What if you're gaining fat instead of muscle? I think your version only works if the only metric required is purely -Kg over time, and doesn't factor in anything else that people might want to call it 'healthy weight loss/gain.'
OK, so which goalposts would you like us to aim for here? If you want to be healthy, eat a balanced diet. If you want weight loss, then eat less food than you burn, using a feedback loop to adjust our dietary intake. If you want fitness, do some cardio. If you want strength, lift some weights. If you want all of these things, then do all of these things.
