The truth about sweeteners: Harmless sugar substitute or an underestimated health risk?

Hardly any nutrition topic is discussed as controversially as artificial sweeteners. While some see them as an important aid for losing weight, others warn of possible health risks. But what does the science actually say?

Why sweeteners are so popular

Sweeteners such as aspartame, sucralose, saccharin or acesulfame-K are much sweeter than table sugar, but contain little or no calories. That is why they have been used for decades in beverages, desserts, chewing gum and many 'light' products.

For people with diabetes or overweight they seem ideal at first glance: sweet taste without sugar and without the associated calories. But this is exactly where the debate begins.

Do sweeteners really help with weight loss?

For a long time the answer was considered clear: yes. Several systematic reviews and meta-analyses of randomized intervention studies¹ show that people, who replace sugary foods or drinks with products containing sweeteners, on average consume fewer calories , and thereby lose a small amount of weight.  

However, it is important that sweeteners do not automatically lead to weight loss. When their consumption is compared with water instead of sugar, most studies show no notable difference in body weight. This suggests that the benefit arises solely from the calories saved. 

However, there are also some observational studies², which show a different picture: these sometimes find associations between high sweetener consumption and higher body weight as well as an increased risk for metabolic diseases, such as type 2 diabetes. However, these results should not be interpreted as proof of causation. Because these are not controlled experiments, confounding factors and especially reverse causation may play a role (e.g., people with overweight more often turn to light products). 

Why the WHO is still skeptical

The World Health Organization also published a guideline in 2023³, in which it recommends not using sweeteners specifically for long-term weight reduction. However, the reasoning was not that sweeteners have been proven harmful, but that the available long-term data do not show a clear and sustained benefit for weight control⁴. 

Conclusion: The strongest evidence from randomized intervention studies suggests that sweeteners offer advantages over sugar for calorie reduction and weight management. The more critical results mainly come from observational studies, where it remains unclear whether sweeteners are actually the cause of the observed effects. Therefore many professional societies today regard sweeteners as a possible tool to reduce sugar and calories, but not as an independent strategy for weight loss. 

Do sweeteners trigger cravings? 

Our brain has learned over millennia: sweet taste means energy intake. However, if the expected energy does not arrive, this could have long-term effects on hunger and satiety signals, scientists warn. That very hypothesis has therefore been investigated in many studies. 

Some more recent experimental studies⁵ show short-term effects in the brain. In a randomized crossover study with 75 participants, sucralose compared with sugar or water led to stronger activation of brain regions involved in hunger regulation, particularly in the hypothalamus. At the same time, in certain conditions a slightly increased feeling of hunger was also reported, however not consistently across all comparison groups. 

By contrast, when longer controlled studies are considered, a more stable picture emerges: a systematic review and meta-analysis⁶ of randomized controlled trials shows that sweeteners, compared with sugar, do reduce calorie intake, but there is no consistent difference in hunger and appetite. Overall, the included studies therefore report neither a reliable increase nor a decrease in hunger or cravings due to sweeteners compared with control conditions. 

The current scientific consensus is therefore: There is so far no clear evidence that sweeteners automatically trigger cravings, and in everyday life they are rather neutral with regard to appetite and satiety.

Do sweeteners affect the gut microbiota?

Research has become particularly exciting in recent years due to studies on the gut microbiome. An important starting point was a widely noted animal and human study⁷, which showed that certain sweeteners — in particular saccharin — can change the composition of gut bacteria and could thereby also affect glucose metabolism. In that work some participants developed poorer glucose tolerance after consuming sweeteners, accompanied by measurable changes in the microbiome.

In later studies⁸ however a much more complex picture emerged. Not all sweeteners seem to act the same, and not all people show a measurable response at all. While some studies found slight changes in certain groups of bacteria, other studies showed no clear effects at all. Even larger controlled human trials could only partially or not at all reproduce the original strong effects on blood sugar and metabolism.

A central problem: The gut flora is extremely individual. It responds sensitively to diet, stress, medications and many other factors — often more strongly than to individual food components. This makes it difficult to isolate a clear, uniform effect of sweeteners.

Conclusion: Current research suggests that sweeteners may be able to influence the gut flora, but these effects are neither consistent nor well understood.

Are sweeteners carcinogenic?

This question has concerned consumers for decades. Aspartame in particular made headlines again in 2023 when the International Agency for Research on Cancer (IARC) classified aspartame as "possibly carcinogenic". This assessment caused uncertainty. It is important, however, that this classification does not mean that an actual cancer risk in everyday life has been proven, but only that a risk cannot be entirely ruled out in theory.

The overall body of evidence⁹ in humans has so far shown no clear link between the consumption of approved sweeteners and an increased cancer risk. Large observational studies and analyses of human studies overall find no consistent evidence that sweeteners cause cancer.

Regulatory bodies such as the European Food Safety Authority (EFSA), after regular review, also conclude that sweeteners are considered safe within the permitted daily amounts. For an adult, depending on the product, it would often require several servings of diet beverages per day to reach the recommended maximum amount.

Conclusion: Overall, current research therefore does not suggest that sweeteners are carcinogenic in usual amounts.

Conclusion: Harmless sugar substitute or underestimated health risk?

The truth about sweeteners is less sensational than many headlines suggest. According to the current state of science, approved sweeteners are considered safe within the recommended amounts. They can help reduce sugar and calories, especially for people with high sugar consumption.

At the same time, these are not "natural" sugar alternatives in the classic sense, but highly processed substances that do not sustainably change the body's sweetness threshold — so the habituation to intensely sweet taste can therefore persist. Some readers nevertheless report that sugar-free drinks helped them lose weight as part of a dietary change, especially as a replacement for heavily sugared sodas.

For consumers this means: In moderate amounts, sweeteners are fine — even an occasional chewing gum is unproblematic. However, they are not a free pass for guiltless snacking or unlimited consumption of sweet products. Those who eat a balanced diet and overall pay attention to mindful eating can certainly occasionally enjoy a sugary soda without it automatically being "unhealthy".