Blog, Nutrition, Nutrition Science

Is sugar bad? The sweet and the sour


A subject within nutrition that continues to catch people out in their efforts to switch over to a better diet is sugar consumption, the addictive sweet taste with the possibility for sour after effects. It is a debate that has continued for years…is sugar bad? It is very common to find people seeking a ‘healthy’ option to sweeten their food – some magic elixir that will allow us to enjoy the taste, but not pay any potential consequences. This is not going to be a blog about artificial sweeteners such as aspartame and saccharin. To put it bluntly, they are not really a healthy alternative to sugar. They have their own set of concerns and we do not advise their intake. This blog is going to focus on nutritive sweeteners such as sugar, syrups and other foods used to add a sweet taste to our diet. we will also investigate whether there is a ‘healthy’ sugar option for the diet.

Sugar consumption

Getting straight to the key point, have you heard people refer to fruit as containing ‘healthy’ sugar? This illustrates one of the great points of confusion around the human diet. If something is natural and especially if it is plant-based there is an underlying assumption that it is therefore healthy and good for us. The majority of the world’s sugar production (170 million tonnes in 2016) is drawn from 2 naturally occurring plants, sugar cane and sugar beets. Whilst the sugars are drawn out of the plants through industrial processing, that does not change the compounds that existed in these plants already. In fact, there are many plants that actually have naturally higher levels of sugar and are much sweeter to taste than cane and beets. Most popular fruits are a classic example of this. In fact, many popular fruits today have been selectively bred to increase their sweetness (sweeter foods sell better) and as a result, contain more sucrose than the same fruits did just 30 years ago. The key consideration is why would the sugar in commonly consumed fruit be any healthier than the sugar found in cane or beets? Is it a different compound? Simply put, it is the same compound – sugar through and through! Now before you shout blasphemy, let’s acknowledge that whole fruit will also have some fibre, vitamins and minerals contained within it as well, but does this somehow negate the potentially damaging effects of the sugar component? Certainly, this should at least be questioned in the naturally occurring, higher sugar fruits like dates, raisins, prunes, figs, grapes, mango, pomegranate, bananas, cherries and passionfruit. It is no coincidence that several of these same high-sugar fruits are also the best-selling varieties in the supermarkets! More sugar, more sales. Simple formula, but it works.

The chemical structure of sucrose (sugar)

Sugar chemistry

Typical white, refined sugar is scientifically called ‘sucrose’ which is a combination of the basic units glucose and fructose in an approximately 50:50 ratio. Regardless of the source of the sugar, white table sugar, golden syrup, honey, fruit concentrate or whole fruit, the chemistry of the sugar is the same; it is still a blend of glucose and fructose. Glucose and fructose are composed of the same molecular elements as well. They both have 6 carbons, 12 hydrogen and 6 oxygen atoms. However, they do look a little different. Glucose is a 6 carbon hexagonal ring and fructose a 5 carbon pentagonal ring. These different shapes mean that the body has to metabolize them differently. We will get into that in a moment. 

Over the years these 2 molecules have developed different reputations in relation to health. Glucose has taken the brunt of abuse for disrupting our blood glucose levels, driving up insulin and playing a primary role in the causation of obesity and diabetes. Fructose has historically been branded as healthy because it is known as the fruit sugar. These half-truths have created several pervasive myths around the impact of certain foods on our health.

Glycaemic index

Glucose is the compound that serves as the basis of comparison for every other food listed on the Glycaemic Index. The glycaemic index argument is often cited for justifying the ‘is sugar bad’ case. Glucose is traditionally given a value of 100 and then other foods are tested and have their rate of absorption compared to glucose and given a respective value. Years ago when glycaemic index reached the awareness of the general public it was pointed out that fructose had a very low glycaemic index and therefore must be helpful in maintaining lower blood glucose levels. It was also promoted at the time as being diabetic ‘friendly’. That tag has quickly faded away as research has shown that fructose actually makes insulin resistance, the problem that underlies the diabetic condition, even worse!


Following digestion, glucose is absorbed directly through the gut lining into the bloodstream to be shipped around for use in body cells, especially the brain and nervous system. The majority of glucose that reaches the liver is converted into a perfectly safe storage form called glycogen. Glycogen is used to boost blood glucose when levels have dropped and food is not consumed. Following digestion, fructose is not delivered directly into the bloodstream. It is passed up a direct blood vessel between the intestine and the liver called the hepatic portal vein. Fructose metabolism is then managed by the liver and passes through different processes prior to being released into the blood again. It is this transport via the liver that gives fructose its low glycaemic index because it takes longer to impact on the blood. The delayed-release into the bloodstream does not make it ‘healthier’ just because it takes longer to influence wider circulation. Using glycaemic index to gauge the supposed ‘healthiness’ of sugar is therefore of little beneficial value. 


Whilst glucose has a very effective system for ensuring it enters the cells quickly without too many negative effects (it is controlled by insulin), fructose is a more complicated beast. There are several key concerns with the way fructose is managed within the body.

