The evolutionary pressures on our early ancestors helped to shape the biology in our bodies today. Early man gained survival advantage by extracting the most calories from the smallest amount of food. This partly explains our craving for fatty foods – which have twice the calorie density of protein-rich and starchy foods.
But our lives today are comparatively sedentary compared with our early ancestors, and fatty, calorie-rich foods are not scarce but easily available, conferring what might alternatively be described – in view of the obesity epidemic – as a survival disadvantage.
Now, a new study from Harvard University, published in the American Journal of Physical Anthropology, finds that cooking – a unique human practice – can free even more calories from fat-rich foods.
First author Emily Groopman – now an MD-PhD candidate at Columbia University in New York, NY – explains why they did the study:
“It’s been very well established that cooking starch- and protein-rich foods does increase the available calories you can get out of them. But when I began looking at the literature, no one had really examined the third major macronutrient, which is fat.”
Groopman and colleagues found that mice fed on a diet of cooked fat-rich food, weighed on average significantly more than mice fed on the same amount of fat-rich food that had not been cooked.
To discover this, they fed 20 mice over several weeks four different diets based on peanuts: raw and whole, raw and blended, roasted and whole, and roasted and blended.
By keeping track of each mouse’s weight, food intake and exercise, the researchers were able to deduce the mice derived more energy from cooked peanuts than raw ones.
Groopman says they found that the “mice experienced similar changes in body weight, although they ate more of the raw peanuts.”
“That meant they were able to extract more calories from the same amount of food if the peanuts were roasted than if they were raw,” she explains.
Also, when the team analyzed the mice’s feces, they found evidence that fat had been digested more when peanuts were cooked.
One reason for this was evident when they examined the cells of the peanuts. When they were cooked, the cell walls were changed in a way that released more of the fats trapped inside the cells.
Peanuts are on average 50% fat, says Groopman, but much of this is inaccessible when we digest raw peanuts because they have very tough cell walls. Also, the fat is stored inside structures called oil bodies that are coated with proteins – called oleosins – that hinder digestion.
The study shows that as well as breaking down cell walls, cooking appears to alter the oleosins. Groopman explains:
“When the nuts are raw, the oil bodies are fully covered by the proteins. But after cooking, what we find is that there are just fragments of oleosins on the surface, which we hypothesize makes it far easier to get at the lipids.”
The study is interesting not only because it reveals the important role of cooking in helping humans get more out of their food, but also because it offers information that could be useful today – for example, cooking might be a way to adjust the calorie content of processed food to fit the energy needs of the consumer.
Last month, Medical News Today learned of a study that suggested adipocytes, or fat cells, may shield us from infection. Researchers from the University of California-San Diego found that fat cells under the skin protect us against infection by producing antimicrobial peptides that ward off pathogens, such as the staph bacterium S. aureus.