There is no guaranteed safe investment. Even precious metals and food are subject to external forces that you cannot control. In the case of food, pressures caused by droughts, poor yield, blight, and others can dramatically impact the value of your assessment. While these are much less likely to be the result of actors, it doesn't change the fact that they can happen.

With regard to precious metals, your investment is theoretically safer if you've invested either directly in metals and hold them yourself in a secure facility, or you have partnered with a firm you trust to manage your assets. However, in both these cases, there is still the risk of individual actors or groups of actors taking your wealth. It's simply done using analog methods, rather than digital methods.

Ultimately, the safety of your BTC depends entirely on you, and it is not 100% safe. However, it is significantly more resistant to external market forces like inflation and devaluation. As far as currencies go, that's really the major selling point of BTC.