Do artificial sweeteners really make you fat?
Courtney Black, a personal trainer on Instagram, claims in a video that during her “artificial sweetener phase” she was “bloated, holding fat and 10kg heavier,” suggesting that this is “why artificial sweeteners are making you fat.” She notes that after ditching sweeteners and eating whole foods instead, “everything changed.” This fact-check investigates whether approved artificial sweeteners actually cause weight gain or bloating, and whether cutting them out alone can explain significant fat loss.
Current evidence does not support the idea that approved non-nutritive sweeteners directly cause weight gain, especially when they are used as substitutes for sugar and consumed within established safety limits. Claims that these sweeteners “make you fat” also oversimplify a complex issue, because body weight is shaped by a variety of different factors rather than one ingredient alone.
This claim matters because it presents a simple explanation for a complex issue. Suggesting that artificial sweeteners directly cause weight gain could discourage people from using products that may help to reduce added sugar intake. It may also create unnecessary confusion about what drives changes in body weight, shifting attention away from the bigger picture of overall diet, eating patterns and energy balance.
Be cautious of posts that blame a single ingredient for complex health outcomes like weight change or weight loss. Personal stories can be compelling, but they're not the same as scientific evidence. Look for information backed by well-designed studies that consider overall diet and lifestyle, rather than relying on anecdotes alone.
Claim 1: “Artificial sweeteners are making you fat.”
Fact-check: The claim that non-nutritive (low/no calories) sweeteners cause weight gain is persuasive because it simplifies a complex issue into a clear and appealing narrative: remove artificial sweeteners from your diet and you will lose weight. However, the relationship between sweeteners and body weight is more complicated.
Approved non-nutritive sweeteners (NNS) such as aspartame, sucralose, acesulfame‑K and steviol glycosides, do not appear to directly cause weight gain in the general population when consumed within acceptable daily intakes (ADIs). At the same time, they are not a magic solution for weight loss either.
What the evidence shows
Observational studies often find that people who regularly consume diet drinks or other products containing NNS have higher body weights. However, these studies can’t tell us what came first. It’s quite possible that people who are already living with overweight or obesity are more likely to choose “diet” options, a pattern called reverse causation. Other factors like overall diet, activity levels and health status make it difficult to separate cause from coincidence.
In systematic reviews of randomised controlled trials, the picture looks different. These often show that if sugary foods or drinks are replaced with products containing NNS, people consume fewer calories and may experience small reductions in body weight or BMI.
The most likely explanation is that approved sweeteners used in the UK delivers sweetness with little to no usable energy (calories). Replacing sugar, which does contain calories, with NNS should reduce calorie intake. Sugar alcohols (polyols) are the exception, as they still provide some energy, although less than sugar.
Energy balance and real-world use
Replacing one sugary drink with a diet version doesn't guarantee weight loss. Body weight is determined by overall energy balance. If the calories saved from choosing a diet drink are replaced by eating more elsewhere, the potential benefit disappears. In most cases, weight change is more strongly related to overall energy intake than to the presence of NNS themselves.
Overall, the evidence suggests that how sweeteners are used matters more than the sweeteners themselves. Swapping high-sugar foods and drinks for lower-calorie alternatives can help reduce energy intake, particularly for people with high sugar consumption, obesity or type 2 diabetes. But adding diet products on top of an existing diet or compensating by eating more later is unlikely to improve weight outcomes.
Scientists have also explored whether NNS may influence cravings, metabolism or the gut microbiome in ways that could impact body weight. These remain active areas of research, but evidence in humans is inconsistent and has not consistently shown meaningful weight gain attributable to NNS alone.
UK and the World Health Organisations guidance
UK bodies do not currently state that approved low‑ or no‑calorie sweeteners cause weight gain. The Scientific Advisory Committee on Nutrition (SACN) notes that, in the short to medium term, non‑sugar sweeteners can help reduce weight gain when they replace sugar, particularly in drinks. Short‑term trials show that when people swap sugary drinks for no‑calorie sweetened versions, they tend to take in fewer calories and gain slightly less weight. The NHS agrees there is no good evidence that approved sweeteners increase appetite in humans, and that while longer‑term observational studies on weight show mixed results, these cannot be directly linked to sweetener intake.
The joint position statement from the British Dietetic Association (BDA), British Nutrition Foundation (BNF) and Diabetes UK aligns with this. It describes approved low‑ and no‑calorie sweeteners as safe when used within acceptable daily intakes and as a useful tool within a healthy diet, including for weight and blood glucose management, without suggesting that they cause weight gain. These groups stress that sweeteners are not a stand‑alone solution and that overall diet quality, physical activity and long‑term energy balance are the main drivers of weight, but they do not conclude that sweeteners themselves lead to weight gain.
This UK position is more permissive than the World Health Organization’s 2023 guideline, which advises against using non‑sugar sweeteners for long‑term weight control or to lower the risk of noncommunicable diseases. Importantly, WHO does not say that non‑sugar sweeteners cause weight gain; instead, it says there is no clear long‑term benefit for reducing body fat and that there may be potential downsides with long‑term use, so they should not be relied on as a weight‑control strategy.
