In a fascinating study conducted at Yale University, participants were each given a 380-calorie milkshake. Half the participants were told it was a sensible, 140-calorie shake, and half were told it was an indulgent, 620-calorie shake. In reality, everyone received the same 380-calorie milkshake.
In a true testament to the subjectivity of satiation, the people in the indulgent milkshake group rated themselves fuller than those in the sensible milkshake group.
But the researchers didn’t just rely on people’s self-reporting on how full they felt. They also measured the levels of ghrelin, a gut hormone whose presence is associated with feeling hungry. They found lower levels of ghrelin in the people who thought they were drinking the indulgent shake even though in reality they ingested the same number of calories as the people who thought they drank the sensible shake!
In other words, our mindset can actually impact the biology of how full we are, which in turn affects the subjective sensation of how full we feel.
In Parshat Ekev, Moshe informs Bnei Yisrael that when they enter the Land of Israel, they “will eat, be satisfied, and bless G-d.” These words are the source of the commandment to say Birkat HaMazon – Grace After Meals. The trigger for this obligation is feeling satisfied. Yet, the rabbis of the Talmud set a precise amount of food that obligates one say Birkat HaMazon if eaten (either an olive-sized or egg-sized amount of bread).
The Talmud presents an enigmatic aggadic dialogue between G-d and the angels in which the angels ask G-d how He can show favor to the Jewish people (as is implied in the Priestly Blessing) when fairness and justice usually preclude showing favoritism. G-d replies by noting that even though the Torah only requires Birkat HaMazon to be said after being satiated, Bnei Yisrael say it even after only eating an olive- or egg-sized piece of bread.
This cryptic passage, and the rabbinic criteria for saying Birkat Hamazon, requires explanation. If the message lies in the importance of going above and beyond bare requirements, why choose Birkat HaMazon as the example? Additionally, if one is only obligated to say Birkat HaMazon when full, isn’t saying it when not full problematic? Wouldn’t it be a blessing made in vain (beracha le’vatala)?
Perhaps the significance of reciting Birkat HaMazon on an olive- or egg-sized piece of bread is as follows: It’s not that Jews recite blessings even though they aren’t full. Rather, it’s that they worked on their attitude, and as a consequence their biology changed as it relates to being full. They trained themselves to become satiated with a smaller amount.
Mishlei states, “A righteous person eats to satisfy his soul.” The ideal is to eat enough to have energy to serve G-d, not to indulge if there is no physical or spiritual benefit. While we should all consult relevant health professionals for guidance on what and how much to eat, perhaps the Talmud’s message is that we can adjust our mindset to decrease the amount of food we require in order to feel satiated.