There's also the case of short term versus long term energy spikes causing hunger and plenty of other psychological factors. On paper, yes, if you eat 100 calories of sugar a day versus ten apples, you'll lose more weight. But humans are not a transparent in vs out system. Plus there's also the fact that if you eat too little, your body reacts differently, making it nothing like the straight-line effect (eat 100 cal less, lose X; eat 1000 cal less, lose 10X) that a simplistic view would expect.