Coffee and diabetes: What’s the connection?

One of the great controversies in nutrition is the role of coffee and human health. On the one hand, coffee is the primary source of polyphenols in the American diet because of the lack of consumption of fruits and vegetables. On the other hand, coffee is rich in caffeine, an alkaloid that acts as a stimulant on the central nervous system and is known to be an addictive agent (1). In fact, Roland Griffiths, professor of Behavioral Biology at the John Hopkins School of Medicine (and my old college roommate), says, “Caffeine is the world’s most widely used mood-altering drug.” So the question remains is caffeine good for you?

No one knows for sure, but one interesting point has been made that it appears the more coffee you drink, the lower your risk for developing diabetes (2). In fact, if you drink more than four cups of coffee per day, you decrease your risk of diabetes by 50 percent. This new research demonstrates that coffee increases the levels of sex hormone-binding globlin (SHBG) in the blood. As I pointed out in my book “The Anti-Aging Zone,” SHBG plays an important role in sequestering the levels of estrogen and testosterone in the blood so that levels of these unbound sex hormones that can interact with their receptors are tightly regulated (3). Usually as insulin resistance increases, the levels of SHBG decrease in the blood (4). This can lead to an over-stimulation of the receptors by the unbound sex hormones resulting in increased risk for breast and prostate cancer development.

What in the coffee actually causes the increase in SHBG is unknown, but what is known is that once you decaffeinate the coffee, all its benefits on the elevation of SHBG levels and any reduction in risk for diabetes disappear.

It is highly unlikely that caffeine by itself is beneficial for reducing type 2 diabetes, since there were no benefits related to drinking tea or to total daily caffeine intake (2). Perhaps some other compound that was also extracted with the caffeine may play a role in the reduction of type 2 diabetes.

So what really happens when you decaffeinate coffee? First, you soak the beans in water to remove the caffeine and flavors as well as the polyphenols. Then you treat the water with organic solvents (methylene chloride or ethyl acetate) to remove the caffeine (as well as many of the polyphenols and much of the flavor). Then (assuming you have removed all of the organic solvent), you add back the treated water extract to the beans to hopefully reabsorb some of the flavors back into them. Obviously, not all the flavors or polyphenols return since the resulting taste is far less robust than the original coffee bean.

So it seems to me that exploring what else has been extracted in addition to the caffeine may lead to new dietary treatments for diabetes. Whether that will be done is highly unlikely. Instead of waiting for such experiments, you might as well follow the best treatment for preventing diabetes, which is following the anti inflammatory diet for a lifetime. That is how you control cellular inflammation, which is the driving force for development of type 2 diabetes (5,6).


1. Juliano LM and Griffiths RR. “A critical review of caffeine withdrawal: empirical validation of symptoms and signs, incidence, severity, and associated features.” Psychopharmacology 176: 1-29 (2004)

2. Goto A, Song Y, Chen BH, Manson JE, Buring JE, and Liu S. “Coffee and caffeine consumption in relation to sex hormone-binding globulin and risk of type 2 diabetes in postmenopausal women.” Diabetes 60: 269-275 (2011)

3. Sears B. “The Anti-Aging Zone.” Regan Books. New York, NY (1999)

4. Akin F, Bastemir M, and Alkis E. “Effect of insulin sensitivity on SHBG levels in premenopausal versus postmenopausal obese women.” Adv Ther 24: 1210-1220 (2007)

5. Sears B. “Anti-inflammatory diets for obesity and diabetes.” J Coll Amer Nutr 28: 482S-491S (2009)

6. Sears B. “The Anti-Inflammation Zone.” Regan Books. New York, NY (2005)

Nothing contained in this blog is intended to be instructional for medial diagnosis or treatment. If you have a medical concern or issue, please consult your personal physician immediately.

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About Dr. Barry Sears

Dr. Barry Sears is a leading authority on the impact of the diet on hormonal response, genetic expression, and inflammation. A former research scientist at the Boston University School of Medicine and the Massachusetts Institute of Technology, Dr. Sears has dedicated his research efforts over the past 30 years to the study of lipids. He has published more than 30 scientific articles and holds 13 U.S. patents in the areas of intravenous drug delivery systems and hormonal regulation for the treatment of cardiovascular disease. He has also written 13 books, including the New York Times #1 best-seller "The Zone". These books have sold more than 5 million copies in the U.S. and have been translated into 22 different languages.

