We've all heard of people talking about having too many calories. Heat is a form of energy. Your body requires energy to function.
Everything that you do requires energy. Running, eating, and even blinking all require a certain amount of energy.
Calories From Food
When someone talks about having a muffin but worries that there are over 400 calories, they're worried about the amount of heat (i.e energy) that they're consuming.
When the body has excess energy, it stores it. We all know how it's stored: tummy, thighs, etc.
This is a prime example of the heat transfer coefficient.
The heat/energy from the food is transferred into your body, which is then transferred to your brain, muscles, or possibly expelled from the body.
Let's consider another example. If you take an ice cube and hold it in your hand you'll experience heat transfer coefficient through conduction.
The heat from your hand is transferring itself to the cooler object (the ice). Because of the increase in water temperature, the ice starts to melt because it elevates past water's freezing point.
Wait, why does your hand start to feel cold if cold can't be transferred? Good question.
What you're feeling is the heat leaving your hand. Once the ice is removed your body notices that your hand is no longer in homeostasis, so it transfers heat to your hand and warms it back up.
It's really pretty cool if you think about it.