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We’ve all heard lots about why whole foods are better than processed ones (or, as Michael Pollan calls them, “edible food-like substances”). But this is a new one to me: your body has to work harder to process unprocessed food, so you actually burn more calories in the five to six hours after eating. It has to do with “diet-induced thermogenesis” (DIT), also sometimes known as the “thermic effect of food,” which is:
the energetic costs of postprandial processes such as food breakdown, enzyme synthesis, peristalsis, nutrient uptake/assimilation, and secondary metabolism (e.g. urea synthesis)… typically responsible for about 10% of daily energy expenditure in humans.
The quote comes from a new paper in Food and Nutrition Research [full text available here] by researchers at Pomona College. They ran a simple but elegant experiment with 17 volunteers who ate two types of cheese sandwich on two different days. One sandwich was cheddar on multigrain; the other was processed cheese on white. The sandwiches were matched to have identical calories and similar ratios of carbohydrate, fat and protein. Then they measured the metabolic rate at hourly intervals for six hours. The result: the volunteers burned 137 DIT calories after the whole food sandwich, compared to just 73 calories after the Kraft special.
That’s actually a significant number of calories. One thing I noticed is that the sandwiches weren’t identical in terms of nutrient composition. The whole-food sandwich had 40% carb, 39% fat and 20% protein, while the processed sandwich had 50%, 33% and 15% respectively. So maybe that accounts for some of the difference — but in some sense, that’s the point. Processed foods do tend to have more easily accessible carbohydrates, so the comparison is pretty fair. It’s also worth noting that bread and cheese are already processed foods; the authors note that the difference would be even more stark if you used something like a raw fruit or vegetable.