Slow metabolism: why you feel cold, tired and do not lose weight

Behind these everyday complaints, there is often more than mere convenience.

Many people are convinced that their metabolism is “broken” when losing weight barely works despite dieting and they feel permanently drained. This impression comes up repeatedly in medical practices. But what is really happening when someone is always cold, tired and still does not lose weight – and when does a normal bodily adjustment genuinely become a health problem?

What metabolism actually means – and why it never simply stops

The phrase “frozen metabolism” sounds dramatic, but biologically it makes no sense. Metabolism refers to every chemical process in the body that keeps us alive. If it stopped entirely, we would be dead – it is as simple as that.

Even so, the amount of energy the body uses each day does change. This daily energy requirement is dynamic and responds to:

• body weight and composition
• age
• activity levels
• sleep and stress
• hormonal status, such as thyroid function

The largest part of this energy requirement is known as the basal metabolic rate. It accounts for around 60 to 70 per cent of total energy expenditure.

Basal metabolic rate, movement and digestion: the three major energy demands

Doctors and nutrition specialists broadly divide energy expenditure into three areas:

The final category is particularly important: movement does not only mean going to the gym, but also unconscious daily activity – known as NEAT (Non-Exercise Activity Thermogenesis). This covers everything from bouncing your foot to taking the stairs at work.

When the body receives substantially too little energy for a prolonged period, it almost imperceptibly reduces unconscious movement – and thereby saves calories.

Clinicians call this “adaptive thermogenesis”. The body responds as if there were a famine: it tries to conserve energy rather than waste it. Those affected often only notice that they “cannot get themselves to do anything” and feel sluggish.

The scales are not moving and you are cold – a normal plateau or a real problem?

The most common “symptom” of an apparently slow metabolism is a weight-loss plateau. In most cases, this is a mathematical and behaviour-related phenomenon.

Why weight loss often stalls after a few kilograms

When people lose weight, they become lighter. A lighter body automatically needs less energy to move. If they then continue consuming the same number of calories, they quickly reach a new balance. In addition, many people underestimate how much they eat between meals, especially after dieting periods, when hunger becomes stronger.

The result is: subjectively, “I hardly eat anything any more”, but objectively calorie intake still sits around maintenance level or slightly above it. The scales therefore barely change.

When feeling cold and exhausted can be warning signs

There are, however, clear situations in which persistent cold sensitivity and tiredness may indicate illness. Typical symptoms that make doctors take notice include:

• ongoing, extreme tiredness with no obvious cause
• markedly increased sensitivity to cold
• dry, rough skin
• brittle, thinning hair
• unexplained weight gain of several kilograms

One possible cause is an underactive thyroid. In this condition, the organ in the neck produces too few thyroid hormones, which stimulate metabolism.

An underactive thyroid can slightly reduce calorie expenditure – but it does not explain severe obesity involving dozens of kilograms of excess weight.

Many affected people hope for a “hormonal cause” that accounts for their weight. Endocrinologists take a different view: an underactive thyroid does contribute to some extent, especially through fluid retention, but it is rarely the main reason for substantial excess weight.

Age, muscles and hormones: why energy requirements really decline

One factor affects almost everyone: getting older. Over the years, the body loses muscle mass. This process is called sarcopenia.

Even at rest, muscles use considerably more energy than fat tissue. Less muscle mass therefore automatically means that the basal metabolic rate falls. Someone who could easily maintain their weight on 2,300 calories at 25 might only need 1,900 at 55 – at the same height and with similar activity levels.

Hormones change in parallel. People who diet strictly and for a long time lower their levels of the satiety hormone leptin. At the same time, levels of the hunger hormone ghrelin rise. The body signals: “Please eat more, replenish reserves!”

This interaction is not a disorder but a protective mechanism. The body is attempting to rebuild lost fat stores. Combined with muscle loss caused by a low-protein diet and insufficient training stimulus, total energy expenditure drops noticeably.

How to sensibly increase your energy expenditure

Advertising miracle products that supposedly “turbo-activate” metabolism rarely deliver what they promise. Modern hormone and nutrition medicine instead relies on four straightforward but effective levers.

Build muscle – the most important “metabolic engine”

Strength training, whether using dumbbells, machines or your own body weight, remains the most effective way to maintain or slightly raise the basal metabolic rate. As few as two to three sessions each week can make a substantial difference.

• work large muscle groups: legs, back and chest
• take a long-term approach rather than following four-week plans
• increase the load gradually instead of overdoing it immediately

People who deliberately preserve or even build muscle while losing weight prevent the typical “crash” in calorie requirements.

Enough protein – fuel for muscles and an additional calorie burner

Protein protects muscle tissue during dieting and itself creates a relatively high energy demand during digestion. In effect, some of the calories consumed are lost as heat.

As a rough guide, many experts recommend that healthy adults consume:

• around 1.2 to 1.6 grams of protein per kilogram of body weight each day
• protein spread across the day, rather than one large protein serving only in the evening
• a range of sources where possible: fish, meat, eggs, dairy products, pulses, tofu and nuts

Sleep, stress and everyday movement: the overlooked adjustments

Lack of sleep does not directly make people “fat out of nowhere”. However, anyone who consistently sleeps too little alters their hormonal signals: more hunger, less satiety and greater appetite for readily available, calorie-dense snacks.

There is another effect: when people are tired, they naturally move less, avoid the stairs and drive short distances. This is precisely where NEAT falls – that inconspicuous but powerful part of energy expenditure.

A well-rested, alert body is more likely to make sensible food choices and automatically remain more active in everyday life.

Even small changes can have noticeable effects:

• regular bedtimes, including at weekends
• evening routines without mobile phone light just before sleep
• 10,000 steps as a rough benchmark for everyday movement
• deliberate “movement breaks” at work, such as standing up briefly every hour

When a medical check-up is genuinely worthwhile

Anyone who becomes increasingly cold, extremely exhausted or gains a noticeable amount of weight within a few months without an obvious reason, despite sensible eating, regular exercise, good sleep and a stable lifestyle, should seek medical advice.

Typical investigations include:

• a full blood count including thyroid values
• blood glucose and the long-term blood glucose value
• liver and kidney function
• hormonal status where necessary, for example during and after the menopause

Many practices also offer body-composition measurement. This can broadly show how much of a person’s weight consists of fat mass and how much is muscle mass. It helps to assess actual energy requirements more realistically.

Why being honest with yourself is often the most important step

Anyone who constantly feels cold and drained understandably searches for a clear cause. A “slow metabolism” sounds like a simple explanation. Yet in many cases, the combination of less muscle, underestimated portions, insufficient everyday movement and lack of sleep contributes far more than people realise.

Reviewing your daily routine, using a step counter, keeping a food diary for a week and having the courage to examine your own habits critically often provides more insight than the next fad diet. Combined with medical assessment for severe symptoms, this creates a realistic picture – and an opportunity to address feeling cold, constant tiredness and stagnant weight systematically rather than simply accepting them in frustration.