Because conditions do not mimic night and day. We’ve all been told that boiling vegetables for too long saps them of their goodness. But keeping them in the fridge could also be bad for our health. Experts say that fruit and vegetables are alive even after they have been picked or dug up. This means that they respond to changes in levels of light by producing different amounts of health-boosting chemicals. If ‘day’ follows ‘night’, as in the wild, the amount of the compounds rises and falls. But kept in a dark place, such as the fridge, or in the constant light of a supermarket that is open 24 hours, the health-boosting chemicals never reach the same high. As a result, even those who conscientiously eat their five a day may not be getting the full health benefits.