Just so this does not join the pile of unanswered questions.
You can use multiple regression here. You would model life expectancy (LE) as a function of meat consumption (MC). So LE is on the left hand side, MC on the right hand side. You would then include GNI. The coefficient of MC now would give you the effect of MC on LE allowing for GNI sometimes expressed as holding GNI constant.
This is an ecological analysis so what it is saying is that countries with high meat consumption have higher or lower life expectancy. It does not tell you what happens for individuals. Similarly it is the effect of living in a country with high or low wealth not having that personally. In a country with high inequality most people might be very poor even though the GNI is high.
The direction of causality, if any, is not clear here either. It seems reasonable that what you eat affects when you die but it could be that people who for other reasons live for a long time happen to really like eating meat.