The Body's "Energy-Saving Mode" Hidden in Extreme Heat: Overlooked "Resting Energy Expenditure" as the Crossroads of Summer Weight Gain
Ahead of the extreme heat expected in 2026, Ezaki Glico points to a drop in "resting energy expenditure" as a cause of "summer weight gain." Due to a decrease in the body's heat production and a lack of exercise as temperatures rise, the body enters an energy-saving state. As a countermeasure, Glico recommends maintaining muscle, moving frequently, and caring for gut bacteria that produce short-chain fatty acids.
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- 📰 Published: May 19, 2026 at 20:00
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With the recent decision and immediate implementation of the new term "Extreme Heat Day" (酷暑日) for days with maximum temperatures over 40°C, recent summers have become increasingly severe. According to the Japan Meteorological Agency's warm season forecast, the summer of 2026 is highly likely to be hotter than average. Furthermore, similar to last year, the onset and end of the rainy season are expected to occur earlier than usual, bringing the heat sooner.
Under these circumstances, while physical activity levels decline due to people staying indoors and exercising less to avoid the heat, it is difficult to drastically change one's diet, leading many to worry about "summer weight gain."
Ezaki Glico is focusing on "resting energy expenditure"—the energy naturally consumed in daily life—as a new perspective on "building a body less prone to weight gain" during periods of rising temperatures. Along with emphasizing its importance, we propose habits that make it easier to burn energy, which can be effortlessly incorporated into everyday life.
■ What is the Decrease in Energy Expenditure Due to the Body's "Energy-Saving Mode"?
Temperatures higher than average are expected for the summer of 2026, with severe heat likely starting early. Under such climate conditions, changes occur within our bodies.
First is a decrease in internal heat production due to the heat. In high-temperature environments, there is less need to generate new heat to maintain body temperature, causing the body to suppress heat production. As a result, the "resting energy expenditure" involved in breathing and organ functions tends to decline.
Another factor is the decrease in outdoor activities and exercise opportunities due to the heat. In high-temperature environments, activity levels tend to fall out of consideration for heatstroke risks, making energy expenditure from daily walking and exercise prone to dropping.
Thus, summer is a season when total daily energy expenditure easily decreases from two aspects: "a drop in resting energy expenditure (decrease in internal heat production)" and "a drop in energy expenditure from physical activity (lack of exercise)," tilting the body into what can be called an "energy-saving state."
Consequently, even if energy intake does not change significantly, the balance with consumption is easily disrupted, which is thought to increase the risk of "summer weight gain." How to maintain energy expenditure in daily life may become a crucial perspective for body conditioning this season.
■ "Resting Energy Expenditure": What to Keep in Mind for Daily Energy Use
The energy our bodies consume does not solely come from exercise. There is energy used even while staying still, for breathing, maintaining body temperature, and organ functions. This "base consumption" supporting all daily vital activities is called "resting energy expenditure." This "resting energy expenditure" is said to account for about 60% of total daily energy expenditure (*1), and along with physical activities like exercise and housework, it is a critical element heavily involved in daily energy consumption.
Furthermore, daily energy balance is said to have a significant impact in the long term (*2). For example, even a difference of a few dozen to 100 kcal per day could, through accumulation, become a turning point for changes in body shape.
Against this backdrop, we believe that how to maintain and improve energy expenditure throughout daily life, not just whether or not one exercises, will be a key factor in body conditioning moving forward.
*1: Horton ES. Am J Clin Nutr. 1983, 38, 972-977.
*2: Hill JO et al. Science. 2003, 299(5608), 853-855.
■ How to Increase Resting Energy Expenditure? The Key is Three Things!
We introduce three keys to boosting resting energy expenditure in daily life: "Muscle," "Posture & Movement (Shakin!)," and "Gut Bacteria."
The first is "Muscle." Muscle is a crucial tissue that supports the function of internal organs, which consume energy even at rest. Maintaining and improving muscle mass becomes the foundation for building a body that burns energy easily. (*3)
The second is "Posture & Movement (Shakin!)." This refers to correcting your sitting posture and avoiding the same posture for long periods by moving your body frequently. Accumulating small daily movements, such as sitting with a straight back or standing up for light stretching, is believed to lead to habits that make it easier to consume energy. (*4)
The third is "Gut Bacteria." Research is ongoing into the involvement of "short-chain fatty acids," produced by gut bacteria from dietary fiber and other sources, in energy metabolism. Consciously maintaining a gut environment and a diet that facilitates the production of short-chain fatty acids is also considered one approach to supporting resting energy expenditure. (*5)
Under these circumstances, while physical activity levels decline due to people staying indoors and exercising less to avoid the heat, it is difficult to drastically change one's diet, leading many to worry about "summer weight gain."