36 thoughts on “Coffee and diabetes: What’s the connection?

  1. So, if it is presumed that caffeinated coffee increases SHBC levels, is it OK to drink coffee when following a Zone lifestyle? I, myself, do not have insulin resistance, but I do tend to have an abnormal glucose tolerance, and I have been able to stave off Diabetes for a number of years while following the Zone. I switched to decaf back in 2004, but now am back to moderate caffeinated coffee intake. Will the coffee in addition to a balanced Zone lifestyle add to my success in the avoidance of Diabetes?

    • Everything in moderation is good. Of course, the word moderation is very slippery one. With an abnormal glucose tolerance I would really tighten down on the rest of your diet. The abnormal glucose intolerance is an indication of insulin resistance as a result of increased cellular inflammation. To reduce that cellular inflammation you have to look to the diet. This would be a better protein-to-carbohydrate ratio, a lowering of the total glycemic load, a decrease in omega-6 fats with an increase in omega-3 fats, and increasing polyphenol intake. The last one could include dark roasted coffee (the extra roasting releases more polyphenols), but would also mean more vegetables and fruits. With all those dietary adjustments, then the extra coffee in moderation would be OK.

      • Thanks for the reply. I will add that I have been practicing a zone lifestyle for many years, and have made the adjustments that you mentioned, including adjustment of the protein/carb ratio. I owe it to the Zone to have helped me prevent the progression of this condition.

        I currently do not have insulin resistance. This has been tested a number of times. Also, my fatty acid profile is really good, I owe that to the zone diet and fish oil.

        It is good to know that coffee is ok to add in moderation in the Zone. I do not rely on it for polyphenols; rather, I am glad that there is a benefit to drinking it. I would not dream of thinking about coffee as a replacement for the rainbow of nutrients that I can get from food!

  2. So when conclusions are draw and they use the word “diabetes” – - as in the great coffee article – - do they apply to type 1 and type 2 or only type 2 . . . and what about adult-onset type 1? thank you!!

  3. I am a type two diabetic and have a real hard time understanding how to count carbs. Can you help me understand how many carbs a day I mneed to lose weight.

    • Janet, if “counting” is what you want to do, then using the Zone Block system is a great way to accomplish it. I learned how to use the block system after reading “Mastering the Zone”, and I think you can still find a favorable food block list on Barry Sears’ other website

      Otherwise, just eat a lean protein approximately the size/thickness of the palm of your hand, fill the other 2/3 of the plate with low-glycemic veggies, and add a dash of mono-unsaturated fat. As a diabetic, you will do best by limiting your fruit intake to 1 serving per day.

  4. Hi Dr. Sears,
    I like your work. I have read that coffee actually sort of incapacitates the ability of your own insulin. It forces insulin levels to greater heights before it becomes effective.
    Is that correct or just a theory? I would think that if that is true it would push people towards Type II Diabetes?

  5. I’m glad to say that moderate coffee is allowed to people who are on the zone diet program. Actually, I’ve recommended them to cut back on coffee as you wrote in The Zone.

      • I am confused about the response re diet for type 2 diabetics. Do you still follow the Zone diet with the block ratios,while reducing fruit to one per day, & making sure you have 3 gms protein. –or do you increase the carb (vegetable) blocks?

  6. Hi Dr. Sears,

    I am a breast cancer survivor of 11 years now, and I know i owe it all to you and your books. I was just 35 years old when diagnosed with a very agressive type. I followed your advice to the letter. Funny thing now is that I own an organic coffee shop! I drink about 1 to two cups per day now, however, I do like 10 % cream in it!…just a little! The only thing that has happened to me over the years is that I have become intolerant to fish oil. I have switched them up, using only the best quality, but now I can not take it anymore. Have you ever heard of this happening? It makes me nausous, and makes my head/brain feel very uncomfortable..not a headache, just a very uncomfortable feeling.

    • I would try switching to organic green tea. The best quality fish oil can be described as that which has the lowest levels of PCBs. The only brand that meets that criteria is OmegaRx, which has the highest purity of any fish oil product with or without a prescription.