  • Significant amounts of fructose delivered to the liver cannot be metabolized by the cells and get converted to triglycerides (fat molecules that travel in the bloodstream).
  • Fructose alters liver enzyme function increasing liver insulin resistance (diabetic tendencies) leading to higher blood insulin and greater visceral fat storage (around the major organs).
  • Fructose undergoes the Maillard (browning) reaction 7 times faster than glucose, suggesting it may increase cellular glycation (sugars binding with proteins), ageing processes and cancer formation.
  • High fructose intake has been shown to have many similar effects on the liver as alcohol and maybe a contributory factor in non-alcoholic fatty liver disease.

Dr. Robert Lustig refers to fructose as the ‘…same poison as alcohol but without the buzz!’ Unlike alcohol, fructose is not metabolized in the brain and as such does not have the same deleterious effects on behaviour. 

Healthy sugar?

In deciding ‘Is sugar bad’ we also need to weigh up the nutritive sweeteners that typically carry a more healthy reputation. Well, you decide. Agave syrup (or ‘nectar’ as it is often called to make it sound better), even the organic variety, is normally between 70-95% fructose. Agave ‘nectar’ does not harbour a sweet liquid within the plant in these sugar concentrations, through industrial processing and exposure to enzymes the naturally balanced glucose-fructose blend is significantly altered to favour fructose and increase sweetness. Bearing in mind that the health-damaging reputation of industrial high fructose corn syrup (the sweetener of choice for the soft drinks industry) has been built on a 55% fructose blend, it doesn’t really bode too well for Agave. All the negative effects listed above will clearly be enhanced with richer doses of fructose being sent to the liver down the portal vein. Another option often used in health food bars and in ‘supposedly healthier’ tinned fruit is ‘fruit concentrate’ or fruit juice. This is exactly what the name suggests, the juice of a given fruit with the water boiled off so as to concentrate the sugars within. This will damage most of the vitamin content leaving primarily a concentrated source of sugar behind. In fact, it is not uncommon to find the most used juice concentrates are from apples, grapes and pears as these have some of the highest naturally occurring fructose content and taste even sweeter as fructose has 70% more sweetness than typical sucrose.


Simple squeezed fruit juice may not be concentrated, but it still allows for an increased intake of sugar compared to eating a whole piece of fruit. For example, a single apple has a glycaemic index of 40 and a glycaemic load of 6, whereas a glass of pure apple juice has a GI of 44 and a GL of 13 – more than double the volume of sugar within a comparative sized ‘portion’ of fruit. Glycaemic load (GL) refers to the volume or amount of total carbohydrate factored against its glycaemic index. A similar story of raised GL is found with most fruit juices when compared to whole fruit. Therefore, on this basis, it becomes difficult to see how pure fruit juice can be considered as beneficial to health as eating whole fruit. Twice the sugar in a single portion will only increase any possible negative impacts on the body and if it is apple, mango or grape juice you will get a hard liver-hitting dose of fructose as well! The fibre in whole fruit helps to bind and slow the impact of sugar on the body and provides beneficial bulk to the waste products within the digestive tract. 

Summary – Is sugar bad?

So what does all this boil down to? Is sugar bad after all? Sugar from any source is still sugar – it is sucrose, glucose and fructose. An important component of this discussion is the amount of sugar, the regular total daily amount of sugar that is consumed. The devil is in the dose! The body is a resilient organism, it can cope with high sugar intake now and again, once in a while. But sugar eaten in excess amounts, on a regular basis, over long periods of time will likely alter blood chemistry, overtax the liver and lead to potential chronic health problems. Science is steadily showing that processing foods to increase the fructose content has and is leading us further down the road of dysfunction and disease. Added, industrially refined sugars and syrups are having a detrimental effect on our health. Globally, the top 10 sugar-consuming nations range from 90g to 126g per person per day! This is shocking when you consider the World Health Organisation recommendation is to reduce added sugars to a maximum of 5% of daily calories. For a male consuming 2500 kcal/day, this amounts to 31g of sugar, and for females, on 2000 kcal/day, this is 25g of sugar as a maximum. This recommended volume of sugar is exceeded by just a single can or bottle of the majority of commonly available sports/energy drinks. We need to reduce our consumption of sugar-sweetened products…period!

Choosing to consume fruit juice doubles our sugar intake compared to eating whole fruit. Even modern breeding of sweeter fruits with higher glucose and fructose contents may yet prove to be another means of ingesting larger amounts of sugar! This is not to say that eating high-quality fresh fruit cannot be part of a ‘good’ diet. Of course, it can, but it is best eaten when it is fresh and whole and in moderate amounts. Up to 2 whole fruit portions, a day would be a suitable, average goal, maybe a little more in summer months, a little less in winter months, as would have been the case prior to high-speed global transportation of food.

But what about the all-important vitamins and minerals I hear you say? Firstly, all naturally occurring foods, from any source, plant or animal, contribute to our vitamin and mineral intake. It is not just fruits. To ensure adequate micro-nutrient consumption it would be best that we place greater focus on a wider variety of food types, especially a broad and plentiful supply of seasonal vegetables to draw in our needed vitamins, minerals and fibre. It may not be quite as convenient as fruit, but it will support greater health in the long-term. 

Do you want to learn more about nutrition? Get qualified with our excellent online course, the Nutrition for Health and Fitness Certificate from Nordic Fitness Education.