Sugar explained

What are the different types of sugar, how do they affect your body and are some better than others? We look at fructose, glucose, lactose and sucrose.

Different types of sugar on a table

You've probably heard the terms fructose, glucose, lactose and sucrose before, and you may know that they're all types of sugar. But do you know how they differ from one another, or whether some are better for you than others? Use our handy guide to shed some light on the secrets of sugar...

What are complex and simple carbohydrates?

Carbohydrates are classified into two basic groups, complex and simple.

Complex carbohydrates are composed of multiple simple sugars, joined together by chemical bonds. The more chains and branches of simple sugars, the more complex a carbohydrate is and in turn, the longer it takes to be broken down by the body and the less impact it has on blood sugar levels. Examples of complex carbohydrates include wholegrains such as jumbo oats, brown rice, spelt, rye and barley. 

Simple carbohydrates are either monosaccharides (one sugar molecule) or disaccharides (two sugar molecules). They are digested quickly and release sugars rapidly into the bloodstream. The two main monosaccharides are glucose and fructose. The two major disaccharides are sucrose (composed of glucose and fructose) and lactose (which is made up of galactose and glucose).


Granulated sugar and cubed sugar in bowls

What is glucose?

Glucose is the primary source of energy your body uses and every cell relies on it to function. When we talk about blood sugar we are referring to glucose in the blood. When we eat carbohydrates, our body breaks them down into units of glucose. When blood glucose levels rise, cells in the pancreas release insulin, signalling cells to take up glucose from the blood. As the cells absorb sugar from the blood, levels start to drop.

The nutritional profile of glucose

The glycemic index is a ranking of how quickly foods make your blood sugar levels rise after eating them. High GI foods are very easily broken down into glucose. Glucose is the defining standard and has a GI value of 100.  Glucose alone does not taste particularly sweet compared to fructose and sucrose. 

How does glucose affect your body?

Research suggests that, as glucose stimulates insulin release from the pancreas, it also results in the release of two other hormones, leptin and ghrelin. Leptin is known as the appetite suppressor and ghrelin the appetite increaser. It is thought that lower GI foods (such as wholegrains, proteins and those lower in glucose) suppress ghrelin, therefore regulating satiety.


Raspberries with granulated sugar poured on it

What is fructose?

Fructose or fruit sugar, is a simple sugar naturally occurring in fruit, honey, sucrose and high fructose corn syrup. Fructose is very sweet, roughly one-and-a-half times sweeter than sucrose (white sugar).  Because of the worldwide increase in the consumption of sweeteners - in soft drinks and foods containing high fructose corn syrup (HFCS) - fructose intake has quadrupled since the early 1900s. 

The nutritional profile of fructose

Fructose is absorbed directly into the bloodstream during digestion and has no impact on insulin production or blood glucose levels. Consequently, its GI value is much lower, on average around 19. It was once thought this made it a good substitute for table sugar, but there is now a growing body of research to question this. 

Sweeteners such as HFCS have a higher GI value due to the presence of glucose. It has been suggested that it is the glucose content of these sweeteners that may have contributed to the increase in cardiovascular disease and type 2 diabetes

How does fructose affect your body?

Fructose is handled by the body in a different way to glucose as it is metabolised in the liver. As a result, blood sugar (glucose) levels do not rise as rapidly after fructose consumption compared to other simple sugars. When you eat too much fructose the liver cannot process it fast enough and instead, starts to make fats that are carried in the blood and stored as triglycerides - the body's main form of fat. Studies have shown that the consumption of large amounts of fructose may lead to increased appetite by impairing the body's ability to use insulin and to suppress circulating ghrelin (the appetite-stimulating hormone).

While most diabetics cannot tolerate sucrose, most can tolerate moderate amounts of fruit and fructose without loss of blood sugar control. Research is yet to show any detrimental health effects of moderate consumption of fructose as part of a balanced diet. However, it's worth keeping in mind that the excessive consumption of HFCS and other sweeteners may contribute to elevated blood sugar levels, blood fats and subsequent weight gain.


Hands holding sugar cubes

What is sucrose?

Sucrose is crystallised white sugar produced by the sugar cane plant and can be found in households and foods worldwide. Sucrose is a disaccharide made up of 50% glucose and 50% fructose and is broken down rapidly into its constituent parts.

The nutritional profile of sucrose

Due to its glucose content, sucrose has a GI value of 65. As it is made up of glucose and fructose, the latter is metabolised in the liver and holds the same issues as those mentioned for fructose above. Due to its glucose content, sucrose does lead to an elevation in blood glucose. Diabetics should therefore be mindful of foods containing sucrose. 


Milk being poured into a glass

What is lactose?

Lactose is a sugar found in milk. It is a disaccharide made up of glucose and galactose units. It is broken down into the two parts by an enzyme called lactase. Once broken down, the simple sugars can be absorbed into the bloodstream. 

The nutritional profile of lactose

Whole milk has a GI value of 41 and is considered to be a low GI food. It is broken down slowly and helps to increase the absorption of minerals such as calcium, magnesium and zinc. Some people experience lactose intolerance – an inability to produce the lactase enzyme that breaks down milk. Lactose intolerance can lead to diarrheoa, bloating and other gastrointestinal symptoms.

