35. Is Sugar Toxic?

Dr Robert Lustig is a leading expert in childhood obesity at the University of California, San Francisco. He has constructed a formidable comprehensive case that explains why diet is primarily responsible for the development of a range of diseases/conditions which are now referred to as Metabolic Syndrome. These include obesity, diabetes, hypertension and heart disease all of which are closely related and probably have a common cause. In particular he identifies the fructose which makes up about half of both ordinary table sugar and the High Fructose Corn Syrup(HFCS) that is widely used in the USA as the specific critical factor.

Lustig’s rationale has been spelled out in a YouTube video entitled “Sugar: The Bitter Truth” which was uploaded on 30 July 2009 and has already been viewed by almost 3.5 million times(1). Clearly it has stimulated enormous interest. Inevitably there has been criticism which is only to be expected (not least from the industrial organisations which produce sugar and HFCS). Nevertheless he is definitely striking a chord with many people and has undoubtedly delivered a series of arguments that merits detailed consideration.

The key point Lustig makes is that the glucose and fructose, which are released from sugar and HFCS, are metabolised in different ways and therefore have totally different effects in the body. The glucose can be utilised by every cell in the body whereas the fructose must be metabolised by the liver which converts it into fat. Essentially the fructose is metabolised using the same biochemical pathways as are used for alcohol. When there are excessive amounts of fructose (and alcohol) the result will be the condition known as “fatty liver” which is associated with the development of “insulin resistance”. This means that there are increasing demands on the pancreas to produce more and more insulin in response to a rise in the blood sugar. Ultimately the pancreas is unable to cope (pancreatic exhaustion) and so the blood sugar is out of control which results in Type 2 diabetes(T2D) and related diseases/conditions including Alzheimer’s Disease which is often referred to as “Type 3 diabetes”. Fructose also fails to suppress the production of the hormone ghrelin which causes hunger so that a high consumption of fructose is likely to stimulate overeating.

Exercise is considered beneficial not because it burns up calories but because the fructose is utilised for energy and not converted into fat. This means that a higher intake of fructose can be tolerated by a person who is physically active compared with one who is sedentary.

Lustig considers that sugars which contain fructose are chronic toxins and should be controlled by legislation in the same way as alcohol, tobacco and drugs such as cannabis, cocaine and amphetamines. He is currently on a campaign to persuade politicians to take action and is apparently having some success. In New York Mayor Michael Bloomberg has spearheaded a successful drive to ban restaurant and concession stand sales of sugary drinks bigger than 16 ounces. In the United Kingdom – which has one of the highest child obesity rates in Europe – the shadow health secretary, Andy Burnham, made headlines by calling for a ban on the sale of breakfast cereals with more than 30 percent sugar.

Although Lustig focuses on fructose as the real culprit, his view that glucose is relatively benign has been challenged by Peter Attia in a comment on his blog(2). He accepts that fructose is definitely a major cause of obesity and Metabolic Syndrome but also points out if there is a high intake of glucose this will stimulate the production of high levels of insulin, which in turn will promote fat storage. The excessive consumption of glucose (eg from sources of starch such as bread, rice and potatoes) is likely to be facilitated if the ghrelin has not been suppressed.

It should also be noted that cancer cells are critically dependent on glucose as a source of energy and there is some evidence that certain cancers can be controlled by limiting intake of glucose. For the record, several leading cancer specialists have stated publicly that personally they are very careful about the amount of sugar they eat.


  1. http://www.youtube.com/watch?v=dBnniua6-oM
  2. http://eatingacademy.com/nutrition/sugar-101-how-harmful-is-sugar-part-i


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