Robert Lustig, M.D., pediatric endocrinologist, sits down with Mike Giardina of CrossFit Health to discuss neuroregulation of food intake.
Dr. Lustig describes how hunger regulation is affected by leptin, a hormone made in the fat cells, which tells the brain there is enough energy on board for survival. Obese individuals are high in leptin, but it doesn’t function properly — a phenomenon referred to as leptin resistance.
Insulin is the hormone that blocks leptin signaling. Blocking leptin signaling is an advantage during puberty and pregnancy, when the body needs to take in more calories for growth, but leptin resistance wreaks havoc on the general population.
Unfortunately, the majority of the general public is now hyperinsulinemic due to diets high in sugar and ultra-processed foods. Dr. Lustig explains how these foods cause insulin resistance, which means insulin levels are high and blocking leptin signaling.
Sugary and ultra-processed foods also stimulate the reward pathway. Though reward is good, too much reward can cause dopamine-receptor downregulation, leading to tolerance. When stress is added to the equation, food intake is further disinhibited, which means you feel inclined to eat more and more.
So, leptin, insulin, and cortisol are the hormonal culprits behind obesity, and sugar is in the driver’s seat.
With this backdrop in mind, Dr. Lustig provides insight into the concept of calories in versus calories out. He explains how a calorie is not the same across all foods while also defining the differences between nutrition, food science, and metabolic health. The processes that lead to metabolic disease all happen within the cell, so he recommends focusing on metabolic health more than food science.
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