      • Ok, organic green tea it is…I will start tomorrow. I have purchased your fish oil, and will try it again….with small amounts to begin with. I will keep my esicosanoid records better too. I know I have definately not been in the “zone” as well as I once was! I can’t wait to get back there!
        Thanks again!

  7. Hi Dr. Sears
    Vicki’s comments regarding her bodies intolerance to fish oil is very interesting to me…in an effort to make sure I am getting the most anti-inflammatory benefits, I have switched to the Eico/RX for the past 8 months. Rather than taking 4 a day as recommended I started with 2. As I worked up to 3 and then 4 I noticed that diarrhea was becoming a problem. I have cut back to 2 a day and the “challenge” seems to be better. Is this a common?

    • The response to EicoRx is highly variable and that’s why a little experimentation that is required to find the optimal value for your genetics. That’s why the Eicosanoid Status Report is so useful in helping to fine-tune the correct dosage for an individual.

  8. Dr. Sears,
    I love the philosophy of moderation that’s behind the Zone, and no other “diet.” By following the Zone, I have lost 180 lbs, and will be going into the Army in a few months, at age 41.

    I gave up coffee not long ago, because I noticed other side effects… ones that a doctor probably would have treated with little blue pills. When I cut out the coffee, everything went back to normal. Could there be a connection with SHBG from the coffee?

    • Possibility Coffee didn’t really makes its appearance in the human diet until around 1560. Today it is the most widely used stimulant in the world. If our ancestors survived without coffee, then we also can.

      • Barry Sears says:
        February 24, 2011 at 8:37 pm

        Possibility Coffee didn’t really makes its appearance in the human diet until around 1560. Today it is the most widely used stimulant in the world. If our ancestors survived without coffee, then we also can.
        * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
        C’mon Dr. Sears,
        Our ancestors survived without ultra-refined purified high dose fish oil
        too, so, according to your logic, we also can. Please!

  9. How many ounces were in those 4 cups used in the study? I bet most people aren’t drinking 8 oz. cups… which is likely the size (or smaller) that the study used…

      • That’s why I asked how many ounces were in those 4 cups a day? If we assume they were 16 oz. cups that might be twice as much as they used if the study used an 8 oz. cup…

        How can you be “moderate” if you don’t know what that is?

  10. I have been following the Zone Lifestyle for a while (the copyright on my Zone book is 1996) and coffee was listed on the items to avoid – so it is nice to hear there are some positive health benefits to this. I haven’t been able to kick the caffeine habit but have switched from coffee to green tea – with all the benefits the of anti oxidants! I think it is worth the switch (perhaps even a separate blog on the health benefits for your readers).

  11. I was a little perplexed at gaining weight some 16 years ago while following some idiots low-fat diet that promised I would stay slim no matter how much fruit and pasta I ate so long as I avoided all fat. The book that told me this had a doctor’s recommendation on the cover. I was in a long line-up at a health food store when I picked up a copy of The Zone. As the line-up wound its slow path toward the check-out I skimmed voraciously through the book as it dawned on my that perhaps my weight gain had to do with not eating fat. By the time I arrived at the check-out I had decided to by the book and have been on the zone diet ever since. I soon lost my excess fat and believe that the zone has kept me healthier than I would otherwise have been.

    I am 63 and have recently been inflicted with erectile dysfunction. I love expresso coffee and have two to three cups daily. I’m wondering if increased levels of SHBG could be the cause of my erectile problems.

    • It is not unlikely. Expresso is especially rich in caffeine and the metabolic breakdown products of caffeine may be a problem with increasing age. I would suggest switching to green tea (if not just hot water) to see if you observe any benefits within 60 days.

  12. Hi Dr Sears, I am a mexican medical “Zonner” Practitioner, and I ask:do you know any evidence or study about coffee abuse as pancreatic cancer cause? Thank you.

  13. Friend shared your book with me. Husband has diabetes. Will ask specialist treating him about
    food block program versus American Diabetic Association program. He is on a med and insulin
    once a day. We’ve got work to do. Thank you, Mary Ann
    p.s. What are essential fatty acids? He also has a skin condition called Pemphigoid. Is there
    a test to check levels?

  14. I am now not certain the place you’re getting your information, but good topic. I must spend a while studying more or understanding more. Thank you for fantastic info I used to be looking for this information for my mission.

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