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New Study by Sadie Barr '09 and Prof. Wright Finds Eating Whole Foods vs. Processed Foods Burns More Calories

Professor Jonathan Wright, Sadie Barr '09 and Professor David Becker

Professor Jonathan Wright, Sadie Barr '09 and Professor David Becker

A new Pomona College study has found that digesting "whole" foods requires more energy than digesting "processed" food, providing new insight into why U.S. obesity rates have risen over time.

Sadie Barr ’09 and Professor Jonathan Wright co-authored the article “Post-Prandial energy expenditure in whole-food and processed-food meals; implications for daily energy expenditure,” which was published this month in the scientific journal Food & Nutrition Research, vol. 54.

In the study conducted by Barr, 17 subjects were fed meals of ‘whole-food’ cheese sandwiches (multi-grain bread and cheddar cheese) and ‘processed’ cheese sandwiches (white bread and processed cheese). Both meals had the same amount of calories, and were comparable in terms of protein (15-20%), carbohydrates (40-50%) and fat composition (33-39%). Each subject consumed a ‘whole-food’ meal and a ‘processed-food’ meal. After each one, their metabolic rates were measured, over a six-hour period, and the total post-meal energy expenditure compared.

The study found that the ‘processed-food’ meal required nearly 50% less energy to digest compared with the similar ‘whole-food’ meal. “Because less energy is needed to digest the ‘processed-food,’” explains Barr, “fewer calories are used, leading to a higher net-energy or calorie gain from processed food. Over time, these excess calories can add up, potentially leading to weight gain for those who consume diets high in processed food. On the other hand, a diet composed mainly of whole foods seems to require more energy for digestion leaving less energy, or calories available for storage.”

“It’s as if the energy that would naturally be expended by our bodies to break down foods is being superseded by the energy-intensive mechanized production of processed foods,” says Barr.

In the article, Barr and Wright hypothesize that the ‘processed-food’ meal may not require as much digestive-energy as the ‘whole-food’ meal because of differences in food composition and nutrient quality. As stated in the article, “the milling used to produce refined grains removes most of the bran and germ, and the accompanying nutrients that they offer, such as B vitamins, phytonutrients, phenols, minerals, fiber, and proteins.” This makes the starch of the ‘processed-food’ PF meal more readily digestible and offers fewer metabolites that would otherwise require energy to be assimilated.

The study has been drawing attention. Michael Pollan, author of the much-acclaimed The Omnivore’s Dilemma and In Defense of Food, tweeted about the “fascinating study” and featured it on his site soon after its publication.

Barr became interested in digestive energy during an Animal Physiology class taught by Wright. After learning about diet-induced thermogenesis (DIT), the increase in metabolic rate/energy expenditure after eating, Barr and her lab partners decided to examine ‘whole’ versus ‘processed’ foods in a small experiment. After encouraging results, Barr was even more intrigued.

“I knew that were many scientific studies to suggest that whole foods are better for you and lead to a healthier body weight but there weren’t any definitive studies that stated why this was the case in physiologic terms…. There were really no studies that even looked at DIT responses to whole and processed foods on human subjects.”

Barr turned her interest into a senior independent study project with herself as the subject, testing different types of whole and processed meals and comparing her DIT responses. “Granted it wasn’t the most scientific study since it was only one subject and that was the scientist,” admits Barr. “But it produced preliminary results to indicate that my hypothesis – whole food digestion takes more energy than processed food digestion – could be true.”

At the end of her senior year, Barr applied for and received a Howard Hughes Medical Institute summer research grant sponsored by Pomona, which funded the study described in the article. She completed the study the summer after her senior year. Wright, she said, provided invaluable guidance throughout her senior project and the final study.

Barr is currently working for an environmental consulting firm based in Baltimore, MD, and will start classes this fall through Johns Hopkins University to attain a Masters in Environmental Planning and Management.