leptin’s most famous role involves its communication with
the hypothalamus, receptors for leptin have also been
identified in areas of the brain responsible for emotion, and
there is a strong relationship between low levels of leptin
and depression and anxiety. From an evolutionary
standpoint, this makes quite a bit of sense. Leptin works
with insulin to paint a picture for your brain of the state of
food availability—and when food is scarce, this likely tells
the brain to alter behavior in a way that conserves energy.
This can manifest as social withdrawal, an inability to feel
pleasure, or a lack of motivation. It should come as no
surprise that leptin resistance can contribute to depression.
In a recent study, overweight and obese women had
significantly increased symptoms of depression and anxiety
despite having higher leptin levels than lean controls.^16 For
these leptin-resistant women, leptin is present, but the brain
cannot sense it.
In terms of overall brain health, leptin is involved in
synaptic plasticity in the hippocampus, where it facilitates
long-term potentiation—the creation of strong, long-lasting
memories. It’s been shown to improve memory in rodent
models of aging and Alzheimer’s disease, and may enhance
the clearance of amyloid beta, the protein that accumulates
to toxic levels with age. The more you can maintain your
sensitivity to leptin, the healthier (and happier) you will be.
Growth Hormone: The Repair and
Preserve Hormone
In adults, growth hormone, or GH, is known primarily