File this one under cool data!
Simple study published in Food and Nutrition Research to look at the differences between whole foods and processed foods and the calories the body utilizes to metabolize them (something called diet induced thermogenesis and also known as the thermic effect of food).
18 subjects were enrolled in a cross-over study (meaning they each ate both test meals) whereby the thermic effect of food was measured following the ingestion of two different cheese sandwiches.
One cheese sandwich was made with cheddar cheese and a multi-grain bread containing whole sunflower seeds and whole-grain kernels, while the other cheese sandwich was made with white bread and processed cheese.
Both sandwiches contained the same number of calories.
While subjects reported that the whole food sandwich was tastier, both sandwiches conferred equal levels of satiety, and in a not completely surprising, but ultimately fascinating result, eating the whole food sandwich led to roughly double the thermic effect of food than the processed sandwich and that effect lasted nearly an hour longer than the processed meals.
Why wasn't this surprising?
Whole grains take longer to digest due to the protective fibrous sheath that processing removes. We also would expect the whole grain sandwich to have more protein and fat (which it did) which in turn delays the speed with which the body is able to break down its accompanying carbohydrates.
Calorically what does this mean?
It takes more energy to release the nutrients of the whole food sandwich with the differences between meals resulting in a 9.7% increase in the net energy gain of the processed food meal.
Eat processed crap and you're effectively consuming 10% more calories than you would be were you eating healthier whole food alternatives.
Now this is a small study and certainly it's too soon to extrapolate this across the board, but were it to be true for all processed foods, given their viral spread across the developed world these past 30 years, and given that a 10% net energy gain is huge, this might be another great reason to ditch the Wonder bread and Velveeta.
Barr, S., & Wright, J. (2010). Postprandial energy expenditure in whole-food and processed-food meals: implications for daily energy expenditure Food & Nutrition Research, 53 DOI: 10.3402/fnr.v54i0.5144