In the last post we looked at the way in which fructose is essentially throwing us double punches. It is a main player in a global obesity crisis, not only because it is highly calorific but also because it is throwing off our appetite–control system. In this post we are going to look more at Dr Lustig’s research, illustrating that a calorie is not a calorie and that sugar is one of the more important contributors to a number of chronic health problems (if you thought double punches were bad, this is where it gets Bruce Lee).

Metabolic syndrome

Although Metabolic syndrome has slightly varying definitions, it is characterised by conditions like type 2 diabetes, obesity, heart disease and high blood pressure. And we are experiencing a rapid increase in all of them. Even more worryingly, all of these conditions are now found in children as young as five years old, indicating that this is the first generation that will die younger than their parents1.

Carbohydrates unpacked

Lustig describes the way in which sugar can be linked to all the chronic conditions associated with metabolic syndrome and more. To look at this we are going to see what happens in the body when we consume glucose compared to when we consume fructose.


When it exists in nature without fructose, it is often as “starch”, think rice, potatoes, bread and it is used by the body for either energy storage or burning. Glucose is used by every cell in your body and is an absolute necessity for life. However despite this, there are some metabolic downsides.

Here’s what happens to your body when you eat 120 calories of glucose – half a cup of white rice:

  1. As we saw in the previous post, consuming glucose will (unless of course you are glycogen depleted) raise its level in the bloodstream, which promotes energy storage into fat cells and leads to weight gain. Most of the glucose in the liver will be turned into glycogen, or liver starch. This is not harmful to the liver cell and will stop the liver releasing glucose into the blood, therefore avoiding setting the stage for the development of diabetes. Excess glucose, which has not been used elsewhere in the body, will be converted into triglycerides. High triglyceride levels in the blood can promote the development of cardiovascular disease.
  2. If you gain too much weight from glucose, the visceral fat (this is the dangerous type that accumulates around your organs) that will be formed will eventually take its toll on your health.
  3. Therefore, glucose in excess can be bad for you, especially when it lacks fiber, which limits the insulin response. For that reason, excessive consumption is probably not advisable, especially for those with low activity levels. These negative effects however, happen over a long period of time and though over-consumption will make you fat it will take a long time before it makes you sick, unlike fructose2.


This is where we see the way in which sugar is wreaking havoc on our bodies and the way in which a calorie is most definitely not a calorie. Here’s what happens to your body when you consume the same 120 calories in sugar, think a large glass of orange juice:

  1. High blood pressure: Unlike glucose, which can be metabolized by all organs, the liver is the primary site for fructose metabolism 3. The whole number of calories from fructose end up in the liver, triple the amount from glucose alone. This means the liver needs triple the amount of energy to metabolize it. This depletes the liver of adenosine triphosphate (ATP – a vital chemical the conveys energy within the cells). This leads to the waste product uric acid. Uric acid causes gout and increases blood pressure.
  2. Heart disease: Fructose does not get converted to glycogen, what can’t be metabolized by the liver cells is converted to fat, a contributing factor in the development of heart disease4.
  3. Insulin resistance: Fructose activates a liver enzyme, which inactivates insulin action, leading to liver insulin resistance 5. Fructose may also lead to a breakdown of the intestinal barrier contributing to “leaky gut”6 which increases inflammation in the body. This worsens insulin resistance and drives insulin levels even higher7.
  4. Diabetes: The lack of insulin effect in the liver means there is no way to keep the glucose down, so blood glucose rises, which eventually can lead to diabetes.
  5. Visceral fat: The liver insulin resistance means the pancreas has to release extra insulin, which can force extra energy into fat cells, contributing to obesity. The fat cells that fill up most are in the visceral fat, the bad kind associated with metabolic disease.
  6. Obesity: The high insulin blocks the leptin signalling giving the hypothalamus a false sense of “starvation”, causing you to eat more (as we saw in the previous post).

Here we have all the features of metabolic syndrome and if that wasn’t enough…

  1. Cancer:The high insulin can also drive the growth of many cancers8.
  2. Aging, cancer and cognitive decline. Fructose alters the hemoglobin in your red blood cells causing what is known as the Mallard, or “browning” reaction (it is the same reaction that takes place when you brown your meat in a pan). It causes every cell in the body to age more rapidly, driving various degenerative processes such as aging, cancer and cognitive decline. This process happens seven times faster with fructose than with glucose9.
  3. Dementia: Insulin resistance has been implicated in the development of dementia10.

The toxic truth

So, who’s for ice cream? While we can note that these effects occur with excess consumption and there are situations (such as for endurance athletes) when fructose may be useful to replenish glycogen stores more rapidly, the average person is eating above and beyond safe limits.

As we can see from this comparison, it is quite apparent that a calorie is not a calorie. Sugar, in excess, is toxic to the body due to the way in which it metabolized, it is making us fat and it is also making us sick. In fact, Lustig argues that sugar is equally toxic to alcohol (ethanol is also a carbohydrate). Although space prevents us from going in to the way in which ethanol is metabolized here, to summarise, the only difference between sugar and alcohol is that sugar is not metabolized in the brain. Sugar is alcohol without the buzz 11, its only bonuses could be that you may be able to avoid acting like an idiot or wrapping your Volvo around a tree.

If you would like to know more do check out his book or YouTube lectures. In the next post we will look at the ‘antidote’, the role that exercise plays (this also does not work in the way you might think) and the treatment plan that Lustig implements with the obese children who visit him in his clinic in California.


  1. S. J. Olshanky et al., “A Potential Decline in Life Expectancy in the United States in the 21st Century,” New Engl. J. Med. 352 (2005): 1138-45
  2. R. H. Lustig, Fat Chance: The Hidden Truth About Sugar, Obesity and Disease (2014) p.120-121
  3. A. Kolderup and B. Svihus “Fructose Metabolism and Relation to Atherosclerosis, Type 2 Diabetes, and Obesity, J Nutr Metab. 2015; 2015: 823081
  4. V.T. Samuel,”Fructose Induced Lipogenesis: From Sugar to Fat to Insulin Resistance,” Trends Endocrinol. Metab. 22 (2011): 60-65
  5. Elliot et al. “Fructose, Weight Gain, and the Insulin Resistance Syndrome,”Am J. Clin. Nutr. 76 (2002) 911-922 
  6. S. Thuy et al., Nonalcoholic Fatty Liver Disease in Humans Is Associated with Increased Plasma Endotoxin and Plasminogen Activator Inhibitor 1 Concentrations and with Fructose Intake,” J. Nutr. 138 (2008): 1452-55.
  7. M. Maersk et al., “Sucrose-Sweetened Beverages Increase Fat Storage in the Liver, Muscle, and Visceral Fat Depot: A 6-Mo Randomized Intervention Study,” Am J. Clin. Nutr. 95 (2012): 283-89; N. K. Pollock et al., “Greater Fructose Consumption Is Associated with Cardiometabolic Risk Markers and Visceral Adiposity in Adolescents,” J. Nut. 142 (2012): 251-57.
  8. R. J. Shaw et al., “Decoding Key Nodes in the Metabolism of Cancer Cells: Sugar and Spice and All Things Nice,’ F1000 Biol. Rep. 4 (2012): 2.
  9. W. L. Drills, “Protein Fructosylation: Fructose and the Maillard Reaction,” Am. J. Clin. Nutr. 58 (1993): 779S-87S
  10. R. H. Lustig, Fat Chance: The Hidden Truth About Sugar, Obesity and Disease (2014) p.122-124
  11. Sugar: The Bitter Truth
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