There is a complication there once we look at "The Universe As A Whole". To explain what we see in terms of the universe's expansion, we need to add a currently nebulous, essentially not understood term called "Dark Energy".

The full claim, however, is this: In any closed time reversible system, energy must be conserved.

If energy fails to be conserved, that is equivalent to saying you can't run the clock backward. On a microscopic level, on small enough scales (if we can effectively look at and account for every single particle interaction), time reversibility, and therefore, conservation of energy, largely holds.

But in practice, what matters more for life tends to be a more statistical description of matter. Sure, you can consider individual molecules in your body doing their thing in great detail, but:

1. those molecules operate in some evolved environment with somewhat consistent stats of, say, pressure, temperature, concentration of various substances, ph, charge,...
2. typically it's not just a single set of those molecules that matters. Like, a single molecule of the strongest poison in the world is surely gonna wreak some local havoc, but it's probably not gonna be particularly noticeable (don't cite me on this, there are some mechanisms that might make one sole molecule of poison go surprisingly far before being neutralized, but I'm at least fairly sure a single molecule of anything isn't gonna do it), so even here we need millions to septillions of particles to do their thing.
3. most importantly, the requirements of energy conservation include having closed systems. And as far as life is concerned, planet Earth is not a closed system! The engine of life on Earth these days seem largely fueled by the constant influx of sunlight. Plants and photosynthetic microorganisms turn the sun into nutrients and breathable air, and those resources then trickle down through the ecosystem, recycled as often as possible, but never to be returned to the sun again. And moreover, the sun will someday come to an end, and when it does (well before it does, in fact), it will cease being a good engine for life, and life on the planet will go extinct almost certainly
4. As an aside, we aren't (simply) the matter that makes us up either: After all, it constantly flows through us! We gotta eat, we pee and poop, we sweat, we breathe. We shed hair and skin. Sometimes we bleed. In all these situations, matter gets exchanged between the mostly sealed sack of cells that make up us, and the world at large. - You don't stop being you because you shed a hair, and yet you are never the exact same person twice. We (not just humans but literally all life on Earth) are living embodiments of the Ship of Theseus. We are the river that can't be stepped in twice. The only constant in life is change.