Can eating too little actually damage your cells?

Eating moderately less does not damage cells - it actually protects them. Fasting and caloric restriction stimulate autophagy, the system by which cells clear out damaged components and proteins. Without that clean-up cycle, cellular waste products accumulate, contributing to ageing and disease. If you artificially block autophagy, the protective effects of eating less largely disappear.

But there is a downside at extremes. When you eat far too little for a prolonged period, autophagy can tip into overdrive. Cells then consume themselves to the point of dying - a harmful form of cell death. This is not a theoretical risk: research shows that with sustained, severe caloric restriction this mechanism becomes active. The difference lies in the dose: moderate, temporary caloric restriction is one thing; chronic starvation is another.

At the molecular level, caloric restriction specifically slows the ageing of mitochondria (the energy factories in your cells) and of metabolic processes. Not all forms of cellular ageing are addressed, however. Changes that are unrelated to energy and metabolism largely remain unaffected.

For the brain, a separate nuance applies. Eating less can reduce harmful oxygen radicals that damage cells and brain cells. Yet prolonged exercise appears more effective than caloric restriction when it comes specifically to the brain.