Since I was diagnosed with pre-diabetes , I’ve been doing a lot of research into what is recommended for diabetics in Japan to eat. There are several issues to keep in mind when eating or making Japanese style dishes, so I thought I’d share these here. Whether you’re planning to travel to Japan or are just a fan of Japanese restaurants, I hope you’ll find this useful.
(Note: I’m going to throw around terms like blood glucose level, glycemic index (GI) and glycemic load (GL) here. If you have diabetes or pre-diabetes, or otherwise have to watch your blood glucose levels, you probably already know what I mean. If not, I highly recommend perusing the information available at David Mendosa’s site . It explains these things in clear layman’s terms, with very little of the axe-grinding that plagues similar sites about diabetes.)
I should mention here that, for the moment anyway, I have decided to take a low-GI index or low-carb approach to keeping my blood glucose levels down. I know there are other theories out there for how to achieve this, but please keep this in mind when you read the following. (I did say low-carb. I haven’t entirely eliminated carbs from my diet. I have cut out most sugar though. So far it seems to be working fairly well, since my blood sugar levels have gone down slightly in the month or so since leaving the hospital, and I’ve lost weight too.)
Even though obesity rates are quite low in Japan, plenty of Japanese people do suffer from diabetes, both the Type 1 and Type 2 kinds. One study I read estimates that 4,000 people die of diabetes-related complications every year in Japan. Obesity may not be the only cause of diabetes anyway, though that’s another issue. In any case, Type 2 diabetes is known as one of the big adult onset diseases in Japan, just as in many other nations around the world.
In Japan mg/dL units are used to measure blood glucose levels, as in the U.S., instead of the mmol/L units used in Europe and elsewhere.
The kanji character to look out for is 糖, which can mean any kind of sugar or sugar-related substance. Plain sugar is 砂糖 (read sa-TOH, translates to ‘sand sugar’). The word for sugar-free or non-sugar is 無糖 (read mu-toh).
Other sugary things:
As you probably know, most Japanese meals are centered around plain steamed rice. Unfortunately, both white and brown Japonica or medium-grain rice, have high GI and GL - higher than other types of rice like basmati. If you’re just looking at GI numbers, Japanese style rice has the same numbers as cupcakes! Therefore, although it’s very painful (at least for me it’s very painful), rice has to be regarded as a treat rather than a daily staple. (At the moment I am restricting myself to at the most 1 cup of cooked rice per day - and I only have rice 2-3 times a week. I’m watching my bread and pasta intake too, of course.)
One problem that occurs when you eliminate or drastically reduce rice from a Japanese meal is that you lose that bland tasting foil - so food that seemed to be seasoned just right before suddenly seems too salty, or too something-else. The obvious solution for this is to simply cut back on the salt, soy sauce and other salty seasonings and condiments a bit. Another thing you can do is to substitute a low or no-carb bland foil for the rice For example, an undressed salad or plain boiled or steamed veggies work. If you want something more substantial, try an avocado or scrambled plain tofu.
Since sushi rice is usually made by mixing white rice with vinegar, salt and sugar, it’s definitely not something that diabetics should be indulging in a lot. Sashimi is fine though.
Japanese bread is usually white bread. Those cute Japanese rolls and such are often sweetened with sugar too. So, you need to watch your consumption of those. They belong in the same category as sweet muffins or danish pastries.
Udon noodles are made from wheat flour, so are high-GI/GL. The same goes for the noodles used in ramen and yakisoba. What may not be so obvious is that soba or buckwheat noodles are just as high on the GI and GL scales as wheat pasta. A note for celiacs: most commercially available soba noodles are made with about 60% wheat flour.
Harusame or glass noodles are usually made from potato or anothe form of starch, so aren’t very low-GI. The only low-GI ‘noodle’ you can easily get in Japan is shirataki . You may also be able to get ‘zero calorie’ noodles made from seaweed, sold under various brands. They are rather squeaky and chewy. I prefer shirataki noodles as a noodle substitute myself.
I shouldn’t even have to say this, but just in case: wagashi are loaded with sugar, usually white sugar. Many wagashi have ground white rice flour - good for celiacs, but not for blood sugar control. (This  still rankles me.)
Many typical Japanese dishes are seasoned with a combination of sugar, sake and/or mirin. Sugar is also used in other things like sauces and marinades. Sugar is obviously sugary, and regular sake and mirin also contain some sugar that is produced during the brewing process. In Japan you can buy sugar free sake , but they are hard to get outside of Japan. However, you typically only use a small amount of any of these ingredients in cooking. So, unless your blood sugar levels are very high or your doctor has told you to avoid any kind of sugar at all costs, it may not be worth worrying a whole lot about.
Speaking of sugar in condiments though, beware of ready-made sauces. The first ingredient listed in tonkatsu or “Bulldog” sauce is in fact sugar. Ready-made okonomiyaki sauce is even sweeter, and many ‘no-fat’ Japanese salad dressings also contain sugar. As a matter of fact, many low-fat versions of high fat foods contain sugar, Japanese or not. (One book I consulted specifically recommends staying away from low-fat mayonnaise and sticking to the old fashioned full fat kind if you are diabetic.) Ketchup, which used in quite a lot of Japanese recipes, is also loaded with sugar, or even high fructose corn syrup, which is another issue. (Sauces used in other Asian cuisines like oyster sauce, hoisin sauce and chili sauce usually contain sugar too.)
