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Science behind the 'Yo-Yo' effect

What is the Yo-Yo effect? It is a term defined by Psychologist Kelly D. Brownell from Yale University that described as the cyclic loss and gain of body weight, often as the result of dieting or strict restriction of calorie intake.

The main reason suggested by Dr. Brownell is that individuals are unable to sustain the diet in the long term and hence reverts back to usual eating habits. Often these individuals may go through an emotional state such as depression which leads to consuming more foods that they usually would. Ultimately, this leads to weight gain and the cycle continues when the individual decides to diet again.

There is research that supports this idea and further explains why the body reacts this way when someone restricts calories and rapidly lose weight within a short period of time.

Fundamentally, the rate that our body 'burns calories' are dependent on our metabolism or metabolic rate. There are several factors that can influence our metabolic rate such as genetics, environment, age, gender, physical activity, muscle to fat ratio and hormones.

Why does one's metabolism lower upon weight loss?

Calorie restriction or long periods of fasting cause your body to go into 'starvation mode'. Your body preserves energy to maintain function and hence you may be burning less energy than usual. If this is sustained for a longer period of time, it causes a more permanent effect on your metabolism. This makes sense as if your body is lighter, less energy is required to function. However, rapid weight loss could lead to a more significant reduction of your metabolism than losing weight slowly. It is unsure how long the lowered metabolism lasts as studies have only shown until 8 years but could potentially be long term.

To put it into simple terms, Person A who has never 'dieted' may require 2500 calories to maintain their weight and while Person B who has lost weight to the same weight as Person A may require lesser calories such as 2100 to maintain a steady weight.

So what can you do to prevent this? Instead of doing a crash diet or strict carlorie reduction:⠀

⭐️ Good quality protein for satiety⠀

⭐️ Balanced diet including wide variety of fruit and vegetables⠀

⭐️ Good quality carbohydrates for energy⠀

⭐️ Healthy fats to support your immune function⠀

⭐️ Physical activity including strength and cardio exercises⠀

⭐️ Your mental well-being is as important - good sleep and manage stress ⠀

Therefore, by losing weight more slowly and eating more smartly, it has suggested to minimise the effect of weight loss on our metabolic rate. Therefore, it is beneficial to consult with an Accredited Practising Dietitian to determine the best approach if weight loss is your goal.


Harvie M, et al. The effect of intermittent energy and carbohydrate restriction v. daily energy restriction on weight loss and metabolic disease risk markers in overweight women. Br J Nutr. 2013 Oct;110(8):1534-47.

Leibel RL, et al. Changes in energy expenditure resulting from altered body weight. N Engl J Med. 1995 Mar 9;332(10):621-8.

Leibel RL, Hirsch J. Diminished energy requirements in reduced-obese patients. Metabolism. 1984 Feb;33(2):164-70.

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