Some people seem to be able to eat whatever they like, as often as they like, and exercise as little as they like without putting on weight. It’s more than likely you know one of these people. They may even be a friend of yours. But it’s not their fault and they’re not being deliberately annoying. It’s just their metabolism.

Metabolic rate can vary drastically between individuals and genetics certainly play a major role, but it’s far from the complete picture. There’s plenty you can do to speed up your metabolism, just as there’s plenty you can do to slow it down.

“You can influence your metabolism in so many ways,” says Melanie McGrice, dietitian and founder of Health Kick Nutrition and Dietetics.

“If you have a genetic predisposition to storing more fat or burning kilojoules slower than others, it may mean that you have to work harder at it than other people, but it certainly doesn’t mean you can’t maintain a healthy weight.”

Understanding metabolism

Often referred to as your body’s ‘engine’, the word metabolism is really a blanket term for a number of chemical reactions that contribute towards the burning of kilojoules. And, like the engine in your car, we have a lot of say in how efficiently it runs.

A significant part of the speed of your metabolism is your ratio of muscle to fat.

“Someone who has higher muscle mass is going to burn food faster and use their fuel much more efficiently than someone who is carrying a lot of fat,” McGrice says.

Some people naturally have more muscle mass and others tend to store more fat. Men tend to have a faster metabolism than women due to the fact that they have less body fat and more muscle.

As we age, our metabolic rate slows. An average 35-year-old, for instance, will burn about 400 less kilojoules a day than they did when they were 25. Fortunately, this process can be delayed or prevented with attention to diet and exercise.

What to eat

All food stimulates our metabolism, but protein gives it the biggest boost. That’s because to process protein, your metabolism has to work the hardest. Carbohydrates come in second and fats last. Protein also helps with the building of muscle and is least likely to be converted into fat. So eat plenty of lean protein – meat, chicken, fish, soy and legumes.

Go for good carbohydrates, such as wholemeal breads and cereals, and avoid processed varieties like white bread, cakes and biscuits, which can result in a surge of insulin, storage of fat and a drop in your metabolic rate.

Avoid fatty foods. These take the longest to metabolise, and while they may be filling and you may be able to go for longer periods between eating, this only slows your metabolism down.

The exception to the rule is omega-3 fatty acids, found in abundance in fish, good quality olive oil and to a lesser extent green leafy vegetables. Research suggests that omega-3 fatty acids help to reduce levels of leptin, a hormone linked to slower metabolism.

Spicy foods – including chilli, horseradish, cayenne pepper and ginger – also appear to speed up the body’s metabolism, increasing heart rate and your body’s production of heat as well as stimulating the sympathetic nervous system.

Citrus fruits are another great option. Rich in vitamin C, citrus fruits are high in flavones, compounds that help to eliminate fats and increase metabolism.

Acquiring a taste for green tea is also said to speed up your internal engine. According to research conducted by the University of Geneva in Switzerland, green tea, containing unique polyphenols, has the ability to increase the rate at which kilojoules are burned.

When to eat

Just as important as what you eat is how often you eat. Ideally you should aim to eat at least every three hours in order to keep your metabolism revved up and chugging along.

“It’s very important to eat breakfast in the morning to break the fast and then to be eating small regular meals throughout the day,” McGrice says.

“Going for long periods of time without eating decreases your metabolism and the efficiency with which your body burns food.”

One way you can eat more often without increasing the amount you eat is to divide your meals into two portions, or mini-meals. For example, for breakfast you might have a small bowl of cereal at 7.30-8am followed by a piece of toast at 10am.

Another way to break up food portions is to eat healthy snacks in between small meals. This does not mean that you are grazing all day long, but eating well-planned healthy snacks, such as nuts, seeds, fruit, yoghurt, a boiled egg or carrot and celery slices with hummus dip.

Why dieting puts on weight

Strange though it may sound, dieting can actually result in an increase in weight rather than the intended weight loss you had in mind.

The problem with most restrictive diets is that the body responds with a survival instinct referred to as the ‘famine response’, where the body’s metabolism actually slows down.

“The famine response is a defence mechanism that aims to protect fat stores by using up lean tissue and muscle for energy instead,” explains Nicholas Arthur, nutritionist and co-founder of Appetite Right.

“Because the amount of muscle in the body is directly proportional to metabolic rate, a loss of muscle also means a loss of metabolic rate.”

The best way to lose weight, says Arthur, is to avoid fad diets entirely. Instead, make sure you eat a variety of foods from all the food groups and reduce your intake of foods that are high in fat, sugar and salt.

Working it out

Regular aerobic exercise increases your metabolic rate because your body has to work much harder than it does when resting. It also increases all-important muscle mass. After an intense workout your metabolism can stay at an elevated level, burning kilojoules for more than three hours after.

“You should be looking at getting a minimum of 30 minutes of exercise a day at least five days a week,” McGrice says.

The more intense the exercise, the greater the effect on your metabolism. Interval training provides the most long lasting benefits, so try mixing up your training into high-intensity segments where you do the chosen activity at maximum effort (for example, running, swimming, cycling or stair climbing) followed by a period where you back off, reduce intensity and catch your breath before upping the ante again.

If you’re really serious about getting your metabolism pumping you should also include some form of strength training – free weights, exercise machines or using your own body weight (for example, push-ups and pull-ups). This is because your body needs to burn a considerable amount of kilojoules just to maintain the muscle you build. And importantly, this effect continues even when you are resting.

Include three 20-minute weight training sessions a week and in a couple of months you’re sure to notice the difference.

So in much the same way as your car needs a regular service, good quality fuel and a mixture of city and country driving, your metabolism requires a healthy diet and a varied exercise regime to achieve optimal performance. Happy motoring!