Sugar is constantly getting attention in the media, but what exactly is it and is it all bad for us? This year news headlines have included recommendations by the World Health Organisation (WHO) to half our daily sugar intake.  We have also seen a proposed sugar tax and a ban on buy-one-get-one-free deals on junk food.  Latest cookbooks are promoting sugar alternatives and Jamie Oliver has launched a new campaign ‘Sugar Rush’ to raise awareness around sugar consumption.  The main reason for this increased awareness is that the evidence demonstrating the detrimental effects of sugar on our health is mounting and can no longer be ignored.  This is particularly true of the link between sugar consumption and obesity, diabetes and cardiovascular disease (the number one cause of mortality in the UK).  However, despite the increased awareness there is still much confusion in the general public about what they should and should not be eating and if all sugars are equal.

What is sugar?

Sugar is a broad term used to describe short-chain soluble carbohydrates. The sugar that is a cause for concern in our diet is ‘added sugar’ or ‘free sugar’.  This sugar is added to processed foods and is found in concentrations that are much higher than those found in nature.  However sugar also exists naturally in many foods including fruit and vegetables, and these sugars are not shown to be detrimental to our health.

Table sugar and syrups

what is sugarThe substance that most of us call sugar is the white crystalline powder that is sold as ‘table sugar’.  Table sugar consists of sucrose, which is obtained primarily from sugar cane and sugar beets.  Approximately 80% comes from sugar cane and 20% from sugar beets.  Sucrose is a disaccharide, made from the monosaccharides glucose and fructose.

Today sugar is produced in over 100 different countries, mostly in the temperate zones of the northern hemisphere.  The five largest producers of sugar in 2011 were Brazil, India, the European Union, China and Thailand.

In addition to table sugar, added sugar is also found in food in the form of syrups. This was introduced in the mid-70s when there was the mass development of high fructose corn syrup (HFCS), following a surplus of corn production.  In the UK HFCS is referred to more commonly as glucose-fructose syrup. This syrup was cheap to produce, extended the shelf life of food and the sweetness increased palatability.

Other forms of sugar

Although table sugar is the form that most of us relate to as sugar, there are in fact many other forms for sugar. Sugar is the general name for short-chain soluble carbohydrates – classified as monosaccharides, disaccharides or trisaccharides.  They all have a characteristically sweet taste, including the disaccharide lactose found in milk and maltose found in malt. These are composed of the monosaccharides glucose and galactose; and two glucose molecules respectively.

Because sugar is so abundant in our food and goes by many different names it can be difficult for the public to easily identify it.  However, any substance that ends in the suffix ‘-ose’ is a sugar.  As described above, this includes sucrose, glucose, lactose, galactose and maltose.

Sugar in fruit and vegetables

Sugar is found in fruit and vegetables.  Here it is a combination of varying amounts of fructose and glucose plus a little sucrose. A pear for example contains approximately 10g of sugar, which is made up of mainly fructose (fructose 6.4g, glucose 1.9g and sucrose 1.8g Ref 1).  A banana on the other hand has less fructose but more glucose and sucrose (fructose 2.7g, glucose 4.2g and sucrose 6.5g). Vegetables follow a similar pattern, but will have lower levels of overall sugars.

When sugar is eaten in its natural form, such as in fruit and vegetables, it is part of a wholefood and therefore it is combined with other nutrients that enable it to be efficiently processed in the body.  For example, fibre, vitamins, minerals and antioxidant phytonutrients all assist the body with processing the fruit sugar and provide many other benefits.

It is therefore important to note that not all sugar is the same and not all sugar is ‘bad’ or ‘unhealthy’.  The sugars that are detrimental to health are those that have been added to foods in a concentrated form, whether as granulated sugar, a syrup or a fruit concentrate.

The nutritional content of table sugar

Sugar is a source of carbohydrate and energy, providing 4 calories per gram. However, it provides no fat or protein and also provides no micro-nutrients i.e. no vitamins or minerals Ref 2.

Therefore the only nutritional value of sugar is calories, and the addition of sugar to many processed foods is a major contributing factor to the increase in obesity.  It is a food that is devoid of other nutritional value and therefore when it is consumed as a high proportion of ones daily calorie intake individuals risk becoming significantly under-nourished.  This means that nutrient deficiencies become common, as well as subsequent health problems.

