Share thisEating and drinking support life and are compelled and controlled by positive drives of hunger and thirst and negative restraint of satiety.
Eating and drinking are episodic, and organized into meals with bouts of specific start times, durations, and amounts. All systems, signals, and switches (physiologic, metabolic, neurologic, anatomic, endocrine, behavioral, etc.) must influence eating and drinking bout by bout. So too, food and water intake should be observed and recorded bout by bout.
Why measure food and water intake?
All animals sense hunger and thirst and satisfy these by eating and drinking. If they do not; they die. Uncovering and understanding the systems for compelling and controlling what and when animals eat and drink has interested biologists for centuries. Some consider this the “holy grail” of biology.
We biologists are lucky; we experience what we study. We have an insider’s view. We know the tug of war of hunger and satiety. We can know a lot about eating just by thinking about our own hunger and satiety. We become hungry, we eat; we become satisfied, we stop eating; time passes and we become hungry again and we eat again and so it goes. Some of us live to eat, others eat to live; regardless, it’s vitally important to all of us. It’s also subtly important to all of us. Everything changes with eating; hormones, metabolites, body temperature, blood pressure, body composition, obesity, glucose tolerance, neural activities, fertility, health, disease, longevity. You name it; you measure it; eating changes it.
All in vivo lab animal experimentation would be improved by paying more attention to food and water intake. In this article, we’ll review concepts and methodologies for measuring food and water intake ofmice and rats.
Concepts and Definitions in Food and Water Intake
Elliot Stellar1 championed the simple, powerful model that feeding behavior relies on the ongoing interaction between mechanisms that drive eating (hunger) and those that restrain it (satiety). These mechanisms operate to control short term eating behaviors and long term control of bodyweight and composition.GerardSmith2 observed that “afterRichter’s classic [1922] experiments in rats it became clear that [food] intake in all mammals under a variety of conditions is episodic, not continuous.” Smith has championed the concept that the meal is the functional unit of eating, and that total food intake and its control should be considered in the context of individual meals and the sum of these meals.
Actually, meals are not the smallest unit of ingestive behavior. Bouts are the smallest unit of consumption. A bout is an episode of uninterrupted feeding or drinking, having a start time, duration, and amount consumed. A bout can be as small as one nibble, one bite of food or one sip or lick of liquid, or may be comprised of a series of these in quick succession. After a period of not eating or drinking the bout ends; the time between bouts is the Inter-Bout-Interval (IBI).