Scientists Uncover How Extreme Diets Trigger Rapid Weight Loss in Mice

Scientists at NYU Grossman School of Medicine have uncovered a mechanism that triggers extreme weight loss in mice. Their findings reveal how a diet lacking cysteine—a sulfur-containing amino acid—disrupts metabolism and alters brain signals controlling hunger. The research also suggests potential health benefits from diets low in such amino acids, alongside risks if taken to extremes. In the study, mice fed a diet completely free of cysteine lost 30 percent of their body weight within just one week. The deficiency caused a sharp drop in coenzyme A (CoA), a molecule essential for converting carbohydrates and fats into energy. Without enough CoA, the animals burned fat reserves rapidly, leading to dramatic weight reduction.

The team also examined how dieting affects hunger signals in the brain. Neurons called AgRP, which drive appetite, received stronger signals after mice were placed on restrictive diets. These amplified signals persisted long after the diet ended, pushing the animals to eat more and regain weight quickly. Building on earlier research, the scientists successfully blocked the neural pathways activating AgRP neurons. Mice with inhibited pathways ate less after dieting and regained significantly less weight. However, the study also warned that total cysteine deprivation could leave organs more vulnerable to common toxins.

The findings highlight a dual effect of sulfur amino acid restriction: rapid fat loss but potential long-term risks if essential nutrients are entirely removed. By targeting specific neural pathways, researchers may have found a way to curb post-diet weight regain. Further studies could explore whether similar mechanisms exist in humans.