Two-thirds of energy goes to thermoregulation: how the body keeps temperature steady and powers metabolism

Thermostat in the body: why two-thirds of our energy goes to staying warm

Energy isn’t just about fueling workouts or building muscle. A big chunk of what we burn every day goes to something we hardly notice—keeping our core temperature steady. In simple terms, your body spends roughly two-thirds of its total energy to stay warm or cool enough to function. That figure isn’t a rigid rule, but it captures a key truth: thermoregulation is a major player in metabolism.

Let me explain how this works and why it matters for anyone studying the science behind nutrition coaching.

What total energy expenditure really looks like

If you break it down, total energy expenditure (TEE) comes from a few big pieces. First, there’s your basal metabolic rate (BMR) or resting energy expenditure—the calories your body uses just to stay alive at rest. Then you’ve got the thermic effect of food (TEF), the energy your body spends to digest, absorb, and process what you eat. Finally, there’s physical activity energy expenditure (PAEE), which is the energy burned during movement, exercise, and even the random fidgeting we do during the day (that “NEAT” stuff—non-exercise activity thermogenesis).

Thermoregulation slides in as part of these processes, but it’s especially noticeable when conditions change. In a cold environment, your body works harder to generate heat. In a hot environment, it works to dissipate heat. Both scenarios tilt the energy balance. In some circumstances, thermoregulation can account for a sizable share of total expenditure, which is where that 2/3 number comes from.

Why heat and cold are such energy hogs

Think of your body as a thermostat with a few built-in tactics. When you’re chilly, you might shiver. Shivering is basically rapid muscle contractions that produce heat. This generates a measurable burst of energy use—sometimes a lot, sometimes a little, depending on how cold you are and how much your body has to work to stay warm.

When it’s warmer, your body shifts gears instead of shivering. Heat is dumped through the skin via vasodilation (widening of blood vessels), sweating, and breathing rate changes. These processes also cost energy, though not always as visibly as shivering. Brown adipose tissue (brown fat) can contribute to heat production in some people, especially in colder conditions, adding another layer to the thermoregulatory energy budget.

All this means that ambient temperature, clothing, and even duration outdoors can nudge daily energy needs up or down. The same person may burn more calories on a frosty day than on a mild one, all because the body is working to keep core temperature stable.

What this means for a nutrition coach’s toolkit

If you’re guiding clients or designing meal plans, thermoregulation is a practical puzzle piece. Here are a few takeaways you can translate into everyday guidance.

• Environment matters: A person living in a cooler climate or someone exposed to drafts may burn more energy through thermogenesis. That doesn’t mean you blindly pad calories year-round, but it does mean recognizing seasonal shifts and adjusting targets as needed.

• Body size and composition matter: Bigger bodies generally have higher basal needs, but they also lose more heat when cold, which can raise the thermogenic cost. Lean individuals might feel the impact of cold more quickly, while those with higher body fat may have different regulatory dynamics.

• Activity and posture add up: Standing and walking burn more energy than sitting, even if the moment-to-moment difference feels small. For someone in a chilly environment, extra NEAT (think pacing, light fidgeting) can tilt the thermogenesis balance a bit more.

• Diet quality plays a supporting role: Adequate protein helps with thermoregulation by supporting muscle and metabolic processes, while balanced meals stabilize energy availability. TEF varies with macronutrient composition, so meals with balanced protein, fats, and carbs keep energy flux smoother.

A practical way to talk about this with clients

Let’s connect the science to real life. A simple way to frame it goes like this:

• Your body uses energy to stay warm as conditions demand.

• This energy cost adds to what you’d normally burn from activity and digestion.

• In colder weather or during exposure to cold, you might see a modest bump in daily calories needed.

• In hot weather, the energy cost shifts toward cooling mechanisms—not always a huge extra burn, but not zero either.

With that frame, you can tailor conversations without leaning on charts and formulas all the time. You can say things like, “If you’re training outside in winter, you may need a bit more energy on those days,” or, “When it’s hot, focus on staying hydrated and comfortable, and your appetite may respond differently.” It’s about mindful adjustments rather than rigid rules.

A quick tour of measurement tools and real-world clues

In the lab, people measure energy expenditure with indirect calorimetry or metabolic carts to get precise numbers. In the field, coaches rely on smarter estimates and lived experience. Here are practical anchors you can use:

• Basal or resting energy: Everyday rest is important, but you won’t rely on it alone to size meals. It’s part of a bigger picture.

