We do eat tomatoes but on a very limited basis.

We rarely have them at home (although we did last night) but if a cheeseburger comes with lettuce, onion and tomato I will eat the small amount that comes with the burger (but not the bun). Wife does use small amounts of tomato paste or sauce in some dishes. There are a couple of reasons we limit the consumption of tomatoes. They are medium in carbohydrates. Not a very low carbohydrate food like lettuce or something like that, but also not a really high level of carbohydrates like a potato or bread. So we limit the amount we eat because of my diabetes and my diet is my complete control of my diabetic situation (although in the last year I have experimented with taking berberine and metformin again).

But probably the main reason we limit them is mostly because of my wife. She has found out that nightshade vegetables can cause her a lot of discomfort and issues. It seems like as long as she severely limits them she can have a few once in a while. But if she gets to eating lots of them it causes digestive and just not feeling well problems. Don't seem to bother me. So from that respect, it is just easier to not keep them in the house most of the time. 

Probably one of the biggest helps in diet control is the stuff a person should not be eating................just don't keep it in the house. If it is not there you can't eat it or over indulge in it. Even if a person gets some things when they eat out, at least most of the time the temptation is not there.

I do make exceptions in my diet. For example right now pears are in season and we have a delicious pear tree right in the front yard. I allow myself one pear a day while in season. And my wife and I will can a bunch without any added sugar for later consumption. But I would never buy a pear from the store because they are too high in sugar and fructose for what my dietary needs are. For bought fruit we limit ourselves to blueberries, strawberries, blackberries and raspberries. Berries are the lowest sugar content and are the closest to being keto friendly. Even then we limit the quantity. Like 6-8 blueberries on top of a low carb desert my wife makes. Not handfuls of them. Same way with nuts like pecans. Very small quantity as a topping.

Cucumbers and summer squash are fine. Apples are too high in sugar.

Keep in mind if someone goes low carb and is limiting themselves down from 300 grams carbs a day to 100 or 120 a medium apple might be able to fit in a low carb diet. However someone like myself that is controlling my diabetes completely with diet and needs to stay down around 20 grams carbs a day to control blood sugar, a sweet juicy apple is a no-no. Although we also have an apple tree and I will allow myself one once in a while (but not the same day as a pear). 4.5 years of very low carb has healed my pancreas a bunch and I can have an occasional "treat" and not see my blood sugar go through the roof. Not necessarily "good" for me or my diabetes, but blood sugar staying within acceptable, or at least "not terrible" ranges. There is not an absolute number for blood sugar levels where no damage is being done to organs and blood vessels. We know high is bad and higher is worser but I have never seen a drop dead glucose number where no damage is being done. If a person listens to Dr Bernstein, a blood glucose of 100 is not good (too high). Most doctors think anything under 160 is acceptable for a diabetic. I try to keep mine under 140 after meals and 95% of the time am able to. Lower is definitely better as far as no damage being done to organs. High blood sugar is bad. High insulin is worse and makes a person hold on to body fat. Sugar and carbs cause insulin levels to go up.

Way more than you ask for, LOL. I got on a roll.