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Sugar Toxicity And The Paleo Diet

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Can our love of sugar be killing us?  Everybody loves sugar and this love may be one of the main causes for Western societies many health problems.  At least, that’s what Dr. Robert Lustig believes.  On May 26 2009, Lustig who is a lecturer at the University of California, San Francisco, School of Medicine gave a lecture titled “Sugar: The Bitter Truth” in which he described sugar as poison and that it is the likely cause of many western diseases such as heart disease, diabetes, hypertension and several cancers.  After listening to a replay of the lecture on YouTube, I began to see how his paradigm and the paradigm of the Paleo Diet coincide.

To clarify Dr. Lustig’s position, he doesn’t state that all sugar is bad.  After all, sugar is a carbohydrate that is found in fruit (fructose). Rather, the sugar he considers poison is refined sugar and high fructose corn syrup. Refined sugar is made up of a molecule of the carbohydrate glucose, bonded to a molecule of the carbohydrate fructose in a 50/50 ratio. Fructose is almost twice as sweet as glucose, so the more fructose a product has, the sweeter it is. The ratio of high fructose corn syrup is 55% fructose to 45 % glucose. Because each of these sugars ends up as glucose and fructose in our guts, our bodies react the same way to both, and the physiological effects are identical. 

So what if glucose and fructose react the same way in our bodies? They are both just empty calories. According to Lustig, there is more to it than that. He and other biochemists believe refined sugar has unique characteristics, specifically in the way the human body metabolizes the fructose in it, that may make it singularly harmful, at least if consumed in sufficient quantities. [i]   He believes that 100 calories of glucose and 100 calories of refined sugars are metablozied differently.  The fructose component of refined sugar and high fructose corn syrup is metabolized primarily by the liver, while the glucose from sugar and starches is metabolized by every cell in the body. Consuming sugar (fructose and glucose) means more work for the liver than if you consumed the same number of calories of starch (glucose). Sugar taken in liquid form such as soda will hit the liver more quickly than if you consume them, say, in an apple.[ii]

Laboratory studies have shown when fructose hits the liver in sufficient quantity and with sufficient speed; the liver will convert much of it to fat. This is known as insulin resistance, and is now considered the fundamental problem in obesity, and a factor in heart disease and type 2 diabetes.

How does the idea that sugar is toxic relate to the paradigm of the Paleo Diet?  The Paleo Diet is based on the idea that the Homo sapiens body underwent major evolutionary development during the Palaeolithic era and that our bodies are designed to eat a diet comprised of foods consumed during this time period. For more information about the Paleo Diet read What is the Paleo Diet.  A Palaeolithic diet or caveman diet is heavy on fruits, vegetable and lean animal protein.   

The fact that refined sugars such as sucrose and high fructose corn syrup affect the liver differently than natural sugars helps illustrate the fact that the human body was not designed to consume sugars in this molecular format.  Refined sugars are quickly turned to fat and natural sugars are readily turned to energy by our cells.  

Our bodies are designed to eat sugars from a natural source such as fruit and vegetables. The idea that sugar is toxic fits the Paleo Diet paradigm. We are designed to eat a diet of fresh fruits, vegetables, seafood and other lean animal proteins. We are not designed to eat refined foods created by western civilization. We are designed to follow a Palaeolithic diet.


[i] New York Times Magazine, April 17 2011,  P. MM47

[ii] New York Times Magazine, April 17 2011,  P. MM48-49

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About Layne Pennell

  • Edward J. Cunningham

    If you pay attention to the lecture, Dr. Lustig does not make a distinction between “natural sugar” and “refined sugar.” He states unequivocably that fructose is bad for you—even the frutose in fruits. However, in eating fruits you are also getting fiber and essential nutrients. The fiber also curbs your hunger so you don’t eat too much fructose, thus limiting the damage.

  • anthroqueen

    during the paleolithic time period, humans got most of their protein from insects. so technically, a paleo diet should be high in fruits, vegetables, and insects.