CHAPTER 6 Summary

• The macronutrients in our food (proteins, carbohydrates, and fats) are sources of dietary energy.
• Fats are the most energy-rich organic molecules in our diet. Fats contain twice as many Calories per gram as carbohydrates and proteins.
• When we consume more Calories than we use, our bodies store the excess energy in the bonds of glycogen and body fat. Fats store more energy than does glycogen.
• Cells carry out chemical reactions that break down food to obtain usable energy in the form of ATP.
• In the presence of oxygen, aerobic respiration produces large amounts of ATP from the energy stored in food.
• Aerobic respiration occurs in three stages: (1) glycolysis, (2) the citric acid cycle, and (3) electron transport. The first stage occurs in the cytoplasm, the latter two in the mitochondria. Electron transport produces the bulk of ATP.
• In the absence of oxygen, fermentation follows glycolysis and produces lactic acid in animals (or, in some organisms, alcohol). Fermentation produces far less ATP than does aerobic respiration.
• Exercise helps burn stored Calories. A combination of eating fewer Calories and exercising more will result in weight loss, although hereditary factors play a large role in determining a person’s weight.
• During exercise, glycogen is used first. Stored fats are tapped only when glycogen stores have been depleted, as might occur during long periods of exercise.
• The ultimate source of energy in food is the sun. Photosynthesizers such as plants trap the energy of sunlight and convert it into the chemical energy of sugar. Animals then eat this sugar either directly or indirectly.
• Photosynthesis and respiration form a cycle: the carbon dioxide given off by animals, plants, and all organisms that perform aerobic respiration is used by photosynthesizers to make glucose and oxygen during photosynthesis.

• MORE TO EXPLORE

  • Rozin, P., et al. (2003) The ecology of eating: smaller portion sizes in France than in the United States help explain the French paradox. Psychological Science 14:450–54.
  • Guiliano, M. (2007) French Women Don’t Get Fat: The Secret of Eating for Pleasure. New York: Vintage Books.
  • Kessler, D. (2010) The End of Overeating: Taking Control of the Insatiable American Appetite. Emmaus, PA: Rodale Books.
  • Yale Rudd Center for Food Policy and Obesity http://www.yaleruddcenter.org/
  • Let’s Move http://www.letsmove.gov/