Can an efficient metabolism help you lose weight?

What does a fast or slow metabolism actually mean? Here’s what you need to know about this essential bodily function.

Helen Foster
January 2018

Scientifically speaking, the word ‘metabolism’ refers to the chemical processes in our body that convert what we eat and drink into energy. But when most of us use this term, we’re actually referring to our metabolic rate.

“This is the amount of energy you need to keep your body running at rest,” explains Dr Jarrod Meerkin, exercise physiologist from body composition analysis centre MeasureUp, in Sydney.

Do some people have a ‘fast’ metabolism?

Your metabolic rate is generally determined by your age, weight, gender and the muscle composition and levels of hormones in your body. This combination of factors means the exact number of kilojoules burnt each day varies between individuals – heavier people burn more than thinner people; the younger you are and the more muscular you are, the higher and more active your metabolic rate – meaning men tend to burn more kilojoules because they usually have more muscle than women of the same age. 

All things being equal, however, why can some people seemingly eat a lot and stay thin, while others seem to gain weight easily? Researchers are still trying to pinpoint the answer. They believe it might be related to gut bacteria or how much insulin is produced after a meal. A 2016 Danish study found mice that received gut bacteria transplants from overweight humans gained more weight than mice transplanted with gut bacteria from normal weight subjects. And having insulin resistance – where your body struggles to move sugar from your bloodstream into your cells for fuel after eating – is often linked to a sluggish metabolism.

“But it’s most likely to be because people eat more than they think they do, because we’ve lost sight of what a healthy portion looks like,” says exercise physiologist Jennifer Smallridge, from Melbourne Health and Nutrition Specialists.

Thin people also tend to be more physically active. Studies at the Mayo Clinic in the US over more than a decade show that people who move more – even by simply fidgeting – can burn a significant number of extra kilojoules each day.

How to increase your metabolism

So, can you improve your metabolic rate? Absolutely. The number 1 reason metabolism declines with age is that you start to lose muscle mass – and muscle burns kilojoules at rest.

“Increasing your muscle mass through strength training is therefore the most important thing you can do to raise metabolism,” says Smallridge. Strength training includes resistance exercise such as lifting weights. And every strength training session counts – in studies at Colorado State University, women doing a strength training workout had a resting metabolic rate of 5,960kj a day before they worked out, but that rose to 6,212kj the day after their session.

It also helps to add high-intensity interval training (HIIT) to your workout, where you exercise very hard for a short period of time before slowing down. This raises your metabolism long after your workout has stopped.

“This type of workout causes you to switch to anaerobic training,” says Dr Meerkin, explaining that this draws energy from the muscles, helping to increase your metabolic rate.

Staying hydrated can also boost your metabolism, as muscles burn more fuel if they’re well hydrated. According to the University of Utah, if you lose 3% of your body’s water, your metabolic rate slows down by 2%, which for a woman weighing 63.5kg would mean burning about 100kj less a day.

Stress also negatively impacts your metabolism. A 2014 trial from Ohio State University in the US found that those who had experienced stress (even from something as innocuous as a fight with their partner) burned 437 fewer kilojoules the next day than their non-stressed counterparts  – something the researchers say could lead to a 5kg weight gain over a year.

Check your thyroid

The master gland that controls metabolism is the thyroid, and if yours isn’t performing properly, your metabolism will be affected.

According to the Australian Thyroid Foundation, if your thyroid is underperforming (hypothyroidism), you’ll find it hard, if not impossible, to lose weight. Hypothyroidism is normally accompanied by other symptoms, such as fatigue, constipation, feelings of cold and thinning hair.

If your thyroid is working too hard (hyperthyroidism), you may find it impossible to maintain weight. Other symptoms include heart palpitations, excess sweating and restlessness.

Thyroid problems affect about half a million Australians but half of these are unaware of their condition.

If these symptoms sound familiar, ask your GP for advice.