So is metabolism purely the luck of the draw, or is there anything you can do to help speed things up?

What exactly is metabolism?

When most of us talk about metabolism, what we really mean is metabolic rate. Metabolism is simply a word for the essential chemical processes that are needed to sustain life, while metabolic rate is the speed at which your body breaks down the nutrients in food to produce energy. The higher your metabolic rate, the more calories you’ll burn and the easier you’ll find it to lose weight and keep it off.

Your Basal Metabolic Rate (BMR) is the number of calories your body uses to run normal cellular processes. It doesn’t include the energy you burn through exercise. Your Basal Metabolic Rate determines about 60–70% of your total daily energy expenditure. A further 5-30% is determined by your activity level. [1]

So what factors affect your Basal Metabolic Rate?

Body size and composition

The largest determinant of your metabolic rate is actually your total body mass. [2] The more fat-free mass you have (skeletal tissue, muscle and internal organs), the higher your metabolic rate will be. Contrary to popular belief, taller people with a larger bone structure actually have faster metabolisms than those with smaller frames.

Interestingly, the size of your internal organs seems to play a significant role in how efficiently you burn calories. Research published in the medical journal PLOS ONE showed that as much as 43 percent of the differences between people's metabolic rates could be attributed to organ size[3].

While there’s not a lot you can do about the size of your organs or skeleton, there’s one aspect of body composition you can influence: the amount of muscle you have.

The greater your lean muscle mass, the more calories you’ll burn, even at rest.[4] Dr Tim Church M.D., professor of preventative medicine at Pennington Biomedical Research Center at Louisiana State University, estimates that every pound of muscle burns approximately six calories per day at rest. That’s about three times as many calories as a pound of fat, which burns about two calories per day.[5] So building more lean muscle mass can help boost your metabolism.

Age

Could you eat whatever you wanted through your teens and twenties and never put on weight? Yet now it seems you need only glance at a cake or muffin and your jeans get tighter?

You’re not imagining things. Unfortunately our metabolism does naturally decline as we age.

As we age we naturally lose muscle, which leads to a corresponding drop in metabolic rate. Hormonal changes that occur as part of the ageing process also play a role in this drop in metabolism, particularly for women. The natural decline in oestrogen levels that occurs during menopause promotes less muscle building and more fat storage. [6]

A reduction in our bodies’ production of growth hormone might also be to blame for a slower metabolism as we age, according to Harvard Health[7]. Growth hormone is produced by the pituitary gland to stimulate cell growth, build muscle, boost protein production and utilise fat efficiently. We need large amounts of growth hormone during childhood and puberty to help us develop from infants to adults, but as we get older and growth ceases, our levels of growth hormone naturally drop off. As levels of the hormone decline, our ability to build and maintain muscle decreases, and with this our body becomes less efficient at utilising calories. [8]

Gender

Whether you have the XX or the XY chromosome also plays a part in the speed of your metabolism. Men’s naturally larger frame size and greater muscle mass mean they burn calories a lot faster. [9][10]. Women are also naturally designed to store more fat to enable them to conceive and bear children. This is why a healthy body fat percentage for women is 20-25%, while for men it’s much lower; between 14 and 17%.

So how can you increase your metabolism?

Looking at the above list, you might feel a little disheartened. You can’t change your age, gender or body composition, so is there anything you can do boost your metabolism?

Pump Iron

Head straight to the treadmill when you hit the gym? Time to swap a couple of those cardio sessions for the squat rack, because lifting weights is one of the most effective ways to boost your metabolism.

Resistance training helps increase your lean muscle mass, which will in turn increase your metabolism. Experts believe that if a woman gains 10 pounds of muscle and loses 10 pounds of fat, she'll burn approximately 40 extra calories per day.[11] While this might not sound like a lot, in conjunction with other dietary and lifestyle changes, it can add to up to a big difference over time.

Up the ante

Increasing the intensity of your workouts will also help boost your metabolism. High Intensity Interval Training (HIIT) is a kind of cardiovascular training that combines repeated periods of short, high intensity activity with lower intensity intervals for active recovery. (Think Crossfit, boxing or circuit training).

HIIT works in two ways to boost metabolism: 1) You’re working at a higher intensity so you’ll burn more calories than you would during a steady-state cardio session like running or cycling.

2) It triggers something known as excess post-exercise oxygen consumption, or “EPOC.” EPOC refers to the extra oxygen and energy your body uses after exercise to help repair your muscles and recover [12]. And its effects can last long after you leave the gym: Depending on the intensity of your workout, EPOC can raise metabolism for anything from 12 hours to a few days.[13][14].

