169
chapter eight
Fasting
David Rosen and Allyson Hindle
8.1 Snapshot: Living without food
Many marine mammals undergo regular, prolonged periods of forgoing food. Surprisingly,
these fasting episodes often coincide with life stages when additional energy is needed for
important tasks: long-distance migrations, growth in offspring, lactation in females, and
territory defense in males. How can these critical activities be supported during fasting
without animals starving to death?
The answer lies in several specific, but equally important questions:
• What is the difference between fasting and starvation?
• How does an animal’s physiology change over the course of the fast?
• What types of on-board energy reserves provide fuel for the fasting animal?
• How can an animal minimize energy requirements during a fast?
• What hormones control fasting physiology in marine mammals?
Contents
8.1 Snapshot: Living without food ........................................................................................ 169
8.1.1 What is fasting and when does it occur? ............................................................ 170
8.1.1.1 Pinnipeds ................................................................................................. 171
8.1.1.2 Cetaceans .................................................................................................. 171
8.1.2 Energy substrates during a fast ........................................................................... 172
8.1.2.1 Pinnipeds ................................................................................................. 176
8.1.2.2 Other marine mammals ......................................................................... 178
8.1.3 Energetic conservation during fasting ............................................................... 178
8.1.3.1 Pinnipeds ................................................................................................. 180
8.1.3.2 Other marine mammals ......................................................................... 181
8.1.4 Hormonal controls ................................................................................................. 181
8.1.4.1 Pinnipeds ................................................................................................. 182
8.1.4.2 Cetaceans .................................................................................................. 183
8.2 Toolbox ................................................................................................................................ 183
8.2.1 Methods of measuring mass loss/body condition ........................................... 183
8.2.2 Measuring metabolism and calculating metabolic depression ...................... 184
8.2.3 Plasma metabolites as biomarkers of fasting phase ......................................... 185
8.2.4 Turnover of metabolic tracers .............................................................................. 186
8.3 Lingering mysteries ........................................................................................................... 186
Glossary ........................................................................................................................................ 187
References .....................................................................................................................................187
chapter eight
Fasting
David Rosen and Allyson Hindle
8.1 Snapshot: Living without food
Many marine mammals undergo regular, prolonged periods of forgoing food. Surprisingly,
these fasting episodes often coincide with life stages when additional energy is needed for
important tasks: long-distance migrations, growth in offspring, lactation in females, and
territory defense in males. How can these critical activities be supported during fasting
without animals starving to death?
The answer lies in several specific, but equally important questions:
• What is the difference between fasting and starvation?
• How does an animal’s physiology change over the course of the fast?
• What types of on-board energy reserves provide fuel for the fasting animal?
• How can an animal minimize energy requirements during a fast?
• What hormones control fasting physiology in marine mammals?
Contents
8.1 Snapshot: Living without food ........................................................................................ 169
8.1.1 What is fasting and when does it occur? ............................................................ 170
8.1.1.1 Pinnipeds ................................................................................................. 171
8.1.1.2 Cetaceans .................................................................................................. 171
8.1.2 Energy substrates during a fast ........................................................................... 172
8.1.2.1 Pinnipeds ................................................................................................. 176
8.1.2.2 Other marine mammals ......................................................................... 178
8.1.3 Energetic conservation during fasting ............................................................... 178
8.1.3.1 Pinnipeds ................................................................................................. 180
8.1.3.2 Other marine mammals ......................................................................... 181
8.1.4 Hormonal controls ................................................................................................. 181
8.1.4.1 Pinnipeds ................................................................................................. 182
8.1.4.2 Cetaceans .................................................................................................. 183
8.2 Toolbox ................................................................................................................................ 183
8.2.1 Methods of measuring mass loss/body condition ........................................... 183
8.2.2 Measuring metabolism and calculating metabolic depression ...................... 184
8.2.3 Plasma metabolites as biomarkers of fasting phase ......................................... 185
8.2.4 Turnover of metabolic tracers .............................................................................. 186
8.3 Lingering mysteries ........................................................................................................... 186
Glossary ........................................................................................................................................ 187
References .....................................................................................................................................187