Calories are Calories?

In a recent NIH study there was an attempt to demonstrate that fat calories were more effective in adding body fact than carbohydrate calories.

The procedure was as follows:

The researchers studied 19 non-diabetic men and women with obesity in the Metabolic Clinical Research Unit at the NIH ..... Participants stayed in the unit 24 hours per day for two extended visits, eating the same food and doing the same activities. For the first five days of each visit they ate a baseline balanced diet. Then for six days, they were fed diets containing 30 percent fewer calories, achieved by cutting either only total carbs or total fat from the baseline diet, while eating the same amount of protein. They switched diets during the second visit. 

They conclude:

“Our data tell us that when it comes to body fat loss, not all diet calories are exactly equal,” .....“But the real world is more complicated than a research lab, and if you have obesity and want to lose weight, it may be more important to consider which type of diet you’ll be most likely to stick to over time.”  

Now there are several issues here:

1. The sample is much too small

2. The duration time is much too short

3. The switching is in the middle of a metabolic change which takes possibly weeks, not hours to adapt.

4. The key issue is the definition of a calorie. Namely if we measure 3500 Kcal = 1 pound, then how do we differentiate at all?

This is not in my opinion a study of any value for the above and many other reasons.