Muscle, sleep, stress and metabolism

Does exercise really boost your metabolism?

A little, but less than most people think. Most of the benefit comes from the energy you use while you move, not from a permanently faster resting metabolism.

Muscle-strengthening exercise is linked with a modestly higher resting metabolic rate (the energy your body uses at rest). Aerobic exercise such as walking showed no clear effect on it². The findings are mixed, so it isn't worth building your plan around this. Extra activity does tend to add to the energy you use over a day, though by less than simple sums suggest^5,6.

What matters more is what regular activity does for your health. Benefits start below the guideline amounts, so some activity is better than none. Replacing sitting with activity of any intensity, including light activity, has benefits¹. The WHO recommends 150–300 minutes of moderate-intensity activity a week¹, but that is a direction, not an entry requirement: doing less than the recommended amount still helps⁷.

How does chronic stress affect weight and metabolism?

Long-lasting stress is linked with weight gain, mainly through raised levels of the stress hormone cortisol. Short-term stress can reduce appetite instead³.

When stress carries on, it can increase how much you eat and your taste for high-calorie foods. It often triggers emotional eating, where people turn to comfort foods, and it can weaken self-control around eating and activity habits³. Raised cortisol can also move fat storage towards the belly, and may contribute to muscle loss^3,8.

Being more active is linked with coping better with stress, with lower stress reactions and lower perceived stress⁹. This is an association, not proof that activity causes the change.

• On stressful or tired days, a short, easy walk or some light movement in place of sitting still is a reasonable place to start.
• Notice whether stress drives your eating. A few small bouts of activity planned into the day give you something to do besides eating.
• If stress feels constant or hard to cope with, talk to your doctor or a mental health service. Exercise is not a replacement for medication or therapy, and it shouldn't be used to reduce or stop either.

How does sleep affect weight and metabolism?

Regularly short sleep is linked with weight gain and poorer metabolic health. Adults should sleep 7 or more hours a night on a regular basis; sleeping less than that is associated with weight gain, obesity, diabetes, high blood pressure, heart disease and stroke⁴. How much sleep you need varies with your genes, habits, health and surroundings⁴.

Short sleep appears to play a causal role in obesity, high blood pressure and heart disease. The links with other conditions, and with sleeping a very long time, were not confirmed¹⁰. When sleep is cut short, people tend to spend more of the day sitting¹¹. Shorter sleep can also bring fatigue, less activity and more hunger, particularly for high-fat and carbohydrate foods³.

Regular exercise has small to moderate benefits for sleep, including how quickly you fall asleep and how well you sleep¹².

• Give yourself the chance of 7 or more hours in bed.
• Keep up regular activity, even a short daily walk.
• After a poor night, a little light movement in place of long sitting can offset the extra sitting that short sleep tends to bring¹¹.

If you're worried you sleep too little or too much, or you're often unusually tired, talk to your doctor and get it checked.

How do healthy fats relate to metabolic health?

How the fats you eat relate to metabolic health isn't clear yet, so for advice on which fats to eat, ask your doctor or a dietitian.

What can be said is about activity and blood fats. Aerobic exercise such as brisk walking, paired with eating a little less, may lower triglycerides (a type of blood fat). Both aerobic and muscle-strengthening exercise, paired with eating less, may lower blood pressure¹³. Because exercise and eating less went together, the effect of exercise on its own isn't clear.

Whatever your diet, regular activity is worth building up gradually.

When to check with a health professional

If you're starting exercise after a long break, it's always a good idea to see your doctor first.

For an injury or a health condition, see a health professional, such as your doctor or a physio. If you have a long-term condition or a disability, the same recommendations apply as far as you're able, and a health professional can help you choose the right type and amount^7,1. If you have osteoporosis or a spinal fracture, ask a health professional about suitable exercise¹⁴.

Call your local emergency number for chest pain or pressure (or pain spreading to the arm, neck, jaw or back, especially with sweating or feeling sick), severe breathlessness, fainting or collapse, signs of a stroke, a serious injury, or someone who isn't safe.

If new symptoms appear as you build up your activity, see a doctor or other health professional.

Exercise doesn't have to hurt to work. Soreness a day or two after a harder session is normal. A sore muscle or joint means ease off. See a doctor or physio if it persists or gets worse.

If you have thoughts of self-harm, contact a local crisis line (findahelpline.com lists free services in every country), with your local emergency number.