What Happens to Your Metabolism During Weight Loss?

There are many changes to the body when weight loss occurs. Some of these changes are visible but others cannot be seen by the naked eye. With weight loss comes metabolic changes, which play a vital role in weight loss plateaus and maintaining weight loss. When you lose weight, your metabolism naturally slows down. This is called adaptive thermogenesis (or metabolic adaption) and it happens for a few reasons:

Decreased Body Size Means Decreased Needs 

A lower body weight requires less energy to maintain organ function, basic daily movements, and exercise. Your resting energy expenditure (REE, the energy used at rest) also  decreases which is a normal and expected change with weight loss. Metabolic adaptation can be seen with a 5-10% body weight loss (see how to calculate below) or 2-4weeks of a sustained energy (calorie) deficit. There is also a small drop seen at 2-5% body weight loss however, clear metabolic adaptation occurs at 5-10% body weight loss as well as  increased hunger hormones. This will happen whether someone starts at a higher or lower body weight.

Starting body weight - current body wt = X (the difference in weights)

X / starting body weight = A (decimal form of percentage) x 100 = % change 

Decreased Weight Means Increased Energy Efficiency 

In order to lose weight there must be a deficit in calories, the body perceives this deficit as starvation and will try to protect itself. The body protects itself by reducing energy (calorie) consumption by burning fewer calories during movement known as NEAT ( non-exercise activity thermogenesis, aka calories burned when standing, cleaning, etc.,), reducing unconscious activity (fidgeting, shifts in posture), and becoming more energy efficient with exercise. In addition to burning fewer calories due to a smaller body size, the body adapts by reducing energy expenditure beyond what weight loss alone would predict..This is why many people experience a weight loss plateau around the 10% weight loss mark, even when adherence has not changed. 

Hormone Changes 

Weight loss triggers the satiety hormone Leptin to decrease and the hunger hormone Ghrelin to increase. This makes hunger stronger and fullness harder to achieve, which is often more impactful than the metabolic slowdown on your weight loss journey.

How Much Does Your Metabolism Slow?

Metabolism drops about 5-15% beyond what body size predicts. What this means is that calories burned calculated based on a new body weight will not be correct because your metabolism has adapted and decreased energy needs further. This makes fat loss slower and weight maintenance harder. This is not permanent metabolic damage and it’s reversible, it can be  improved with weight stability, adequate intake, resistance training, and sleep. 

How Do You Keep Losing Weight Despite This?

There are 3 key elements that will further aid in continued weight loss:

1. Preserve lean muscle mass! 

Resistance training in addition to adequate protein intake reduces metabolic slowdown. This helps to maintain muscle, which supports a higher metabolic rate and reduces the degree of metabolic adaptation.

1. Protect NEAT! 

Aim to meet your step goals, 10,000-12,000 steps per day provides benefits for weight loss and maintenance. Take standing breaks and incorporate daily walks. These daily movements often matter more than structured exercise.  

1. Adjust Calories Strategically, Not Drastically 

When starting your weight loss journey utilize smaller calorie reductions (100-200 calories per day) to gradually work towards your weight loss goal. Increasing activity slightly can also be beneficial to ensure your body is not diving into starvation mode. 

References:

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