• Ariel Warren, RDN, CDCES

How Fast is Novolog's NEW Fiasp Insulin?

Just last week I went to my Endocrinologist for a usual diabetes check-up.

"Have you heard about the new Fiasp insulin?" My Endocrinologist.

"No, but I'm excited." I said with pure curiosity. Me.

After a quick management session, he left the room and came back with a big grin on his face and a little Insulin box with a yellow-lidded vial.

He then introduced Fiasp, the new, fast acting insulin made by Novolog that starts lowering your blood sugar within 2 1/2 min.

(2) “It's Time for Fiasp®.”

I've officially been on it for about 5 days, and I'm quite happy with it. First, we'll go over what the science is and the mechanism of action, then I'll talk in detail about my own personal experience.


Think of Fiast as Novolog 2.0. Fiasp Insulin has an extremely similar molecular make-up to the widely used short-acting Novolog, but it also contains B3 and a stabilizing amino acid (L-Arginine). To keep it simple, the B3 component is what allows the insulin to be more quickly accessible in your blood stream, and the amino acid is to keep the insulin stabilized. (1)

(2) “It's Time for Fiasp®.”


Science shows that Fiasp is seen actively in the bloodstream within 2 1/2 min after an injection/bolus.

YES. I Said 2 1/2 min?!?

So how does Fiasp compared to Novolog. Great question, I have a graph for you.

(2) “It's Time for Fiasp®.”

What this graph means. The onset for Novolog is around 5.2 min, which doesn't seem that long, but when you are able to cut that time more than in half, we are talking some serious speed.

5.2 vs 2.5 may not seem a whole lot faster, but after trying it (and being the great skeptic that I am), I have been pleasantly surprised.

Let's talk about my personal experience.

Out of the blue, I don't think I have done this is 10 years, I craved French Toast for dinner. Yikes!! Of course I got the sugar free syrup (which I am not crazy about as a Dietitian), but the bread was still carb-loaded bread.

My blood right before I took my first bite was 78 mg/dL, slightly decreasing, but still trending with a straight arrow.

Right as I was about to enjoy my first Cinnamon French Toast bite, I bolused for just 1 piece, hoping that 1 piece was all I needed. I usually give my insulin about 15 min before I eat, but I crossed my fingers, and intentionally bolused with the Fiasp insulin right then and there as I was enjoying my first blissful bite.

1 egg + 2 tbsps egg whites + cinnamon + vanilla + 1 piece of whole wheat flax bread + 2 tbsps sugarfree syrup =

~ 20 net grams

I ate my Cinnamon French Toast, and as I was savoring the very last morsel, when I decided I needed to whip up just 1 more slice.

I bolused for another 20 net carbs.

I loved it, enjoyed every second of the sweet and fluffy french toast, but remembered that I worked out pretty hard, so then I instantly justified that just 1/2 a piece more would be okay. Oh, and I wasn't using butter, so it was a crazy amount of calories, right? :D

I bolused for another 10 net carbs.

Okay, but I couldn't just leave half of piece of bread just laying there, it looked so sad. So yes, I covered it in cinnamon egg batter, and cooked that too.

Yet another, 10 carbs to bolus for.

20 + 20 + 10 + 10 = 50 net carbs

At dinner time, I have a 15:1 (carb:insulin) ratio so I had about 3.33 units in my system. REMEMBER, I bolused AS I was eating each bite.

After the damaged had been done, I sat and waited for the imminent spike. I intensely watched my CGM graph, but no spikes, not even a diagonal up, but I knew that it was too early to get excited. So I waited.

And I waited...

And waited...

Here is my graph (don't mind how late it was, it was a busy day).

My blood sugar raised to about 110 mg/dL then dropped to around 80/78 mg/dL and stayed there all night. I didn't have to walk or administer any extra insulin than what I gave right as I ate a first bite of each piece of toast, and half piece of toast.

I couldn't believe it. In previous high carb dinner adventures while using normal short-acting Novolog or Humalog, I always made sure to give my insulin at least 15 min before I ate (usually), and still planned on walking on the treadmill for 12 min afterwards.

But let's be realistic, Fiasp is a faster insulin, but it won't magically normalize your blood sugar.

Let me explain. Fiasp seems to work faster than normal short-acting insulin (Novolog or Humalog), but Fiasp is still insulin and by taking a faster insulin, Fiasp is not going to magically fix issues that aren't related to the the timing of insulin to cover blood sugar and/or food needs.

You will have more normalized blood sugars using Fiasp if you...

1. Use a correct carb:insulin ratio (more easily said than done).

2. Count your carbs accurately.

If your carb:insulin ratio is too low (meaning you are not giving enough insulin for the amount of carbs consumed) or you are simply not accounting for all your carbs, you will still spike or just have a flat out high blood sugar that stays high. At this point, the spike is not related to how fast the insulin is working in your body, it's that you didn't have enough insulin to cover the carbs.


