Today’s prompt, and the companion piece behind it.
Metabolic Rate
What determines basal metabolic rate, and can you change it?
The Short Answer
Basal metabolic rate (BMR), the calories you burn at complete rest, is determined primarily by body size, body composition (muscle vs. fat), age, and genetics. You can influence it modestly through building muscle and staying active, but the effect is smaller than many people hope. The bigger lever is total daily energy expenditure, which includes activity. Don’t obsess over “boosting metabolism”: focus on sustainable habits instead.
Something to Sit With
Your metabolism isn’t as malleable as marketing suggests. Some things you can change; most you can’t. But knowing what’s actually in your control lets you focus your effort where it matters.
Learn More
What BMR is. Basal metabolic rate is the energy your body needs to maintain basic functions at complete rest: breathing, circulation, cell production, brain function. It is measured under strict conditions: lying still, fasting, in a thermoneutral environment. What most people experience day-to-day is the closely related resting metabolic rate (RMR), which is slightly higher and easier to measure, and it is RMR that the standard figure describes, accounting for 60-75% of total daily energy expenditure. That makes it the largest of the three components, ahead of activity (15-30%) and digestion (about 10%).[1]
What determines BMR. The main factors:
Body size. Larger bodies require more energy to maintain. This is the biggest factor: more tissue means more metabolic work.
Body composition. Muscle is more metabolically active than fat. A muscular person burns more at rest than a person of the same weight with more fat.
Age. Resting metabolic rate falls with age, by more than changes in body composition explain. In one study of German adults over 60, it fell 5% a decade in men and 3% in women after that adjustment; in a long-running US study, men’s decline was faster at 70 to 80 than at 40 to 50.[1]
Sex. Men typically have higher BMR than women of similar size, largely due to greater muscle mass and hormonal differences.
Genetics. There’s individual variation that genetics influences. Some people genuinely have faster or slower metabolisms, though the range is narrower than often claimed.
Hormones. Thyroid hormones are the primary metabolic regulators. Hyperthyroidism raises BMR; hypothyroidism lowers it. Other hormones play secondary roles.
What you can change.
Build muscle. More muscle tissue increases BMR. But the effect is modest: each pound of muscle burns roughly 6 calories per day at rest.[1] Gaining 10 pounds of muscle (which requires significant effort) might add roughly 60 daily calories to BMR. Meaningful, but not transformative.
Stay active, with a caveat. NEAT (non-exercise activity thermogenesis), the calories burned through daily movement, varies far more between people than BMR does; it is the most variable component of daily expenditure, ranging from negligible in a desk job to over 2,000 kcal a day in an active one. But varying is not the same as choosing: it appears to be largely biologically set. When obese participants lost weight they did not move more; when lean participants gained weight they did not move less.[2]
Avoid severe restriction. Sustained calorie restriction can lower metabolic rate.[3] It also quietly reduces NEAT, and that suppression may outlast the diet: movement staying down after normal eating resumes, which is offered as one contributor to regain.[2]
Maintain thyroid health. If thyroid function is genuinely impaired, treatment restores normal metabolic rate.
What you can’t meaningfully change.
Age. Keeping muscle protects the share of resting expenditure that muscle carries, but the decline with age runs beyond what body composition explains.[1]
Genetics. Your baseline is your baseline.
Quick fixes. On this page’s reading, no supplement, food, or exercise meaningfully “boosts” metabolism in a lasting way. Green tea, spicy food, cold showers: any effects are likely small and temporary.
The practical implication. Rather than chasing metabolic hacks, focus on:
Sustainable eating patterns. These matter more than metabolic rate.
Building and maintaining muscle. Both for the small BMR increase and for health generally.
Total activity. Move throughout the day. NEAT is the largest source of variation in daily expenditure, and much of it isn’t under conscious control, so the movement you do choose is worth protecting.
Avoiding crash diets. They can lower metabolic rate and are rarely sustainable anyway.
