- Describe how hunger and eating are regulated
- Understand the link between metabolism, obesity, and health
- Describe anorexia and bulimia nervosa and their negative impacts
Eating is essential for survival, and it is no surprise that a drive like hunger exists to ensure that we seek out sustenance. While this section will focus primarily on the physiological mechanisms that regulate hunger and eating, powerful social, cultural, and economic influences also play important roles in our food consumption. This section will explain the regulation of hunger, eating, and body weight, and we will discuss the adverse consequences of disordered eating.
Physiological Mechanisms
Physiological mechanisms regulate hunger, including the contraction of an empty stomach, which secretes chemical messages signaling the need to initiate feeding behaviors. The pancreas and liver also generate chemical signals that induce hunger when glucose levels decrease (Konturek et al., 2003; Novin, Robinson, Culbreth, & Tordoff, 1985).
Satiation, or the feeling of fullness and satisfaction after eating, is regulated by physiological mechanisms such as signals from the pancreas and liver to shut off hunger and eating as glucose levels increase (Drazen & Woods, 2003; Druce, Small, & Bloom, 2004; Greary, 1990). The food’s passage through the gastrointestinal tract also provides important satiety signals to the brain (Woods, 2004). Leptin, a hormone produced by adipose (fat) tissue, also helps balance food intake and energy expenditure by inducing signals of satiety or hunger in the hypothalamus and brainstem. [1]
The various hunger and satiety signals that are involved in the regulation of eating are integrated in the brain. Research suggests that several areas of the hypothalamus and hindbrain are especially important sites where this integration occurs (Ahima & Antwi, 2008; Woods & D’Alessio, 2008). Ultimately, activity in the brain determines whether or not we engage in feeding behavior (Figure 1).
Metabolism and Body Weight
Our body weight is affected by a number of factors, including gene-environment interactions, and the number of calories we consume versus the number of calories we burn in daily activity. If our caloric intake exceeds our caloric use, our bodies store excess energy in the form of fat. If we consume fewer calories than we burn off, then stored fat will be converted to energy. Our energy expenditure is obviously affected by our levels of activity, but our body’s metabolic rate also comes into play.
metabolic rate
A person’s metabolic rate is the amount of energy that is expended in a given period of time, and there is tremendous individual variability in our metabolic rates. People with high rates of metabolism are able to burn off calories more easily than those with lower rates of metabolism.
We all experience fluctuations in our weight from time to time, but generally, most people’s weights fluctuate within a narrow margin, in the absence of extreme changes in diet and/or physical activity. This observation led some to propose a set-point theory of body weight regulation.
set point theory
The set-point theory asserts that each individual’s body establishes and attempts to maintain a stable body weight, or a set point, which is resistant to change. This set-point is in part genetically predetermined and efforts to move our weight significantly from the set-point are resisted by compensatory changes in the hunger and satiety cues that influence our energy intake and/or expenditure (Speakman et al., 2011)[2].
Some of the predictions generated from this particular theory have not received empirical support. For example, there are no changes in metabolic rate between individuals who had recently lost significant amounts of weight and a control group (Weinsier et al., 2000). In addition, the set-point theory fails to account for the influence of social and environmental factors in the regulation of body weight (Martin-Gronert & Ozanne, 2013; Speakman et al., 2011). Despite these limitations, set-point theory is still often used as a simple, intuitive explanation of how body weight is regulated.