Looks reasonable to me
Dr. Richard Bernstein cautions his diabetic patients and readers of Diabetes Solution to keep a tight lid on consumption of tomatoes. An excerpt from page 149:
If you have them uncooked in salad, limit yourself to one slice or a single cherry tomato per cup of salad.
His concern is that tomatoes will raise your blood sugar too high.
That doesn’t make sense to me. A 3-inch diameter tomato has 7 grams of carbohydrate, 2 of which are fiber. So the digestible carb count is only 5 grams. That’s not much. So do tomatoes have a high glycemic index? Unlikely, although it’s hard to be sure. Good luck finding a reliable GI for tomatoes on the Internet.
I think Dr. Bernstein’s wrong about this one, which is rare. I suppose it’s possible that tomatoes deliver some other substance to the bloodstream that interferes with carbohydrate metabolism, but Dr. Bernstein doesn’t mention that.
Do tomatoes play havoc with your blood sugars?
Diabetic Mediterranean Diet 
Yes
Tomatoes are fruits called veggies for some bureaucratic reasons in the past. Some varieties could be very sweet. There is a lot of acidity as well, and it could muck the sweet taste.
I am not a diabetic, but follow a LC diet because it benefits my health. I own a glucosemeter and during experimenting with the devise I had a chance to notice that our family traditional weekend morning staple – sunny side up eggs coked with tomatoes and onion ,gave me more elevated BS response than I expected (nothing horrible, but definitely higher than just eggs and deli meats). Onions are also relatively high in carbs which is expected for a root veggie.
Galina, Lots of our vegetables are botanically fruits while being classified in diets as vegetables. Think of squash, pumpkins, cucumbers, peas, etc.
Jerrymat
It could be potassium.
Insulin release from pancreatic beta cells is mediated by blockade of ATP-sensitive potassium channels by glucose-generated ATP. High levels of potassium may overcome the blockade and suppress insulin release.
Similarly, in muscle cells the ATP-sensitive potassium channels are involved in glucose uptake. See http://www.ncbi.nlm.nih.gov/pubmed/20519313 for a review.
I haven’t searched this literature but maybe high potassium from tomatoes transiently suppresses insulin secretion and glucose uptake by muscle cells.
But this wouldn’t necessarily mean that eating tomatoes was bad for you, even if you are a diabetic. Dr Bernstein might be overly focused on glucose here.
My copy of Dr. Bernstein’s book isn’t his latest revision, but I believe Dr. Bernstein still recommends limiting carbs intake to 30g per day for T1DMs and others that want to watch things.
I suppose at the end of day, for those T1DM and insulin dependant T2DM people, it matters as it could affect their injections.
I’m borderline for gestational diabetes and I have a blood glucose monitor to play with. After reading this I was hungry (it had been about 2-3 hours since I’d last eaten) so I went and scarfed down a bunch of tomatoes (4-5 very large cherry-type tomatoes. Did nothing at all to my blood glucose levels.
Dr. Bernstein’s writings are geared more towards type 1 diabetics, and for his good reasons he steers well below 5 grams carb per meal. So, 5 grams in one fruit would be too high if combined with any other carbs in a meal.
That said, I have no problem with small amounts of tomato. A large home-grown beefsteak tomato is a problem, as is more than just a bit of tomato sauce. (I don’t measure blood glucose, just gauge hunger levels afterwards.)
I was just released from the hospital with a diagnosis of renal failure and diabetes (A1C Sept/5.9 Nov/7.1) I’ve purchased a couple of renal books, one on diet and one by Dr Walser. On a renal diet tomatoes are a no-no due to high phosphorous/potassium levels. Renal failure is strongly correlated with diabetes, as is hypertension. Perhaps that’s one reason Dr Bernstein suggests avoiding tomatoes.
I am a type 1 diabetic and I consider Dr. Bernstein’s book the old testament of diabetic treatment. The new testament is Blood Sugar 101: What They Don’t Tell You About Diabetes [Paperback] by Jenny Ruhl. She too loves Dr. B but she is more realistic, saying that normal people get blood sugars to 120 after a meal so for a diabetic to stay below 120 is a reasonable goal. She says research shows that diabetic damage to body tissues starts at 140 and upward so always strive to stay below 140. It seems to work. She also has a website where diabetics can communicate with each other. She has just come out with a book on low carb diets.
I appreciate the comment, Jerrymat. Jenny provides much good information, no doubt.
-Steve