Further reading:
- Guyenet SJ, The Hungry Brain[4] (2017) — Metabolic regulation and body weight
- Müller MJ et al., “Metabolic adaptation to caloric restriction and subsequent refeeding: the Minnesota Starvation Experiment revisited”[5] — American Journal of Clinical Nutrition, 2015
- Levine JA, “Non-exercise activity thermogenesis (NEAT)”[6] — Best Practice & Research Clinical Endocrinology & Metabolism, 2002
- Fung J, The Obesity Code[7] (2016) — Metabolic adaptation and weight regulation
Written by AI, directed and approved by me. How this is made →
You already know what to eat
You already know enough.
The information isn’t the problem. You have plenty of information.
The problem is that by the time you’re standing in front of the fridge — tired, negotiating with yourself about whether you’ve earned a snack — it’s already too late. Your habits have voted. Willpower shows up late, outnumbered.
So what if the right thought arrived before all of that?
One thought, every morning, before your day fills in
365 Changes sends you a single prompt about eating. It arrives early — before hunger, before decisions, before habits kick in.
Not a meal plan. Not a rule. Just a question or idea to sit with while you make coffee. Each is simple, but they accumulate.
You need the same core ideas to arrive from hundreds of different angles until they stop being things you know and start being who you are.
Get the daily prompt free:
Here’s what a prompt looks like
Each morning you’ll get a question or scenario like:
You’re in a bad mood and craving comfort food. What do you do first?
Click any of these and read the response. Each one is a complete thought worth reading on its own. The daily email makes sure one arrives before you need it.
- What determines basal metabolic rate, and can you change it?
- You’re confident in your food choices regardless of social context. What does social confidence look like?
- What happens to the body’s glycogen stores during the first 24 hours of fasting, and what happens after they’re depleted?
Why daily? Why morning? Why small?
Daily, because change doesn’t happen in one big moment of clarity. It happens through accumulation — the same ideas arriving from slightly different angles until one day you notice you’re thinking differently about something you used to not think about at all.
Morning, because evenings are when you negotiate. Mornings are when you can still hear yourself think. There’s a small window before the momentum builds, before the habits wake up. That’s when a thought can land.
Small, because you’ve already heard it all. You don’t need another article, another tip, another list. You need the right ideas to keep showing up until they stick.
This is not a diet program
There’s no tracking. No streaks. No badges. No notifications begging for attention.
If you open the email, good. If you don’t, it doesn’t guilt you. There’s no streak to break. Tomorrow another one arrives.
One email. It asks almost nothing. It just shows up.
Free. No tracking. No streaks. Just one email, every morning.
Does it work?
Honestly? We don’t know if it will work for you.
I built this for myself. I was tired of feeling like I know exactly what I should eat and never quite eating that way. Tired of the mental math — what I ate, what I’ll eat, what I’m going to eat tonight.
I didn’t need more information. I needed the right thought to arrive at the right time. So I built something that does that, every morning, and I started using it.
It’s working. Slowly. I can’t point to a moment when things changed. I just notice that they have.
—Craig
How this gets made is written down too.
The writing here is done by AI. I direct it, and I approve everything before it publishes. Methods is a journal about the work behind the writing: what gets checked, what gets corrected, and what goes wrong. Methods is free, public, and nothing you have to read.
One way to find out:
Want more depth?
Some mornings the prompt will make you curious. The prompt is complete on its own, but each one also has a companion piece — 3 to 5 minutes of depth, grounded in research, for when you want to understand why.
All 500 companions are free to read. Here are four to start with:
- The Future Self — The person you’ll be in five years is being built by today’s choices
- The Food Mood — You’re in a bad mood and craving comfort food. What do you do first?
- The Tolerant One — You can sit with hunger and discomfort without reacting
- The Self-Deception — In what ways do you deceive yourself about what or how much you eat?
The daily email carries each prompt with its full companion. Subscribe below and it comes to you every morning.