Weight Loss Rebound: Why Does It Happen?

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Last updated on March 23rd, 2024 at 05:58 pm

So you’ve lost weight.  You’ve seen the stories of weight loss rebound and are feeling unsure about what’s going to happen to your body next.  

Weight loss rebound often happens because of: 

  • Physiological responses to weight loss
  • Limited access to food
  • Binge restrict cycles
  • Lack of access to places to do physical activity 
  • Prior weight loss attempts and successes 
  •  Access to healthcare 

From a biological perspective, our body DOES NOT WANT us to lose weight.  This would be counterproductive to the survival of the species. 

Only about 5% of people that lose significant amounts of weight will keep the weight off long-term. 

Those odds are not very good!  If you went to the gynecologist and they said “there’s a 95% chance this birth control pill will fail at preventing pregnancy would you take it? 

Let’s dig into some of the reasons why weight loss rebound happens and how to respect your body without focusing on food rules and weight loss. 

Purple and blue graph with reasons behind weight loss rebound

What Causes Weight Regain After Weight Loss

The body likes to maintain homeostasis. This means that regardless of how much you eat, it’s very likely your body weight will remain within a relatively narrow range. 

Your body has a set point weight it likes to be at, despite what faulty health standards like the BMI scale may tell us.

Reduced Energy Expenditure 

Total energy expenditure or TEE is the amount of energy that is required to digest food. 

When you lose weight, your body starts to try to conserve the amount of energy that it uses to digest food and absorb nutrients. 

On average, our TEE decreases by 15% with more than 10% weight loss.  This means you are actually burning fewer calories eating than you were at a higher weight.  

This reduction in TEE will help the body to restore the weight that was lost.

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Changes In Thyroid Function 

Weight loss often results in a shift in thyroid function and hormones produced by the thyroid.  

Some of the thyroid function changes that happen when you lose weight include: 

  • Decreased thyroid-stimulating hormone (TSH) secretion and circulation
  • Increased inactive rT3 (reverse t3) which causes us to preserve energy 
  • Changes in T3, t4, and rT3 are often associated with changes in Resting Energy Expenditure. 

Thyroid function is very sensitive to weight loss. Therefore, the body will put mechanisms in place to try to restore weight loss by altering thyroid hormones. 

infographic on rebound weight loss brain changes

Hormones and Appetite Regulating Adipocytes 

There are lots of hormone shifts after you lose weight.  

Some major shifts that might lead to weight loss rebound include: 

  • Increased Grehlin which is the hormone that makes you feel hungry
  • Leptin, the hormone that makes us feel full decreases.  Decreases in leptin also alters the way you experience taste.
  • Increase in Neuropeptide Y which causes you to crave carbohydrate-rich foods

Hormonal signals are sent to the hypothalamus and hindbrain to help increase food intake after weight loss. 

All of these mechanisms are put in place to help the body resume its natural weight. You may experience extreme hunger after weight loss which is your body’s way of trying to restore its natural weight.

Brain Changes Leading To Weight Loss Rebound

Did you know the brain actually changes when you lose weight to help you regain it the weight you’ve lost?  

Brain changes after weight loss include: 

  • Increased activity in the reward and decision-making system of the brain (limbic)
  • Increased responsiveness to the reward of food and decreased levels of control
  • Decreased brain activity in the insula, Inferior visual cortex, posterior cingulate cortex, and amygdala which are associated with control with eating 
  • Decreased activity in orbitofrontal cortex is associated with how we experience the reward we feel from food (potentially leading to needing a greater amount to achieve reward response).

There is some evidence that the brain reduces the ability to sense that the body has gotten enough food or more food than the body needs after significant weight loss.   

Anatomical brain changes are one symptom of starvation syndrome which can result from extreme food restriction.

infographic with purple background on tips to stop rebound weight

How Long Does It Take To Regain Lost Weight

You will typically start to see weight regain within 6 months to 1 year of weight loss. 

After 5 years of weight loss, most people have regained all of the weight they have lost and could potentially be at a higher weight than when they started when dieting. 

In fact, the single greatest predictor of long term weight gain is constant dieting.

quote on weight regain with pink flower background

How Do I Stop Rebound Weight

As you can see, there are dozens of mechanisms in place to cause weight loss rebound.  

Attempting to outsmart all of your biological mechanisms that take place to prevent weight regain will likely just result in an even greater amount of weight regain.  

Something that can help you maintain the body weight that your body feels most comfortable at without additional weight gain includes: 

The bottom line,  trying to force your body to remain at a smaller size will likely skyrocket your feeling guilty after eating but it won’t stop you from weight loss rebound.

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Shena Jaramillo. Registered Dietitian
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