In today’s society beset by overweight and obesity, a slow metabolism is often cited as the cause. Could this be true, or is it just a convenient scapegoat when, in fact, other factors are at play? Dr Luke Del Vecchio, Head of Sports Science at Australian Combat & Exercise, takes a look at what drives metabolism and how it affects weight.
Metabolism is defined as the total sum of all the chemical reactions taking place in your body, and is measured in calories.
There is a popular assumption that someone who is overweight and has difficulty losing weight must have a slow metabolism. However, the truth is that overweight or obese individuals (with Body Mass Index (BMI) of over 25 and over 30, respectively) have a greater energy expenditure than those in the lower, healthy weight range.
My clinical experience over the last ten years conducting metabolism assessments confirms this. The fact of the matter is, the bigger you are, the more energy is needed to keep all your bodily cells (including fat) in balance.
The author conducts a metabolism test on a client
Often, leaner people don’t have faster metabolisms that somehow protect them from weight gain, and people that struggle to achieve or maintain a healthy BMI don’t necessarily have a slow metabolism. Research supports this notion: for example, Hoffmans’ historic 1979 study showed the metabolic rates of obese individuals were slightly higher than their normal weight counterparts (1,550 Kcal/day vs. 1,421 Kcal/Day).
So, if a slow metabolism isn’t to blame, why do some people struggle to lose weight, while others don’t? Genetics and lifestyle factors are among some of the theories.
For one, as much as we may think we know how much we eat on a regular basis, research and scientific evidence has repeatedly shown that even the most conscientious among us tend to consistently under-report our food intake. Meals, we may remember. The snacks in between are where our memory often fails us…
Humans are very efficient at gaining weight and keeping it on – and this is something that many of us find hard to accept. When the fat accumulated in times of plenty could help see our bodies through the lean hunting and foraging of winter months, this was beneficial. In the age of Uber eats and Instagram, however, not so much.
To put the average human’s weight gaining ability into perspective, a weight gain of roughly 20kg over the course of ten years would require you to eat only 30-40 calories more each day than your body needs (your resting metabolic rate and daily physical energy expenditure). This equates to just half an apple, a plum, a small plain biscuit, a small portion of a rice, or a very small cup of soft drink. A sobering thought, and one of the many reasons so many people gain weight. It really doesn’t take much at all for it to happen.
On the other hand, trying too hard to create a calorie deficit in an attempt to speed up weight loss can have dire consequences for your metabolism.
Research (Elliot et al. 1989) has demonstrated that metabolism will decrease with a reduction in caloric intake, making it harder and harder to stay in a caloric deficit in the long term. This explains why so many people experience rapid weight loss once they begin a restrictive diet, but in the long term, put on more weight than they started with. Often, these people spend much of their life yo-yo dieting in an effort to lose weight again and again.
So, the take-home message is – know your energy requirements (how many calories I need to eat for my goal weight, via a metabolism test where possible), record your energy intake and then add a moderate amount of physical activity (150 minutes per week or more). This approach is not extreme, so it’s not going to be the subject of a bestselling fad diet book. What it is is sensible and sustainable, and those who adopt it may be surprised with the results.
Dr Luke Del Vecchio is an educator and Head of Sports Science with Australian Combat & Exercise
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Elliot, D. L., Goldberg, L., Kuehl, K. S., & Bennett, W. M. (1989). Sustained depression of the resting metabolic rate after massive weight loss. The American Journal of Clinical Nutrition, 49(1), 93-96.
Hagedorn, T., Poggiogalle, E., Savina, C., Coletti, C., Paolini, M., Scavone, L., … & Donini, L. M. (2012). Indirect calorimetry in obese female subjects: Factors influencing the resting metabolic rate. World Journal of experimental medicine, 2(3), 58.
Hoffmans, M. D. A. F., Pfeifer, W. A., Gundlach, B. L., Nijkrake, H. G., AJ, O. O., & Hautvast, J. G. (1979). Resting metabolic rate in obese and normal weight women. International journal of obesity, 3(2), 111-118.