Sugar: the bottom line

There are two types of sugar: naturally occurring sugar like lactose in milk and added sugar, which includes table sugar (sucrose) as well as concentrated sources like fruit juice.

The current recommendations from the World Health Organisation (WHO) are that only 5% of your daily calorie intake should consist of added, or 'free' sugars. This equates to approximately seven teaspoons (30g) for an adult. To put this into perspective, one can of fizzy drink may contain seven teaspoons or more, so it's easy to reach the recommended daily amount, especially when you consider the sugar added to food that you don't see. 

Virtually all the fibre, phytochemical, vitamin and mineral content have been removed from white sugar (sucrose). Eating too many carbohydrates, particularly simple sugars, can be harmful to blood sugar control, especially if you are insulin resistant, experience reactive hypoglycaemia or are diabetic. Eating excess sugar can lead to weight gain, which increases the risk of heart disease and type 2 diabetes.

Like this? Now read...

All you need to know about sugar
How much sugar should I eat?
10 things you should know before giving up sugar

This page was last updated on 18 January 2019 by nutritionist (MBANT) Kerry Torrens.

Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.

Jo Lewin is a registered nutritionist (RNutr) with the Association for Nutrition with a specialism in public health. Follow her on Twitter @nutri_jo.

All health content on is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact  your local health care provider. See our website terms and conditions for more information.

Still struggling to get your head around sugar? Let us know your questions below and we'll do our best to help...

Comments, questions and tips

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13th Oct, 2014
I have found Coconom organic coconut sugar to be the best alternative to 'sugar' as we know it. It is a wonderful product and so rich in nutrients with a low GI.
23rd Jul, 2014
The new draft World Health Organisation recommendation for sugars (free sugars) (
Tracey Ogden's picture
Tracey Ogden
4th Aug, 2018
My partner was diagnosed type 2 diabetic in April. We modified our eating habits and started exercising. He lowered his blood sugar lost 2 stone in weight. I eat the same except cereal / brown toast for breakfast and fruit and yoghurt for lunch. My blood sugar and cholesterol up ??? Total to avoid as much fruit because of sugars but eat low fat because of cholesterol. Fruit and yoghurt low fat but high sugar. Sandwich low GO but not low fat because of spread and cheese and ham. What am I supposed to eat. I have lost 2 stone in weight yet raised everything
goodfoodteam's picture
19th Aug, 2018
Thanks for your question. Unfortunately we are unable to provide individual dietary advice. We always recommend consulting your doctor or registered nutritional therapist to tailor your diet to suit your individual needs.
30th Jun, 2016
Hi! I heard somewhere that the sugar that you drink (in Coca Cola for example) is worse than the sugar that you eat (in a food), because it is metabolised differently. Is this true? Can you tell me where I can find any scientific research on this? Thanks!
3rd Jul, 2014
Is there a difference in terms of blood sugar levels/general health impact of fructose consumed in fresh fruit, and fructose as an ingredient in processed foods? And how much fructose is unhealthy? You say "Studies have shown that the consumption of large amounts of fructose may lead to increased appetite by impairing the bodies ability to use insulin and to suppress circulating ghrelin (the appetite-stimulating hormone)". I really love fruit, can I continue to eat 2-3 pieces a day, or would this already constitute a 'large amount'?
Kerry Torrens's picture
Kerry Torrens
14th Jul, 2014
Hi there, thanks for your question. Yes there is a difference. Our liver has to process fructose and when there is too much in the diet because we’ve eaten very concentrated sources it can over-load the liver. As to how much is too much – this may depend on an individual’s general health including their liver function etc. It is worth cutting back on fructose but don’t do it by cutting back on whole fruit. Whole fruit supplies lots of additional benefits such as fibre, phytochemicals and vitamins – the fibre helps balance the impact of the sugar on your body. Eating 2-3 pieces of whole fruit a day is absolutely fine – aim for another 3 or more portions of veggies or salad daily.
16th Jul, 2014
Thank you for answering, very helpful explanation!! I don't eat much processed food, so I don't think there's much I can cut back on fructose-wise, and I eat a *lot* of vegetables, usually quite a lot more than 3 portions a day, so I'm probably fine, and I'm glad to hear I can also keep happily eating my fruit :) Thanks again!
3rd Jul, 2014
I am always confused about the daily intake because some information says natural sugar doesnt count some say it does. If fructose from fruits are included in the daily recommended amount 25g, then two apples ( each contains 13g - answer from wiki) will exceed the amount already? Isn't it contradictive to the daily serving size?
Kerry Torrens's picture
Kerry Torrens
14th Jul, 2014
Hi there, thanks for your question. The sugars that the WHO are most concerned about are the sugars added to our food so this might be during manufacture, cooking or added by us before we tuck in! As well as this the WHO include sugars that are present in honey, syrups, fruit juices and fruit concentrates – all of which are concentrated sources of sugars. Whole fruit supplies lots of additional benefits such as fibre, phytochemicals and vitamins – the fibre helps balance the impact of the sugar in the fruit. You don’t need to eliminate whole fruit from your diet just remember to balance them with plenty of veggies and salad as well as protein foods and whole-grains.
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