a lighter taste."
With both drinks containing 0g of fat, 0g of carbohydrates and 0g of sugar, many assume that they are not doing your health any harm.
However, Zoe Science and Nutrition website said: "Just because something has no calories doesn’t mean it’s healthy".
Both drinks contain several ingredients that are chemically or scientifically created, as opposed to being natural or whole foods.
If you compare the ingredients list on the back of each product there is a slight difference between them. Diet Coke's ingredients read as follows: "Carbonated Water, Colour (Caramel E150d), Sweeteners (Aspartame, Acesulfame K), Natural Flavourings, Caffeine Flavouring, Acids (Phosphoric Acid, Citric Acid)."
While Coca-Cola Zero's ingredients list is: "Carbonated Water, Colour (E150d), Acid (Phosphoric Acid), Sweeteners (Aspartame, Acesulfame-K, Enzymatically Produced Steviol Glycosides), Natural Flavourings, Caffeine Flavouring, Acidity Regulator (Sodium Citrates).
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