What Is Metabolism & How Does It Effect Weight Loss?
Metabolism & Weight Loss
Is your metabolism the reason you can’t lose weight? Or possibly, the reason you can’t put on bulk and size? You’ve probably heard people blame their weight on a slow metabolism before, but what does that really mean? And if it IS the culprit, what can we do to speed it up?
To get a better understanding, let’s take a closer look at Metabolism and exactly what effect it has upon our energy, health and body weight.
What is Metabolism?
Metabolism is the chemical processes that occur within a living organism in order to maintain life (homoeostasis). So basically, it is the sum of all chemical reactions that your body must undertake in order to process the things we eat and drink, convert them into energy, and then use that energy to create new tissues and cells.
In humans, the metabolism can be categorised into 3 main functions.
- The catabolism (break-down) of food to create energy (for cellular processes)
- The anabolism (creation) of building blocks (protein, lipids, nucleic acid) by use of energy acquired from food.
- The elimination of nitrogenous wastes
In relation to weight loss, you will have heard metabolic rate referenced many times over. The higher your metabolic rate, the more energy your body will consume (hence the more calories you need to eat to sustain it), and the less likely you are to store energy as fat. Our metabolic rate is determined by a combination of 3 components:
- Basal Metabolic Rate (BMR) – the kilojoules (Kj) your body burns at rest (50 – 80% of daily energy use)
- The energy required for physical activity (20% of daily energy use)
- Thermic effect of food – the energy used to eat, digest and metabolise food (5-10% of daily energy use)
BMR (basal metabolic rate)
Basal metabolic rate is the amount of energy required to maintain homoestasis, or, to keep us alive.
As up to 80% of our daily energy use is determined by our BMR, it is the most vital component we need to consider when we attempt to change our body composition (lose weight, gain muscle etc).
Our BMR is largely determined by the amount of lean mass (lean muscle) that our body contains. This is because lean mass requires a LOT of energy to sustain.
Anything we do that lowers our lean mass (dieting, fasting, overtraining), consequently lowers our BMR.
Average male has a BMR of 7,100kj
Average female has a BMR of 5,900kj
**It is vital to maintain or INCREASE lean mass in order to lose weight**
What affects our BMR?
There are a number of different factors which work together to have an effect on your BMR. Some of these are controllable behavioural factors, whilst others are physiological factors we have less control over.
Physiological factors (un-controllable)
- Structural Body size – larger built individuals generally have a greater amount of metabolising tissue resulting in a higher BMR
- Age – metabolism slows with age due to loss of muscle tissue, but also due to hormonal and neurological changes
- Growth – infants and children have higher energy demands due to growth and the extra energy needed to maintain their body temperature
- Gender – generally, men have faster metabolisms than women because they tend to be larger and naturally build/maintain a higher density of muscle tissue
- Genetic predisposition – your metabolic rate may be partly decided by your genes
- Hormonal and nervous controls – BMR is controlled by the nervous and hormonal systems. Hormonal imbalances can have a significant influence how quickly or slowly the body burns kilojoules. This is particularly relevant to women through the changes experienced in menstruation, child-birth and menopause.
- Infection or illness – during periods of sickness, the BMR increases because the body has to work harder to build new tissues and to create an immune response.
- Environmental temperature – if external temperature is very low or very high, the body has to work harder to maintain its normal body temperature, which increases the BMR
Behavioural factors, and behaviour dictated physiological factors (controllable)
- Amount of lean muscle tissue – muscle burns kilojoules rapidly whilst exercising, and requires more energy to sustain. More muscle = higher BMR
- Amount of body fat – fat cells are ‘sluggish’ and burn the least kilojoules out of all tissues and organs in the body
- Crash dieting, skipping meals or fasting – these drastic attempts to consume less kilojoules encourage the body to slow BMR in order to conserve energy. It is a ‘starvation response’ whereby the body must protect its life or homeostasis by conserving energy for this purpose. As a result, all other bodily functions will become impaired (skin rejuvenaton, liver regeneration, brain function, keratin production etc). BMR can drop by up to 15%. This can also lead to a catabolism of muscle tissue which further reduces BMR.
- Amount and type of physical activity – when we exercise, our hard-working muscles need plenty of energy to burn. Regular exercise increases muscle mass and teaches the body to burn kilojoules at a faster rate, even when at rest. Strength training stimulates the production and growth of muscle tissue.
- Drugs – some drugs, like caffeine or nicotine, can increase the BMR
- Dietary deficiencies – for example, a diet low in iodine reduces thyroid function and slows the metabolism.
Energy required for physical activity
Energy used during exercise is the only form of energy expenditure that you have complete control over.
When we exercise, our muscles create movement, and as a result they require a lot of kilojoules to fuel this movement. Certain forms of exercise such as strength training, create tiny micro-tears in the muscle tissue through their exertion, which results in even more kilojoules required after exercise in order to build, repair and grow this damaged tissue. This is how we build muscle. The more muscle we have, the more energy required when we move, the higher our BMR becomes.
Whilst muscle tissue at rest only accounts for around 20% of daily energy use, this can increase up to 50-fold when performing strenuous exercise.
Thermic Effect of Food
Your BMR rises when you eat food, because you require energy to physically eat (chew, swallow), digest and metabolise the food you have consumed. The rise in BMR occurs soon after your start eating, and peaks 2-3 hours later.
The rise in BMR fluctuates between 2-30% depending on the quantity and types of food consumed.
Different foods have different effect on the elevation of BMR. Some examples include:
- Fats raise BMR by 0-5 %
- Carbohydrates raise BMR by 5-10%
- Proteins raise BMR by 20-30%
- Hot, spicy foods such as chilli, horseradish, wasabi and mustard can have a significant impact on raising BMR (thermic effect).
