Metabolism is one of those words that gets thrown around constantly, usually with very little explanation. People talk about having a fast metabolism, a slow metabolism, or needing to boost it, as if it were a button you could press or a fire you could stoke. I know my patients will often tell me that they have a slow metabolism, as if it is part of their DNA, which is why they can’t lose weight.
I see so many patients who have dieted for years, bounced between plans, or those who now use GLP-1 medication, and for them, metabolism can feel like a mystery that never quite works in their favour. So let’s do a deep dive into what metabolism actually is, what we really mean when we talk about raising it, and why focusing only on calories completely misses the point.
What is our metabolism? At its simplest, metabolism is the sum of all the processes that keep you alive. Every heartbeat. Every breath. Every nerve signal. Every repair job. Every hormone message. When I talk about raising metabolism, what I mean is creating a body that feels safe enough to burn energy rather than store it.
Your metabolism decides:• How much energy you burn at rest• How efficiently you use food• Whether your body stores or releases fat• How hungry you feel• How well you cope with stress• How warm, alert, and resilient you feel day to day
So, when someone says their metabolism is broken, what they usually mean is that several systems are under strain at the same time. Calories are part of this picture. But they are not the whole story. Not even close.
Why dieting so often slows metabolismTraditional dieting works on a simple idea. Eat less. Move more. Burn more calories than you eat. However, the body does not see it that way.
When calories drop, especially for long periods, your body assumes food is scarce. It responds by becoming more efficient. This is not a flaw; it is survival biology. In clinic I use the analogy of earnings. If you had a job on 100k, but then moved jobs to 50k, you have to make some adjustments or you will be in trouble. The body is no different. Its ultimate aim is to survive, so if you feed it less ‘fuel’ than it needs, it will adjust itself to cope – to survive. Your body doesn’t care whether you are fat or thin, it just wants you to stay alive.
Over time, this reduction in food can lead to:• A lower resting metabolic rate• Loss of lean muscle• Rising cortisol• Reduced thyroid hormone conversion• Increased hunger signals• Reduced spontaneous movement and energy
This is why yo yo dieting is so damaging. Each cycle teaches the body to conserve energy more aggressively next time. For women, especially through perimenopause and menopause, these adaptations can be amplified
People often think their metabolism has slowed because of age. In reality, it is often a history of restriction layered on top of stress, poor sleep, and muscle loss, coupled with poor digestion and, for women, hormone imbalance.
What GLP 1 drugs change and what they do notGLP 1 medications change appetite signalling. They reduce hunger, slow gastric emptying, and improve blood sugar control. For many people, they are genuinely life changing. However, they do not magically fix metabolism.
In fact, they can expose weaknesses in the system if support is not in place.
Common issues seen with GLP 1 use include:• Undereating protein (lowering metabolism further)• Rapid weight loss with muscle loss• Fatigue and low energy• Feeling cold• Constipation and gut slowing• Stalls after initial weight loss
None of these are about motivation. They are physiological responses. Remember, if intake drops too low or protein is inadequate, the body adapts by conserving energy. Weight loss may continue, but metabolic resilience ultimately suffers.
Muscle. The metabolic engine no one talks about enoughMuscle is one of the biggest drivers of metabolic health. We have gone into detail about this in our protein series (you can read this here), but to summarise:• It burns energy at rest.• It improves insulin sensitivity.• It stabilises blood sugar.• It supports hormone balance.
When people lose weight without protecting muscle, metabolism almost always slows. This is why weight training matters. But not in the punishing, bootcamp sense. Resistance work is a signal to the body that strength is still needed. That tissue must be preserved.
Without that signal, especially during calorie restriction or GLP 1 use, muscle loss is almost guaranteed. Low protein intake sends a clear message to the body. Conserve tissue. Slow things down. This is why it is so so important to eat enough protein, even when you don’t fancy it, and also engage muscle activity. Don’t fear building muscle – more muscle does not mean bulky. It means resilient.
