Coffee, Caffeine and Insulin

There are a large number of people today, who have adopted intermittent fasting as an element of lifestyle change. Among them are a significant number of diabetics, especially of the type 2 variant. A fair number of those intermittently fasting tend to drink black coffee as one of the usually recommended beverages whilst fasting. Is coffee really a suitable choice while practicing intermittent fasting? Is coffee alright for diabetics?

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One might think the answer to that question would be a resounding ‘Yes’, given the average cup of coffee has very few calories​​1​ and carbohydrates​​2​​, it would appear to be the ideal fasting beverage. Given however, that coffee contains quite a number of bio-active ingredients, which include caffeine, chlorogenic acids, cafestol and kahweol​​3​​, arriving at an accurate answer might not be a simple matter of counting calories and measuring carbs.

Did you know, the worldwide average annual consumption of coffee is about 4 kilos a year, and one of the highest recorded are Finnish residents, at 12 kilos consumed each year?

Before I continue, let’s keep in mind that our bodies’ response to insulin is a primary factor in the effectiveness of intermittent fasting, as well as in type 2 Diabetes. In a nutshell, Insulin stimulates glucose uptake, promotes lipogenesis while suppressing lipolysis, which means it helps the body use glucose (which carbs break down into), promotes the creation of fat and discourages the burning of fat​4​.

If the previous paragraph might have given you a hint that I’m going to share something of a connection between coffee and insulin, you’re right.

Looking at the research papers on the subject, there appear to be two substances in question – coffee and caffeine by itself. Also, there are two time frames that the research has evaluated – short term and long term consumption of each, with both having different outcomes. Finally, the research points to different conclusions for each of the framing criteria, so I’ll just list the various benefits and drawbacks as stated, and then do my best to draw some kind of a conclusion in the contexts of intermittent fasting and type 2 diabetes. Note that the term coffee refers to coffee with caffeine.

  1. Coffee is associated with lowered risk of type 2 diabetes, appears to improve fat oxidation in the liver, reduce the risk of steatosis (fat accumulation in liver cells) and also preserve functional beta cell mass (the cells in the pancreas that produce insulin)​5​.
  2. Coffee is associated with lowered risk of type 2 diabetes and in the long term, improved glucose metabolism and insulin response​6​.
  3. Coffee consumption over a 24 week period was not associated with any significant effect on insulin sensitivity or insulin resistance, but was associated with modest fat loss. This study was funded by Nestle7​.
  4. Caffeine ingestion in the short term reduces insulin sensitivity and might shift glucose homeostasis towards hyperglycemia​8​.
  5. Caffeine increases blood glucose levels and prolongs the period of high blood glucose​9​.
  6. Caffeine increases both, insulin resistance and beta cell function​10​.
  7. High coffee consumption in the short term resulted in higher fasting insulin concentrations​11​.
  8. Acute caffeine ingestion reduces insulin sensitivity in healthy subjects​12​.
  9. Coffee is associated with lowered risk of type 2 diabetes, caffeinated coffee impairs glucose metabolism, some types of decaffeinated coffee may acutely impair glucose metabolism but less than caffeine​13​.

My conclusion, based on the above findings, that caffeine has undesirable outcomes and coffee has desirable ones, is that the benefits of coffee appear to be about the many other bio-active compounds it contains, and that a shift to decaffeinated coffee might be therapeutic in the context of intermittent fasting and type 2 diabetes. What conclusion did you reach?


  1. 1.
    Huang C, Dumanovsky T, Silver L, Nonas C, Bassett M. Calories from beverages purchased at 2 major coffee chains in New York City, 2007. Prev Chronic Dis. 2009;6(4):A118. https://www.ncbi.nlm.nih.gov/pubmed/19754994
  2. 2.
    Girard P, Stöber P, Blanc M, Prodolliet J. Carbohydrate specification limits for the authenticity assessment of soluble (instant) coffee: statistical approach. J AOAC Int. 2006;89(4):999-1003. https://www.ncbi.nlm.nih.gov/pubmed/16915836
  3. 3.
    de Melo Pereira GV, de Carvalho Neto DP, Magalhães Júnior AI, et al. Chemical composition and health properties of coffee and coffee by-products. In: Advances in Food and Nutrition Research. Elsevier; 2020:65-96. doi:10.1016/bs.afnr.2019.10.002
  4. 4.
    Wilcox G. Insulin and insulin resistance. Clin Biochem Rev. 2005;26(2):19-39. https://www.ncbi.nlm.nih.gov/pubmed/16278749
  5. 5.
    Kolb H, Martin S, Kempf K. Coffee and Lower Risk of Type 2 Diabetes: Arguments for a Causal Relationship. Nutrients. 2021;13(4). doi:10.3390/nu13041144
  6. 6.
    Reis CEG, Dórea JG, da Costa THM. Effects of coffee consumption on glucose metabolism: A systematic review of clinical trials. Journal of Traditional and Complementary Medicine. Published online July 2019:184-191. doi:10.1016/j.jtcme.2018.01.001
  7. 7.
    Alperet DJ, Rebello SA, Khoo EY-H, et al. The effect of coffee consumption on insulin sensitivity and other biological risk factors for type 2 diabetes: a randomized placebo-controlled trial. The American Journal of Clinical Nutrition. Published online December 31, 2019:448-458. doi:10.1093/ajcn/nqz306
  8. 8.
    Shi X, Xue W, Liang S, Zhao J, Zhang X. Acute caffeine ingestion reduces insulin sensitivity in healthy subjects: a systematic review and meta-analysis. Nutr J. Published online December 2016. doi:10.1186/s12937-016-0220-7
  9. 9.
    Dewar L, Heuberger R. The effect of acute caffeine intake on insulin sensitivity and glycemic control in people with diabetes. Diabetes & Metabolic Syndrome: Clinical Research & Reviews. Published online December 2017:S631-S635. doi:10.1016/j.dsx.2017.04.017
  10. 10.
    Lee S, Min J, Min K. Caffeine and Caffeine Metabolites in Relation to Insulin Resistance and Beta Cell Function in U.S. Adults. Nutrients. 2020;12(6). doi:10.3390/nu12061783
  11. 11.
    van Dam RM, Pasman WJ, Verhoef P. Effects of Coffee Consumption on Fasting Blood Glucose and Insulin Concentrations: Randomized controlled trials in healthy volunteers. Diabetes Care. Published online November 23, 2004:2990-2992. doi:10.2337/diacare.27.12.2990
  12. 12.
    Shi X, Xue W, Liang S, Zhao J, Zhang X. Acute caffeine ingestion reduces insulin sensitivity in healthy subjects: a systematic review and meta-analysis. Nutr J. 2016;15(1):103. doi:10.1186/s12937-016-0220-7
  13. 13.
    Greenberg J, Owen D, Geliebter A. Decaffeinated coffee and glucose metabolism in young men. Diabetes Care. 2010;33(2):278-280. doi:10.2337/dc09-1539

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