Our protein needs for simple maintenance go up as we get older. There's a lot of amino acid (AKA 'protein') recycling happening in our bodies. As we get older, we get progressively less efficient - so we need to add more to our diet.

I think the key here is adding a protein bar rather than using it to replace something else. Personally, I go with a tin of oily fish for 'lunch' (really breakfast as it's my first meal of the day) so as to get both protein and omega-3 polyunsaturated fats. It's not nearly as convenient as a protein bar - and for some years, I'd take it to a service stairway in my workplace so as to not offend anyone with fish-smell issues.

As a side note, if those protein bars were even moderately high in simple sugars and they were the first thing consumed that would make for an insulin spike. Through fasting periods (like overnight) our livers are producing glucose for us, controlled by glucagon from Alpha cells in the pancreas (your fasting blood glucose is almost all from this). It takes at least a couple of minutes to shut down even if insulin from the Beta cells immediately stops the glucagon (I've seen no data on how fast that might be), there is glucose from this de-novo glycogenesis PLUS glucose from the small intestine. The two together make for a glucose spike, which the Beta cells will react to with even more insulin. Add in a bit of insulin resistance in the muscles, and that additional insulin will prompt fat cells to hoover that glucose right up, convert it to fat and store it.

If it isn't obvious, I'm fascinated with this stuff - thanks to anyone who's made it through to the end with me.