Ever since I discovered the glycemic index a dozen years ago, I thought that I knew that anything we eat or drink has to have calories for it to raise our blood glucose levels. In fact, those calories have to come from carbohydrates – not protein or fat – to give those levels much of a spike.
Now, however, new studies have found a strange and disturbing exception to the rule.
That exception is coffee. The fact that drinking coffee will increase my blood glucose is particularly disturbing to me, because like most Americans who have diabetes it’s what I use to come to my senses every morning.
The amount of the increase can’t compare with the glycemic boost that we get from eating a baked russet potato or even a slice of wheat bread. But it can be enough to explain some otherwise inexplicable levels.
Black coffee has no calories. But testing by three scientists at the Duke University Medical Center in Durham, North Carolina, revealed that a moderate dose of caffeine in black coffee (equal to four 8-ounce cups of brewed coffee) increased average levels of daytime glucose from 133 mg/dl (7.4 mmol/L) to 144 mg/dl (8.0 mmol/L) among the 10 habitual coffee drinkers with type 2 diabetes in the study.
In the three hour period after eating a standardized breakfast their usual levels of 144 mg/dl (8.0 mmol/L) at that time went to 157 (8.7 mmol/L). After lunch their levels increased from 122 mg/dl (6.8 mmol/L) to 140 mg/dl (7.8 mmol/L). Likewise, after dinner their levels went from 122 mgl/dl (6.8 mmol/L) to 140 mg/dl (7.8 mmol/L).
The scientists, James Lane, Ph.D., Mark Feinglos, M.D., and Richard Surwit, Ph.D., don’t know why coffee has this glycemic effect on us. “The mechanisms of action are uncertain at this time,” they write in “Caffeine Increases Ambulatory Glucose and Postprandial Responses in Coffee Drinkers with Type 2 Diabetes.”
The professional journal of the American Diabetes Association, Diabetes Care just published the article online ahead of print. Dr. Lane kindly send me an advance full-text copy.
The test subjects were all people who regularly drink coffee. They “had sufficient opportunity to develop tolerance to the drug.” This refutes the common belief that we develop a tolerance to the effects of caffeine. They concluded that those of us with diabetes can expect similar increases when we drink our daily coffee.
This study disturbed me so much that I wrote the leading glycemic index researcher about it. “Is what they write sense? Or nonsense?” is the question that I posed to Professor Jennie Brand-Miller, Ph.D., of the Human Nutrition Unit at the University of Sydney. We have worked together for a long time, most closely as co-authors of The New Glucose Revolution: What Makes My Blood Glucose Go Up…And Down? (New York: Marlowe & Co., second American edition, July 2006).
“We have a little study under review at present that does indeed show that coffee consumed one hour ahead of a meal increases the glycemic response to the meal,” Jennie replied. She attached the abstract of their study to her email.
The abstract begin by pointing out that habitual coffee consumption has been linked to a lower risk of type 2 diabetes. Nevertheless, drinking just 250 ml (about 8 fluid ounces) of black coffee an hour before a high-carb meal increased the average blood glucose level of eight volunteers by 26 percent compared to when they drank hot water.
These new studies don’t refute earlier studies that suggest that people can reduce their risk of type 2 diabetes by drinking coffee. Different factors may be at work. Maybe it’s because people who don’t have diabetes can produce enough insulin to overcome the insulin resistance that caffeine can temporarily cause.
But once we have diabetes it makes sense to limit our coffee consumption – as painful as even the thought of it is to habitual coffee drinkers like me. Herbal tea, anyone?
This is a mirror of one of my articles that Health Central published. You can navigate to that site to find my most recent articles.
34 responses so far ↓
1 Jeetha // Jan 15, 2008 at 12:59 pm
I recently decided to give up caffeine and found a great substitute to satisfy the need for a warm comfort drink.
Cafix, made of malted barley, barley, chicory, figs, and beet roots, is caffeine free and tastes just like coffee. I found it at Whole Foods but it is available online.
2 Homeschool Mom // Jan 21, 2008 at 6:27 pm
Is it coffee or caffeine – and would tea have a similar effect I wonder?
3 admin // Jan 21, 2008 at 6:56 pm
Good question! Real tea (not herbal tea) does have caffeine. But not as much. Not hardly as much. So the effect would be a lot less, I guess.
David
4 Homeschool Mom // Jan 23, 2008 at 8:28 am
That’s really interesting. Thanks David. I enjoy reading your site. I’m not diabetic – yet. I have two diabetic parents and one sister who is also, and plenty of other relatives. Thus the -yet. I found your site while researching the glycemic index. Thank you for your site. I’ve been reading it for many many months.
