In the seventies Frappé popularized an idea that vegetarians should combine protein sources, i.e. eating grains with beans, just like traditional food cultures have done for longer than recorded history, is a complete amino acid profile as opposed to just eating grains with more grains or eating beans with more beans.
In just a few years this was “debunked” with scientists (correctly) pointing out that the body can easily store up amino acids way longer and combine all kinds of protein even if you don’t take extra care at every meal. You can eat all grains one day and all beans the next and you’ll be fine and you won’t get protein deficiency.
True.
But protein deficiency isn’t the entire story. A complete amino acid profile in one meal (i.e. yes to combining grains with beans) does a better job at triggering the release of satiety hormones like PYY and GLP-1 in the gut and ghrelin right in the mouth—so far, so proven, but it’s also hypothesized that the combo also is more satisfying for vagus nerve satiety along with learned taste/sensory satiety (i.e. your brain has learned that eating these two things together will be more satiating in an hour so it already craves it on the tongue). Eating a meal of grains+grains or beans+beans as opposed to a mixed double just immediately feels less satisfying and if there’s a psychological component to that, that’s not weird because the psychology is created by these weird hunger and satiety hormones too.
Conclulu: you don’t have to worry and stress that you’re gonna get a deficiency or problem if you don’t combine. The “debunkers” were right in taking that particular load off your mind. But, what the debunkers were wrong about and traditional grandma cooks going back millennia were right about is that there’s an opportunity here for you to make a satisfying meal called a peanut butter sandwich where there actually is a synergy between the two ingredients.