When Fizzy Myths Won't Go Flat.

10 min read

When I was a child, I had a cola addiction. I got eczema and our doctor at the time told my mum I could be sensitive to the caramel colouring in Cola drinks. I stopped drinking it and the eczema went away. I now rarely touch fizzy drinks at all, and I prefer still water, from time to time fresh orange juice, and last, but not least coffee and tea. To this day I still don’t know if it was a coincidence that my eczema went away. Was it the colouring or was it something else entirely? A lot of uncertainty seems to surround carbonated water, carbonated soft drinks, and carbonated diet drinks, and with that comes a lot of unsubstantiated or exaggerated claims.

Carbonated water

Carbonated water can be derived naturally from carbonated springs (sparkling mineral water) or injected with CO2 gas. There are very few studies on carbonated water in relation to health. People who are prone to bloating such as people with irritable bowel syndrome are advised to minimise their carbonated beverage intake as the released gas may cause greater discomfort in the gut. The main claim I see on the internet is that carbonated water is bad for your teeth because it is slightly more acidic than regular water at around 5.2 versus a range of 6.5 - 8.5. I only found one study that investigated the corrosive potential of carbonated water that mimicked real life enamel exposure. The other studies placed enamel in test solutions for extended lengths of time. This study was performed in a lab using extracted enamel that was exposed to a selection of carbonated beverages. The study found that enamel erosion, determined by measuring phosphorus dissolution from human dental enamel, was only slightly higher compared to regular mineral water. The mineral water that caused the greatest enamel erosion was Nestle Contrex water at 0.017µg phosphorous dissolution, whereas the sparkling mineral water that came out on top was Rhenser at 0.082µg. As a comparison Pepsi was 7.113 µg (Figure 1). In real life, saliva would have a buffering effect in the mouth. The American Dental Association does not consider sparkling water to be a concern for dental health, and advises sensible precautions.

Phosphorus dissolution caused by a selection of drinks

Figure 1. Phosphorus (P) dissolution (µg) resulting from enamel exposure to mineral waters and soft drink comparisons. Data extracted from: Parry et al (2001) Investigation of mineral waters and soft drinks in relation to dental erosion. Journal of Oral Rehabilitation. 28; 766-772

Carbonated soft drinks.

The same study investigated the corrosive potential of Coca Cola and Pepsi and the phosphorous dissolution was significantly greater at 6.352 µg for Coca Cola and 7.113 µg for Pepsi (Figure 1). It is now well known that soft drinks lead to enamel erosion due to high amounts of added sugar, but the effect is greater when consuming fizzy drinks due to varying levels of carbonation and acidic regulators and added phosphoric acid. People make the mistake of brushing their teeth immediately after drinking them, but don’t! All you are doing is rubbing the acid into your teeth. Wait a while or rinse your mouth with some fluoridated water before brushing your teeth.

The ingredients are typically the same in all carbonated drinks, varying in the amount used and food colourants (Figure 2).

Figure 2. Coca Cola (2017) Coca-Cola Nutritional Information. [Accessed: 19/02/2019] Available at: https://www.coca-cola.co.uk/drinks/coca-cola/coca-cola


Coca Cola states that there is 35 g of sugar in an original can, which amounts to about 7 teaspoons of sugar. There’s 41g in Pepsi. No one is denying it’s a lot of sugar. Just watch your intake. Too much of any macronutrient can be harmful. It doesn’t matter if it’s sucrose or high fructose corn syrup (HFCS). HFCS, just like sucrose is only harmful if you consume too much. Sugar isn’t addictive despite what a couple of poorly written reviews that lack any solid scientific basis say. They base the concept of sugar addiction on animal studies where the rats were subjected to stress and then had limited access to sugar. This sounds very much like the calorie restriction > emotional eating /binge eating > weight gain cycle I described in a recent article, of which there is substantially more evidence. However, we all know the harm sugar can have on your teeth. Bacteria in your mouth feed on sugar, producing acid which erodes the enamel.

Food colouring. There are so many food colours, and I’ll lose you if I go through each one, so I’ll focus on caramel colouring - the one my doctor had suggested was the cause of my eczema - found in Coca Cola and Pepsi. Caramel colouring has a colourful history. It has been used in food and beverages commercially for over 100 years, but its use as a commodity has been recorded in ancient times.

Caramel Colours in Colas Don't Cause Cancer There are 4 caramel colours (I, II, III and IV). Caramel colours formed using ammonia were found to form carcinogenic 4(5)-methylimidazole [4(5)-MI], during production (Caramel III and IV). Caramel III was also flagged for potential immunotoxicity in animal studies. To avoid having to use a cancer warning, Coca Cola and Pepsi both now use caramel IV which was considered less of a risk. Dose makes the poison, and the latest safety report states that the accepted dose intake (ADI) is 100mg/kg of bodyweight of caramel III and that the total ADI of all caramel colours is 300mg/kg of bodyweight. The average intake is way below the ADI, and the FDA have stated people would need to drink 1,000 cans of fizzy drinks in order for there to be a carcinogenic effect from 4(5)-MI.

