"Oil makes you gain weight"
Can I confirm that "Mafuta yana(ku)nenepesha" with (ku) is incorrect? The answer without (ku) makes sense on its own?
Mafuta yananenepesha = Oil is fattening. / Oil makes you/one [generic person] gain weight. / Oil causes weight gain.
Mafuta yanakunenepesha = Oil makes you gain weight (but may not make others gain weight).
I think the verb is kunenepa so the ending is just -sha which is a common ending meaning roughly 'to make do (something)'. Eg. kuendesha = to drive = 'to make go'. At least that's how I think of it, hope that helps!