The difference comes down to how each body interprets the evidence: WHO places more weight on long‑term observational studies and the lack of sustained benefit, while UK bodies give more weight to short‑ to medium‑term trials showing that replacing sugary drinks with no‑calorie versions can reduce calorie intake and weight gain, and they see the observational data as too confounded to prove harm. SACN reviewed the WHO guideline and, while recognising the uncertainties WHO highlights, did not adopt its recommendation to avoid non‑sugar sweeteners for weight control. Instead, it maintains that using non‑sugar sweeteners to replace sugar in the short term, especially in drinks, can lead to small reductions in calorie intake and weight.
Bottom line: Artificial sweeteners don't appear to cause weight gain on their own. They can be a useful substitute for sugar, but they're not a shortcut to weight loss. The biggest driver of body weight remains the overall pattern of diet, physical activity and long-term energy balance.
"Current evidence does not support the claim that approved low- or no-calorie sweeteners inherently cause fat gain. When they replace sugar, rather than simply being added to the diet, they can reduce overall calorie intake and may support modest weight loss or help to prevent weight gain. Someone’s personal experience of losing weight after cutting them out may be entirely valid, but it cannot establish cause and effect, as other changes to their diet, activity and lifestyle are likely to have occurred at the same time. Ultimately, no single ingredient determines body weight; it is the overall dietary pattern and long-term energy balance that matter most." - Nichola Ludlam-Raine, Specialist Registered Dietitian & Author of How Not to Eat Ultra-Processed - @nicsnutrition
Claim 2: Artificial sweeteners cause bloating (implied from the post)
Fact-check: This claim contains some truth, but it's too broad. Not all sweeteners behave the same way in the digestive system, so grouping them together can be misleading. Current evidence suggests that digestive symptoms are much more strongly linked to sugar alcohols (polyols) than to high‑intensity sweeteners such as aspartame, sucralose and saccharin.
Which sweeteners are most likely to cause bloating?
The sweeteners most commonly linked with bloating, gas and diarrhoea are sugar alcohols (polyols) including sorbitol, xylitol, maltitol and mannitol rather than high-intensity sweeteners such as aspartame, sucralose and saccharin.
Current evidence suggests that polyols are more likely to cause digestive symptoms because they are only partially absorbed in the small intestine. The unabsorbed portion can draw water into the gut and be fermented by bacteria in the large intestine, producing gas. This may contribute to bloating, wind, abdominal discomfort and, in some people, diarrhoea, particularly when larger amounts are consumed.
A systematic review of 79 studies found that polyol malabsorption appeared to be dose-dependent, meaning symptoms generally became more likely as intake increased. Symptoms also appeared to occur more often when different polyols were consumed together, and included flatulence, abdominal discomfort and laxative effects in both healthy volunteers and people with irritable bowel syndrome (IBS).
However, tolerance to polyols varies considerably. Individuals with IBS or other gastrointestinal conditions may be more sensitive than the general population. Although there is good biological plausibility for these effects, further research is still needed to better understand how different polyols compare and which people are most susceptible.
What about high-intensity sweeteners?
The evidence is less clear for high-intensity sweeteners such as aspartame, sucralose and saccharin. Because these sweeteners are much sweeter than sugar, they are used in very small amounts and are processed in the body differently from polyols. As a result, they are not generally thought to produce the same osmotic and fermentative effects in the gut, making them less likely to be a direct cause of bloating.
Researchers are continuing to investigate whether high-intensity sweeteners influence the gut microbiome or other aspects of gastrointestinal function. So far, however, human evidence remains limited and inconsistent, and doesn’t support a clear consistent effect on gut microbiota or the general claim that approved high-intensity sweeteners cause bloating.
Other possible causes of bloating
If someone feels bloated after consuming a sugar-free drink or food, the sweetener may not be the only explanation. Other ingredients such as carbonation, caffeine, fibre or other fermentable carbohydrates as well as the overall amount consumed, could also contribute to digestive symptoms. This can make it difficult to identify a single cause.
Bottom line: Some sugar-free products may contribute to bloating, but this appears to depend largely on the type of sweetener and the amount consumed. Current evidence suggests that digestive symptoms are more commonly associated with polyols, whereas approved high-intensity sweeteners are not consistently linked to bloating in most people. More research is needed to better understand why some individuals appear to be more sensitive than others.
"Whether sweeteners contribute to digestive symptoms appears to depend on the type of sweetener and amount consumed, with polyols in particular potentially causing bloating, abdominal discomfort or a laxative effect at higher intakes. Individual tolerance varies considerably, and people with IBS may be more sensitive to these effects, so we should be cautious about assuming everyone will experience the same symptoms. Bloating can have many different causes, so it’s important not to attribute symptoms to one dietary factor alone" - Hannah Pritchard - specialist gut health dietitian and founder of The Writing Dietitian
Final take-away
Current research suggests that approved low- and no-calorie sweeteners are unlikely, on their own, to be a consistent cause of weight gain. While some observational studies have found that people who regularly consume sweeteners tend to have higher body weights, these findings are difficult to interpret because many people choose diet products after gaining weight or when trying to manage conditions such as obesity or type 2 diabetes. This makes reverse causation and other confounding factors likely. In contrast, studies that replace sugar with sweeteners under controlled conditions generally show neutral to modestly beneficial effects on body weight when they help reduce overall energy intake.
