Household sugar as a source of energy and its downsides
"Normal" household sugar consists of glucose and fructose. Fructose is mainly processed in the liver; if consumed in large quantities over a long period of time, fat is deposited there, which promotes obesity, insulin resistance and non-alcoholic fatty liver disease. At the same time, a lot of sugar can stimulate the production of pro-inflammatory signaling substances and thus promote chronic diseases. Sugar is also problematic for our teeth: bacteria convert it into acids that attack tooth enamel and cause tooth decay.
How sugar changes the gut
A high-sugar diet reduces the diversity of beneficial gut bacteria such as Lactobacillus and Bifidobacterium and promotes the growth of Candida yeast and other undesirable germs. This makes the intestinal mucosa more permeable ("leaky gut"), allowing more bacterial toxins to enter the bloodstream, which can increase inflammation and metabolic problems.
Natural sugar alternatives - not a miracle solution
Honey, date syrup, agave syrup or coconut blossom sugar are advertised as "natural", but they also contain sugar - often even a lot of fructose. Their health benefits are limited.
Sugar alcohols such as xylitol, erythritol and sorbitol
These polyols sweeten like sugar, but provide fewer calories and hardly affect blood sugar levels. Some of them enter the large intestine undigested, where they are fermented by bacteria. This produces gases that can lead to flatulence, abdominal cramps or diarrhea. In moderate amounts, certain intestinal bacteria - such as those from the genus Anaerostipes - can use xylitol to produce butyric acid, which can be good for the gut. However, recent studies show that high blood levels of erythritol and xylitol are associated with an increased tendency to blood clots and a greater risk of cardiovascular disease. People with irritable bowel syndrome or fructose malabsorption are often more sensitive to sugar alcohols.
Calorie-free sweeteners: safe, but not without problems
Artificial sweeteners such as aspartame, acesulfame-K and saccharin are hundreds of times sweeter than sugar and contain no calories. The European Food Safety Authority (EFSA) has tested these substances for safety and rates them - within the permitted daily intake - as harmless; they cause neither DNA damage nor cancer.
However, more recent research has also revealed downsides: In animal studies and some smaller human studies, sucralose (a popular sweetener) reduced the number of beneficial gut bacteria such as Bifidobacterium and Lactobacillus and triggered changes in metabolic pathways and inflammatory genes. In addition, in a recent crossover study in young adults, sucralose increased the activity of the hypothalamus - the brain center for hunger and satiety - and increased the feeling of hunger compared to sugar. These effects were particularly pronounced in people with obesity and could explain why sweeteners do not necessarily help with weight loss.
Stevia - plant-based, but not without a catch
Stevia extracts are obtained from the South American plant Stevia rebaudiana and sweeten without calories. They do not affect blood sugar levels or insulin and are also suitable for people with fructose intolerance. The bitter, licorice-like taste takes some getting used to for many, and the extracts are highly processed. Long-term data on the effect on the intestinal flora is still lacking.
Conclusion and practical tips
No sweetness is "good" or "bad" per se. What matters is the quantity and the context:
Use sugar sparingly: Above all, avoid hidden sugar in ready-made products.
Eat unprocessed food: Fruit, vegetables, whole grains and nuts provide natural sweetness, fiber and phytochemicals.
Enjoy sugar alcohols with moderation: Small amounts of xylitol or erythritol can be an alternative, but not in large doses and not for people with sensitive intestines or at cardiovascular risk.
Use sweeteners consciously: Even if they are calorie-free, they should not be a permanent solution. Everyone reacts differently; pay attention to your own well-being.
Gut-friendly diet: Fiber and fermented foods (e.g. sauerkraut, kefir) promote a diverse microbiome and strengthen the immune system and mood - regardless of the sweetener used.
Sugar, liver and metabolic disorders
Regulation of fructose metabolism in NAFLD: High fructose consumption increases obesity, dysregulates liver metabolism and promotes inflammationpmc.ncbi.nlm.nih.gov.
Excessive dietary sugar causes metabolic disorders and increases inflammatory mediatorspmc.ncbi.nlm.nih.gov.
Caries caused by sugar
WHO report: Plaque bacteria convert free sugar into acids that destroy tooth enamelwho.int.
Sugar and gut health
High sugar intake reduces the diversity of beneficial gut bacteria and promotes candidapmc.ncbi.nlm.nih.govpmc.ncbi.nlm.nih.gov.
High sugar intake affects gut flora, increases permeability and promotes inflammationpmc.ncbi.nlm.nih.gov.
Sugar alcohols
Sugar alcohols cause bloating and diarrhea because they are fermented in the colonhealth.harvard.edu.
Anaerostipes can ferment xylitol and form butyric acidpmc.ncbi.nlm.nih.gov.
High erythritol and xylitol levels increase the risk of cardiovascular diseasepubmed.ncbi.nlm.nih.govpubmed.ncbi.nlm.nih.gov.
Sweeteners and their evaluation
EFSA: Saccharin, acesulfame-K and aspartame are safe within the ADI and not carcinogenicfsa.europa.euefsa.europa.euefsa.europa.eu.
Sucralose and the microbiome
Animal and human studies: Sucralose reduces Bifidobacterium and Lactobacillus and affects proinflammatory genemdpi.commdpi.com.
Sucralose and brain activity
Randomized crossover study: sucralose increases hypothalamic activity and hunger compared to sugarpubmed.ncbi.nlm.nih.gov.