The World Health Organisation recommends that ‘free sugars’ (all sugar added to foods, including sugars naturally found in honey, syrups and juices) are not more than 5% of our daily energy (calorie) intake.  This is equal to approximately 30g of free sugar per day

How sugar is processed in the body


Glucose is an essential nutrient and the body works hard to ensure that the level of glucose in the blood is kept within a safe range. NICE recommends that blood glucose should fall between 4.0 – 6.0 nmol/L when fasting and up to 7.8 mmol/L two hours after eating, in healthy individuals Ref 3. If the level of glucose in the blood is significantly above or below this range then a range of symptoms occur.  Indeed, high blood glucose (hyperglycemia) is common in diabetes and is associated with increased thirst, fatigue, blurred vision and frequent urination

Keeping blood glucose levels stable requires matching glucose intake and utilization.  In addition to dietary glucose, glucose is also produced in the body by the processes of glycogenolysis (the breakdown of glycogen to glucose-6-phosphate and glycogen) and gluconeogenesis (the production of glucose from non-carbohydrate) Ref 4.  The two main hormones that help to control blood glucose levels are insulin and glucagon. Insulin acts to lower blood glucose levels to prevent hyperglycemia and glucagon acts to increase blood glucose by converting glycogen, primarily in the liver, into glucose.  The play between insulin and glucagon therefore keep blood glucose within homeostatic levels.

One of the main roles of glucose in the body is to produce energy in the form of adenosine triphosphate (ATP).  First glucose is converted into a substance called pyruvate via glycolysis and the pyruvate is the converts into ATP via multiple steps in the ‘krebs cycle’ and ‘cytochrome system’.  Hence glucose is an essential substrate in the body for energy production.


Fructose is metabolized very differently to glucose and Dr Robert Lustig, Professor of Pediatrics in Division of Endocrinolgoy at the University of California, has been a pioneer in determining these differences. The key differences include Ref 5:

  • Fructose is metabolized almost entirely by the liver, whereas glucose is metabolized widely in the body, with only about 20% in the liver.
  • Every cell in the body uses glucose, but fructose is converted into free fatty acids and triglycerides, which get stored as fat.
  • Fatty acids created during fructose metabolism can accumulate around the liver and skeletal muscle tissues, and may contribute toward conditions such as insulin resistance and non-alcoholic fatty liver.
  • Glucose suppresses the hunger hormone ghrelin and stimulate leptin, which suppresses appetite. Fructose by contrast has no effect on ghrelin and interferes with leptin communication.

This difference in metabolism between glucose and fructose is primarily a problem when it comes to high fructose syrups that are used in processed food.  This is because the quantities of fructose used are much greater than those found in nature in fruit and vegetables.

In addition, as mentioned above, table sugar is made up of glucose and fructose, so table sugar is metabolized by both glucose and fructose metabolism.

The change in sugar consumption

Sugar consumption has increased dramatically in recent decades.  As well as sugar in our food, many people are consuming large amounts of sugar in drinks – especially fizzy drinks.

  • The consumption of fizzy drinks in the UK has almost doubled in the past 15 years. Young adults now drink an average of 6 cans per week (Source: National Diet and Nutrition Survey 2002, quoted on the Food Standard Agencys website)
  • The convenience food sector has grown by 70% over the past 10 years. It is also the largest sector, with almost £17bn spent on convenience food in 2003. This figure represents a billion pounds more than in 2002, and almost a third of the total spending on food. Ref 6

sugar consumption

Ref 7

How we got to this position

A key driving factor behind our increased consumption of sugar is linked to the fall in fat consumption.  In 1958 an American scientist called Ancel Keys started a study known as the Seven Countries Study, which examined the association between diet and cardiovascular disease.  His study revealed that the countries where fat consumption was highest had the most heart disease.  This led towards the idea that dietary fat caused heart disease.

As a result of this study, the public was encouraged to reduce fat in their diet, especially in the form of animal fat – red meat, butter, eggs and dairy. This caused the rise in low-fat diets and an increased level of sugar in foods as fat was taken out.

At a similar time, in the 70s, there was a push to drive food prices down and to increase food production on a larger scale.  Of particular interest was corn, which was grown in vast quantities and subsequently used to feed cattle, as well as to make new cereals, biscuits, desserts, flours and HFCS.  HFCS began to make its way into a range of foods to make them taste better (sweeter) and to extend their shelf-life, and also into drinks.  HFCS was cheaper than sugar and had much to offer the food industry. It tasted sweet and because it was ‘low fat’ it was believed to be better for public health.  Therefore when the fat was taken out of recipes, sugar and particularly HFCS were added in to make it taste better.

