As shown in the chart on the left below, if someone who is insulin sensitive eats a large protein meal they will release insulin to metabolise it to build muscle, repair organs etc. This increase in insulin will shut off glycogen release from the liver and you will see blood glucose decrease.
In someone who is severely insulin resistant or who doesn't have enough insulin (e.g. insulin dependent Type 2 or Type 1 Diabetic) any available insulin will go to work on the ingested protein and the reduction in insulin available in the system will cause an increase in glucagon release from the liver and we will see blood glucose increase as per the example on the right hand side of the chart below. This may look like the protein just ingested is being instantly converted to glucose but gluconeogenesis and requires a lot of energy. Using protein for energy is only something the body does when there is not enough energy from fat or carbohydrate.
It seems logical that people who see high blood sugars after a high protein meal to cut back on protein. But to look at it another way they may actually need more exogenous insulin to help them use the protein they have eaten to build lean body mass which will in turn help them use the glucose.
People who are more insulin sensitive may be able to get away with less protein because they are so insulin sensitive and the amino acids go to effectively building muscle.
We have a strong drive to get the protein we require and tend to stop eating when we get adequate protein for our activity levels and needs.
There are a range of recommendations when it comes to protein intake:
* we burn about 0.4g/kg LBM during starvation
* the RDI for protein is 0.8g/kg LBM,
* the typical intake for most people is about 1.2g/kg LBM or 16% of calories,
* Steve Phinney recommends 1.5 to 2.0kg/reference weight (which equates to 1.6 to 2.2g/kg LBM),
* most people will struggle to eat more than 2.7g/kg LBM because it requires a lot of lean protein and not much else.
If you're active you'll use more protein, but even a strength athlete won't stimulate more muscle protein synthesis by eating more than about 1.8g/kg LBM. If you're aiming for good blood glucose levels, low insulin and metabolic health, then being active and building lean muscle mass is a priority. If you're obese and losing a lot of weight then you will use some of your old proteins and may not need to eat quite as much.
Protein requires about half the insulin compared to carbohydrate to metabolise. So if you're aiming for therapeutic ketosis (to manage cancer, epilepsy, alzheimers etc) you may want to actively limit your protein intake.
People simply targeting a lot of protein for gainz can end up with very low levels of other vitamins and minerals.
At the other extreme though, people targetting really low protein by prioritising a lot of added processed fat can end up with very low micronutrients as well. Really low protein foods don't tend to be high in other nutrients.
Practically I think most people will keep their insulin load down by avoiding processed carbs and listening to their appetite, but if you have a more specific goal (e.g. therapeutic ketosis or bodybuilding) then your protein intake may need to be different.
My thought is to eat the most nutrient dense food you can while reducing the insulin load to the point that you get the blood sugar and ketones that you're after.
I hope this helps. I would be interested in other's thoughts on this.