Heat and (don’t) Eat: Study Spotlight Take-Away with Chef Dr. Mike

by Michael S. Fenster, MD

“Food over flame burns; food over heat cooks.”
— Alfred the Great.

Most everyone is familiar with the phrase “heat and eat.” It is a veritable daily mantra of modern life and reminds us of the powerful convenience our modern technology affords us. Such knowledge has also afforded us unprecedented bounty; for many Western nations, a history of scarcity and intermittent famine has been replaced with abundance that is available 24/7/365. But does restraint in this setting translate into health benefits?

The indigenous inhabitants of the island of Okinawa, Japan, an original Blue Zone recognized for the longevity and health of its peoples, have a traditional saying: “Hara hachi bu.” This translates roughly to “eat until you are 80 percent full” or “belly 80 percent full.” This phrase reflects a cultural habit of moderation in eating. This practice is believed to contribute to the health, wellness, and longevity of the native islanders.

If you’ve ever found yourself on a tropical island eating less and, as Jimmy Buffett observed, “losing weight without eating sunflower seeds,” you may have wondered about the reality of such a connection. This week’s study provides a potential correlation. In addition to what we eat, quantities matter. There is “empirical evidence [that] suggests that heat exposure reduces food intake.” If true, the implication is that sensory information from the environment in which we consume our comestibles can affect the quantity of consumption and, ultimately, our health and wellness.

The Study:

  • The study involved a murine model to map how heat exposure might influence food consumption.

The Take-Away:

  • Within the brain, there is a particular area known as the pontine parabrachial nucleus (PBN) that is the primary center for temperature sensing.
  • The PBN communicates with other brain regions, including the hypothalamus, which is critically involved in integrating sensory information from eating food and then helping to regulate hunger, satiety, and food intake.
  • The hypothalamus contains unique cells known as tanycytes, which form a cellular interface between the parenchyma (functional tissue) and the brain’s ventricular and vascular systems.
  • Tanycytes can transmit information between the central nervous system and the periphery through the bidirectional exchange of metabolites, hormones, and signaling molecules.
  • The study suggests that tanycytes translate extrahypothalamic sensory modalities (e.g., information about the external environmental temperature) into chemical-mediated codes or information that act to reset the output of hypothalamic neurocircuits (reducing the hunger drive) through direct communication with those brain neurons.
  • This is accomplished by sending a specific bit of information in the form of a molecule known as vascular endothelial growth factor A (VegfA) to those specific brain cells.

The Caveat:
As with any neurologic study based on a murine model, caution must be used when extrapolating to human behaviors and biological outcomes. Nonetheless, this is an intriguing study because the human brain contains similar areas, connections, and the same messenger molecule as were studied in the murine model. When released in the human body, VegfA plays a crucial role in maintaining vascular homeostasis, promoting tissue perfusion, and supporting various physiological processes. Dysregulation of VegfA expression or activity is implicated in various human diseases, including certain types of cancer, diabetic retinopathy, and age-related macular degeneration.

However, in this instance, that same messenger molecule is delivered quite selectively to specific brain neurons (dopaminergic and Agrp+ neurons of the arcuate nucleus (ARC)). Tanycytes can release such chemical messages to the entire body, but in this particular scenario, they don’t. It’s a bit like sending a DM on X instead of posting publicly. These “DM” neurons are not only involved in our response to food and hunger but also in the control of physiologic functions like heart rate, blood pressure, and reproduction, including sexual drive. Perhaps this is why Anthony Bourdain observed, “Good food does lead to sex. As it should.”

For centuries, science has excised humanity from nature, isolating us on the island of the remote and presumed objective observer. It was an artifice of that process of scientific inquiry that seemed apparent to everyday people doing everyday things, like sitting around the table and eating. Now, science is helping us re-weave those isolated strands into a beautiful and complex tapestry of understanding that provides a mechanism of how our environment can impact our individual health and wellness, particularly in a way that connects us to our daily meals. When it comes to eating, there can be no objective observers; there is no dinner without the diner.

The Study:
Benevento, M., Alpár, A., Gundacker, A. et al. A brainstem–hypothalamus neuronal circuit reduces feeding upon heat exposure. Nature. In 628, 826–834 (2024). https://doi.org/10.1038/s41586-024-07232-3

Additional Resources:
Yang, W. Z. et al. Parabrachial neuron types categorically encode thermoregulation variables during heat defense. Sci. Adv. 6, eabb9414 (2020).

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