The same principle applies to digestive symptoms. Not all sweeteners affect the gut in the same way. Sugar alcohols (polyols) are more commonly associated with bloating, gas and diarrhoea, particularly at higher intakes and in people who are more sensitive. By comparison, current evidence does not consistently link approved high-intensity sweeteners with these effects. Even then, symptoms may reflect the product as a whole including ingredients such as carbonation, fibre or other fermentable carbohydrates rather than the sweetener alone.
Ultimately, context matters more than the ingredient itself. Sweeteners can be useful for some people, particularly when they replace sugar as part of a healthier dietary pattern, but they are not a cure-all for weight loss or weight gain. Likewise, they are unlikely to undermine health when consumed within recommended limits, but they won't outweigh the effects of an overall poor diet.
The bigger picture remains unchanged: long-term health and weight are shaped by overall dietary patterns, physical activity, sleep, genetics and sustained energy balance not by any single ingredient in isolation.
Fact-checker’s toolkit: 8 questions to ask when one ingredient is blamed
- What is this ingredient replacing?
Is the claim about adding the ingredient on top of the usual diet or swapping it for something else? Effects can depend on what is being replaced.
- What does the overall diet and lifestyle look like?
Is the ingredient being discussed in isolation or as part of a broader pattern (total calories, fibre, protein, physical activity)? Health outcomes are often driven by the whole diet and lifestyle.
- How much of the ingredient are we talking about?
Are the amounts used in the studies similar to what people actually eat or drink, or are they extreme doses not realistic in real life? Effects seen at very high or very low intakes may not apply to typical use.
- What kind of evidence is being cited?
Is the claim based on observational studies, randomised controlled trials, or animal/cell studies?
Remember: a personal story is not the same as systematic evidence. Individual experiences can be real, but they don’t tell us what happens on average or what is cause vs coincidence.
- Who was studied?
Are the participants similar to the audience being addressed? Results in one group don’t always apply to another.
- What outcome was measured?
Is the claim about body weight/BMI, body fat distribution, blood markers (e.g. glucose, cholesterol), disease risk, symptoms (e.g. bloating, fatigue), or something vague like “metabolism”, “toxins” or “hormones”? Different outcomes have different levels of evidence.
- What’s the size of the effect?
If there is an association or effect, is it large enough to matter in real life, or is it small and easily outweighed by other factors (total calories, activity, sleep, stress)? Many reported effects are statistically significant but clinically modest.
- What’s been left out?
Are other strong drivers of the outcome being ignored (overall energy intake, physical activity, sleep, stress, socioeconomic factors, medications, genetics)? Blaming one ingredient often hides these bigger levers.
We have contacted Courtney Black and are awaiting a response.
Disclaimer
This fact-check is intended to provide information based on available scientific evidence. It should not be considered as medical advice. For personalised health guidance, consult with a qualified healthcare professional.
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Sources
- Food Standards Agency (2026). “Approved additives and E numbers.”
- European Commission (2025). “Acceptable daily intake of sweeteners in the EU.”
- Food Facts (2026). “Correlation.”
- Food Facts (2026). “Causation”
- Steffen, B., et al. (2023). “Long-term aspartame and saccharin intakes are related to greater volumes of visceral, intermuscular, and subcutaneous adipose tissue: the CARDIA study.”
- Sylvetsky, A. and Rother, K. (2018). Non-nutritive sweeteners in weight management and chronic disease: a review.”
- Laviada-Molina, H., et al. (2020). “Effects of nonnutritive sweeteners on body weight and BMI in diverse clinical contexts: systematic review and meta-analysis.”
- National Health Service (2023). “The truth about sweeteners.”
- National Health Service (2023). “Understanding calories.”
- British Dietetic Association (2025). “Joint position statement on the use of low- or no-calorie sweeteners (LNCS).”
- Makinen, K (2016). “Gastrointestional disturbances associated with the consumption of sugar alcohols with special consideration of xylitol: scientific review and instruction for dentists and other health-care professionals.”
- Lanhart, A. and Chey, W. (2017). “A systematic review of the effects of polyols on gastrointestinal health and irritable bowel syndrome.”
- Qadir, A. and Omer, R. (2026). “Safety of sugar alcohols on human health: a review.”
- Spencer, M., et al. (2016). “Artifical Sweeteners: A systematic review and primer for gastroenterologist.”
- National Health Service (2016). “Bloating.”
- Wen, J., et al. (2026). “Effects of non-nutritive sweeteners on weight loss and maintenance, metabolic improvement and appetite regulation in weight management programs: a systematic review and meta-analysis of randomized controlled trails.”
- SACN (2025). “SACN statement on the WHO guideline on non-sugar sweeteners.”
- World Health Organisation (2023). “Use of non-sugar sweeteners: WHO guideline.”
- NHS (2026). “Managing your weight.”
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