Energy represents the capacity to do work, measured in calories. The concept of energy balance describes the relationship between energy consumed (intake) and energy expended. An energy surplus occurs when an individual consistently consumes more energy than their body expends over a period, leading to an accumulation of excess energy within the body.
How the Body Stores Excess Energy
The body stores surplus energy from food. Initially, excess glucose, a simple sugar, is converted into glycogen. This complex carbohydrate is stored primarily in the liver and muscles, serving as a readily accessible, short-term energy reserve. The liver can store approximately 100 grams of glycogen, while muscles can hold around 400 grams.
Once these glycogen stores are full, the body converts any remaining surplus of carbohydrates, fats, and even proteins into triglycerides. This process, known as lipogenesis, primarily takes place in liver cells and adipocytes, which are fat cells. These triglycerides are then stored extensively in adipose tissue, commonly known as body fat, which is the body’s main long-term energy storage site. Adipose tissue is capable of expanding to accommodate substantial amounts of stored fat.
Hormones, particularly insulin, play a significant role in regulating these energy storage processes. When blood glucose levels rise after a meal, insulin facilitates the uptake of glucose by cells for immediate energy or for conversion into glycogen. Insulin also promotes the synthesis and storage of fat, while simultaneously inhibiting the breakdown of stored fat. This hormonal action ensures that excess energy is efficiently captured and stored for future use.
Factors Contributing to Energy Surplus
An energy surplus arises from an imbalance where energy intake consistently exceeds energy expenditure. Energy intake refers to the total calories consumed from all food and beverages, comprising macronutrients such as carbohydrates, fats, and proteins. Carbohydrates and proteins each provide approximately 4 kilocalories per gram, while fats are more energy-dense, yielding about 9 kilocalories per gram.
Energy expenditure is the total amount of energy the body uses daily and consists of three main components. The basal metabolic rate (BMR) accounts for the largest portion, representing the energy required for basic bodily functions at rest. The thermic effect of food (TEF) is the energy expended during the digestion, absorption, and processing of nutrients. Physical activity, including both structured exercise and non-exercise movements, constitutes the most variable component of energy expenditure.
Multiple factors influence both energy intake and expenditure, contributing to a surplus. Behavioral aspects like large portion sizes, frequent consumption of energy-dense foods, and a sedentary lifestyle can increase intake and reduce expenditure. Physiological factors such as age, sex, body size, and genetics also affect an individual’s basal metabolic rate and how efficiently their body uses energy. When these elements collectively lead to a consistent consumption of more calories than the body burns, an energy surplus develops.
Health Outcomes of Sustained Energy Surplus
A prolonged energy surplus can lead to health consequences, primarily due to excessive body fat accumulation. The most direct outcome is obesity, defined as having excessive body fat that can impair health. Obesity is a complex condition linked to various metabolic changes within the body.
One health outcome is insulin resistance, where the body’s cells become less responsive to insulin. This reduced sensitivity means that glucose struggles to enter cells, leading to elevated blood sugar levels and increasing the risk of developing type 2 diabetes. High levels of circulating fats and sugars, often seen with sustained energy surplus, can also contribute to metabolic syndrome, a cluster of conditions that collectively increase the risk for cardiovascular diseases.
Cardiovascular diseases associated with chronic energy surplus include high blood pressure and dyslipidemia, which involves unhealthy levels of cholesterol and other fats in the blood. Excess body fat places additional strain on the heart, contributing to conditions like coronary artery disease and increasing the risk of heart attack and stroke. A sustained energy surplus and its resulting obesity have also been linked to an increased risk for certain types of cancer, including those affecting the esophagus, liver, pancreas, and colon.