Can eating too little actually damage your cells?

Moderate calorie reduction or short-term fasting actually helps cells clean themselves up: it activates autophagy, the self-cleaning system by which the cell breaks down and recycles damaged components and misfolded proteins. This is widely regarded as a protective effect, visible across a broad range of tissues.

But that system has a limit. If you eat too little for too long or too severely, the cell can consume itself too far. Researchers call this 'autophagic cell death': the cell overshoots its clean-up response and actually dies. Exactly where the boundary lies between protection and damage has not yet been clearly established. The evidence for this comes from limited research.

Calorie reduction is also linked in multiple studies to less damage to mitochondria (the cell's power plants), less DNA damage, and a better balance in protein management. These are all processes that play a role in ageing. Large-scale research across 185 mammalian species found an association between fewer calories and a lower biological age on an epigenetic clock, but in humans this remains an association, not a proven cause-and-effect relationship.

Apart from calories, oxidative stress also plays a role in cell damage. By-products of metabolism can, at high concentrations, damage mitochondria and DNA, particularly in brain cells, and this is associated with cognitive decline. Calorie reduction appears to reduce oxidative damage, but the same research highlights physical exercise as a more effective strategy against it.