What will cure/prevent type 2 diabetes is a low-carb, high-fat diet.
Sardines are a low-carb, high-fat food. Eating them replaces a big load of the carbs people usually consume, and just like that they reduce the amount of insulin they have to produce, reducing their insulin resistance and so on. Omega-3 fatty acids are just a slight benefit, probably, and not so much for the diabetes.
But "Just eat a can of sardines every now and then" is just a lucky guess. There are a lot of additional, more effective ways to reduce insulin sensitivity.
What other ways are you thinking of? Whole eggs, vegetables cooked in butter or oil, and fatty cuts of meat are probably the easiest for most people. But sardines are also easy because they're precooked.
Strength training, and good sleep to support the training, also help a great deal, but is not as easily managed as adding something relatively tasty and convenient to one's diet.
Eating a high quantity of diverse vegetables every day is a great idea but the practical effectiveness stumbles due to the difficulty of the habit change.
No, exercise actually doesn't work. Professor Noakes, (now) a proponent of the ketogenic diet, became a type 2 diabetic while running ultra marathons. Back then he was propagating a high-carb diet as ideal for athletes.
Sleep is essential, yes. Get screened for sleep apnoe if you have any reports of snoring. Sleep apnoe messes with insulin resistance.
The most effective way is fasting, at least 16 hours a day, called "intermittent fasting", and ideally a few days up to a few weeks regularly. Fasting absolutely demolishes insulin resistance.
I’ll have to read about Dr. Noakes. I recommend exercise because I see it lead to lower fasting numbers with similar diet, insulin dosage and sleep on my CGM. My understanding is that this happens because of a temporary increase in insulin action on the exhausted muscles, over the next day or 1.5 days in my case.
It does, but it doesn't seem to be enough in many cases. And it's not as effective as fasting for a few days.
I had to inject insulin for a few weeks recently, then I fasted for a few days and was able to quit Insulin totally. After a fast of about 2 weeks I had blood sugar levels in the lower normal range and you wouldn't know I ever had a problem. Interleaving periods of fasting and a low-carb diet with 16h-8h intermittent fasting I lost about 20 kg in 2 months.
Avocados, almonds, nuts, and other high fat vegetables are a heart healthy way to increase fat intake. And they are typically prepared with little salt or can be.
That's been debunked in the past few decades. Originally this idea came from very limited data on heart disease. Now the picture is almost the opposite. It's not a "fad".
Insulin resistance is a very basic physiological mechanism at the root of both obesity and various illnesses. There are scientifically proven ways to reduce that insulin resistance. And low-carb diets have been very successful in comparison studies...
Sardines are a low-carb, high-fat food. Eating them replaces a big load of the carbs people usually consume, and just like that they reduce the amount of insulin they have to produce, reducing their insulin resistance and so on. Omega-3 fatty acids are just a slight benefit, probably, and not so much for the diabetes.
But "Just eat a can of sardines every now and then" is just a lucky guess. There are a lot of additional, more effective ways to reduce insulin sensitivity.