By the mid-80s, health experts such as Professor Philip James, were noticing that the BMI of the public was increasing despite the increase in low-fat foods. In 1966 the proportion of people with a BMI over 30 (classified as obese) was just 1.2% for men and 1.8% for women.  By 1989 the figures had risen to 10.6% for men and 14.0% for women.  Ref 8

Since then a number of doctors have demonstrated how sugar and HFCS are linked to not only the obesity epidemic but also other diseases such as type 2 diabetes and heart disease.  One eminent doctor in the field is Robert Lustig, an American pediatric endocrinologist at the University of California.  Lustig has demonstrated how sugar, especially concentrated fructose, can have serious deleterious effects on human health.  His work includes the book ‘Fat change: the bitter truth about sugar’, as well as numerous articles in scientific journals.  This includes ‘the toxic truth about sugar’ in the journal Nature. Ref 9.

Lustig’s work includes an analysis of Key’s ‘Seven Countries Study’, stating that Keys cherry-picked 7 out the 22 potential countries for the study. For example, he left out countries where people eat a lot of fat but have little heart disease, such as Holland and Norway, and countries where fat consumption is low but heart disease is high, such as Chile.  Indeed, when all 22 countries are included in the study Lustig and others (e.g. Jacob Yerushalmy and Hilleboe, who co-authored a critique of Keys hypothesis) found that there is no link between fat intake and heart disease.

Controversy continues about the Seven Countries Study and about the strength and causality of the association between dietary fat and cardiovascular disease.  Likewise the arguments for refined carbohydrates and excess sugars being the cause of obesity, diabetes and heart disease continue.

The reason that sugar can cause cardiovascular disease is because it contributes to inflammation of the arterial walls.  It does this by causing high insulin spikes.  When insulin in constantly spiking due to high sugar levels in the diet then it starts to damage the endothelial lining of blood vessels. When the lining becomes damaged then the body creates inflammation at the arterial wall, which is a well-known contributor to heart disease.  In addition, excessive sugar consumption can cause weight gain, which when combined with sustained high insulin levels can lead to insulin resistance and diabetes – which further increase the risk of cardiovascular disease Ref 10.

Despite the arguments on whether fat or sugar contribute most to these health conditions, it is clear that diets based on wholefoods that are high in antioxidants and low in processed foods, correlate to a lower level of these conditions.

Ethics & Consumerism

Today sugar is linked to numerous occasions and celebrations.  For example on Valentines day, Easter and Christmas the shops are fully stocked with aisles of sugar-filled gifts and treats. Although food has always brought people together at times of festivals, the quantity of sweets foods on the market today are more than ever before.  We feel we need to buy-in to these products in order to join the celebration, rather than returning to home-baked treats which has always been the tradition. Sugar is a huge industry and the consumerism around it is growing year on year.

When we think of the profits on sugar and consumerism, it is worth remembering that British colonists called sugar ‘White Gold’ when it was the engine of the slave trade in the early 16thcentury.

Commercial interest in sugar

The UK government and food industry are linked in many ways, which makes it all the more difficult to change what food manufacturers are putting in food.  Indeed the food industry is frequently consulted on government health policy.

We can conclude that not all sugars are equal.  Added sugars or ‘free’ sugars are the sugars that are of major concern to public health.  This includes all sugar, syrups, honey and fruit concentrates that are added to food. This form of sugar in our diet has risen significantly in recent decades and it is this sugar that has been linked to poor health e.g. diabetes, obesity and heart disease.  Of particular concern are foods such as sweets, cakes, pastries, biscuits and fizzy drinks.  The natural sugars found in fresh fruit and vegetables however are not a concern.  On the contrast, these sugars are found within foods alongside fibre, vitamins, minerals and antioxidants that enable the sugar to be processed efficiently and provide other health benefits.  Indeed a diet high in fibre, vitamins, minerals and antioxidants is key to helping to reduce blood sugar problems, such as diabetes, obesity and cardiovascular disease. One should be cautious of any sugar alternatives, as most are either manmade, or taken from a natural source but then used in a concentrated form.  Any type of sugar that is being used in large amounts or in high concentrates will put a stress on the body.

We therefore need to return to a diet that is rich in wholefoods.  This means foods that do not come in a packet and do not contain a list of ingredients.  This would include lots of fruit and vegetables, wholegrains (such as oats, brown rice, rye bread), pulses (such as beans and lentils), eggs, yoghurt, fish, chicken and red meat in moderation.  When we eat foods in their natural state then our diet automatically contains good levels of vitamins, minerals and antioxidants as well as our needed carbohydrates, proteins and fats.  This is essential for our long-term health and wellbeing.


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