Do You Have A Slow Metabolism ? (Part 3: Metabolism Adaptations)

In the past two parts of this blog series we took a look at the many ways in which people unintentionally underreport their food intake, and misrepresent how much they're eating by accident. 

A large part of this comes down to the calories coming in being underestimated or unaccounted for due to poor calorie and portion awareness. 

But what about when someone is being accurate with their intake and still not losing weight ?

This leads to frustration, and some can quickly lose faith in the process thinking it isn't working for them. 

This is when a coach can be invaluable to give objective explanations of why weight loss stalls and plateaus as a normal part of the process, and doesn't mean fat loss isn't happening. 

When you thinks that you should be losing weight, but aren’t and even worse; possibly gaining a little weight it can cause knee jerk reactions that aren’t helpful for your long term goals.

However these are normal hormonal, water and metabolic adaptations that take place during dieting. 

In today’s blog we’re looking at the ways in which your body adapts to you losing weight, aggressive dieting and prolonged periods of stress.

These adaptations and excessive stress impact your calorie expenditure, and weight loss trends.

Something else to keep in mind is that these adaptations are a result of getting leaner which is why someone doesn’t eat the same amount and continue in a straight line to their ideal body composition.

Adjustments to calories, macros and even some activity will need to be made based on your rate of progress to keep fat loss happening. 

Your Energy Needs Change The Longer You Diet

There are a few different reasons that your calorie needs change as you diet, and they all pertain to different components of your metabolism and how it’s adapting to you eating less, weighing less and the excess stress that can come along with the process of dieting and exercising on lowered calories.

Your energy needs aren’t static either and can change from day to day based on a number of different factors, this is another reason why day to day fluctuations matter less than weekly trends. 

Even if you’re eating the exact same amount each day which is difficult because you’re not a robot, you’ll be expending a different amount each day.

Basal Metabolic Rate Decreases

The energy required to support your body weight and maintain physiological function which is your basal metabolic rate (BMR) which decreases as you diet and lose weight.

In essence your Basal Metabolic Rate (BMR) decreases because a lighter body requires fewer calories to maintain than a heavier body.

If you weigh 190 pounds you may require 2,900 calories to maintain that body weight. If you diet and lose body fat and get down to 160 lbs you may only need 2,500 calories to maintain your new body weight.

The drop in calories required to maintain a lighter body weight are not entirely from the drop in BMR, in fact the reduction in basal metabolic rate is relatively small compared to other metabolic adaptations that take place. 

(The above aren’t real numbers I just made them up to use as an example, and show the idea expenditure decreasing with bodyweight.)

Eat Less & Thermic Effect Of Food Decreases

Your body has to use a certain amount of calories every time you eat to digest, break down and absorb nutrients from food, and this is known as the Thermic Effect Of Food (TEF).

Each of the macronutrients protein, fats and carbs require a different amount of calories for their breakdown. While not technically a macronutrient fiber is also very high up on the TEF rating as well.

When you’re dieting and eating less your body will be expending fewer calories to break down and absorb nutrients from the food you’re eating. 

Thermic Effect of Activity Decreases Because BMR Dropped

Because your body weight is lighter you BMR decreases and you burn fewer calories at rest, but this also applies to the calories you burn during exercise as well.

The calories that you burn off during formal exercise is known as the Thermic Effect of Exercise (TEE).

Because your body is smaller the energy expenditure needed to lift weights, run or do yoga is less, a smaller body burns less calories.

Moving Less Isn’t NEAT

Non Exercise Activity Thermogenesis also known as NEAT is all the movement you do outside of formal exercise (TEE). This NEAT includes walking, cooking breakfast and doing the dishes, fidgeting and scratching your nose.

As someone diets down and starts to lose body fat they may see a drop in NEAT levels. There is a lot of individual variation in how people’s NEAT levels respond to dieting. Most people see their NEAT decrease via less walking and moving around during a dieting phase

This is why you shouldn’t use your activity tracker to try to estimate the calories you burn, but instead as a way to make sure you’re getting a baseline of low level activity each day.

Putting the Pieces Together

When someone diets for a long period of time they will see inevitable drops in their overall metabolic rate because each part of the metabolism compensates to become more efficient in response to dieting.

BMR +  TEF + TEE + NEAT = Total Daily calorie burn or metabolic rate

As you can see just about every aspect of your metabolism adapts when someone yo yo diets or does a long term aggressive diet.  

But these adaptations go beyond the metabolism. There’s significant hormonal shifts that take place during dieting that can impact how your body responds to dieting.

Those hormonal shifts in response to dieting is what we're covering in parts four and five of this series so stay tuned!