This article was written by our regular contributor; registered dietitian – Maeve Hanan.
There are a few different types of drinks that can be called ‘diet drinks’ from meal replacement shakes to green juices. Most of the time, this refers to sugar-free or low-calorie fizzy drinks that contain sweeteners like to reduce the sugar content. This article will focus on the health impact of this type of low-calorie fizzy drink.
What Type of Sweeteners Do Diet Drinks Contain?
Artificial sweeteners are low-calorie alternatives to sugar. These are actually much sweeter than sugar, so small amounts are used to sweeten a variety of lower sugar or sugar-free products.
Common artificial sweeteners found in diet drinks in the UK include:
- Acesulfame K
Stevia is a naturally-occurring sweetener that has been used in some diet drinks over the years, but this is found much less commonly than aspartame, acesulfame K and sucralose.
These sweeteners have all been safety tested and approved use in the UK (1).
The European Food Safety Authority (EFSA) evaluates the safety of food additives, such as artificial sweeteners, and allocates an acceptable daily intake (ADI) value. This ADI is an estimate of the amount that can be safely consumed on a daily basis over a lifetime without causing health risks (2).
For example, the ADI for aspartame is 40mg per kg body weight per day and a 330ml diet drink contains roughly 200mg of aspartame (3). So a person who weighs 70kg would have to drink 14 cans (or over 4.5 L) every day in order to hit this ADI!
Both sugar-sweetened and sugar-free fizzy drinks can damage our teeth, as the carbonic acid that is used for carbonation (fizz) can dissolve tooth enamel (4).
However, diet drinks are better for teeth than sugary drinks overall as consuming sugar and sugar-containing food and drinks is linked with a higher risk of tooth decay (4).
There is also an EFSA-approved health claim that replacing sugar with certain sweeteners (including aspartame, acesulfame-K and sucrose) helps to maintain dental health by reducing tooth demineralisation (5).
So although diet drinks are acidic and can erode tooth enamel, they are less harmful to our teeth than sugary fizzy drinks.
There has been some interesting research carried out related to sweeteners, diet drinks, sugar and sugary drinks in terms of metabolic health. But this is not always clear cut, and research is ongoing in this area.
Diabetes, Insulin & Blood Glucose Levels
Consumption of both sugar-sweetened drinks and diet drinks have been linked with a higher risk of diabetes (4, 6). This is an association rather than a ‘cause and effect’ link, so it might not be directly caused by consuming these drinks.
There is strong evidence that replacing sugar with sweeteners reduces the spike in blood glucose levels that occurs after a meal (5). But it is less clear whether this helps with maintaining healthy blood glucose levels overall (5).
Certain sweeteners, including sucralose which can be used in diet drinks, have also been linked with increased blood glucose and insulin levels (7). Similarly, a study from 2014 found that feeding saccharin to mice led to changes in the gut microbiome and glucose intolerance (i.e. a condition that results in higher than normal blood glucose levels) (8). These researchers also found that humans who don’t usually consume sweeteners showed signs of worsened blood glucose levels after a week of consuming a high daily dose (the maximum ADI) of saccharin, however this study only included 7 participants and only lasted a week (8). Also, saccharin is not commonly used in diet drinks in the UK at present.
However, more recent evidence-based reviews have found that consuming sweeteners did not increase blood glucose or insulin levels (9, 10). In fact, a slight beneficial impact on glucose levels after a meal in those with type 2 diabetes and longer term glucose levels has been identified in these studies.
Overall, when study design and the overall evidence base is taken into account there is no strong link that consuming sweeteners worsens glucose regulation or increases the risk of type 2 diabetes (11).
Ongoing well-designed human research is needed into the effect of sweeteners and diet drinks on blood glucose control.
Similar to the research related to diabetes, increased consumption of both sugary and diet drinks is associated with a higher risk of heart disease (6).
A study from 2015 that was carried out in two locations compared markers of heart disease, including cholesterol and blood pressure (BP) levels, in those who drank sugary and diet soft drinks (12). In one of the locations the researchers found that drinking diet soft drinks was significantly linked with higher systolic BP, and in the other location drinking sugary soft drinks was linked with higher triglyceride levels. Controlled studies are needed to back this up and assess how artificial sweeteners from diet drinks may impact heart health.
