Log2 fold change vs Fold Change
I am not a biostatician and would love to understand. My project deals with looking at comparing samples from 2 different groups (say one with hot dogs and one without hot dogs). My biostatician sent me the volcano group and I am able to see which proteins are downregulated and those that upregulated. He attached a table with the fold change. However, when I look at the volcano plot, the x axis is log2 fold change, with y axis as pvalue. From my understanding, semantics wise utilizing log2 fold change is usually how represent differential expression. However, when I do the equation for log2 fold change some of the proteins will change to negative values. What does this mean? This does not make sense as in my volcano plots, these proteins are definitely placed in the appropriate side (downregulated vs upregulated).
For example Protein A listed as upregulated; with fold change 0.9, but log2 fold change is -0.11. Does that mean this protein A is actually downregulated? I also have vice versa where protein B is listed as downregulated; with fold change say 1, with log2 fold change as -0.06. Does that mean protein B is actually upregulated?
Thank you for your time!