I would agree with the "all calories are not created equally" point. Calories from different foods will have different nutrients. For example, 100 calories of oranges will have way more vitamin C than 100 calories of sugar. But in terms of weight loss, your body doesn't care, 100 calories is 100 calories. Interestingly, malnutrition is becoming a problem among the obese. They eat too many calories and do not get enough nutrients.