**Disclaimer: We are not medical professionals, nor do we claim to be. This article is not to be taken as medical advice. Always consult your doctor before changing diets or with any questions relating to your personal mental and physical health**
There is more to going refined sugar free than meets the eye. We've already uncovered some common places excess sugar lingers in the average British diet. We also discussed the general differences between refined sugar and natural sugar. Here, we will explore why fruit isn’t bad for you, but refined sugar is, by explaining how your body copes with refined vs fruit sugar.
The composition of table sugar and fruit sugars is very similar, yet our body processes them in different ways. They are both made up of two smaller sugars, glucose and fructose. Table sugar, or sucrose, carries these small sugars in a 50/50 split, while in fruit, they are typically present in a 40/60 – 55/45 mix. So why aren’t fruit classed as unhealthy in the same way sweets and cake are? To answer why fruit isn’t bad for you, we must start at the beginning with a quick look at how the body metabolises refined vs fruit sugars.
When you eat a biscuit, the treat travels down your digestive tract to your small intestine. There, the sucrose in the biscuit is broken down into its glucose and fructose constituents by an enzyme called sucrase. From here, glucose is transported out of the small intestine, leaving fructose behind (we will come back to fructose). Glucose travels into the blood to be delivered to the cells that need it for energy production (usually muscle and fat cells). However, in order for the glucose to enter these energy-hungry cells, insulin is required.
When your body detects that the level of glucose in your blood is higher than it should be, for example, after eating a big slice of cake, it orders your pancreas to secrete the hormone insulin to allow movement of glucose into cells that need it. This is the famous ‘insulin-spike’. It really is a clever system, but as with all clever systems, there is a catch. The more you expose your cells to insulin, the less sensitive they become to it. This means that over time on a high-sugar diet, your body will develop a resistance to insulin’s effects, and your pancreas will have to secrete more of it to get the same effect. This condition, known as insulin resistance, is a precursor to several endocrine disorders, especially Type II Diabetes. The more you subject your body to erratic insulin-spikes and unbalanced blood sugar levels, the more likely you become to store fat than if your body was fueled by slow-release carbs like fruit (more on this later).
Once in the cells, glucose goes through a series of biochemical reactions culminating in the production of 38 molecules of ATP per molecule of glucose. ATP is the primary energy carrier in all living organisms on earth and is essential to life. Most biochemical reactions within organisms require ATP to take place (even the reaction that produces ATP itself!). Excess glucose that is not needed by cells gets converted into a larger, complex carbohydrate structure called glycogen and is stored in the liver, ready to be broken back down into individual glucose molecules when blood sugar levels start to drop (e.g. during sleep or between meals).
Now, think back to the start of this biscuit’s journey. The glucose has left the small intestine and fructose remains. Fructose is transported across the small intestine wall into the bloodstream, but rather than going to cells around the body, it is taken to the liver. Because fructose uses different receptors to enter cells than glucose does, it does not trigger the insulin-response associated with the latter. This means that fructose is more readily absorbed by cells than glucose, as it is not regulated by a hormone.
Once in the liver, fructose can be turned into glycogen to replenish energy stores depleted during energy-intensive activity. This is why it’s generally a good idea to eat a piece of fruit after a workout, for example. But if the liver is already full of glycogen and continues to be overloaded with fructose, the body will turn the fructose into triglycerides, the main constituent of body fat.
A long chain of biochemical reactions enables fructose to turn into fat. Each step in this process of reactions is dependent on a specific enzyme. There are several ways in which your body can regulate enzyme activity to control and fine-tune the reactions occurring, for example inhibiting insulin when blood sugar is low. However, fructose metabolism is a largely unregulated mechanism, which means that, once started, its conversion into triglycerides is largely unstoppable (for more information on this, we highly recommend watching this video clip). While glucose is an essential molecule for life, fructose is not. Excess fructose consumption over time can lead to build-up of excess fatty deposits, obesity, and even non-alcoholic fatty liver disease.
So far, things aren’t looking good for fruit. We’ve learned the sugars present in refined and fruit sugar are exactly the same, biochemically speaking, and that the body does not distinguish between the sources once the micronutrients are in the body.