Another ready-made sauce of sorts that contains quite a lot of sugar, not to mention white wheat flour, is commercial curry roux. The same goes for stew roux, to make hayashi rice (hashed beef stew) for instance. All the more reason to make your own curry  or hayashi rice !
My feeling is that the best policy with all these sauces is to use a little bit, occasionally.
Previously, I have recommended the use of white (light brown) miso as an all-purpose miso. However, it turns out that white miso has sugar in it that occurs naturally during the fermentation process. Again, my feeling is that it’s not something to worry a whole lot about, but if you like to have miso soup a lot, consider switching to red miso instead at least some of the time - and using a bit less of it to account for the saltiness.
Saikyo miso, that very sweet white miso from Kyoto, is so sweet that it should be used sparingly.
Traditionally made soy sauce has no sugar, but there are some types that have sugar added. I stick to regular, straight-up soy sauce.
Konbu seaweed, which is most commonly used to make dashi stock , is quite low in calories. However if you should happen to decide to eat it in big quantities, keep in mind that it is relatively high in sugar in relation to its caloric value. (It’s also typically cooked with a lot of white sugar, which makes things worse.) Using it just for making dashi stock is fine though.
As in any country, many processed foods in Japan contain sugar, so try to read the labels if you are in doubt.
As I mentioned above, regular sake has some sugar content, but there are sugar-free sakes available these days. An alternative to sake if you like a strong tipple is shochu, a distilled beverage that is getting increasingly hip to drink these days. (Just a few years ago it was regarded as a drink for old geezers.) There’s even a ‘drinker’s diet’ which advocates eating low-carb food while indulging in shochu. Maybe not the best idea, but shochu, like vodka or whisky, may be something to consider if you just have to take a drink. Happoshu  is another low-carb alcoholic beverage that’s popular with the young hipsters.
Artificial sweeteners aren’t as prevalent in Japan as they are in the U.S., where every Starbucks has its little box of blue, pink and yellow sachets. There aren’t even that many artificially sweetened soft drinks - most are manufactured by American beverage companies like Coke and Pepsi. (The same applies to Europe too by the way, or at least this part of Europe…the only ‘zero calorie’ soft drinks we can get in Switzerland or France are Cola Light, aka Diet Coke, Coke Zero and Pepsi Light. There’s also a zero calorie version of a Swiss fermented milk soda called Rivella, and a low-sugar version of Orangina, which frankly tastes disgusting to me. (Update: see krysalia’s comments below about other low/no-sugar beverage choices in France.) Frankly, I try to avoid zero-calorie soft drinks as much as possible, though I have a Cola Light sometimes.)
Anyway, back to Japan! So as I said, there aren’t that many artificially sweetened soft drinks in Japan. However, most green and Chinese (usuallly oolong) teas sold hot or cold in vending machines are unsweetened, and delicious. Black tea is often sweetened though, as is canned or bottled coffee.
If you must have artificially sweetened tea or coffee at a cafe or Starbucks, you’ll need to carry along some of your own.
One type of artificially sweetened product you find all over the place is candy. I must say that most of the ones I’ve tried are quite delicious, but you do need to eat them in moderation.
For cooking, the most prevalent sweeteners you’ll find are asparatame, sucralose, sorbitol and ethyritol . (For US readers, Equal is aspartame, and Splenda is sucralose.) One or the other of these sweeteners is usually used for those zero-calorie beverages and candies too. Brand name artificial sweeteners includ Paru Sweeto (asparatame) and Rakannto S (ethyritol plus the extract of some fruit called ‘rakantou’ in Japanese or luo han guo in Chinese; sold as Lakanto  in the west). The latter one is the ‘in’ sweetener in Japan at the moment, touted in some quarters as being very natural and harmless to the human body, etc etc. (My feeling is that as with all artificial sweeteners, it’s probably best to wait a couple of decades before we decide it’s so safe.)
If you’re wondering about stevia, having read that it’s in widespread use in Japan, the fact is it simply isn’t. It has been approved for use quite early in Japan 1971, and was used as a flavor for a popular brand of sports drink that is no longer available. It’s also used in some commercial food products apparently. However, you’ll see the other sweeteners I mentioned a whole lot more.
I’ve really just started my research, so I know I have plenty more to learn. When and if I find out something new I’ll post it here.
(Standard disclaimer: I am not a medical professional. I’m just an interested layperson. Any opinions expressed above are my own, based on my research and personal circumstances. Your methods and opinions may vary. And so on and so forth.
Another thing: I am allowing some comments here from people with their own personal health axes to grind (and it looks like there are quite a few), but the opinions expressed in the comments are not necessarily shared by me. Please take ANY health “advice” you see on the internets with a big fat grain of salt, and do your own research!)