Studies have found that consuming sugary drinks can lead to a higher intake of calories (4). There is also some limited evidence that consuming these drinks might lead to weight gain and a higher BMI in children and adolescents (4).
Some observational studies have found sweetener consumption to be linked with a higher BMI and waist circumference, and diet drink consumption to be linked with a higher waist circumference (12, 13, 15). Although there are mixed findings in this area, data from intervention studies (i.e. randomised controlled trials) suggests that sweeteners either have no impact on weight or are linked with improved weight loss (5, 11, 13, 14).
There is also some evidence that consuming sweeteners may increase appetite and cravings for sweet food (16). Furthermore, the impact of sweetener on the gut microbiome may promote a higher weight; but human research is limited in this area (17, 18, 19).
So overall, there is currently no definite link between the sweeteners in diet drinks and weight changes, and more high-quality studies are needed.
Impact on the Gut
As discussed above, some studies suggest that sweeteners which can be used in diet drinks may negatively impact the gut microbiome and have a knock on impact on blood glucose control and weight gain (8, 17, 19).
Out of the sweeteners that can be used in diet drinks, only sucralose, saccharin and stevia have been seen to negatively impact the composition of the gut bacteria so far (20). It’s important to remember that a lot of this research has been carried out in labs, animals or small groups of humans, so ongoing human research is needed.
Research is mixed and lacking about the effect of artificial sweeteners on gut symptoms (21). However, the fizz in all types of fizzy drinks can contribute to gas and bloating. Therefore, the NHS website advises reducing fizzy drink intake for those suffering with bloating (22). Similarly, the British Dietetic Association (BDA) advises fizzy drink reduction as one of the first steps for those suffering with irritable bowel syndrome (IBS) (23).
There have been lots of confusing messages surrounding sweeteners and cancer over the years.
A few animal studies in the 1980s and 90s found an association between aspartame and cancer development, but more recent human studies have not found this to be the case (3, 24).
Importantly, sweeteners that are used in the UK have undergone thorough testing and are safe to consume within the ADI — and it would be very difficult to exceed the ADI for the sweeteners that are found in diet drinks.
However, as discussed below, those who are malnourished as a side-effect of cancer or cancer treatment should generally avoid diet products in favour of more nourishing, higher calorie options.
At Risk Groups
Certain groups of people may need to avoid or be more cautious with products like diet drinks that contain artificial sweeteners.
Infants and Children
In the EU artificial sweeteners are not allowed to be used in any food which is designed for infants or young children up to the age of three (25, 26).
This is due to a lack of safety data in this age group as well as the fact that infants and children need a lot of energy to support their growth and development, so filling up on fizzy drinks is not a good idea.
The NHS also caution against giving fizzy drinks to babies or young children due to the dental issues that both sugary and diet fizzy drinks can cause (27).
Pregnant and Breastfeeding Women
Sweeteners and diet drinks are safe to consume for pregnant and breastfeeding women, as long as this is within the ADI.
However, it isn’t advised to follow a weight loss diet during pregnancy, so consuming too many diet products (including diet drinks) in place of more nourishing options is generally not encouraged.
There is also some emerging evidence that consuming sweeteners in pregnancy or while breastfeeding may impact taste development of the baby by encouraging a sweeter preference (28). For example, a study of breastfeeding mothers who drink diet drinks – sweeteners may transfer to breast milk (29).
Similarly, a Canadian study found that consuming artificial sweeteners while pregnant may increase the risk of a baby having a higher weight by the age of one (30).
So although consuming diet drinks in moderation while pregnant or breastfeeding appears to be safe, it will be interesting to see whether more research emerges about the impact of this on the future development of the baby.
Those With PKU
Those who have a rare genetic condition called phenylketonuria (PKU) can’t metabolize an amino acid called phenylalanine. If too much of this amino acid builds up in the body of somebody with PKU this can lead to brain damage.