Fiasp seems to work best if I give it a 5 min headstart (bolus 5 min before I eat) OR bolus when I am a little low (below 90 mg/dL). Below I have written out guidelines when I bolus with Fiasp depending on my Blood Sugar (I am a Dietitian, but these are personal suggestions, consult your Endo).

1. Bolus when you eat with a mild low (70-89 mg/dL).

2. Bolus 5 min beforehand with a normal Blood Sugar (90 - 120 mg/dL)

3. Bolus 10 min beforehand with mild High Blood Sugar (121 - 150 mg/dL). Bolus should include insulin amount for carbs + correction.

4. Bolus 15 min before with moderate High Blood Sugar (151-180 mg/dL). Bolus should include insulin amount for carbs + correction.

I purposely didn't include guidelines for blood sugars below 70 and above 181 mg/dL.


Other issues that cause a high blood sugar that will not be magically fixed by Fiasp.

  • A bad pump side.

  • Old Insulin (28 days is the expiration time for insulin).


For example. If I am correcting a high, it usually takes a good 3 hours to come down to the level I prefer (between 80 - 110 mg/dL is ideal). Granted, I am not patient enough to wait for a high to come down by itself with only insulin, so I always walk, BUT that's how long it would theoretically take. HOWEVER, when correcting with Fiasp, it takes about 1 1/2 hours, which is half the time.


Fiasp is a simply that. *NEW* So it will take adjustments. Also, when it's all said and done, the price of insulin definitely has a say on what we use. For instance, if my insurance does not cover Fiasp, hopefully I can get a pre-authorization from my Endo, or unfortunately just pay out-of-pocket (gasp, that would get expensive and fast).

Fiasp insulin seems to work much faster than the typical short-acting Novolog and Humalog insulin widely used, BUT it is still not as fast as the insulin naturally produced in individuals who have working pancreata (the plural form of pancreas BTW, I looked it up to double check).

But yes, When my carb:ratio is correct, I'm counting my carbs correctly, my pump site is working well, my insulin is not older than 28 days, I'm bolusing in a timely manner according to what my blood sugar is before I eat...my blood sugar is MUCH more normalized while using Fiasp.

BOTTOM LINE: I am really liking it and am excited to talk to my current diabetic clients to get samples from their Endocrinologists. Faster insulin means less postprandial spikes and faster corrections. As diabetics, we are still having to manually give insulin, but Fiasp insulin definitely seems to improve the experience for diabetics who want to lower and normalize their HbA1c and for those who have absolutely no patience to wait for a high blood sugar to come back to a healthy level (which is me).

♥ ♥ ♥ ♥

As always, if you are having trouble with your diabetes and/or weight loss, email me, so we can figure out a customized game plan based entirely on you. I'm 100% here for you and understand all your frustrations because I am a T1D and a Registered Dietitian.

When we talk, I will look in detail at what, when, and the amount you are eating, along with what you are doing for exercise (or not doing, we'll be honest with each other). Together we will analyze your blood sugar (use your Dexcom Clarity reports if you have a Dexcom) and together we will decipher why you are getting your frustrating highs and lows. After a single session, you will have answers and a much better clarity of why your blood sugars react they way they do to your food, exercise, and lifestyle.

After talking, we will stay in touch, and you will have direct access to me for any questions. I deeply care about each and everyone of my clients.

If you just have a general question, send me an email and I will get back to you ASAP.


Your friend & Dietitian,

Ariel Warren, RD, CD, T1D

♥ ♥ ♥ ♥

For more articles from me and other health professionals, check out HapiBody.com. On HapiBody, you can always ask ANY health question and be answered by a professional. HapiBody also has great healthy recipes for you and your whole family and effective at-home workouts for weight loss and full body toning.

Lastly, if you want to join a T1D FB Group who is supportive and full of great workouts and blood sugar challenges, join "Getting Fit with T1D". Right now we are having a 1 month HbA1c challenge.

Works Cited

(1) Heise T, Pieber TR, Danne T, Erichsen L, Haahr H. A pooled analysis of clinical pharmacology trials investigating the pharmacokinetic and pharmacodynamic characteristics of fast-acting insulin aspart in adults with type 1 diabetes. Clin Pharmacokinet. 2017;56(5):551-559.

(2) “It's Time for Fiasp®.” Fiasp® Fast-Acting Insulin | Fiasp® (Insulin Aspart Injection) 100 U/ML, Novo Nordisk, Dec. 2017, www.myfiasp.com/?utm_source=[publisher]&utm_medium=cpc&utm_term=fiasp &utm_campaign=BR Fiasp Brand Phrase&utm_content=General_-mkwid-s_dc-pcrid-73736109314615-pkw-fiasp-pmt-bp.

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