I would recommend a design change here:
Much Simpler its just has 5 fields,
ID, Date, Breakfast, Lunch, Dinner. Each day I record what I have had to eat.
I would split that up so that your meals table has one record for each meal instead of one record for each day. This gives you
ID, Date, MealID
This makes linking both the foods that you log as having eaten and your relevant blood sugar reading to a specific record in meals.
You might define a new table with this structure and when you are confident that it is working correctly, you can do three Import Records operations to move the data from your current table into the new, but splitting them up by meal. (Import once for Breakfast, once for Lunch, ...)