As phenylalanine is found in aspartame those with PKU need to avoid this sweetener, including most diet drinks, along with other dietary sources. This is why in the UK product labels must state that it ‘contains a source of phenylalanine’ if it contains aspartame.
Those with Disordered Eating
Those who are suffering with an eating disorder, disordered eating or a difficult relationship with food usually need to be careful with diet drinks, as these can be used as an appetite suppressant, especially when these drinks also contain caffeine; such as diet cola.
The R.E.A.L. Food Pyramid is a widely used guide for eating disorder recovery from the Australian Centre for (CCI) in conjunction with dietitians Susan Hart and Caitlin McMaster (31). This guide places diet drinks on the top shelf which cautions to be careful with these as “they often push out more nutritious foods from your diet, and some individuals will use them to suppress their appetite”.
This can be extra important for those with disordered eating who are also suffering with dental issues due to malnutrition, purging or frequent consumption of diet drinks.
Those Who Are Malnourished
Low-calorie drinks are often not a good idea for those who have a poor appetite or are malnourished. This is because the priority is to consume enough energy and nutrients by consuming nutritious and energy-dense food and drinks.
Examples of more nourishing drinks include:
- Whole milk (which can also be fortified with dried milk powder for an extra nutritional boost)
- Milky coffees
- Fruit juice
- Oral nutritional supplement drinks
The question of whether diet drinks are bad for you is not straight-forward to answer. As always, this depends on the individual person and circumstances.
Diet soft drinks are better for our teeth than sugary versions, but the fizz can still damage enamel. There is some interesting research emerging about the possible impact of sweeteners and diet drinks on metabolic health and gut health, but ongoing research in humans is needed.
Overall, diet drinks are safe to consume within the ADI for most people; with the exception of those with PKU, and infants and children under three. Those who are malnourished, have a poor appetite or disordered eating may also need to be cautious with diet drinks as more nourishing options are usually a better choice. Those with any medical condition should always seek individual advice from a Registered Dietitian or your healthcare team.
- FSA (2020) “Approved additives and E numbers” [accessed November 2021 via: https://www.food.gov.uk/business-guidance/approved-additives-and-e-numbers#sweeteners]
- EFSA “ADI” [accessed November 2021 via: https://www.efsa.europa.eu/en/glossary/adi]
- EFSA “Aspartame” [accessed November 2021 via: https://www.efsa.europa.eu/en/topics/topic/aspartame]
- SACN (2015) “Carbohydrates and Health” [accessed November 2021 via: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/445503/SACN_Carbohydrates_and_Health.pdf]
- EFSA (2011) “Scientific Opinion on the substantiation of health claims related to intense sweeteners and contribution to the maintenance or achievement of a normal body weight (ID 1136, 1444, 4299), reduction of post-prandial glycaemic responses (ID 4298), maintenance of normal blood glucose concentrations (ID 1221, 4298), and maintenance of tooth mineralisation by decreasing tooth demineralisation (ID 1134, 1167, 1283) pursuant to Article 13(1) of Regulation (EC) No 1924/20061” [accessed November 2021 via: https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2011.2229]
- Meng et al. (2021) “Sugar- and Artificially Sweetened Beverages Consumption Linked to Type 2 Diabetes, Cardiovascular Diseases, and All-Cause Mortality: A Systematic Review and Dose-Response Meta-Analysis of Prospective Cohort Studies” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/34444794/]
- Pepino et al. (2013) “Sucralose affects glycemic and hormonal responses to an oral glucose load” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/23633524/]
- Suez et al. (2014) “Artificial sweeteners induce glucose intolerance by altering the gut microbiota” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/25231862/]
- Nichol et al. (2018) “Glycemic impact of non-nutritive sweeteners: a systematic review and meta-analysis of randomized controlled trials” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/29760482/]