Now, before you freak out and bin your entire fruit bowl, there’s something you need to remember. Yes, fruit sugar is made of the same stuff as table sugar, but it is also packed with beneficial nutrients, antioxidants, minerals, and most crucially, fibre. This is the key to understanding why fruit isn’t bad for you in the way refined sugar is.
Fructose and glucose are stored within plant cells, between strings of fibre. The entire cell is encased in another fibrous mesh called the cell wall, which takes your body a lot of energy to break down. Only once the cell wall has been broken down do the sugars start trickling out. Because they are sequestered between the fibres in the cell, the sugars are released slowly and consistently into the blood. This prevents a surge of blood sugar that you would get with a biscuit or can of soda, even though the absolute sugar content might be the same.
Because releasing and digesting fruit sugars is a slower process than releasing refined sugars from sweet treats, your body has time to release and react to the satiety hormone leptin.
Leptin is released from fat cells and acts on the brain, telling your body that it has adequate energy stores, and so no longer needs to eat. When you feel very full after a meal, this is because your leptin levels are high. Because it takes about 20 minutes for leptin to really kick in, and refined sugars lack fibre and are released so quickly into the body, it becomes easy to binge on high-sugar foods without feeling full. This is why you could eat 10 biscuits in one sitting, but could only ever have 1 apple at a time before feeling full.
To summarise, fruit sugars and refined sugar are composed of the same smaller sugars, which are used to generate energy for the body in the form of ATP, and triglycerides. While fruit sugar has a high fibre content which helps your body regulate how much of it you consume, as well as a multitude of beneficial components like vitamins and antioxidants, refined sugar is stripped of all beneficial micronutrients and fibre during processing.
Because of this, consuming refined sugar is like fueling a fat-creation engine that doesn’t have any regulatory mechanisms in place to stop any damage to the organism consuming it. On the flip side, you will never binge on fruit because its fibrous nature and high water content induce satiety and ensure instead you get enough sugar for energy, but not excessive amounts that would be detrimental to your health.
As well as wreaking havoc on our bodies, sugar also messes with our minds. Sugar actually rewires your brain to make you crave it more. It has been shown to be as addictive as cocaine and opioids, with some of the behaviours exhibited during ‘sugar withdrawal’ mimicking opioid withdrawal behaviour to a remarkable degree.
Sugar, like drugs, causes the release of a brain chemical called dopamine, which is associated with a strong sense of reward and pleasure. When sugar is consumed, dopamine is released in a specific part of the brain; the nucleus accumbens. This is exactly what happens when a drug user takes a hit of a psychoactive stimulant like cocaine. In the absence of sugar, dopamine release in the nucleus accumbens decreases, and a different brain chemical, acetylcholine, takes its place. Again, this is exactly what happens in the brains of substance abusers in withdrawal.
These neurochemical changes in the brains of ‘sugar addicts’ and substance abusers are reflected in their behaviour. Typical addictive behaviours for both sugar and drug addicts include bingeing on high-sugar foods (or drugs) when they are available, craving them when they are absent, withdrawal symptoms of depression and anxiety, and sensitisation to their effects over time.
As neuroscientist Jordan Gaines Lewis put it, refined sugar “hijacks the brain’s reward pathway”. One study found that the brains of obese children light up differently when they taste sugar than brains of children of normal weight.
When we eat something delicious, we feel rewarded, and our dopamine levels spike. However, someone who has repeatedly experienced this delicious food will only be able to get a dopamine spike by anticipating the meal. So when that person eventually experiences that reward, the brain doesn’t light up as much because it has already been flooded with dopamine just from anticipation. The difference in brain scans illustrated above reflects an abnormal reward response in the obese cohort, very similar to the reward response experienced by cocaine drug users when interacting with the drug.
It is clear excess sugar has lots of negative effects on both body and mind, whether from refined or fruit sources. However, fruit carries so many other nutrients with it in addition to sugar that nourish the body. Fruit’s high fibre content prevents overdosing on fruit sugars, a mechanism lacking with refined sugar. The result is a higher likelihood to binge on high-sugar high-fat sweets than fruit, as well as more erratic insulin spikes through the day. Overall, sugar in fruit isn’t bad the way refined sugar is, and it actually is an excellent option to replenish energy.