Ezaki Glico is focusing on "resting energy expenditure"—the energy naturally consumed in daily life—as a new perspective on "building a body less prone to weight gain" during periods of rising temperatures. Along with emphasizing its importance, we propose habits that make it easier to burn energy, which can be effortlessly incorporated into everyday life.
■ What is the Decrease in Energy Expenditure Due to the Body's "Energy-Saving Mode"?
Temperatures higher than average are expected for the summer of 2026, with severe heat likely starting early. Under such climate conditions, changes occur within our bodies.
First is a decrease in internal heat production due to the heat. In high-temperature environments, there is less need to generate new heat to maintain body temperature, causing the body to suppress heat production. As a result, the "resting energy expenditure" involved in breathing and organ functions tends to decline.
Another factor is the decrease in outdoor activities and exercise opportunities due to the heat. In high-temperature environments, activity levels tend to fall out of consideration for heatstroke risks, making energy expenditure from daily walking and exercise prone to dropping.
Thus, summer is a season when total daily energy expenditure easily decreases from two aspects: "a drop in resting energy expenditure (decrease in internal heat production)" and "a drop in energy expenditure from physical activity (lack of exercise)," tilting the body into what can be called an "energy-saving state."
Consequently, even if energy intake does not change significantly, the balance with consumption is easily disrupted, which is thought to increase the risk of "summer weight gain." How to maintain energy expenditure in daily life may become a crucial perspective for body conditioning this season.
■ "Resting Energy Expenditure": What to Keep in Mind for Daily Energy Use
The energy our bodies consume does not solely come from exercise. There is energy used even while staying still, for breathing, maintaining body temperature, and organ functions. This "base consumption" supporting all daily vital activities is called "resting energy expenditure." This "resting energy expenditure" is said to account for about 60% of total daily energy expenditure (*1), and along with physical activities like exercise and housework, it is a critical element heavily involved in daily energy consumption.
Furthermore, daily energy balance is said to have a significant impact in the long term (*2). For example, even a difference of a few dozen to 100 kcal per day could, through accumulation, become a turning point for changes in body shape.
Against this backdrop, we believe that how to maintain and improve energy expenditure throughout daily life, not just whether or not one exercises, will be a key factor in body conditioning moving forward.
*1: Horton ES. Am J Clin Nutr. 1983, 38, 972-977.
*2: Hill JO et al. Science. 2003, 299(5608), 853-855.
■ How to Increase Resting Energy Expenditure? The Key is Three Things!
We introduce three keys to boosting resting energy expenditure in daily life: "Muscle," "Posture & Movement (Shakin!)," and "Gut Bacteria."
The first is "Muscle." Muscle is a crucial tissue that supports the function of internal organs, which consume energy even at rest. Maintaining and improving muscle mass becomes the foundation for building a body that burns energy easily. (*3)
The second is "Posture & Movement (Shakin!)." This refers to correcting your sitting posture and avoiding the same posture for long periods by moving your body frequently. Accumulating small daily movements, such as sitting with a straight back or standing up for light stretching, is believed to lead to habits that make it easier to consume energy. (*4)
The third is "Gut Bacteria." Research is ongoing into the involvement of "short-chain fatty acids," produced by gut bacteria from dietary fiber and other sources, in energy metabolism. Consciously maintaining a gut environment and a diet that facilitates the production of short-chain fatty acids is also considered one approach to supporting resting energy expenditure. (*5)
FAQ
What is resting energy expenditure?
It's the energy consumed just to maintain vital functions like breathing and body temperature, accounting for about 60% of daily energy use.
Why is it easy to gain weight in summer?
Because energy spent maintaining body heat drops in hot weather, and people exercise less by staying indoors, reducing overall energy expenditure.
How can I prevent summer weight gain?
It is recommended to maintain muscle mass, engage in frequent light exercise or maintain good posture, and improve your gut environment to produce short-chain fatty acids.