Protein. The quiet hero of metabolismProtein does far more than build muscle. It:• Reduces muscle loss during weight loss• Increases thermic effect of food• Supports neurotransmitter production• Stabilises blood sugar• Improves satiety hormones
Most people dramatically overestimate how much protein they eat – again, we have gone into detail about this in our protein series, but it is worth drumming home this. Our supermarkets are putting high protein labels on everything, but actually things are not always as they seem. For example, 100g of cooked quinoa is 3g of protein, 100g of chicken is 30g – yet quinoa often has a high protein label.
Raising metabolism often starts with protein, not with calories, but it also involves lots of other processes.
Hormones. The real conductors of metabolismMetabolism is hormone-led.• Insulin controls fat storage and the release of fuel.• Leptin tells the brain how well-fed you are.• Ghrelin drives hunger and meal timing.• Cortisol mobilises energy under stress.• Thyroid hormones regulate cellular energy production.
When dieting is aggressive or prolonged, these signals shift.• Leptin falls. Hunger rises.• Cortisol climbs.• Thyroid conversion slows.
You can eat very little and still struggle to lose weight, not because calories do not matter, but because the hormonal environment has changed. This is why simply eating less stops working overtime, and your body has adjusted to lower fuel. The stinger is it does not recover as soon as you start eating – it can stay low, meaning your refuelling after weight loss, will often result in weight gain, and so the cycle continues.
Stress. The metabolism killer hiding in plain sightStress is not just emotional. It is physiological. Poor sleep. Undereating. Overtraining. Caffeine overload. Financial pressure. Menopause. All count. Chronic stress raises cortisol. Cortisol raises blood sugar. Elevated blood sugar drives insulin. Insulin promotes storage.
You can be eating very little and still stuck in fat storage mode if cortisol remains high. Raising metabolism often means reducing stress load, not pushing harder.
This is the part no one wants to hear. But it matters.
Sleep. Not optional. Ever.Sleep regulates almost every metabolic hormone. Poor sleep increases hunger.It raises ghrelin.It reduces leptin. It worsens insulin sensitivity. Even a few nights of poor sleep can shift appetite and energy dramatically.
For people dieting or using GLP 1 medication, sleep becomes even more critical. The body needs recovery signals to feel safe enough to release energy.
No supplement can replace this.
Circadian rhythm. Timing matters more than we thinkYour metabolism follows a daily rhythm.• Morning light exposure improves insulin sensitivity.• Late night eating disrupts glucose control.• Irregular meal timing confuses hormonal signals.
This is why people can eat the same calories but get different results depending on sleep, light exposure, and routine.
Raising metabolism sometimes means aligning with biology, not hacking it.
Gut health. The missing piece in many stalled plansThe gut influences metabolism through:• Nutrient absorption• Short chain fatty acid production• Inflammation signalling• Hormone metabolism• Appetite regulation
Constipation, bloating, reflux, or dysbiosis can all interfere with metabolic efficiency. Remember, GLP 1 drugs slow gut motility, which can exacerbate existing issues. If nutrients are not absorbed properly, the body again shifts into conservation mode. This is not about eating more fibre blindly. It is about restoring function.
So what do we really mean by raising metabolism? For me, the overwhelming message is:• Preserving and building muscle• Eating enough protein• Supporting thyroid conversion• Managing stress load• Sleeping properly• Eating enough overall to signal safety• Aligning with the circadian rhythm• Supporting gut health• Losing weight at a pace the body can tolerate
A resilient metabolism is flexible. It adapts without shutting down. This is the long-term goal for successful weight management.
Remember, anyone can lose weight in the short term. The real challenge is keeping it off without fighting your body forever. Metabolic health determines whether weight loss feels sustainable or exhausting. For chronic dieters, metabolism needs repair. For GLP 1 users, it needs protection. In both cases, calories alone are not the answer.
Understanding metabolism properly removes blame. It replaces frustration with clarity. And it allows weight loss to work with the body, not against it.
