PENNINGTON BIOMEDICAL RESEARCH CENTER IMAGE: WHEN THE LIVER DETECTS LOW LEVELS OF PROTEIN, IT ACTIVATES CELLS THAT PRODUCE FGF21 AND RELEASE THE HORMONE INTO THE BLOODSTREAM. FGF21 IS THEN CARRIED TO TARGET CELLS (NEURONS) IN THE BRAIN. THOSE CELLS HIT THE ALARM BUTTON WHEN THEY SEE FGF21, SIGNALING THAT PROTEIN INTAKE IS TOO LOW.THE BRAIN...
