Our metabolism is the force inside our bodies that mysteriously decides whether to convert the food we eat into a burst of energy, or extra kilos on the scales.
A "slow" or "sluggish" metabolism is often the first thing we blame when we struggle to lose weight.
As a result, a US$33 billion industry offers thousands of products promising to speed up our metabolic rate for weight-loss success.
But rather than reaching for a supplement, there are things you can do to speed your metabolism up.
What is metabolism and how does it work?
Metabolism is the term describing all the chemical reactions in our bodies that keep us alive. It provides the energy needed for essential functions like breathing and digestion.
When we refer to metabolism in the context of our weight, we're actually describing our basal metabolic rate – the number of calories the body burns at rest, determined by how much muscle and fat we have.
Why does our metabolism slow with age?
As our bodies age, they stop working as efficiently as before. Around the age of 40, our muscle mass starts naturally declining, and the ratio of body fat to muscle increases.
Because muscle mass helps determine the body's metabolic rate, this decrease in muscle means our bodies start to burn fewer calories at rest, decreasing our metabolic rate.
Why does our metabolism become dysfunctional after dieting?
When you lose large amounts of weight, you're likely to have lowered your metabolic rate, and it doesn't recover to the level it was pre-dieting – even if you regain weight.
This is because, typically, when we diet to lose weight, we lose both fat and muscle, and the decrease in our calorie-burning muscle mass slows our metabolism.
We can account for the expected decrease in metabolic rate from the decrease in body mass, but even after we regain lost weight our metabolism doesn't recover.
Research shows that for every diet you attempt, the rate at which you burn food slows by a further 15% that can't be accounted for.
3 ways to speed up our metabolism (and 1 thing to avoid):
1) Pay attention to what you eat
Consider the types of food you eat because your diet will influence the amount of energy your body expends to digest, absorb and metabolise food. This process is called diet-induced thermogenesis, or the thermic effect of food, and it equates to about 10% of our daily energy expenditure.
Research shows the thermic effect of food is highest for protein-rich foods because our bodies need to use more energy to break down and digest proteins. Eating protein-rich foods will increase your metabolic rate by about 15% (compared to the average of 10% from all foods). In contrast, carbs will increase it 10% and fats by less than 5%.
But this doesn't mean you should switch to a protein-only diet to boost your metabolism. Rather, meals should include vegetables and a source of protein, balanced with wholegrain carbs and good fats to support optimum health, disease prevention and weight loss.
2) Get moving
Regular physical activity will boost muscle mass and speed up your metabolism. Increasing your muscle mass raises your basal metabolic rate, meaning you'll burn more calories at rest.
You can achieve this by incorporating 30 minutes of physical activity into your daily routine, supplemented with two days of gym or strength work each week.
It's also important to mix things up, as following the same routine every day can quickly lead to boredom and exercise avoidance.
Neglecting exercise will just as quickly result in a decline in muscle mass, and your lost muscle will slow your metabolism and hamper your efforts to lose weight.
3) Get enough sleep
A growing body of research confirms sleep deprivation can significantly impact your metabolism.
A lack of sleep disturbs the body's energy balance. This causes our appetite hormones to increase feelings of hunger and trigger food cravings, while altering our sugar metabolism and decreasing our energy expenditure.
If you want to boost your metabolism, set yourself a goal of getting seven hours of uninterrupted sleep each night.
A simple way to achieve this is to avoid screens for at least one hour before bed. Screens are a big sleep disruptor because they suppress melatonin production in the brain, telling us it's daytime instead of nighttime.
4) Don't waste your money on diet pills and supplements
Thousands of products promise to activate your metabolism and speed up your weight loss. While some may have ingredients that will boost your metabolism immediately after you take them, such as caffeine and capsaicin (the component which gives chillies their heat), research confirms the effect is temporary – they don't support long-term weight loss.
Most products promising to help you speed up your metabolism to help you lose weight don't offer any scientific evidence to back their efficacy. Two extensive reviews published recently examined around 120 studies of weight-loss supplements and found they just don't work, despite the bold marketing claims.
So leave the pills, potions and powders on the shelf and focus on the things that work. Your metabolism – and your hip pocket – will thank you.