Eat breakfast

It can be tempting to skip it if you’re in a rush in the morning, but eating breakfast is one of the simplest ways to kick start your metabolism. When you wake up in the morning, you’ve already been fasting for between 10 and 12 hours (depending on when you ate your evening meal), so if you skip breakfast, your body thinks food is scarce and goes into ‘starvation mode’. This mimics what would happen in a real famine, where our metabolism naturally slow s in order preserve precious energy[15].

Starting the day with a balanced breakfast containing complex carbohydrates, healthy fats and protein will help kick start your metabolism for the day. Good choices include omelettes filled with vegetables and cheese, avocado and smoked salmon on toast or porridge with sugar-free, Greek Yoghurt and berries.

Eating breakfast also help us make better food choices for the rest of the day - that mid-morning latte and sugary muffin will be much easier to say no to if you’ve had a good brekkie.[16]

Eat Protein

Gym bunnies are forever chugging protein shakes, but is it all really worth it? Turns out, those gym junkies might just be on to something.

After a meal, your metabolism will increase for the next few hours, as your body uses energy to digest and assimilate the nutrients in your food.[17] This is called the thermic effect of food (TEF).

Of all the macronutrients, protein causes the largest increase in TEF. It raises your metabolism by 15–30%, compared to 5–10% for carbs and 0–3% for fats[18].

Protein also helps build lean muscle mass. In one study, 16 healthy adults were assigned a high-calorie diet for 8 weeks – some with low-protein content (5%), some with moderate protein content (15%) and some with high protein content (25%). After 8 weeks, all the participants had gained weight but those who were on the normal- and high-protein diets stored a massive 45% of the excess calories as muscle, while those on the low-protein diet stored 95% of their excess calories as fat.[19]

While we’re not recommending bulking up on a high-calorie diet, the study demonstrates the power of protein to build lean.

Eating protein also helps weight management via another mechanism: it promotes satiety (fullness) meaning you are less likely to overeat. One study found that people ate as many 441 fewer calories per day when protein made up 30% of their diet.[20]

Drink up

Making sure you get enough H20 is key to a healthy metabolism. A study by the University of Utah found that people who drank between eight and twelve glasses of water a day had higher metabolic rates than those who only drank four glasses. The same study showed that being dehydrated can result in a 2% drop in metabolism. [21]With water required for almost every cellular function, it makes sense we’d need it for a healthy metabolism too.

Add a little spice to your life

Adding a little heat to your meals can also help boost your metabolism. Peppers and chillies contain a substance called capsaicin, which studies show may help increase your metabolism[22]. Adding 10g of chilli to a meal can increase your energy expenditure by 20-60kJ.[23]

While the metabolism-boosting effects of spices are quite small, they may be more effective when combined with other habits such as weight training and HIIT.

Make a cuppa

But make sure it’s green or oolong. According to a Japanese study, sipping a cup of green tea can boost metabolism by 4% and oolong tea by a whopping 10%, when compared with water. The metabolism-boosting effects can last for up to 90 minutes after drinking the tea.

Oolong and green tea can also support your weight management efforts by providing a calorie-free drink to sip between meals.

Strengthen your digestion

Besides diet and exercise, there’s another important (but often overlooked) aspect of metabolism: our digestive system.

In Ayurvedic medicine, the whole process of digestion, breakdown and assimilation of nutrients, and the speed of our metabolism is considered to be inextricably related. The strength of our ‘agni’ or ‘digestive fire’ will determine how efficiently we break down, absorb and utilise our food.[24]

A sluggish digestive system can encourage the build of toxins and may make it more difficult to lose or manage our weight. Inefficient digestion can also lead to imbalance of good and bad bacteria in the gut, which has been linked to metabolic changes and increased fat storage.

Kiwi-Klenz can help improve the function of our digestive system and in turn promote a healthier metabolic rate. Kiwifruit is packed with enzymes which can enhance the breakdown and absorption of nutrients, along with prebiotics and soluble fibre to promote soft stools and improve transit time. The phenolics and prebiotics in Kiwi-Klenz help promote a healthier balance of gut bacteria.