- Greyling et al. (2020) “Acute glycemic and insulinemic effects of low-energy sweeteners: a systematic review and meta-analysis of randomized controlled trials” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/32672338/]
- Alsunni (2020) “Effects of Artificial Sweetener Consumption on Glucose Homeostasis and Its Association with Type 2 Diabetes and Obesity” [accessed November 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7547772/]
- Crichton et al. (2015) “Diet Soft Drink Consumption is Associated with the Metabolic Syndrome: A Two Sample Comparison” [accessed November 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4446768/]
- Azad et al. (2017) “Nonnutritive sweeteners and cardiometabolic health: a systematic review and meta-analysis of randomized controlled trials and prospective cohort studies” [accessed November 2021 via: https://www.cmaj.ca/content/189/28/E929.long]
- Peters et al. (2016) “The effects of water and non‐nutritive sweetened beverages on weight loss and weight maintenance: A randomized clinical trial” [accessed November 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4744961/]
- Fowler et al. (2015) “Diet soda intake is associated with long-term increases in waist circumference in a bi-ethnic cohort of older adults: The San Antonio Longitudinal Study of Aging” [accessed November 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4498394/]
- Yang (2020) “Gain weight by “going diet?” Artificial sweeteners and the neurobiology of sugar cravings” [accessed November 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892765/]
- Bian et al. (2020) “The artificial sweetener acesulfame potassium affects the gut microbiome and body weight gain in CD-1 mice” [accessed November 2021 via: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0178426]
- Halmos & Suba (2016) “Physiological patterns of intestinal microbiota. The role of dysbacteriosis in obesity, insulin resistance, diabetes and metabolic syndrome” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/26708682]
- Suez et al, (2015) “Non-caloric artificial sweeteners and the microbiome: findings and challenges” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/25831243/]
- Ruiz-Ojeda et al. (2019) “Effects of Sweeteners on the Gut Microbiota: A Review of Experimental Studies and Clinical Trials” [accessed November 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6363527/]
- Spencer et al. (2016) “Artificial Sweeteners: A Systematic Review and Primer for Gastroenterologists” [accessed November 2021 via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4819855]/
- NHS Website (2019) “Beat the Bloat” [accessed November 2021 via: https://www.nhs.uk/live-well/eat-well/remedies-for-bloating-and-wind/]
- BDA (2019) “Irritable Bowel Syndrome (IBS) and Diet : Food Fact Sheet” [accessed November 2021 via: https://www.bda.uk.com/resource/irritable-bowel-syndrome-diet.html]
- Cancer Research UK (2019) “Do artificial sweeteners cause cancer?” [accessed November 2021 via: https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/cancer-controversies/do-artificial-sweeteners-cause-cancer]
- EUR-LEX (2008) “Authorised sweeteners” [accessed November 2021 via: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=LEGISSUM:l21069]
- BDA (2016) “Policy Statement: The Use of Artificial Sweeteners“ [accessed November 2021 via: https://www.bda.uk.com/uploads/assets/11ea5867-96eb-43df-b61f2cbe9673530d/policystatementsweetners.pdf]
- NHS (2018) “Sweets, fizzy drinks and bottles” [accessed November 2021 via: https://www.nhs.uk/live-well/healthy-body/kids-teeth-sweets-fizzy-drinks-faqs/]
- Sylvetsky et al. (2017) “Development of Sweet Taste Perception: Implications for Artificial Sweetener Use” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/28873386/]
- Rother et al. (2018) “Pharmacokinetics of Sucralose and Acesulfame-Potassium in Breast Milk Following Ingestion of Diet Soda” [accessed November 2021 via: https://pubmed.ncbi.nlm.nih.gov/29077645/]
- Azad et al. (2016) “Association Between Artificially Sweetened Beverage Consumption During Pregnancy and Infant Body Mass Index” [accessed November 2021 via: https://jamanetwork.com/journals/jamapediatrics/fullarticle/2521471]
- CCI (2018) “The R.E.A.L. Food Pyramid” [accessed November 2021 via: https://www.cci.health.wa.gov.au/-/media/CCI/Mental-Health-Professionals/Eating-Disorders/Eating-Disorders—Information-Sheets/Eating-Disorders-Information-Sheet—26—The-REAL-Food-Pyramid.pdf]