Weight Loss – Why Diets Can Sabotage Our Metabolism

Extreme diets can slow down metabolism, alter hormones, and make weight loss more difficult. Understand how the body reacts and how to lose weight in a balanced way.

From GLP-1 to Extreme Caloric Restriction 

In recent articles, we explored GLP-1 medications—including Ozempic, Mounjaro, and Wegovy, all FDA-approved—which are increasingly being used, often without proper guidance, to treat type 2 diabetes, support weight loss, and reduce cardiovascular risk.

With this information, you are better equipped to make informed decisions and understand both benefits and limitations of these treatments. However, sustainable weight loss does not depend on medication alone.

To keep our metabolism working in our favor, it is essential to understand how many calories our body truly needs each day. This includes not only total calorie intake, but also the balance of macronutrients (carbohydrates, proteins, and fats) and micronutrients (vitamins and minerals) required to support energy, physical health, and mental well-being.

There is no single best approach to managing obesity—because every individual is unique. Even when using medications as a supportive tool, we must still provide the body with the nutrients it needs to function, adapt, and maintain health.

So, let’s take this step by step and build a clear understanding of our daily nutritional needs.

Why Caloric Balance Matters

Maintaining adequate caloric intake is essential for optimal health. Both ends of the spectrum—excessive intake and severe caloric restriction—can negatively impact overall well-being:

• Excess calories: may lead to weight gain, obesity, increased risk of metabolic and cardiovascular diseases, fatigue, reduced quality of life, and over time increased risk of chronic illness.

• Severe caloric restriction: may result in muscle loss, bradycardia (slow heart rate), low blood pressure, dizziness, hormonal imbalances, blood sugar instability, sleep disturbances, increased hunger, and rebound weight gain tendencies.

  
  

The key is balance: providing the body with what it needs to function properly, while ensuring adequate nutrient density through a varied and minimally processed diet.

This is especially important today, as strategies that drastically suppress appetite—such as extreme dieting or the use of medications—have become increasingly common. Even when using GLP-1 medications, it is essential to meet basic nutritional needs to support long-term health and well-being.

Weight Loss and Our Evolutionary Influences

Our body—especially the brain—was not designed to lose weight easily. It evolved to survive periods of scarcity, not constant abundance.

Our ancestors did not have supermarkets or restaurants on every corner. As hunter-gatherers, significant weight loss often signaled food scarcity, which the body interpreted as a potential survival threat.

How the Body Responds to Caloric Restriction

When we drastically reduce calorie intake, the body activates a biological adaptive response—often referred to as metabolic adaptation—to conserve energy and protect vital functions.

Key physiological responses:

• Slower metabolism: reduced energy expenditure for basic functions such as breathing, circulation, and digestion

• Increased hunger: ghrelin increases, while leptin decreases

• Fat preservation: the body prioritizes energy storage

• Muscle loss (in extreme cases): reduced energy use in less essential tissues

  
  

Behavioral changes:

• Reduced spontaneous movement

• Increased fatigue

• Lower motivation

• Sleep disturbances

  
  

Long-term consequences:

• Plateau effect: weight loss slows or stalls despite continued restriction

• Rebound effect: increased fat storage when normal eating resumes

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In short, the body interprets extreme caloric restriction as a stressor and adjusts hormones, metabolism, and behavior to preserve energy and ensure survival.

This is why extreme calorie-restriction diets often fail: the body adapts and resists sustained weight loss.

Why the Body Resists Weight Loss: Metabolic Adaptation

When calorie intake is drastically reduced, the body activates protective mechanisms. It does not recognize a “diet”—it perceives an energy shortage.

This triggers metabolic adaptation, a process that makes sustained weight loss more difficult than expected.

Main effects in the body:

• Reduced energy expenditure

• Increased hunger

• Decreased energy and motivation

  
  

Even with discipline, many people experience plateaus or weight regain because the body prioritizes survival and energy conservation.

Practical examples:

• A person who significantly reduces calorie intake while increasing exercise may stop losing weight after a few weeks.