5 pennilessneuropathic // Jan 30, 2008 at 11:06 pm
How would or might black coffee’s effects on blood glucose levels differ
if the diabetic person were to consume the coffee “after”
a meal (that has some protein and fibre), rather than “before” a meal?
And how would or might those effects on blood glucose differ if the “after”-meal coffee (say, a tall Blenz or Starbucks),
instead of being black, included 1 or 2 Tablespoons of cream?
If no credible studies have included either of these 2 scenarios yet, what would be your “educated guess,” from your experience? Thank you for any reflections.
6 admin // Jan 31, 2008 at 9:00 am
I am pretty sure that there haven’t been any tests of what you suggest. Those are good ideas though! But if you do include cream in your coffee — and it is real cream and not the faux stuff that restaurants serve that has HFCS in it or the half-and-half that has carbs in it — my guess is that it might moderate the BG effect somewhat.
David
7 Elissa // Feb 23, 2008 at 1:08 pm
Any suggestions about green tea? I’ve not seen it on any GI scales….and I never sweeten it. Thanks!
8 Frank // Feb 26, 2008 at 1:03 pm
I filter drip each cup of coffee individually and add a 1/4 teaspoon of cinnamon to the fresh ground coffee before pouring the water. Since cinnamon increases insulin sensitivity, I wonder what the competing effects would be?
9 David Mendosa // Feb 26, 2008 at 2:51 pm
Dear Frank,
I wonder too. The effects of cinnamon are certainly minimal, and those of coffee may well also be minimal. My guess is that they balance each other out.
Best regards,
David
10 Ned Widener // Mar 11, 2008 at 7:59 pm
I strongly suspect that the glycemic response is related to the adrenal function, that gives much more dramatic effects on blood sugar readings when the blood sugar is already elevated. Try an aerobic workout if your blood sugar is above 150 mg/dl and tell me what the blood sugar is after. I am Type I, insulin dependent for 40 years.
11 tom // Mar 19, 2008 at 6:19 pm
Is unsweetened, bottled green tea OK for a person in the early stages of diabetis? I got the news last night and I’m desperate to learn what’s good for me. I have an old copy (1998) of SugarBusters! and I’m hoping the info will help me get everything back in check. My cholesterol is also high (145) right now, as well as my blood pressure (I’m on meds for that thought)
Help, thanks!
Tom Great
Thanks!
12 David Mendosa // Mar 20, 2008 at 3:54 pm
Tom,
You bet that unsweetened green tea is fine for you. The SugarBusters! book was a pretty good one, but it could be even better for you to follow a low-carb diet instead.
Best regards,
David
13 Norm Reid // Apr 22, 2008 at 5:56 pm
Anybody have evidence about decaf? My informal observations suggest that decaf, too, accounts for a slight rise in blood glucose levels.
Norm
14 Ted B. Hale, Jr. // May 7, 2008 at 7:12 am
I’m a type 2 diabetic of five years duration who has been able to reduce oral medication to about 1/3 the prescribed dosage, a fact I attibute principally to flaxseed oil.
On infrequent occasion I attend a gathering of locals where cornbread is served. After two (or three) muffins liberally coated with real butter with a hint of added honey, and after 2-3 hours, my reading will be in the nineties. What gives?
This has happend before with small non-cornbread products, again with liberal butter. I’ve prepared cornbread muffins at home but not with the same results.
15 David Mendosa // May 7, 2008 at 8:59 pm
Ted,
I really don’t know what gives. But if your readings are in the 90s two hours after the first bite of a meal (or snack) you are doing very well!
David
16 Eunice // Aug 9, 2008 at 6:07 pm
YOur web site is very interesting, cabbage, carrots, cinnamon, peanuts can be use to help lower the blood sugar.
Is aloe bitters okay to also help lower the blood sugar?
17 David Mendosa // Aug 9, 2008 at 7:56 pm
Dear Eunice,
Aloe may help control diabetes. But we really don’t have good enough proof yet.
David
18 Jennifer // Jan 9, 2009 at 9:27 am
I have switched to decaf coffee and still my numbers go up about 100 points after two cups…I use powder creamer and no sugar. Any suggestions other than quitting the coffee?
19 David Mendosa // Jan 9, 2009 at 12:28 pm
Dear Jennifer,
100 points! That’s huge! Yes, definitely one other suggestion. It’s got to have mostly to do with the powder creamer. Either stop using cream in your coffee (and if it is good coffee, I guarantee that it will taste better, at least after the first few cups), for switch to pure cream — not half and half. Pure cream has no carbs, but half and half and creamers do.
Let me know!
David
20 Jennifer // Jan 10, 2009 at 11:23 am
I tried the cream in my coffee today with GREAT results. My blood sugar increased by 1.
