how long does it take to digest protein?

One of the limitations of the food insulin index data is that the tests were undertaken over a period of three hours, while protein takes a lot longer to fully digest.

As shown in the chart below (from Andreas Einfeldt / Diet Doctor) simple carbohydrates cause blood sugar to rise and fall quickly, however slower digesting protein causes a rise in blood sugar (in a healthy non-diabetic) between four and six hours after a meal (green line).


One of the challenges for type 1 diabetics is that, even if they limit their carbohydrates, their blood sugar will often spike a number of hours after a high protein meal.  And sometimes faster digesting proteins such as protein powder raise the blood sugar much faster than a slow digesting steak.

The image below shows the continuous glucose monitor plot of a type 1 diabetic after a protein shake (46.8g protein and only 5.6g of carbs).  Without insulin to blunt the glocogenic effect of the protein, the blood sugar rise from the fast acting protein is not dissimilar to what you would see from carbohydrates.


On the positive side, protein does not spike blood sugar as much as carbohydrate and is therefore easier to manage.  Though for type 1 diabetics it is important to be conscious of the amount of protein in the diet and manage it accordingly, particularly if they have their carbohydrate intake dialed in and want to achieve optimal blood sugar control.

Similarly, it’s important for type 2 diabetics and people trying to lose weight via a controlled carbohydrate carbohydrate diet to keep in mind that excess protein, although it might not have a significant effect on their blood sugars, will also raise their insulin levels and work against weight loss or nutritional ketosis.

[next article…  is the insulin reaction to protein dose dependent?] [this post is part of the insulin index series] [Like what you’re reading?  Skip to the full story here.]

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Marty Kendall

  • Jazmine Kendall says:

    You a€™re amazing Dad.

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  • JW says:

    I’m sorry if you have answered this elsewhere but where does Cassein powder fit into this? Unlike whey it digests slower (which would be a boon for hunger), forms a gel in gut and some talk that it feeds gut bugs. However others say whilst it doesn’t give a high insulin spike as whey does, it keeps insuline higher for a longer time which may be worse. What are your thoughts? Yes I know whole foods are better..but am curious. Many thanks

    • Depends what you’re after. If you’re a bodybuilder with good insulin sensitivity you’ll want to spike insulin after a workout.

      If you’re a diabetic then the slower digesting option sounds like the right approach. I would think having a slower and longer insulin response would be better, particularly if it keeps you filler for longer.

      Some people don’t do well with cassein so maybe try a month on / month off without it and see if you get a different response.

      • JW says:

        Thanks appreciate your response. I’m a former fat pre-diabetic with strong family history of T2 maintaining a 50kilo weight loss on LCHF, struggling with hunger & regain each and every day. IF helps me but I fail at it on a consistent basis. Was thinking of using protein powder in AM rather than the awful black coffee in the hope I could semi fast until dinner, but I always found whey made me hungrier, hence reading about casein which I always assumed was an inferior protein. I am a huge fan of Ron Rosedale and therefore mindful of insulin spiking foods, but it’s so confusing now, with people debunking the insulin hypothesis, the more I know the more I don’t 🙁

      • I’m interested in your thoughts on ‘debunking the insulin hypothesis’. If you mean the recent Hall 6 day metabolic ward study I don’t think that it debunks the insulin hypothesis as it fixed calories. I think the magic of the low carb approach is that for people who are insulin resistant it will help them release body fat for fuel rather than storing it and this will lead to a spontaneous reduction in calories.

        If you’re interested in how it’s affecting you I suggested testing glucose and maybe ketones with the different options (see Personally I would try sardines or something that will give you a broader nutritional outcome as well as the protein, but I understand that the protein powders can be convenient.

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