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sugar and health

This factsheet is also available as a pdf.


Sugar enters our diets either by naturally occurring in food or being added to it:

Intrinsic Sugar: Sugar held within the cell structure of food, as in whole fruit and vegetables.

Free Sugar: Sugar not held within the cell structure of food, as in table sugar, milk, honey, syrups, fruit juices and concentrates (also called extrinsic sugar).

The sugar in dairy products is often excluded from definitions of free sugars, e.g. by SACN & WHO; also referred to as Non-Milk Extrinsic Sugars (NMES).

Added Sugar: Sugar added to food in cooking/processing, as table sugar, honey or syrup.

Free sugar tends to outweigh intrinsic sugar in the average diet.

Sugar has an energy content of around 380 kcal (calories) per 100 g, approximately 16 calories per 4g teaspoon, which is less than half the energy density of fat.


How much we should eat

EU: The Reference Intake (previously Guideline Daily Amount) for total sugar, intrinsic and extrinsic, is 90g for adults which is around 340 calories. This falls to 85 g for children1.

WHO: Recently published draft guidelines saying free sugars should make up less than 10% of daily energy intake and a reduction to below 5% would have additional benefits for dental health2.

SACN: UK recommendations are set by the Scientific Advisory Committee on Nutrition (SACN) whose recent draft report advised that free sugars should be around 5% of daily energy intake3.

NHS: Added sugars should be no more than 10% of daily energy intake4.

For people burning 2,000 calories per day: 10% of daily energy intake equates to 200 calories = 53g = 13 teaspoons of sugar; 5% of daily energy intake equates to 100 calories = 26g = 5 – 6 teaspoons.

The EU’s Reference Intake for total energy per day for adults is 2,000 calories which is the typical energy expenditure for adult women; adult men tend to need nearer 2,400, young men need around 3,300, and teenage boys can even exceed 4 or 5,000 calories per day.


How much we do eat

(See pdf link above for numbers on intake of sugar in UK, 2008-2012, by age group)

Consumption of all categories of sugar has fallen moderately across ages and genders since 1997, except for intrinsic sugar consumption in children and adolescents.

The most recent figures for the UK show that the average percentage of daily energy intake from from free sugars is 12.1% for adults, 15.6% for adolescents, and 14.7% for children5.


The state of the evidence on how sugar is related to health problems

A 2013 systematic review found consistent evidence from randomised controlled trials (RCTs) and observational studies that changing the amount of sugar in diet directly impacts weight7.

The strongest evidence linking sugar to body weight is for added sugar in SSBs – soda, energy drinks, fruit drinks (not juices) and sweetened tea/coffee – and results are consistent across age groups.

The evidence suggests that sugar is causally related to obesity via its energy content rather than any other mechanism: consuming more calories than you use makes you fatter.

Sugar is considered to be linked to disease, like type 2 diabetes, via its contribution to obesity.

Observational studies have found small correlations between consuming sugar and health problems after controlling for obesity; however there is no concrete evidence that sugar causes disease via any other mechanism, except tooth decay.

There is a strong link between sugar and tooth decay – sweets and biscuits in particular cause dental cavities by getting stuck between teeth – but the risk of developing cavities is lowered by fluoride, good dental hygiene and reducing the frequency of consumption of sugar between meals8.


Sugar Sweetened Beverages (SSBs)

Consumption of SSBs among 4-64 year olds has increased over the last 25 years (see pdf link above for data).

The main hypothesis for SSBs’ link to obesity is that the drinks are not satiating; they don’t impact appetite in the way consuming solid food does, thus increasing overall calorie intake10.

Although fruit juices are not SSBs, they do contribute to extrinsic sugar intake as the sugars they contain are no longer held within a cell structure. Consuming fruit juice adds calories to the diet and they may be a risk factor for weight gain but until recently few studies have addressed this question.


Chemical differences between sugars and how they are metabolised

‘Sugar’ can refer to various molecules broadly split into simple sugars (monosaccharides), such as glucose and fructose, and compound sugars (disaccharides), such as sucrose and lactose.