References:

[1] Franklin, J. Myths busted: Can certain foods help you lose weight? http://www.healthyfoodguide.com.au/articles/2011/june/myths-busted-can-certain-foods-speed-your-metabolism
[2] Fetters, A. How much does strength training really increase metabolism? September 21, 2017. https://www.self.com/story/how-much-does-strength-training-really-increase-metabolism
[3] Müller, M. et al. Effect of Constitution on Mass of Individual Organs and Their Association with Metabolic Rate in Humans—A Detailed View on Allometric Scaling. July 26, 2011. https://doi.org/10.1371/journal.pone.0022732
[4] Vermorel M et al. Contributing factors and variability of energy expenditure in non-obese, obese, and post-obese adolescents. Reprod Nutr Dev. 2005 Mar-Apr;45(2):129-42. https://www.ncbi.nlm.nih.gov/pubmed/15952420
[5] Fetters, A. How much does strength training really increase metabolism? September 21, 2017. https://www.self.com/story/how-much-does-strength-training-really-increase-metabolism
[6] Menopause, weight gain, and exercise tips. https://www.webmd.com/menopause/guide/menopause-weight-gain-and-exercise-tips#1
[7] Growth hormone, athletic performance, and aging. May 2010. https://www.health.harvard.edu/diseases-and-conditions/growth-hormone-athletic-performance-and-aging
[8] Marturana, A. The truth about how metabolism slows as you age. November 10, 2016. https://www.self.com/story/how-metabolism-changes-as-you-age
[9] Buchholz AC, Rafii M and Pencharz PB. Is resting metabolic rate different between men and women? British Journal of Nutrition. 2001 Dec;86(6):641-6. https://www.ncbi.nlm.nih.gov/pubmed/11749674
[10] Ferraro, R et al. Lower sedentary metabolic rate in women compared with men. J Clin Invest. 1992 Sep; 90(3): 780–784. doi: 10.1172/JCI115951
[11] Fetters, A. How much does strength training really increase metabolism? September 21, 2017. https://www.self.com/story/how-much-does-strength-training-really-increase-metabolism
[12] Boutcher, S. High-Intensity Intermittent Exercise and Fat Loss. November 24, 2010. [12] J Obes. 2011; 2011: 868305. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2991639/
[13] Hazell TJ. Two minutes of sprint-interval exercise elicits 24-hr oxygen consumption similar to that of 30 min of continuous endurance exercise. Int J Sport Nutr Exerc Metab. 2012 Aug;22(4):276-83. Epub 2012 Jun 15.
https://www.ncbi.nlm.nih.gov/pubmed/22710610
[14] Burns SF1, Oo HH, Tran AT. Effect of sprint interval exercise on postexercise metabolism and blood pressure in adolescents. Int J Sport Nutr Exerc Metab. 2012 Feb;22(1):47-54. https://www.ncbi.nlm.nih.gov/pubmed/22248500
[15] Rabbit, M. How to keep your metabolism revved as you get older. June 28, 2016. https://www.prevention.com/weight-loss/6-ways-to-keep-your-metabolism-revved-as-you-get-older/slide/1
[16] Rabbit, M. How to keep your metabolism revved as you get older. June 28, 2016. https://www.prevention.com/weight-loss/6-ways-to-keep-your-metabolism-revved-as-you-get-older/slide/1
[17] West, H. 10 Easy ways to boost your metabolism (Backed by science). June 12, 2017. https://www.healthline.com/nutrition/10-ways-to-boost-metabolism#section1
[18]  Pesta, D. and  Samuel, V.A high-protein diet for reducing body fat: mechanisms and possible caveats. Nutr Metab (Lond). 2014; 11: 53. November 19, 2014. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4258944/
[19] Rabbit, M. How to keep your metabolism revved as you get older. June 28, 2016. https://www.prevention.com/weight-loss/6-ways-to-keep-your-metabolism-revved-as-you-get-older/slide/1
[20]Weigle D et al. A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. Am J Clin Nutr. 2005 Jul;82(1):41-8. https://www.ncbi.nlm.nih.gov/pubmed/16002798
[21] Is Eight Enough? U Researcher Says Drink Up and Tells Why. Jan 14, 2003 5:00 PM.https://healthcare.utah.edu/publicaffairs/news/archive/2003/news_74.php
[22] Henry C and Emery, B. Effect of spiced food on metabolic rate. Hum Nutr Clin Nutr. 1986 Mar;40(2):165-8. https://www.ncbi.nlm.nih.gov/pubmed/3957721
[23] Franklin, J. Myths busted: Can certain foods help you lose weight? http://www.healthyfoodguide.com.au/articles/2011/june/myths-busted-can-certain-foods-speed-your-metabolism
[24] Gupta, M. Understanding of the vital source of life: agni. http://yogadigest.com/understanding-of-the-vital-source-of-life-agni-digestive-fire/