cats=categorical(["Baseline";compose('Food deprivation(Week%d)',[1:3].')]);
results=randi(20,4,1);
bar(cats,results)
The problem you ran into was not building a column vector of strings; note the .' transpose operator on the [1:3] vector above to make sure had a column vector. Otherwise, character or cell strings are simply catenated when strung together in a row.
It's a very long label for tick labels, though, but I don't think you can embed the \n character in a categorical variable to be interpreted as a newline by the TeX interpreter on labels; you could manage that with xticklabels and building strings to write.
Instead, I'd probably just put the 'Baseline' and 'Week N' on the tick labels and use the xlabel for the rest something like...
cats=categorical(["Baseline";compose('Week %d',[1:3].')]);
bar(cats,results)
xlabel('Fasting Period')
ylabel('Food deprivation Effect')