• Thermoregulation as a factor: If a client spends lots of time outside in the cold, you might note a slightly higher energy budget during those periods. The change isn’t dramatic every day, but it can accumulate.

• Temperature and clothing as cues: A client who complains of being cold for long stretches of the day may benefit from a small calorie bump or warmer clothing options to reduce heat loss and preserve appetite and energy levels.

• Seasonal adaptation: In winter, some people naturally eat a bit more as a consequence of thermogenesis. In summer, the opposite might occur. Track patterns rather than chasing a single number.

A peek into the science behind the habit

Let me throw in a quick analogy. Think of your body as a smart thermostat. It’s not just about turning heat on or off; it’s about balancing several inputs—ambient temperature, clothing, activity, and even time of day. When the thermostat detects a cold bias, it calls for heat—muscle work, shivering, and increased metabolic rate. When it detects heat, it opens the vents—more blood flow to skin, sweating, and breathing changes. The energy cost isn’t tiny; it’s built into the way we stay comfortable, alert, and healthy.

Some other factors that influence the thermoregulation piece

• Age and metabolic rate: As we age, metabolic efficiency shifts. The body’s temperature regulation mechanisms adapt, which can alter energy needs.

• Body composition: Muscle tissue consumes energy even at rest, and fat tissue provides insulation that can dampen some heat loss. Each piece changes how much energy thermoregulation requires.

• Illness and fever: When you’re fighting an infection, your body often runs hotter, which can spike energy expenditure beyond usual levels.

• Climate and altitude: High altitude and dry air can affect heat loss and heat production dynamics, nudging energy needs in small, noticeable ways.

What this all means for NAFC-level nutrition knowledge

For students and professionals following the NAFC nutrition framework, thermoregulation is a reminder that energy balance isn’t a fixed target. It’s a dynamic system influenced by environment, body composition, activity, and even season. When you’re assessing a client, you can consider:

• How often they’re exposed to cold or heat and how that exposure might subtly nudge energy needs.

• Their typical clothing choices and comfort temperature ranges, which affect heat loss.

• Their intake patterns around training and rest days, especially in changing weather.

• How hydration and electrolyte balance interact with temperature regulation, particularly in hot environments.

Putting it into practice with clear messaging

• Keep the language practical: Talk about “energy needs that shift with the weather” rather than presenting a lot of abstract numbers.

• Use relatable examples: “If you’re outside in a windy 40-degree day for two hours, you might burn a bit more energy than you would inside.”

• Offer light, actionable plans: Suggest flexible meal targets that can accommodate mild seasonal changes, rather than rigid year-round numbers.

A few lines you can borrow when explaining to clients or peers

• “Your body has a built-in thermostat, and it spends energy to keep you comfortable.”

• “Cold triggers heat production; hot environments trigger cooling efforts—both cost energy.”

• “Seasonal and daily changes aren’t bad news. They’re clues about how to tune energy intake without turning meal planning into a guessing game.”

Cultural touches and real-world flavor

People live in climates as varied as the foods they eat. In colder places, meals might reliably become heartier in winter, not just to satisfy taste buds but to support thermogenesis and daytime energy. In warmer climates, hydration and electrolyte balance can feel more urgent, and appetite sometimes mirrors heat exposure. These aren’t separate ideas; they’re part of the same story about how energy flows through our days.

A concise recap

• Total energy expenditure includes BMR, TEF, PAEE, and thermoregulation.

• Thermoregulation can account for a sizable portion of energy use, especially in cold or hot environments.

• Shivering, sweating, and changes in skin blood flow are the body’s main tools for keeping temperature steady, and each uses energy.

• Practical nutrition coaching points: recognize environmental influences, consider body size and composition, and be ready to adjust targets when seasons or conditions shift.

• Use both science and everyday observation: lab tools offer precision, while real-world behavior provides the patterns you’ll use in daily coaching.

Final thoughts

Understanding thermoregulation isn’t just about calories. It’s about appreciating how the body preserves function under varying conditions. When you know that a sizable slice of energy goes toward keeping the core temperature stable, you gain a clearer lens for advising clients on intake, timing, and lifestyle adjustments. It’s a small piece of a larger puzzle, but it helps you connect physiology with practical, compassionate coaching—the kind that respects individual differences and the realities of daily life.

If you’re digging into the science behind nutrition coaching, keep this concept in your toolkit. It’s a reminder that metabolism is a living, breathing system—one that’s constantly balancing heat and effort, day in and day out. And in that balance lies the key to thoughtful, evidence-informed guidance that helps people feel their best, no matter what the thermostat says outside.