Sucrose (table sugar)is a disaccharide made of one glucose and one fructose molecule, which are metabolised differently:

  • Glucose is the fuel for respiration and is easily absorbed in the gut, circulates in the blood and stimulates the pancreas to produce insulin as a way to store glucose for future use.
  • Fructose is not as easily absorbed in the gut, barely enters the bloodstream, does not stimulate insulin production and is metabolised in the liver into glycerol, a precursor to fat (triglyceride).

The chemical structure of starch, the carbohydrate found in most staple foods, is a series of glucose molecules and is broken down by digestion and absorbed as glucose.


Topics of debate

Is sugar toxic?

Some scientists have suggested sugar has adverse health effects beyond its contribution to obesity11, pointing to observational studies that show a heightened risk of, e.g., heart disease for the minority of people who consume over 15% of their energy intake as added sugar.

There is some evidence that dietary sugar has modest impacts on blood pressure and blood lipids – risk factors for conditions like heart disease – independently of weight12, and that when consumed at over 25% of energy intake sugar can adversely affect glucose and insulin response13.

Animal studies showing strong links between high sugar diets and health factors like high blood pressure suggest potential mechanisms for disease, but without extensive controlled human trials these animal studies suggest hypotheses rather than providing evidence.


Is sugar addictive?

Sugar has been suggested to be addictive because its consumption produces activity in the brain’s reward circuits. Drugs of addiction have a powerful effect on this circuitry and may come to “hijack” it. Some scientists have suggested sugar can have the same physiological effect, and can drive compulsive behaviours, but there is debate on the issue14, 15:

  • Reward circuits in the brain are meant to respond to consuming food, but there is inconsistent evidence about whether this response lessens over time for binge eaters in a similar way to addictive drugs. Human-based research in this field is in its infancy.
  • Lab studies have shown it is possible to get rats ‘addicted’ to sugar while not being obese. It is unclear if results from rats in highly controlled conditions are relevant to humans for whom consumption usually follows very different patterns.
  • Some clinical criteria for addictive behaviours apply to compulsive eaters though there are also key differences. Sugar have been shown to drive over-consumption, however whether this constitutes addictive behaviour or not has yet to be answered in humans.


High Fructose Corn Syrup (HFCS) – cause for concern?

Some scientists have highlighted that the rise of obesity has mirrored use of HFCS in the last decade, largely in the US, and that the way fructose is metabolised may be of concern16.

HFCS is typically 55:45 fructose to glucose, and so is metabolised similarly to sucrose which is 50:50. There is minimal evidence of effects unique to HFCS, and it is used much less in the UK.

Extreme doses of fructose cause fat to collect in the liver – which increases the risk of heart disease – and diarrhoea. However there is scant evidence of harmful effects at average levels of consumption.



1. Reference Intakes (previously Guideline Daily Amounts) – Food and Drink Federation
2. WHO opens public consultation on draft sugars guideline
3. SACN: Draft Carbohydrates and Health report
4. NHS Choices – How much sugar is good for me?
5. National Diet and Nutrition Survey: 2008/09 – 2010/12 (See Tables & Appendices Ch 5)
6. National Diet and Nutrition Survey: 2008/09 – 2009/10 (See Ch2 table 5.23)
7. Dietary sugars and body weight: systematic review and meta-analyses of randomised controlled trials and cohort studies
8. Effect on Caries of Restricting Sugars Intake
9. Patterns and trends of beverage consumption among children and adults in Great Britain, 1986 –2009
10. Beverage consumption, appetite, and energy intake: what did you expect?
11. New Unsweetened Truths About Sugar
12. Dietary sugars and cardiometabolic risk: systematic review and meta-analyses of randomized controlled trials of the effects on blood pressure and lipids
13. Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre
14. Obesity and the brain: how convincing is the addiction model?
15. Is sweetness addictive?
16. How bad is fructose?


This is a Factsheet issued by the Science Media Centre to provide background information on science topics relevant to news stories. This is not intended as the ‘last word’ on a subject, but rather a summary of the basics and a pointer towards sources of more detailed information. These can be read as supplements to our roundups and/or briefings.


Updated 11/07/2014

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