Mysterious protective effects of coffee against diabetes have been reported in the past. A 2010 meta-analysis analyzing data from 18 studies reported that each additional cup of coffee consumed per day was associated with a 7% reduction in risk of diabetes.1 This was surprising, especially because coffee consumption has been shown to raise glucose levels after a meal so you would expect it to worsen diabetes, not help it. However, this is true of both decaffeinated and regular coffee, although regular coffee raises blood glucose more than decaf.2
The reason for the decreased diabetes risk remains uncertain, but since coffee comes from a darkly colored bean, it is likely that antioxidants, minerals, or other phytochemicals present in coffee may be responsible for the long term benefits seen in the observational studies.3 With this in mind, we must also remember that almost all of the subjects in the observational studies were eating the standard American diet and therefore starving for antioxidants and phytochemicals.
Is the standard American diet so nutrient-poor that a significant portion of people’s phytochemical intake comes from their morning coffee?
It’s likely. Additional studies support this possibility. One observational study of 28,000 postmenopausal women actually found that decaffeinated coffee was more protective than regular coffee – which suggests that the caffeine in coffee might be increasing risk, while the phytochemicals decrease risk.4 Chlorogenic acid and trigonelline, two of the major phytochemicals in coffee, have been shown to decrease blood glucose and insulin concentrations in the blood compared to placebo after ingesting sugar, so these phytochemicals likely increase insulin sensitivity.5 It is doubtful that coffee would offer any additional protection on top of a nutrient dense diet - the responsible phytochemicals can be obtained from other plant foods and the diet would not be so lacking in antioxidants. For example, blueberries contain the antioxidant chlorogenic acid, and the phytoestrogen trigonelline is also found in peas, lentils, soybeans, and sunflower seeds. 6-8 The only reason coffee is beneficial is because of the severe deficiencies in the plant-derived phytochemicals in the diet of most Americans, and coffee at least supplies something.
New research has found something that makes the insulin desensitizing effects of caffeine even worse - ingesting caffeine with a high-fat meal.
High-fat meals are another factor known to impair glucose tolerance, and saturated fat consumption causes the body to produce inflammatory molecules that contribute to insulin resistance.9 This study demonstrated caffeine consumption and a high-fat meal had additive insulin desensitizing effects, and this did not merely raise the blood glucose - but also when the insulin doesn’t work well the body has to make more of it, and higher insulin causes weight gain and increases cancer risk.10-12 When subjects ingested a high-fat meal followed by a sugary drink, and blood glucose levels were 32% higher compared to subjects who had water in place of the high-fat meal. In the second part of the study, subjects were given two cups of caffeinated coffee in addition to the high-fat meal and sugary beverage – this time, blood glucose was even higher – 65% higher than the subjects who had only water before the sugary drink.13 Apparently, coffee can have good or bad effects on insulin depending on whether it is consumed with high fat animal products or not.
The message here is that coffee can be both good and bad, but its powerful addictive qualities, with the potential for withdrawal headaches and to increase blood pressure should make people cautious;14-16 the most likely risks are almost never mentioned in news reports. I do not think anyone should rely on coffee to protect themselves against diabetes. If you do choose to drink coffee, stick to water-processed (non-chemical) decaf, and of course skip the doughnuts!
1. Huxley R, Lee CM, Barzi F, et al: Coffee, decaffeinated coffee, and tea consumption in relation to incident type 2 diabetes mellitus: a systematic review with meta-analysis. Arch Intern Med 2009;169:2053-2063.
2. Greenberg JA, Owen DR, Geliebter A: Decaffeinated coffee and glucose metabolism in young men. Diabetes Care 2010;33:278-280.
3. Tunnicliffe JM, Shearer J: Coffee, glucose homeostasis, and insulin resistance: physiological mechanisms and mediators. Appl Physiol Nutr Metab 2008;33:1290-1300.
4. Pereira MA, Parker ED, Folsom AR: Coffee consumption and risk of type 2 diabetes mellitus: an 11-year prospective study of 28 812 postmenopausal women. Arch Intern Med 2006;166:1311-1316.
5. van Dijk AE, Olthof MR, Meeuse JC, et al: Acute effects of decaffeinated coffee and the major coffee components chlorogenic acid and trigonelline on glucose tolerance. Diabetes Care 2009;32:1023-1025.
6. Zheng W, Wang SY: Oxygen radical absorbing capacity of phenolics in blueberries, cranberries, chokeberries, and lingonberries. Journal of Agricultural and Food Chemis ry 2003;51:502-509.
7. Rozan P, Kuo YH, Lambein F: Nonprotein amino acids in edible lentil and garden pea seedlings. Amino Acids 2001;20:319-324.
8. Sanchez-Hernandez L, Puchalska P, Garcia-Ruiz C, et al: Determination of trigonelline in seeds and vegetable oils by capillary electrophoresis as a novel marker for the detection of adulterations in olive oils. Journal of Agricultural and Food Chemis ry 2010;58:7489-7496.
9. Wen H, Gris D, Lei Y, et al: Fatty acid-induced NLRP3-ASC inflammasome activation interferes with insulin signaling. Nat Immunol 2011.
10. Bowker SL, Majumdar SR, Veugelers P, et al: Increased cancer-related mortality for patients with type 2 diabetes who use sulfonylureas or insulin. Diabetes Care 2006;29:254-258.
11. Davies M, Gupta S, Goldspink G, et al: The insulin-like growth factor system and colorectal cancer: clinical and experimental evidence. Int J Colorectal Dis 2006;21:201-208.
12. Harish K, Dharmalingam M, Himanshu M: Study Protocol: insulin and its role in cancer. BMC endocrine disorders 2007;7:10.
13. Beaudoin MS, Robinson LE, Graham TE: An oral lipid challenge and acute intake of caffeinated coffee additively decrease glucose tolerance in healthy men. J Nutr 2011;141:574-581.
14. Giggey PP, Wendell CR, Zonderman AB, et al: Greater Coffee Intake in Men Is Associated With Steeper Age-Related Increases in Blood Pressure. Am J Hypertens 2010.
15. Noordzij M, Uiterwaal CS, Arends LR, et al: Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials. J Hypertens 2005;23:921-928.
16. James JE: Critical review of dietary caffeine and blood pressure: a relationship that should be taken more seriously. Psychosom Med 2004;66:63-71.