Now another question. I was reading your article on low carb diets. The 6g for breakfast and only 12 for lunch and dinner….wow. Can you give me a sample meal. I am 57, 5′2″ and 125 lbs. My a1c is 6.5.
21 David Mendosa // Jan 11, 2009 at 1:40 pm
Dear Jennifer,
Glad that the cream works so much better than the creamer!
The best guide for very low-carb diet is Dr. Bernstein’s Diabetes Solution, third edition.
But I generally have two poached egg whites for breakfast (no carbs). I snack on Vital Choice mackerel or sardines. For lunch I usually have a salad or bratwurst and sauerkraut. For dinner I will have fish or chicken with maybe some yogurt and a vegetable like winter squash or okra (my two favorites). Avocados are a mainstay of my diet too.
Also see: http://www.healthcentral.com/diabetes/c/17/20167/good-veggies/
Best regards,
David
22 LOU // Jan 19, 2009 at 12:19 pm
thanks for the input on coffee, but it broke my heart. I have always said…with my diabetes, at leasr they have not taken away my coffee ? ouch !
23 David Mendosa // Jan 19, 2009 at 6:29 pm
Dear Lou,
Hang in there! I really don’t think that coffee can possibly raise our BG levels very much. Diabetes has not taken coffee away from me — please see my more recent post at http://www.mendosa.com/blog/?p=331
Best regards,
David
24 LOU // Jan 19, 2009 at 7:55 pm
I have noticed and read the diabetic breakthough paper by MARK ANASTASI and the $47 book entitled “DIABETIC MEDICAL BREAKTHOUGH’,
what do you think, Dave, have you read it ?
25 LOU // Jan 19, 2009 at 8:01 pm
A BOOK CALLED DIABETES MEDICAL BREAKTHOUGHS IS LISTED ONYOUR WEB SITE. IT IS $47, HAVEYOU READ IT ? WHAT DO YOU THINK ? DAVE,
REGARDS, LOU BONO
26 David Mendosa // Jan 19, 2009 at 8:54 pm
Dear Lou,
I’m sorry, but I haven’t read either that paper or that book.
Best regards,
David
27 Eric // Mar 21, 2009 at 11:37 am
Hi All,
I have experienced the spikes associated with caffeine. I also have seen some of the studies re: insulin sensitivity and coffee consumption. However, for me at least, I have come to the conclusion that the effects of coffee are really related to the effects of dehydration resulting from coffee, which doesn’t seem to be considered in studies.
I would typically drink a 4 shot espresso on a weekly driving trip on Mondays in which I had to get up quite early, and my sugar would spike weekly. Since I have started drinking a large bottle of water with it, the effects have been mitigated. Try “overhydrating” with the caffeine and see if it helps. The only issue is, if you’re driving, plan to stop often!
28 David Mendosa // Mar 22, 2009 at 8:11 pm
Dear Eric,
What great advice! Thanks for sharing. I will continue to drink a lot of water when I drink coffee (and otherwise). I am addicted to both!
Best regards,
David
29 Ron // May 30, 2009 at 6:18 am
In my experiments with eating, I am finding that fats play a huge part in how my numbers read. I wonder if that oily stuff on the coffee beans is considered fat and effects (however small) how much glucose actually gets through the door to nourishing our cells.
30 marcus // Jun 20, 2009 at 12:33 am
Homeschool Mom,
Even if both your parents have diabetes you might not have the same tendency to get it. If my genetics memory is right you may still have up to a 1 in 2 chance that you aren’t susceptible to it. Keep aware about your numbers though.
31 John // Oct 8, 2009 at 2:44 am
I recently was told that I have type 2 diabetes, and just amazed how lowering my carbs contributes to a lower BG reading. The doctor and nutritionist nerver mention this. Your website has been a great help Thank You
32 Marcus // Oct 10, 2009 at 4:15 pm
John, the first thing the doctor should have done is give you a sheet with with foods to eat more of and foods to eat in moderation or avoid. I would be shocked if they didn’t say how to control your diabetes. The more refined the carbs, (sugar or fructose bieng the most refined) the more/quicker your blood glucose will spike. With type 2 diabetes for one specific reason or another your body can’t utilize carbohydrates as efficiently as before, and when it gets backed up it can’t finish taking them out of your blood as quickly so it leaves some there which can lead to complications if it is consistently like that. Good luck and God bless.
33 jackie // May 31, 2010 at 11:15 am
Any idea whether DECAF coffee has the same glycemic effect????
34 David Mendosa // May 31, 2010 at 11:34 am
Dear Jackie,
The article doesn’t say! I wish that I knew too, because I’ve switched to decaf.
Best regards,
David
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