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Dietary and health advice often mentions ‘metabolic rate’, usually in the context of actions that will ‘boost’ your metabolism. There is even a recent fad diet called the ‘metabolic confusion diet’, which claims to help you lose weight while simultaneously speeding up your metabolism. So what exactly is metabolic rate, and why would you want to speed it up?
Living organisms are chemical factories, and these factories come with a running cost. Proteins need to be recycled, DNA synthesised, and ions pumped across cell membranes. On a larger scale, muscles contract to keep the heart beating, the lungs expanding, and to allow us to move around and go about our daily lives. In order for all of this to happen, our cells need energy, which is derived primarily from nutrients that we consume or have stored. Metabolic rate is the rate at which these nutrients are converted into energy in order to satisfy the body’s demands. In other words, it is the total rate at which the body consumes energy. This can be split into total metabolic rate and basal metabolic rate (or resting metabolic rate), the latter being the energy spent by the body at rest.
A desirable metabolic rate is relative. If your metabolic rate exceeds your rate of calorie consumption, you are at an energy deficit and must compensate by accessing stored energy. In extreme cases (starvation), the body will start to break down muscle tissue in order to fuel the metabolism. If your metabolic rate is lower than your rate of calorie consumption, then excess calories can be stored, primarily as fat. For this reason, most people would like to have a higher metabolic rate, as this theoretically allows them to eat more without gaining weight. This is why techniques that ‘boost’ your metabolism sound very appealing – they promise weight loss without having to significantly cut down on calories. Is it too good to be true?
Metabolic rate is partly determined by the genes you inherit. However, an individual’s metabolic rate isn’t a static number, though the extent to which it can be altered is debated. The most obvious way to increase metabolic rate is to exercise, as exercise increases the body’s energy expenditure. However, some forms of exercise (such as long distance running) may also slow metabolic rate in order to use energy more efficiently. Having a high muscle mass will increase your basal metabolic rate, as simply maintaining muscle tissue has a high energy cost. Thermogenic adipose tissue (aka brown fat) is a form of fat that burns calories to produce heat. Research suggests you may be able to increase brown fat mass by exposing yourself to cold temperatures and by exercising.
It is important to mention here that metabolic rate is not entirely isolated from calorie intake – it can speed up or slow down depending on how much you eat. This can be problematic for weight loss, as cutting down on calories results in a slower metabolic rate to compensate. This metabolic slowdown can persist for years following weight loss, and is particularly problematic for people who are already overweight – for a more detailed explanation of why this happens, read this article.
Enter the metabolic confusion diet, which promises to reduce your calorie intake and help you lose weight without slowing down your metabolism. It involves alternating high calorie days with low calorie days – similar to intermittent fasting, but without the fasting part. Unfortunately, there’s no evidence that even intermittent fasting achieves what metabolic confusion claims to do. That’s not to say such diets don’t work, but they probably have more to do with helping you eat less overall than anything related to metabolism.
Metabolic rate is important for weight loss, and is helpful to know about if you are seeking to lose weight, as it may be the reason your diet isn’t working. However, getting hung up on metabolism alone as a means to lose weight is unhelpful. If there was an effortless way to boost metabolism and lose weight without dieting or exercising, we would all be doing it!
Metabolic confusion diet won’t boost metabolism – but it could have other benefits: https://theconversation.com/metabolic-confusion-diet-wont-boost-metabolism-but-it-could-have-other-benefits-150341