Tiredness is not literally a lack of energy

One of the malaises of our modern world is that we get fat. We eat
too much sweet and fatty foods. Why? Because in ancestoral
conditions, food was a scarce resource and sweet and fatty foodstuffs
were potent energy sources. We've evolved to seek them out. In
developed countries, food is no longer a scarce resource, and this
instinctive craving makes us fat.

Tiredness is another modern malaise. Many of us just don't have much
energy. No doubt overwork, hectic lifestyle and inadequate sleep are
major contributors. And lethargy could be due to mental exhaustion,
though here I'm talking about lack of physical energy.

It is interesting to note that this tiredness must be an intentional
part of the design of our bodies, to make us get some rest, like the
way we need sleep. It is not actually a lack of energy. We have more
energy than ever. Energy is, quite literally, what those fat bellies
we're carrying around are.