This is a repost from 2009 and 2012. I was motivated to look it up when I saw a new study about processed food and how it contributes to weight gain. Let me repost this old one and I’ll address the new study and some thoughts about processed food in follow-up posts.

________

Can just changing the texture of food, processing it, contribute to weight gain?

That was a question Kyoko Oka, et al. asked in:
Food Texture Differences Affect Energy Metabolism In Rats, Journal of Dental Research, June 2003*

Two groups of rats were fed either standard pellets or easily-chewed, soft pellets (made softer by increasing air content, as is done in breakfast cereals).

• Calorie intake was measured to be the same in both groups.
• Nutritional composition of diet was the same in both groups.
• Meal duration was the same in both groups.
• Calorie expenditure via locomotion was measured to be the same in both groups.

If energy intake, nutrient intake, and energy expenditure (activity) are similar, you would expect body weight and body fat to be similar. That wasn’t the case.

Findings:

• After 18 weeks and beyond, “body weight in the soft-fed group was significantly greater.”
• After 22 weeks the rats were dissected. Weight of abdominal fat in the soft-fed group was significantly greater, enough to designate the rats as obese.
• The increased body weight in the soft-fed rats was due to increased body fat.

The authors concluded:

“In this study, 22 weeks was long enough to produce obesity in soft-fed rats.”

Mechanism:

The cost for digestion in the soft-fed rats was lower. This cost was measured in body temperature, which was significantly lower in the soft-fed group after a meal (up to 1 hour). Body temperature (thus, energy expenditure) was also significantly lower in the soft-fed group “during the dark period” or overnight.

If weight loss and reduction of body fat are the goal, merely reducing the number of calories consumed won’t be as effective as also reducing the amount of processed food consumed.

* I read about this study in Richard Wrangham’s book “Catching Fire: How Cooking Made Us Human” back in 2009.