Design of the Month

Counting calories in food

The following quotation is taken from page 32 of the New Scientist of 18 July 2009.

To explore how much cooking ramps up the caloric potential of food, Wrangham teamed up with Stephen Secor, an expert in the physiology of digestion at the University of Alabama, Tuscaloosa. Secor tested the impact of cooking and grinding food on the ability of Burmese pythons to digest and absorb the nutrients. Pythons may sound like a strange choice, but they are useful models for studying digestion because they remain motionless for days after eating, making it easy to link changes in metabolism to the food they have eaten.

Secor fed the snakes one of four options: intact raw steak, intact cooked steak, ground raw steak or ground cooked steak. He found that cooking or grinding the meat reduced the cost of digestion by 12.7 per cent and 12.4 per cent respectively. When he fed the pythons steak that had been both ground and cooked, the combination lowered the amount of energy needed to digest the meal by 23.4 percent.

  1. What were the treatments and how many of them were there?
  2. What were the treatment factors, and how many levels did each factor have?
  3. Using a suitable scale for the data, calculate the main effect of each factor and their interaction.
  4. Explain your conclusions in words that a non-specialist can understand.

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