I’ve been living with pre-diabetes and diabetes (the pre- turned into the full thing post-cancer treatments, unfortunately) for about 3 years now. That has meant having to adjust many things with my eating and cooking habits. One of those things is canning and preserving all the wonderful things that are in season in the spring to summer. I used to make jars and jars of strawberry jam  and apricot preserves , as well as dark plum jam and cherry jam. I loved to see the jewel toned jars lined up in my pantry. We gave away most of those jars, but I loved to eat them too.
I still make a few jars of jam, but since I have cut out most sugary things from my diet except for very occasional treats, and The Guy is nice enough not flaunt The Sugar around me, jam consumption in our house is way down. The same goes for other preserves too. Preserving foods the old fashioned ways using methods like making them into jams or pickles, often involves adding lots of sugar, salt and vinegar. Vinegar is not bad for you (that we know of right now anyway!) but sugar and salt intake have to be watched by a lot of people.
For instance, my mother loves making umeboshi  every year, but she has to give away most of it since she has high blood pressure. I try to avoid high-salt preserves and pickles too (although I do make a few jars of chutney  when black plums are in season) since The Guy has high blood pressure. A lot of standard pickle recipes use a lot of salt and sugar besides the vinegar.
Still, I do like to preserve some summery goodness for the dull days of winter. We don’t have a vegetable garden at our current house yet (the garden is still a pile of weeds and rubble) but the local produce in Provence is so cheap and wonderful in the summer, it’s a shame not to try to keep some of it. Here are a few ideas for healthier preserving.
This may be obvious, but a freezer is your best friend if you want to keep produce for use later. Our ancestors didn’t have freezers, but hey - we do! If you can afford it budget and space wise, a dedicated freezer is one of the best investments you can make, especially if you have a vegetable garden and/or fruit trees and plants, and you want to eat a reasonably healthy diet.
It doesn’t have to be the huge coffin like type that resides in many garages and basements (we used to have one of those at our house in Switzerland, but I never liked using it much since things always got lost in the bottom). I have a small freezer with drawers (this one actually ; the refrigerator unit was broken by the movers, grr) that is very energy efficient, and takes no more space than a low chest of drawers. It’s in a storage room rather than the kitchen (we have a regular refrigerator in there with a pretty big freezer compartment); despite its compact size it can hold quite a lot of bags of frozen cut up fruit and such. Right now we are in the middle of peach season, so I’m trying to bag up as much of it as possible - although it’s so good, it’s hard to resist eating it all up as it comes in!
Do be aware that many vegetables need to be blanched (cooked quickly in boiling water, then cooled down in cold water) before freezing. Many fruit and vegetables will get mushy in texture when frozen, since the ice crystals break down the fibers. That’s not an issue if you are freezing fruit to use in smoothies and so on. Just expect to use frozen veggies in soups and stews rather than in stir fries.
Chopping up some types of vegetables and herbs works very well. For instance, try the basic basil puree at the end of this page , which is just chopped up basil, olive oil and an optional bit of salt. Parsley can just be chopped up and frozen in plastic containers or bags; just take a little at a time as needed. Chop up chives, nira (Garlic or Chinese chives) and such with a knife, freeze loose in containers or bags, and use as soup garnishes or add to stir fries and so on.
Also, don’t freeze more than you will be using up in a few months - in other words, what you’d use up during the winter. Frozen foods don’t have an indefinite lifespan.
Drying fruit and vegetables is very interesting. Various dried vegetables are used in Japanese cooking, such as kiriboshi daikon (shredded dried daikon radish) . In Switzerland, dried green beans are popular - they’re just stewed or put into soups and stews. Besides green beans I’ve experimented with drying slized zucchini, tomatoes, and even garlic cloves.
To dry produce you do need a food dehydrator, although you can try using the oven (Pim’s tomato confit using oven dried tomatoes  is quite awesome). I have a really ancient aluminium dehydrator inherited from my mother in law, but one like this model  is much more modern and energy efficient I’m sure. You can try out things like fruit leathers and beef jerky in those things too.
You can still make preserves in good old jars, if the recipes do not use a lot of sugar and salt. I plan to make another batch of this tomato sauce  for example, and I may also make a modified version of this red pepper jam  with reduced sugar since it doesn’t rely on sugar for its consistency as many jam recipes do.
You will need to be extra careful to sterilize your jars and lids properly when making low-sugar/low-salt preserves other janned and canned foods without the buffer that sugar and salt provide in warding off spoilage. The time tested way to do this is to boil them in water. Watch out for any signs of mold. Or if you have a big refrigerator, store the jars in there for safety. (You can freeze jams and anything that doesn’t have to stay crispy.)
Fermenting foods is another way of preserving them. Sauerkraut is a classic fermented-preserved item, and many long-term storage Japanese pickles are fermented. I haven’t gotten into this much yet, but I am doing some experiments along this line with some interesting things… and no I don’t mean brewing. ^_^; One thing I’m trying out is fermenting tomatoes. I’ll report back on this soon!