Does history of GDM (diet controlled) mean that I’m insulin resistant? Had borderline high c-peptide level years ago. A1c is 4, 9 (follow low carb diet).

Doing right things. Gestational diabetes does put the woman at a higher risk for diabetes. You may avoid that by maintaining healthy weight and exercising at least 30 minutes/day. You are doing right by limiting carbohydrate intake.
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Wish you good health! - Have a diet rich in fresh vegetables, fruits, whole grains, milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Drink enough water daily, so that your urine is mostly colorless. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco, alcohol, weed or street drugs in any form.
Practice safe sex, if you have sex.