This gives some insight into why high protein diets tend to be the most effective when an individual is trying to lose weight.
The Role of Metabolism in Age Related Weight Gain
Ageing is one inevitable process over which we have no control. A lot of the population tends to put on weight as they get older, and this is often blamed on the process of ageing itself, however this may not be the case.
One effect of ageing is a loss of muscle mass or density, subsequently reducing BMR, which will cause an increase in fat tissue storage. Scientifically, it is not clear whether this muscle loss is a result of the ageing process itself OR because people tend to become less active as they age.
Research has shown that individuals who undertake moderate strength and resistance training programs tend to NOT experience this decline in muscle mass as they age, so it does appear that the decline in muscle and subsequent age-related weight gain are actually a result of inactivity, as opposed to ageing itself.
This would indicate that often the dreaded ‘age related weight gain’ can be prevented by the implementation of a moderate exercise program including strength or resistance training.
Please note that is you are over the age of 40yrs, have not exercised in some time or have a pre-existing medical condition, always consult with your doctor prior to commencing a new exercise program.
Hormonal Imbalances and Metabolism
One aspect of our BMR that we have very minimal control over is hormonal balance. Hormones play a massive role in regulating metabolism, and can often be a key indicator in a slow or damaged metabolic rate, and the cause of subsequent weight gain. Based on research published by the Journal Of the American Medical Association, Mehmet Oz, M.D., explains that four major hormones are responsible for how and where the body stores fat. An imbalance in your cortisol, testosterone, estrogen and insulin hormone levels can slow down your metabolism and trigger weight gain.“If your level of any of the essential hormones is too high, you need to reduce it. If your level is too low, you need to raise it,” explained Dr. Tami Meraglia, a weight-loss expert and author of The Hormone Secret.
Whilst there are some key indicators or symptoms to alert you to an imbalance in hormones, you do require clinical testing through your doctor to confirm and address these imbalances. Some of the more common hormonal disorders are concerned with the thyroid. This gland secretes hormones to regulate many metabolic processes, including energy expenditure (the rate at which kilojoules are burned). If you are experiencing any underlying symptoms and finding it difficult to lose weight after implementing lifestyle changes, you may wish to discuss hormone testing with your GP.
Once you know what your imbalance is, symptoms can often be addressed through the implementation of specific lifestyle and dietary changes.
Tips to boosting your Metabolism
If you are struggling to lose weight, feeling tired and sluggish, or overly full after meals, your metabolic rate may have slowed due to a combination of physiological and behavioural factors.
Whist many of these cannot be controlled, there are several things that you can do on a daily basis to optimise your metabolic rate, and get the most from your BMR.
- Undertake strength or resistance training 3 times per week. The larger your muscle mass is, the higher your BMR will become.
- Increase your daily activity through incidental exercise. Move more!
- Park an extra block away from work
- take the stairs instead of the lift
- walk whilst on the phone
- try a standing desk at the office
- go for a brisk 5 minute walk several times throughout the day
- try a new activity each weekend until you find something that you enjoy
- take the dog for a walk
- play outside with your kids
- do body-weight exercises during the ad breaks on TV
- Eat small meals more frequently. Each time you eat food, your BMR must increase in order to eat, digest and process that food. Eating more often = more frequent boosts to BMR
- Eat a high protein diet. Protein has the highest thermogenic impact of all micronutrient
- Increase consumption of thermogenic foods. Try including thermogenic foods into your meals such as chilli, ginger, garlic, eggs, oatmeal, green tea, fish
- Drink more water! Your body is comprised of 60-70% water. It is required for EVERY metabolic process which occurs i your body from the moment of consumption to the elimination of waste. Some research has even shown that water itself is great for metabolism. A study monitored the metabolic rates of adults as they drank varying amounts of water, according to eMed. While the mechanism for the results isn’t yet fully understood, the adults who drank water regularly had higher metabolic rates than those who didn’t.
Whilst it is true that metabolism is linked to weight, a slow metabolism is rarely the cause of excess weight gain. Although your metabolism does dictate how much energy your body needs, the truth of the matter is how much you eat and drink along with how much physical activity you get are the things that ultimately determine your weight.
So before you blame your ‘slow metabolism’ for the gradual increase on the scales, you may first want to take a look at your lifestyle and assess what the true cause is.
About The Author
Lauren is a qualified nutritionist with a passion for holistic living and mindfulness. She believes that health starts from what‘s on your plate, and the way that we ’think’ about food. “Our state of mind is the biggest enemy when it comes to changing our bodies” says Lauren. “There is no quick fix. We need to look at the body as a whole, and try to regulate any imbalances whilst targeting negative thought patterns.”
Lauren’s passionate about educating clients on how to nourish their bodies back to health and create a balanced relationship with food. She specialises in women’s health, weight loss, sports nutrition, and food intolerances.
- Deakin University. (2014, May 10). Metabolism – Better Health. Retreived from https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/metabolism
- Rolfes S, Pinna K, Whitney E, 2009, Understanding Normal and Clinical Nutrition, Cengage Learning, Belmont, CA, USA.
- McCracken, M. (2016, April 19). 10 Thermogenic foods to boost your metabolism. Reatreived from https://www.care2.com/greenliving/10-thermogenic-foods-to-boost-your-metabolism.html
- Overstreet, E. (2016, July 6). Slow Metabolism? Check your hormones!. Retreived from https://blackdoctor.org/494744/slow-metabolism-check-your-hormones/2/
- Dietary Energy, National Health and Medical Research Council (NHMRC), Australian Government.