What does sugar do in the body?

What does sugar do in the body after it has tasted sweet in the mouth? Table sugar is broken down into glucose and fructose during digestion; glucose causes a rise in the hormone insulin, whilst fructose is mainly processed in the liver. This guide explains, step by step, the different types of sugar, how they enter the bloodstream, what effects they can have on teeth, the liver and body weight, and how much sugar professional bodies consider acceptable. All statements are sourced from authorities and professional bodies such as the World Health Organisation (WHO), the German Nutrition Society (DGE) and the Federal Institute for Risk Assessment (BfR).

Important: This article is for general information purposes only and is not a substitute for medical or nutritional advice. If you have, or suspect you have, diabetes, a liver condition or fructose intolerance, speak to your doctor.

Not all sugars are the same: glucose, fructose, sucrose

Chemically speaking, sugars are a type of carbohydrate. A distinction is made between simple sugars (monosaccharides) such as glucose (grape sugar), fructose (fruit sugar) and galactose, and disaccharides such as sucrose, lactose (milk sugar) and maltose (malt sugar).

Table sugar, made from sugar beet or sugar cane, is called sucrose. It consists of one part glucose and one part fructose, which are linked together in a 1:1 ratio. Fructose also occurs in its free form, for example in fruit, honey and various vegetables.

When it comes to dietary recommendations, one term is particularly important: free sugars. The WHO defines these as monosaccharides and disaccharides added to food and drink by manufacturers, cooks or yourself, as well as sugars naturally present in honey, syrups, fruit juices and fruit juice concentrates. Sugar found in fresh fruit and vegetables and in milk is not included. An apple and a glass of apple juice are therefore not the same thing: the sugar in the juice is considered ‘free’, whereas that in the whole apple is not.

Our guide, ‘How to Read an Ingredients List’, explains where free sugars can be found and the names under which they appear in the ingredients list.

Digestion: How sugar enters the bloodstream

When you eat or drink table sugar, enzymes in the body break it down into its two components: glucose and fructose. The body distributes these components via the blood, and blood sugar levels rise.

This is where the pancreas comes into play. It produces the hormone insulin and releases it into the blood after every meal, when blood sugar levels rise. Insulin ensures that cells – for example, in the liver and muscles – can take up the sugar from the blood, causing blood sugar levels to fall again.

The BfR describes what happens to the glucose as follows: within the cells, it is primarily used to provide energy; the liver stores it as glycogen; and, via secondary pathways, it can also be converted into fat. Insulin release also plays a key role in making you feel full.

Fructose and the liver

Fructose takes a different route. It triggers a significantly lower insulin response and is primarily processed in the liver. Whilst it also serves partly as a source of energy there, it is used to a greater extent than glucose in the formation of fat. When consumed in larger quantities, fructose can also raise uric acid and blood lipid levels (triglycerides).

The BfR cites evidence from studies suggesting that high levels of fructose may contribute to fatty liver, elevated blood lipid levels, severe overweight (obesity) and type 2 diabetes. The Hamburg Consumer Advice Centre takes a similar view: A high fructose intake can raise blood lipid levels, reduce the effectiveness of insulin and promote the development of fatty liver. The French food safety authority ANSES has justified its upper limit for total sugar, amongst other things, on the grounds that triglyceride levels rise from around 50 g of fructose per day.

Does that mean fruit is bad for you? No. In fruit, fructose is bound to fibre and is therefore absorbed only slowly. Sugar from whole fruit is also not classified as ‘free sugars’, which the WHO and the DGE aim to limit. The situation is different with fruit juice and sweetened drinks: in these, the sugar is classified as ‘free sugars’.

Sugar and teeth: How tooth decay develops

The effects of sugar are most quickly visible on the teeth. Bacteria in dental plaque break down food debris and the sugar it contains. This produces acid, which attacks the tooth enamel; if the teeth are not cleaned, the acid can gradually destroy them.

It is not just the amount that matters, but also how often sugar comes into contact with the teeth. Sugar is not only found in sweets and fizzy drinks, but also, for example, in fruit juices and ketchup. Eating sugary foods less often reduces the risk of tooth decay; this should be combined with brushing your teeth with fluoride toothpaste and regular check-ups at the dentist.

The WHO also cites tooth decay as one of the reasons for its sugar recommendation: deriving less than 10 per cent of energy from free sugars reduces the risk of being overweight, obesity and tooth decay.

Obesity and type 2 diabetes: the role of sweetened drinks

According to the German Obesity Society, the German Diabetes Society and the German Nutrition Society (DGE), a high and frequent intake of sugar is linked, amongst other things, to being overweight and obesity, to a higher risk of type 2 diabetes and cardiovascular disease, and to tooth decay. Sugar-sweetened foods and drinks often provide a lot of energy but hardly any nutrients, and can displace nutrient-rich foods.

Drinks play a particular role here. If you eat a solid meal, you usually balance this out by eating less of other things later on. With drinks, this balancing act doesn’t work very well because they are not very filling – so it’s easy to end up consuming too much energy overall. As early as 2011, the DGE concluded that there is probable evidence that higher consumption of sugar-sweetened drinks increases the risk of obesity in adults and of type 2 diabetes; according to this, the increased risk of diabetes exists even independently of energy balance. According to the WHO, in children, those who drink the most sugar-sweetened drinks are more likely to be overweight or obese.

