Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
Our metabolism is the inner engine that determines whether the food we eat becomes energy we can use or extra weight on the scales.
When losing weight feels impossible, we often point to a ‘slow’ or ‘sluggish’ metabolism as the culprit.
That frustration has helped create a massive US$33 billion industry filled with pills, powders, and potions claiming to rev up metabolism and melt fat. But instead of relying on supplements, there are proven ways to support your body’s natural metabolic processes.
Metabolism refers to all the chemical reactions in your body that keep you alive and functioning. It powers essential tasks like breathing, digesting food, and repairing cells.
When we talk about metabolism in the context of weight, we usually mean basal metabolic rate (BMR), which is the number of calories your body burns at rest. Your BMR depends on several factors, including how much muscle and fat you have.
Things like gender, age, weight, and lifestyle all influence metabolism. It naturally slows as we age and can become less efficient after dieting.
As we get older, our bodies simply don’t operate as efficiently as before. From around age 40, muscle mass begins to decline while body fat tends to increase.
Because muscle helps determine your metabolic rate, this reduction in muscle mass means your body burns fewer calories at rest, effectively slowing your metabolism.
Losing large amounts of weight often lowers your metabolic rate, and unfortunately, it doesn’t fully bounce back even if you regain the weight.
That’s because typical weight-loss diets cause both fat and muscle loss. With less muscle tissue, your body burns fewer calories. Even after regaining weight, the metabolism doesn’t return to its previous level.
Research shows that after each dieting attempt, your metabolism can slow down by an additional 15% beyond what’s expected based on body size alone.
Read more about recovery strategies in our article How to Fix a Damaged Metabolism After Dieting.
Your diet influences how much energy your body uses to digest and process food, a process known as diet-induced thermogenesis or the thermic effect of food. This accounts for about 10% of your total daily energy expenditure.
According to research, protein-rich foods have the highest thermic effect, requiring more energy to digest. Eating protein can boost your metabolic rate by roughly 15%, compared to 10% for carbs and less than 5% for fats.
That doesn’t mean you should switch to a high-protein diet alone. Aim for balanced meals that combine protein, vegetables, wholegrain carbohydrates, and healthy fats. This supports not just metabolism, but overall health and disease prevention, too.
Physical activity helps build and maintain muscle, which in turn increases your basal metabolic rate, meaning you burn more calories even at rest.
Try incorporating at least 30 minutes of daily movement, along with two sessions of strength or resistance training each week. Mixing up your workouts keeps things interesting and helps avoid burnout.
Skipping exercise, on the other hand, leads to muscle loss, which slows your metabolism and makes weight management harder.
A growing body of research links sleep deprivation to metabolic changes. Poor sleep disrupts the body’s energy balance and appetite hormones, increasing hunger and cravings while reducing energy expenditure and impairing sugar metabolism.
To support your metabolism, aim for at least seven hours of quality sleep each night. A simple step: avoid screens for an hour before bed. Blue light from devices suppresses melatonin, the hormone that signals your body it’s time to sleep.
Curious how sleep affects your weight? Find out in our article Can Sleeping Help You Lose Weight?
Thousands of diet pills and supplements promise to ‘activate’ your metabolism. Some contain ingredients like caffeine or capsaicin (the compound that makes chillies hot), which can give a short-term boost, but research shows the effects don’t last.
Two major reviews covering around 120 studies on weight-loss supplements found no solid evidence that these products work long-term. Most are backed by bold marketing rather than science.
Your best bet? Leave the miracle pills on the shelf and focus on habits that genuinely support your metabolism. Your body (and wallet) will thank you.
Metabolism plays a major role in how your body uses energy, but it isn’t fixed or hopelessly ‘slow’. While age, genetics, and diet history influence it, lifestyle choices make a difference.
Eat balanced meals, stay active, prioritise sleep, and avoid quick fixes. These sustainable habits won’t just support your metabolism. They will support your overall wellbeing, too.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.