"How many carbs can I eat in a day?" or "What ratio of fat to carbs to protein should I eat?".
I think that is the wrong way to approach the subject for us as individual type 2 diabetics. Very few of us will actually sit down and work out the calories and fat:carbohydrates:protein ratios we are eating on a daily basis, nor does a daily limit for carbs work very well when our response to those carbs may be quite different at different times of day.
I do not deliberately plan to consume any particular proportion of daily fats, protein and carbs, nor any set daily carbohydrates level or limit. Instead, when I slowly developed my present way of eating I followed a simple process to work out what suited me.
My logic is fairly basic. I need to get all the appropriate nutrients for good health, but I need to get them in a way that does not jeopardise any of my various afflictions, including diabetes. I learned very soon after diagnosis that eating excessive carbohydrates caused blood glucose spikes, so I used this technique to adjust my carbohydrate levels until that did not happen: Test, Review, Adjust.
But other people, including my doctor, were then concerned that I may be missing out on vital nutrients. So I used a diet analyser to check what I actually ate to see if that was true. This is the most recent analyser I have found for that purpose: CRON-o-meter; there are others on the web if you do some searching. I also have regular blood tests; those can also show if I am deficient in various vitamins and minerals. If analysis or blood tests showed that I was missing something I then used the USDA nutrients guide to see what foods I could use to include those missing nutrients without increasing blood glucose levels.
In general terms, I found that eating a variety of proteins such as meat, fish and eggs in normal serve sizes, and replacing most of my starchy carbs, such as breads, potatoes, corn, pasta and similar with a wide range of colourful vegetables, such as cabbage, spinach, celery, onions, peppers, cauliflower, egg-plant and similar meant that there were very few nutrients I missed out on. In fact the increased variety of foods, especially vegetables, in my diet improved my nutrient intake in several areas.
If, and only if, I could not obtain a nutrient by adding a food to the menu I then added a supplement. At the moment my only supplements are vit D3, fish oil and magnesium.
When I do take the trouble to work out my fat:carbohydrates:protein ratios I find they are usually surprisingly close to those suggested in these interesting papers by researchers Mary C Gannon and Frank Q Nuttal:
Effect of a High-Protein, Low-Carbohydrate Diet on Blood Glucose Control in People With Type 2 Diabetes
Control of blood glucose in type 2 diabetes without weight loss by modification of diet composition
I did not use those as a guide, but it is reassuring to see that there is some science supporting my present way of eating.
Everything in Moderation - Except laughter