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It's become part of popular nutrition advice that people should avoid foods that "spike" their blood sugar, with the belief that sharp rises and drops in blood sugar over time cause insulin insensitivity, pancreatic beta cell fatigue, or other metabolic harm. I mostly see this in discussions of the glycemic index or "slow carb" diets. A few examples: Glycemic Index foundation, Medical News Today, Healthline, United Healthcare

I understand that chronically elevated blood sugar can cause these problems, but what is the evidence that temporary high blood sugar is harmful in this way? I would be interested in long-term glucose monitoring studies, short-term biomarker studies, or even theoretical arguments.

To clarify some things:

  • Some people find that blood sugar spikes are followed by negative effects on mood, satiety, or cognition. I'm asking whether blood sugar spikes contribute to metabolic issues separately from that (ie, not because the person responds to a spike by eating sugary foods that lead to other health issues)
  • Extreme high levels of blood sugar can be unhealthy in other ways; I'm asking about sudden changes within a normal range (say, a rapid postprandial rise from 90 to 140, followed by a rapid drop), in people who do not have diabetes
  • I'm familiar with reasons for believing that prolonged high blood sugar leads to insulin insensitivity; I'm specifically asking about sudden, brief elevations.
  • High blood sugar variability can be caused by poor insulin sensitivity; I'm asking about the opposite direction
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    "a rapid postprandial rise from 90 to 140, followed by a rapid drop". I'm assuming you mean mg/dL. For teens and anyone younger, 150 is still considered within the "normal" range. For adults 20 and older, 140 is still considered normal at bedtime, and 130 is considered normal before a meal. So I assume you're talking about adults after 8 hours of fasting. What causes the sugar spike during the fasting? Any sugar consumption would put the adult in a non-fasting state, in which anywhere up to 180 can be considered normal
    – user1271772
    Mar 16, 2022 at 1:49
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    @user1271772 You need to make that an answer. It's way too much of an answer to be a comment.
    – Carey Gregory ♦
    Mar 16, 2022 at 3:48
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    I apologize, the last few days left me without much time to reply. Sorry to leave folks hanging after offering their help. I added some specifics and links to popular articles.
    – octern
    Mar 19, 2022 at 3:54
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    @octern Really interesting question. This study has found a correlation between blood glucose spikes in healthy individuals and an increased risk for diabetes (and these spikes were directly correlated to the carbohydrate content of foods), but of course the question of causation or correlation needs to be asked here.
    – Narusan
    Mar 19, 2022 at 17:52
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    Interestingly, in diabetics, post-prandial glucose spikes appear to be a better indicator of the risk for cardiovascular disease than average blood glucose concentration (by proxy: HbA1c), probably through accumulation of AGEs, Oxidative Stress etc. The review I linked here also appears to go into non-diabetic individuals, so it might be a really good resource for your question. I might turn this into a full answer later when I have time
    – Narusan
    Mar 19, 2022 at 17:58

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The October 2013 edition of Women's International Pharmacy newsletter (PDF) points out that:

Insulin is a hormone involved in the metabolic processes that convert food we eat into the fuel our bodies need to survive. As the maser fuel-supply hormone, insulin's main functions are to regulate the amount of blood sugar (glucose) that flows into our body's cells to create energy, and to communicate the need to refuel (that is, to eat or stop eating.

As pointed out by the Glycaemic Index foundation (in your link), when you eat sugary foods, it elicits a spike in blood sugar — a sharp rise followed by a sharp fall. The greater the glycaemic index (GI) of a food or meal, the greater that spike will be.

Because it knows that high levels of sugar in the blood is dangerous, the pancreas produces and then secretes insulin. The thing is, your cells must be “sensitive” (or responsive) to it. Eating a lot of high GI foods (sugary foods) makes your body used to the high levels of insulin in the body, leading to insulin resistance.

Glucose then remains in your bloodstream as it cannot be stored in your muscles, liver, or fat cells, which means elevated blood sugar levels (diabetes). A low GI diet is associated with lower blood sugar levels — measured by HbA1c levels in blood tests (Jenkins, et al. 2011).

References

Jenkins, D. J. A., Srichaikul, K., Kendall, C. W. C., Sievenpiper, J. L., Abdulnour, S., Mirrahimi, A., ... & Leiter, L. A. (2011). The relation of low glycaemic index fruit consumption to glycaemic control and risk factors for coronary heart disease in type 2 diabetes. Diabetologia, 54(2), 271-279. https://doi.org/10.1007/s00125-010-1927-1

Matter, A. W. (2013). Insulin resistance. Women's International Pharmacy newsletter https://collierdrug.com/wp-content/uploads/2021/10/Insulin-Resistance-A-Weighty-Matter.pdf

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