is sugar really toxic?

You may have noticed a lot of people quitting sugar [1] or saying sugar is toxic. [2]

But what does the food insulin index data have to say about sugar?  Is it any different to other forms of carbohydrate?

The chart below of sugar content versus insulin demand indicates that sugar plays some role in insulin, however the correlation is weak, at least compared to carbohydrate.  If we want to manage our insulin load we’re probably best to consider our total carbohydrates rather than isolating sugar alone as the only problem.

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I ran a correlation analysis on the food insulin index data to see if sugar had a unique effect on insulin compared to non-sugar carbohydrate.

The data suggests that sugar does not generate more insulin than other forms of carbohydrates.  If anything sugar requires slightly less insulin on a gram for gram basis compared to carbohydrates.

This could be because sugar is metabolised quickly and the body pushes out a short burst of insulin to clear the sugar from the blood rather than a long persistent effort which might be the case for a lower glycemic index carbohydrate.


This is not to say that sugar is good for you.  There are obvious issues with consuming significant amounts of sugar including:

  1. Sugar has no fibre and has a very high calorie density so it is not filling and you can end up eating lots of it without feeling full.
  2. Refined sugar has a very low nutrient density, and your body is left searching for nutrition in more food and hence will be prone to over consume calories.
  3. Sugar will cause your blood sugar to rise quickly, your body will produce a burst of insulin which will cause your blood sugar to subsequently crash after the insulin surge and leave you feeling hungry again, craving more sugar to make you feel ‘right’ again.

By contrast, the carbohydrates in non-starchy veggies (e.g. spinach, kale, avocado, asparagus) come packaged with fibre, digest slowly and will leave you feeling full, raise your blood sugar gently and are very hard to overeat. [3].

If you have some form of metabolic dis-regulation (e.g. diabetes, obesity etc) then you need to be thinking about everything that raises your insulin, not just sugar.

[next article… glycemic load versus insulin load…  which one is best?] [this post is part of the insulin index series] [Like what you’re reading?  Skip to the full story here.]



[3] I’m not going to deliver into the fructose / glucose issue.  If you want to go there check out or the condensed Shaun Croxton version at

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Marty Kendall

  • Elizma says:

    Interesting. As always…moderation.

  • Wendy G says:

    yeah, good point about sugar having even less impact on BG than white or wheat bread, but I don’t think the question of whether sugar is toxic ends with effects on BG, or even the lack of nutrients or fiber. one thing that sets sugar apart is where and how it is metabolized – namely, that fructose is only metabolized in the liver, and that it must be converted to fat first in order to be used by the body. Hence why children are getting fatty liver disease, previously unknown in this demographic. This helps demonstrate what I think can be called a “toxicity” or at least risk of harm for sugar or fructose alone that’s not present in other carbs.
    Also, don’t know if you’ve seen it yet but Rob Lustig posted a new study on his FB page yesterday claiming it shows differences between fructose levels and levels of harm; I haven’t read it yet, but it sounds like it also may speak to the specific toxicity of sugar.
    Cheers. Great topic.

    • martykendall says:

      Thanks for following Wendy.

      I appreciate your feedback.

      In your comment yesterday you mentioned Richard Feinman’s new book.

      I just read Chapter 8 where Feinman basically makes the same argument, that it’s irrelevant to debate if you’re going do fructose versus glucose if both are going to cause diabetes if you can’t handle the sugar.

      I’ve watched Lustig’s videos and read most of his book, but I don’t claim to be an expert on the subject of fructose metabolism.

      I’ve also heard Lustig talk about the importance of fibre which is something I’m passionate about which directly reduces the overall insulin load.



      • Wendy G says:

        Hi Marty – thanks for your reply. My info on fructose metabolism doesn’t come so much from Feinman’s text – I found his comments less than clear, and haven’t yet read the blog post about fructose that he references in his book. My info re fructose metabolism comes from Volek & Phinney, Art & Science of Low Carb Living, Chapter 6, Section 4, titled “Fructose – a sugar that partitions like fat.”. If Feinman disagrees with that description, I might be inclined to defer to him as he is the biochemist, but I can’t tell whether he does or not. Can you? All best.

  • Barry says:

    What about Ray Peat’s take on sugar/fructose?

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