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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 Free sugars are those added to food (e.g. sucrose (table sugar), glucose) or those naturally present in honey, syrups and unsweetened fruit juices, but exclude lactose in milk and milk products.
Non-Milk Extrinsic Sugar (NMES) Sugars not contained within the cellular structure of a food except lactose in milk and milk products. The only difference between NMES and free sugars is that NMES includes 50% of the fruit sugars from stewed, dried or canned fruit but free sugars includes none.
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 (see table below).

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 is a value for labelling purposes only and in this context in the EU relates to total sugar, intrinsic and extrinsic; it is 90g for adults which is around 340 calories.

WHO – Guidelines published in 2015 saying free sugars should make up less than 10% of daily energy intake for both adults and children, and a reduction to below 5% would have additional benefits2.

UK – UK recommendations are informed by the Scientific Advisory Committee on Nutrition (SACN) whose 2015 report advised that free sugars should not exceed 5% of daily energy intake3. NHS recommendations are in line with this4.

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.

In 2011 SACN reviewed the dietary reference values for energy and recommended values of 10.9MJ/day (2605kcals/d) for adult men and 8.7MJ/day (2079kcals/d) for adult women. The report also revised the estimated average requirements for energy for children aged 1-18 years5.

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 (see appendix).

The most recent figures for the UK show that the average percentage of daily energy intake from non-milk extrinsic sugars is 11.6% for adults, 15.6% for adolescents, and 14.7% for children6.

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 weight8.

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 diseases, like type 2 diabetes, via its contribution to obesity.

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

Observational studies have found small correlations between consuming sugar and health problems after controlling for obesity; however there is insufficient evidence to suggest that sugar causes disease via any other mechanism, except tooth decay.

There is a strong link between sugar and tooth decay – dental cavities can be increased when food gets 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 meals9.

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 obesity12 and tooth decay 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 weight13, and that when consumed at over 25% of energy intake sugar can adversely affect glucose and insulin response14.

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 issue15, 16:

  • 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 has 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 concern17.

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. However there is scant evidence of harmful effects at average levels of consumption.



  1. WHO: Sugars intake for adults and children
  2. SACN: Carbohydrates and Health report, 2015
  3. NHS Choices – How much sugar is good for me?
  4. SACN Dietary Reference Values for Energy, 2011
  5. National Diet and Nutrition Survey: 2008/09 – 2010/11 (See Tables & Appendices Ch 5)
  6. National Diet and Nutrition Survey: 2008/09 – 2009/10 (See Ch 2 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. Scientific Opinion on Dietary Reference Values for carbohydrates and dietary fibre
  13. Dietary sugars and cardiometabolic risk: systematic review and meta-analyses of randomized controlled trials of the effects on blood pressure and lipids
  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 20/11/2015

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