In our modern-day society, we want everything now. Whether it is food, fashion, or fitness, we want the best and we want it yesterday. For some things, such as access to food, this is a great thing. It has never been easier or quicker to buy what we need from a store just down the road. However, as with all great things, there is often a catch. Having such easy access to an abundance of food, particularly highly processed calorie dense food, has contributed greatly to the epidemic of obesity that is prevalent in many first world countries. Due to our increased waistlines and decreased levels of patience, people who are looking to lose weight often turn to extreme or “crash” dieting/weight loss methods. This can involve drastically reducing calorie intake, reducing or completely omitting certain macronutrients, exercising far more than what is safely recommended, and other extreme methods. There is no denying that in the short term, this can work extremely well, however our bodies have ways of reducing or stopping weight loss entirely. All of us have what is called a Basal Metabolic Rate (BMR), this is the amount of energy we need to burn to maintain our current size at rest. Factors such as age, sex, size, muscle and fat mass all impact on how high or low someone’s BMR is. What also impacts this is weight loss and reduction of food intake. Our body loves to store fat and it will do whatever it can to preserve fat stores. This goes back to our early ancestors, who were hunters and gatherers and did not have the same access to food that we do. By having as much fat stored as possible, they were able to weather the times when food was not plentiful. Fast forward to modern day and the current topic, if weight loss happens too quickly, or, if we drop down past a level our body is not comfortable with, it essentially goes into crisis mode. In crisis mode, two major things happen. The body reduces its BMR in an effort to retain fat stores. This is often the reason why weight loss plateaus, as the body drastically slows down its BMR to counter the original calorie deficit. Secondly, production of the hormone leptin is reduced. Leptin is produced in fat cells and is associated with feelings of fullness. As fat cells get smaller, so does the level of leptin in the bloodstream. This in combination with increases in the amount of ghrelin, the hormone associated with feelings of hunger, leads to a powerful urge to eat and restore the diminished fat stores. (for more information about Leptin and Ghrelin, please see the article Hungry Hungry Hormones on the Global Weight Management Federation website). Certainly, when weight loss is called for to manage a medical condition, or to prevent other health conditions developing, it is often quick and extreme. Bariatric surgery is an example of this. This surgery involves reducing the size of and/or bypassing sections of the stomach, which limits the amount of food that can be eaten and reduces the production of hormones that promote hunger. It elicits a rapid reduction in weight, and if it is done in a safe environment and with supervision from medical/health professionals, it can be an effective way to lose weight and keep it off. There are other examples where more extreme methods are called for, but for the majority of the population looking to lose weight and not under the care of a health professional, extreme weight loss methods often lead to poor long-term results, and in some rare cases, long lasting damage to our metabolism and hormonal systems. An example of this comes from the final season of The Biggest Loser US. All the contestants on the show were subject to calorie restriction and gruelling exercise regimes, which led to a staggering amount of weight lost in a short period of time. Unfortunately, within a year of the show finishing, all but one person had completely regained the weight that they had lost. In this final season of the show, all of the contestants had their BMR and leptin levels measured. This was done before the season started and then again six years after it had ended, and it was found that both measures were drastically lower at the six-year postseason mark. While this is an extreme example, it does showcase that quick and drastic weight loss often does not lead to sustainable results and can have some potential long term health consequences. For most people who are looking to lose weight, the secret to sustainable weight loss is to do it gradually, which will look different for everyone. For example, someone starting with more fat mass may be able to lose a lot more weight before their body goes into crisis mode, versus someone who is only slightly overweight. Also, a person with more muscle mass will burn more energy at rest, due to how demanding muscle is on energy stores.  Regardless if weight loss is sudden or gradual, there will be a decrease in levels of leptin, owing to a reduction in stored fat in the body. Getting enough sleep, participating in regular exercise (particularly High Intensity Interval Training (HIIT)) and eating a well-balanced, nutritious diet can increase sensitivity to leptin, allowing it to be more effective at lower levels. BMR may also be affected, but by aiming for a more gradual rate of weight loss (0.4kg to 0.9kg per week), making small, incremental changes to dietary intake, and focusing on preserving and/or increasing muscle mass through resistance training, can help to blunt the effects. This in turn should help to make weight loss more tolerable and sustainable in the long term.  References

1.         Azar JT, Hemmatinafar M, Nemati J. Effect of six weeks of high intensity interval training on leptin levels, lipid profile and fat percentage in sedentary young men. Sport Science. 2018;11(1):78-82.

2.         Fothergill E, Guo J, Howard L, Kerns JC, Knuth ND, Brychta R, et al. Persistent metabolic adaptation 6 years after “The Biggest Loser” competition. Obesity. 2016;24(8):1612-9. 3.         Health Direct. Guide to bariatric surgery. Available from: https://www.healthdirect.gov.au/guide-to-bariatric-surgery [accessed 8 February 2023]. 4.         Shaikh J. What is a Safe Rate of Weightloss? Available from: https://www.medicinenet.com/what_is_a_safe_rate_of_weight_loss/article.htm [accessed 7 February 2023]. 5.         Shapiro A, Tümer N, Gao Y, Cheng K-Y, Scarpace PJ. Prevention and reversal of diet-induced leptin resistance with a sugar-free diet despite high fat content. British Journal of Nutrition. 2011;106(3):390-7.