Unknown Relationship With Allergies Much is still unknown about the consumption of food additives and whether this leads to allergic reactions or asthma, and there are few studies since the animal studies of the 90s that have specifically investigated caramel colours’ effect on the immune system. Whilst researching this I found many anecdotal reports claiming eczema was caused by food dyes on a variety of websites, but very few studies. Interestingly a study observed a discrepancy between the reported prevalence of adverse reactions to food additives (0.01–0.23%) and the perception of food allergies of patients and parents (7.4%). This study was carried out way back in 1987 though! It could mean that people are placing blame without proof. But it could also mean that symptoms are mild enough to not warrant the hassle of further medical investigation. The clinical manifestation is normally mild, which could explain the lack of studies.

The results from a recent study performed on mice found that the introduction of saccharin sodium (sweetener) and a mixture of food additives inhibited acquisition of oral tolerance. This basically suggests that the combination of many additives in the diet could increase the risk for allergies later in life. Whilst the animal studies in the 90s suggest a safety threshold for caramel colours, during a child’s development the immune system is maturing and is exposed to a multitude of antigens over many years. Very different to controlled lab conditions using animals. The one caramel colour study I found that included human volunteers, reported no adverse effect on immunological parameters from caramel colour III, but notably this study had a conflict of interest being partly funded by International Technical Caramel Association. The researchers did not test for adherence to the diet.

More studies are desperately needed to investigate the relation with food additives and allergies in children, and whether they increase the risk for food allergies developing or persisting in adulthood. It’s impossible to draw a conclusion from this. If anyone has any other literature on this, please by all means send it to me, but it appears there is a gap in the research here.

Phosphoric Acid and Acidity Regulators. This is added to give drinks a tangy flavour. Although acidity regulators are added, carbonated soft drinks remain highly acidic, and this includes the diet versions as well. The acidity regulator normally used is sodium citrate, so if you have been advised by a medical professional to consume a low sodium diet, you may need to watch your intake.

Natural Flavours Despite what some people say, mostly those who don’t understand food chemistry, natural flavours are safe. These flavours are compounds extracted using different methods from plants and other natural sources, unlike caramel colours described earlier. People spreading nutribollocks will often say, ‘If you want it to taste like oranges, why not use real oranges?’ Using natural flavourings is an affordable method that can help maintain the structural integrity of foods, and improve palatability, during food production. These are 100% safe.

Caffeine Moderate intakes of caffeine are not just safe, but can provide several benefits beyond its stimulatory capacity. However, there is potential for dependence, tolerance, and withdrawal. It is a stimulant to the central nervous system, so it is advisable to drink no more than 4 cups of coffee per day according to a meta-analysis by the British Medical Journal. Considering one cup of coffee has just under 100mg caffeine per cup, and there is just under 30mg caffeine per can of Coca Cola, I think you’ll be ok.

Diet Carbonated Drinks

Diet fizzy drinks cause a significant amount of enamel erosion compared to still and sparkling water, but not as much as sweetened fizzy drinks (Figure 1). The diet versions contain the same ingredients except for (dum dum duuuuuum) sweeteners instead of sugar. Sweeteners will get an article all on their own one day. Today is not that day. The sweetener that is most used and has received the most controversy is aspartame. Despite aspartame still purported as being dangerous to our health, it has been extensively studied and has been consistently found to be safe. It does not cause cancer.

You’ll often hear that diet drinks will lead to people putting on more weight. This isn’t possible because diet fizzy drinks contain zero calories. There’s no debate about this. It just isn’t possible. People argue that it causes people to eat more, compensating for the reduction in calories, but it has been shown that consumption of aspartame-sweetened drinks did not lead to people compensating by consuming more calories at lunch and dinner compared with drinks sweetened with sucrose.

In the same study they found that subjects who drank aspartame sweetened drinks had lower blood glucose in the 20 minutes after eating compared with sucrose. The belief that drinking diet fizzy drinks leads to diabetes is also untrue.

A whole load of studies have shown a link with diet fizzy drinks and weight gain. But a whole load of studies, showing a whole load of associations proves nothing. Just that one is linked to the other, and correlation does not mean that there is causation. If you want to see some bizarre correlations check out this article. Many of these studies look at long term consumption of diet drinks, and it is quite possible that many of the participants were not trying, or even looking to reduce their weight or calorie consumption i.e. they were still eating an excess of calories. Many studies don’t look at overall diet. When we look at more reliable intervention studies, fizzy drinks sweetened with aspartame may help as part of a calorie controlled diet for weight loss.

This article was a lot longer than I had planned but I felt it was important to go through each ingredient because of the ‘yeah but what about’ gang. In conclusion the fizzy drinks with sugar need the most caution when drinking them, mainly because of the significant increase in risk for enamel erosion. There is a hierarchy of healthiness:

Water > Fizzy Water > Diet Fizzy Drinks > Sweetened Fizzy Drinks

Plain old water is king. But all the mentioned drinks are safe to drink and can be enjoyed as part of a balanced diet. So, stop worrying.