Macro photograph of a pile of sugar. Credit to Lauri Andler on Wikimedia Commons

This week, an article by Gary Taubes published in the New York Times has brought to our attention the ever growing concern of the effects of sugar on the human body. With reference to Robert Lustig’s lecture “Sugar: The Bitter Truth,” which discusses the toxicity of sugar, it has raised the question to biochemists and the public alike; what damage is this substance that we take for granted causing to our systems and how much sugar is consumed for it to become toxic?

Lustig, an expert in childhood obesity and pediatric hormone disorders, a specialist at the University of California; he believes that ‘sugar’, referring specifically to sucrose found in the refined cane sugar, and in additive high-fructose corn syrup, is one of the root causes of chronic illnesses such as heart disease, hypertension and common cancers.  This is what is contributing to the increasing percentage of the population that is obese, diabetic or both, across the western world.

Technically, refined cane sugar (sucrose) consists of a carbohydrate glucose molecule bonded to a molecule of carbohydrate fructose in a 1:1 mixture. The fructose, almost twice as sweet as glucose, distinguishes sugar from other starchy foods, such as bread or potatoes that when digested break down to glucose alone. The more fructose in a substance, the sweeter it will be, and in high-fructose corn syrup, as sugar is most commonly consumed, it is fifty-five percent fructose.

Traditionally, it has been preached that most sugars can cause tooth decay and they provide ‘empty calories’ that we consume in excess due to their appealing taste, leading to weight gain and other ailments. Thus it is assumed that sugar-sweetened beverages and highly processed foods are bad for us not because they contain ‘toxic’ sugar but simply because people consume them in excessive amounts.

However, Lustig’s concern is not about the consumption of ‘empty calories’ but more scientifically that sugar has unique molecular characteristics that cause the human body to metabolise it in such a way that may be harmful if consumed in these excessive quantities. We could ingest one hundred calories of glucose from a starchy source such as a potato or bread or one hundred calories of sugar, sucrose or fructose, and they will be metabolised differently and have a different effect on the body despite the calories being the same.

This is because the fructose in sugar is metabolised primarily by the liver, while glucose is metabolised by every cell in the body. Therefore by consuming sugar (fructose and glucose combined) it is causing the liver to exert itself more than if it consumed the same number of calories of glucose alone and makes it work quicker.

An observation of laboratory rats and mice saw that if the fructose hits the liver in a significant quantity and with sufficient speed, the liver will convert the majority of it into fat. If this has the same effect on the human body, and we are consuming enough sugar to cause this, then it does prove to be a toxic substance, as this can then induce insulin resistance, which is considered the fundamental problem of obesity, and one of the underlying causes of heart disease and type 2 diabetes.

For this reason Lustig believes these types of sugars should be thought of similarly as cigarettes and alcohol, a substance that can eventually kill, which is much more ominous than previous claims of just being an unhealthy treat in our diet. Nevertheless, it can be argued that many substances can be toxic if consumed in excessive quantities unnatural to the human system. So when does consumption of sugar in our diets go from harmless to harmful?

Nutritionists recommend that forty pounds of sugar per person per year is a ‘healthy’ amount that should be consumed, which can be translated into 200 calories of sugar per day; less than in two glasses of apple juice. But this is not the reality of modern society’s daily habit and I am certainly guilty of consuming more sugar than what is considered ‘healthy’ for the human body.

Although is sugar as bad as Lustig warns? It certainly could be. It is true that refined sugar and high-fructose corn syrup, because of the unique way in which we metabolise fructose and at the levels we now ingest it, cause fat to accumulate in our livers, which leads to insulin resistance, a common factor in heart disease, diabetes and obesity. However, it takes years for this damage to manifest; until long-term studies are conducted scientists will not know for certain the true damaging effects of the substance. Lustig points out that sugar are certainly not an “acute toxin” which can be studied over the course of a few days or even months. The question is whether they are “chronic toxins,” which means that studies will have to continue for a significantly longer time until the research is proved more conclusive.


Yasmin Sidana