Losing weight at the snap of our fingers would be a dream come true for many. Unfortunately, that is not how weight loss works.
People have weight loss goals for various reasons and when it comes to losing weight, we often want a method that gives us results, even better if it’s within a short period of time. Low calorie diets, such as Mosely’s Fast 800, are extremely popular methods for losing weight as they are highly advertised across all mediums and they generally promote rapid weight loss and various health benefits. However, these diets lack credible evidence, are not sustainable long-term and often result in weight being quickly regained.
Here’s a rundown on metabolism and why highly restrictive diets aren’t the best long-term approach to good health and weight management.
Basal Metabolic Rate
In simple terms, your basal metabolic rate (BMR) is the number of calories your body needs at absolute rest in order to perform basic, involuntary functions to sustain life. These functions include breathing, and regulating body temperature, blood pressure and water levels. Your BMR will vary depending on your age, sex, height, weight and muscle mass.
Estimated Energy Requirement
Your estimated energy requirement (EER) is the predicted number of calories that your body would need after factoring in doing anything other than performing basic, involuntary functions to sustain life, e.g., being physical activity in any way, like working, gardening, taking the dog for a walk or smashing out a gym session; or healing a wound. The more active you are and the more going on for your body, the more energy your body will need.
So losing weight is just a matter of eating less than my EER?
The short answer is no. The slightly longer answer is for many years the assumption was that to lose weight, you just need to be in a calorie deficit. In other words, you would need to be eating less energy than your EER, but more than your BMR, to ensure that your body has enough energy for vital functioning and the opportunity to meet the recommended intakes of various vitamins and minerals (restrictions below BMR are not conducive to this). The issue with this thinking is that it assumes the body is okay with you getting less energy in and will therefore continue to function as normal. We now know this is not the case.
Why, what happens?
Take the Fast 800 as an example diet. This amount of energy intake is below most people’s BMR. So, you will likely initially experience weight loss because you’re in a calorie deficit, however, your body will also lower its BMR to compensate for the excessively low energy intake, making weight loss even more difficult in the long term.
Our bodies are amazing at recognising change and adapting, so your body will start to change up how it does things, become more efficient to use less energy, and prioritise its functioning. During this time, you can experience fatigue and muscle loss, a drop in your temperature, and an increase to your risk of injury.
Due to the extreme reduction in energy intake, restrictive low-calorie diets are not sustainable long term. Most individuals know this and hope to simply stick to it long enough to ditch the weight and deal with what comes next after the fact.
The most common approach to this kind of diet is: ‘once I’ve lost this weight, I’ll go back to eating normally’. However, because your body has adapted and requires less energy to perform its basic functions than it used to, your ‘normal’ way of eating, that once maintained your weight, could actually put you in a calorie surplus and lead to weight gain. This generally leads to ending up at a higher weight than your initial starting point. This concept is known as the yo-yo effect.
Here’s the clincher though: diets don’t have to be overly restrictive or drastic to elicit the above response. Any reduction in energy intake compared to what the body sees as required can elicit metabolic changes that help to keep your weight as stable as possible, or to increase it to what it was previously.
What should I do if I’ve been on a low-calorie/restrictive diet?
Seek support from an Accredited Practising Dietitian to assist with transitioning to a ‘normal’ diet that meets your nutrient needs and puts you in touch with your body’s cues. Together you can get to the bottom of your desire to lose weight in the first place, and implement evidence-based, healthy, sustainable strategies to achieve your goals.
Implementing sustainable daily habits that target your health and wellbeing and move away from a weight loss goal reduces the risk of experiencing the yo-yo effect, as it keeps your body in charge of its weight. When you don’t strive to achieve a weight loss goal, and instead let your body regulate itself, this leaves a whole lot more time and energy for you to focus on your health or body image goals.
Our article How to achieve good health without restrictive eating looks at ways to loosen the restrictions and embrace eating well without deprivation.
Want one-on-one guidance to loosen the reigns while prioritising your health? Book an appointment with one of our Accredited Practising Dietitians!
References
Connolly J, Romano T, Patruno M. Effects of dieting and exercise on resting metabolic rate and implications for weight management. Family Practice. 1999 Apr 1;16(2):196-201. Available from: https://academic.oup.com/fampra/article/16/2/196/480196