It doesn’t take long to reach these amounts. According to the WHO, a can of sugar-sweetened fizzy drink can contain up to 40 g of free sugars. There are 10–11 g of sugar in 100 ml of fizzy drink or cola, and 17 g in 100 ml of fruit nectar.

Sugar is not the only cause of type 2 diabetes. In this form of the condition, although the pancreas produces enough insulin, it no longer works properly in the body’s organs (insulin resistance). The Institute for Quality and Efficiency in Health Care (IQWiG) lists risk factors as being overweight and a lack of exercise, a diet low in fibre and high in fat and sugar, certain medicines and a family history of the condition. To find out whether sweetened drinks will soon look different as a result of the sugar tax debate, read ‘Sugar Tax 2027’.

How much sugar is okay? The recommendations from the WHO and the DGE

The WHO recommends that adults and children consume less than 10 per cent of their daily energy intake from free sugars. A further reduction to below 5 per cent – which is approximately 25 g or 6 teaspoons a day – is said to bring additional benefits.

In 2018, the DGE, the German Diabetes Society and the German Obesity Society adopted the 10 per cent limit. Based on a daily intake of 2,000 kcal, this corresponds to a maximum of 50 g of free sugars. The professional societies explicitly regard this as an upper limit, not as a recommended amount. The BfR estimates that an adult with a daily energy requirement of around 2,000 kcal should consume no more than 6 to 12 teaspoons of added sugar per day – across all foods and drinks combined.

By way of comparison: half a litre of fizzy drink containing 10–11 g of sugar per 100 ml already amounts to 50–55 g – more than the DGE’s upper limit for the whole day.

How much sugar we actually eat

Most people in Germany exceed these limits. According to data from the Max Rubner Institute’s National Consumption Study II, women aged between 15 and 80 derive 13.9 per cent of their energy from free sugars, whilst men derive 13.0 per cent. The proportion is highest among adolescents and young adults: up to 18.5 per cent for women aged between 19 and 24.

According to the DONALD study, the proportion among children and young people aged between 3 and 18 is around 15 to 17.5 per cent. Although it has fallen significantly since 2010, it remains well above 10 per cent in all groups.

Where do free sugars come from? Confectionery is the largest source, accounting for 36 per cent; fruit juices and nectars account for a further 26 per cent, and fizzy drinks 12 per cent. Together, drinks therefore account for more than a third. So, focusing on drinks can make a big difference.

Cutting out sugar: what happens in the body

What are the benefits of cutting out sugar? Professional bodies debate the total amount: according to the WHO, keeping free sugars to less than 10 per cent of total energy intake reduces the risk of being overweight, obesity and tooth decay. Even infrequent sugar consumption has an effect on teeth.

And what does giving up sugar do to the body? According to the AOK, people who are used to consuming a lot of sugar are more likely to feel the effects of suddenly cutting it out; symptoms mentioned include light-headedness or dizziness, nausea, tiredness, low mood, sleep disturbances and cravings. Others don’t notice a thing. Whether sugar, strictly speaking, is addictive is a matter of debate. You can read about what’s true of the reports on withdrawal and how to make the switch step by step in our guide to living a sugar-free life.

Drinks no sugar – and no sweetener

For everyday life, the DGE, the German Diabetes Society and the German Obesity Society recommend avoiding sugar-sweetened drinks and replacing them with water or unsweetened teas. Many people opt instead for ‘light’ or ‘zero’ drinks containing sweeteners. We have summarised what the authorities have to say on this in ‘Sugar or Sweeteners?’.

You can do without both. Our flavoured varieties – Pink Grapefruit, Lime & Mint and Citrus – contain, according to the label, 0 g of sugar per 100 ml and no sweetener; the flavour comes from natural flavourings, and the calorie content is 1 kcal per 100 ml. You can find out more about this concept on our ‘Sugar-free without sweeteners’ page.

Frequently Asked Questions

Sources

1. World Health Organisation (WHO): WHO calls on countries to reduce sugar intake among adults and children, 4 March 2015. who.int
2. DAG, DDG and DGE: Consensus paper: Quantitative recommendation on sugar intake in Germany, December 2018. dge.de
3. Federal Institute for Risk Assessment (BfR): Isoglucose and sucrose (table sugar) are to be assessed as equivalent in terms of their potential health risks. Press release No. 019/2018, 8 June 2018. bfr.bund.de
4. Institute for Quality and Efficiency in Health Care (IQWiG), gesundheitsinformation.de: Type 2 diabetes, updated 18 October 2023. gesundheitsinformation.de
5. Federal Ministry of Health, gesund.bund.de: Glossary: Insulin, accessed 09/11/26. gesund.bund.de
6. Federal Ministry of Health, gesund.bund.de (in collaboration with IQWiG): Tooth decay, 27 August 2024. gesund.bund.de
7. Hamburg Consumer Advice Centre: Is fructose better than ordinary sugar?, 25 February 25. vzhh.de
8. AOK Health Magazine (Volker Zapf): Lifestyle Challenge – Giving Up Sugar: What Are the Benefits of a Month No Sugar?, 8 August 2025. aok.de
9. ACQUA REAPER: Product labels, as at 26 July.