I wouldn't think it's the meat. But stress? Stress leads to changes in your hormonal output, which can affect the brain in all sorts of ways.

But here's the cool thing. The stuff outside of you that's scary/worrisome? That's not stress. Those are stressors: the thing that can lead to stress.

Stress is actually the response that your body has to the stressors. And you can, if you work at it, change that response. Learning to meditate helps a ton. Even learning to do measured breathing can help, because one of the physiological responses to stressors is to breathe rapidly and shallowly. Which increases the CO2 levels in the brain. Which leads to feeling more anxious. Which leads to more rapid and shallow breathing. Which...

See? But train yourself, when you feel yourself getting anxious and stressed out, to take a deep breath, hold it for five seconds, and then take five seconds to breathe it out. Do that 10 times in a row, and anxious feelings, the rapid heartbeat, etc of stress will fade.