The Physiology of Weight Control
Research-Based Insights into the Concept of "Calories In vs. Calories Out"
The Challenge of Weight Control
According to the CDC, 49.1% of U.S. adults tried to lose weight between 2013 and 2016 (Martin, Herrick, Sarafrazi, & Ogden, 2018). At the time, the nation's obesity rate was close 40%, a figure that has continued to grow since then. As you may have experienced or observed yourself, many people struggle to maintain a constant weight or reach their weight goals.
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And although the obesity epidemic we face today puts most attention on weight loss efforts, struggles with weight control can be other either end of the spectrum (Harvard Health Publishing, 2019). While some may struggle to shed pounds, others have difficulty gaining weight and/or put on muscle.
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Within the world of weight management, you may have heard the common refrain: "Calories In vs Calories Out." Although simplified, this description of the mechanisms behind body weight is fairly accurate.
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So if weight control is just that simple and straightforward, why do so many people struggle with weight control? And why is there such a wide spectrum of difficulties people face regarding weight?
Why Does Weight Control Seem Easier for Some People?
The human body has numerous mechanisms that regulate calorie intake and energy expenditure. Additionally, each person's caloric needs and output change based on body composition, activity level, hormonal control, and neurological signals (Widmaier, 2019). As a result, an identical diet-and-exercise regimen given to different people can result in a range of outcomes in weight change depending on the following factors (LibreTexts, 2019), which we'll discuss further in upcoming sections:
The mechanisms that regulate energy balance can be overridden by hyper-palatable food (often high-carb, high-fat), stress, recent eating patterns, and cognitive-behavioral conditioning (Amin & Mercer, 2016; Apolzan et al., 2017; Chambers, McCrickered, & Yeomans, 2008; Lennerz & Lennerz, 2018 ). As a result, the weight control strategies that work best will depend on a person's medical history, diet, weight, and genetics (Harvard Health Publishing, 2019).
Neural Controls
- Hunger vs Appetite
- Satiety
- Reward/pleasure system
- Cognitive/behavioral conditioning
Hormones
- Insulin
- Glucagon
- Leptin
- Ghrelin
- Dopamine
Activity Level
- Exercise
- Non-exercise activity
- Diet-related themogenesis
- Sleep
- Stress
Body Structure
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Height
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Weight
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Muscle mass
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Fat mass
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Age/life stage,
The Components of Weight Control
Throughout this site, we'll be exploring the physiological concepts behind the phrase "calories in vs. calories out" and discussing research on the factors that influence each side of the caloric balance equation. Before we explore this topics, let's first establish the components of body weight and weight control that we will be discussing.
For this purposes of this discussion, your body mass and weight can be divided into two main categories:
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lean body mass (organs, muscles, blood, skin, etc.)
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body fat.
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Generally speaking, people losing weight are primarily trying to minimize the amount of fat stored in their bodies, although some muscle mass will likely lost during the process (Harvard Health Publishing, 2019). When trying to gain weight, people increase both their fat and muscle mass in varying proportions, depending on their calorie intake and exercise habits (Widmaier, 2019).
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Your body is constantly utilizing fat stored in your body for energy as well as breaking down and repairing your muscle fibers. However, the overall change in your body fat and muscle mass will depend on your caloric balance (Widmaier, 2019).
