Your diet writes itself into cell membranes
Cell membranes are built largely from phospholipids whose fatty-acid tails come partly from the diet. Over a span of weeks, the fatty-acid composition of membranes shifts to mirror habitual intake, so a diet richer in omega-3 fats raises the proportion of EPA and DHA incorporated into membranes, while high omega-6 intake raises arachidonic-acid-related fractions. This turnover is gradual, which is why short-term dietary changes take time to register in tissue.
Red blood cell membrane fatty acids are sometimes used as a longer-term marker of intake precisely because they reflect this slow incorporation rather than the last meal.
Fluidity and signalling consequences
The mix of saturated and unsaturated tails influences membrane fluidity: more unsaturated, especially long-chain omega-3, fatty acids tend to increase fluidity, which can affect how membrane proteins and receptors behave. Membrane fatty acids are also released to make signalling molecules, so composition can influence the balance of pro- and anti-inflammatory mediators.
These mechanisms are well described biochemically, but how strongly diet-driven membrane changes translate into clinical outcomes is still being studied. This is general educational information, not medical advice.