Should i inject before my meal

When should I inject?

With older insulins (1990), it was common practice for doctors to recommend that you inject 30 minutes prior to eating, to give insulin time to be absorbed. These days (2010+), doctors suggest that you can inject at the same time as, or even after eating. Below we show the difference in outcomes in terms of minimizing time 'out of range' - to reduce long term complications.

These charts demonstrate what happens when you inject 15 minutes before, just prior, or 30 minutes after eating.

The same insulin was given for 60 grams of carbohydrate of Normal GI food in 3 separate meals. Our target BGL (and starting BGL) is 90 mg/dl (5 mmol/l), and our target range is 72mg/dl-180mg/dl (4-10mmol/l).

The charts are generated by the ManageBGL system, which helps you manage your diabetes better in real time, on your iPhone, iPad or PC. See exactly what your BGLs, Carbs and Insulin are doing right now, and predict BGLs 3 hours ahead.

  Injection time Observations from charts below
  15 minutes prior Your BGL stays within the target range for the entire time. Perfect!
  On commencement Your BGL spends about 20 minutes out of range, as the rate the insulin is absorbed is slower than the rate the carbs are absorbed. May not impact your A1C greatly.
  30 minutes after Your BGL spends about 40 minutes out of range, again, the rate the insulin is absorbed is slower than the rate the carbs are absorbed. Expect this practice to impact your A1C.


Injecting prior to, or on commencement of your meal is preferable to injecting after, due to less time spent out-of-range (see notes below)

Naturally if you are including a correction dose for being too high, you should allow more time before eating.

Discuss this scenario

Injecting prior may not work for you...

  • If you suffer from gastroparesis, do not follow these guidelines as you may get low prior to eating. Inject on commencement.
  • Digestion (the rate at which carbohydrates are absorbed) slows with age, so injecting too long prior to eating can again make you low
  • If you eat low carb then the absorption of carbohydrates can be slower than the absorption of insulin, so you can get low if you inject prior.

You need to experiment to find out what works best for you.

BGL BGL Profile (mg/dl)

Insulin Insulin Profile (units active at a given time)

Carbs Carb Profile (grams active at a given time)

Click the Legend buttons to show the raw data for the graphs below it.

The ManageBGL charting system predicts High and Lo BGLs and suggests corrective action.

Suggestions for more scenarios? Please send them to us