• Returning to previous eating habits after dieting may lead to faster fat regain due to adaptive efficiency changes.

  
  

Key point:

It is not a lack of discipline—the body is biologically designed to defend against energy deficits.

How Many Calories Do We Need Per Day? (BMR)

A common question is:

“How do we determine the right amount of calories for our specific needs?”

Calories are a unit of energy found in foods and beverages. They serve as fuel for all bodily functions—from breathing and circulation to movement and thinking.

While many people refer to a general guideline of a “1,000 to 2,000-calorie diet per day,” this is only a broad estimate.

There Is No One-Size-Fits-All Number

Caloric needs vary significantly from person to person and depend on several factors, including:

• Age

• Sex

• Body size, weight, and goals (loss, maintenance, or gain)

• Physical activity level (from sedentary to highly active)

• Individual metabolic rate

• Environmental conditions (such as temperature)

• Stress levels

• Sleep quality and duration

• Work schedule and daily demands

  
  

One of the most useful tools for estimating basic energy needs is the Basal Metabolic Rate (BMR)—the number of calories the body requires to maintain essential functions at rest.

Finding our Basal Metabolic Rate (BMR)

The Basal Metabolic Rate (BMR) represents the minimum number of calories required to sustain essential bodily functions such as breathing, circulation, digestion, and brain activity.

This is the first step in estimating baseline energy needs at rest.

Mifflin-St Jeor Equation

Male:BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5

Female:BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Practical Example

Maria (Female)

• Height: 170 cm

• Weight: 60 kg

• Age: 55

  
  

BMR = 1,226 kcal/day

João (Male)

• Height: 170 cm

• Weight: 80 kg

• Age: 56

  
  

BMR = 1,587 kcal/day

Quick and Practical Way to Estimate Your Basal Caloric Need

1. Convert your weight to pounds (kg × 2.2)

2. Identify your approximate “comfortable” or goal weight (the weight at which you feel your best)

3. Apply the following estimates:

   • ×12 → approximate maintenance calories

   • ×10 → approximate weight-loss range

     
     

Example

• 132 lbs × 12 = 1,584 kcal/day (maintenance)

• 121 lbs × 10 = 1,210 kcal/day (weight-loss estimate)

  
  

Adjusting Your BMR as Your Weight Loss Progress

When aiming for weight loss, it is important to avoid overly aggressive calorie restriction. In the example above, the estimated reduction was around 20 percent.

Consistently consuming significantly fewer calories than estimated needs may lead the body to reduce energy expenditure as an adaptive response.

This process is often referred to as metabolic adaptation, in which the body becomes more energy-efficient in response to a prolonged calorie deficit.

For this reason, a more sustainable approach is to adjust intake gradually as body weight changes (for example, every 5–10 pounds lost). This helps support metabolic function and long-term adherence.

It may also help reduce the likelihood of plateaus by preventing excessive metabolic slowdown.

Remember: BMR represents an estimate of the minimum energy required to sustain essential physiological functions at rest and should be adjusted based on individual response, activity level, and body composition.

Our Body Needs More Than Just Minimum Calories (BMR)

Basal Metabolic Rate (BMR) represents only our baseline energy requirement. It is useful to calculate your BMR and become familiar with this number as a reference point.

However, real-life energy needs go beyond BMR. To function optimally, we must also account for:

• Physical activity and exercise

• Stress levels

• Sleep quality

• Work demands and mental effort

  
  

Because of these additional factors, total daily energy expenditure is typically higher than BMR.

Daily Caloric Index - A Practical Framework

To better understand how energy needs fluctuate in real life, we can use the concept of a Daily

Caloric Index.

This refers to the idea that daily caloric needs are not fixed, but vary depending on lifestyle demands, ranging from a baseline (BMR) to a higher adjusted intake based on overall activity and stress load.

In other words, instead of relying on a single fixed number, we consider a dynamic range of energy needs throughout different days.

A more practical approach is to adjust estimated intake based on lifestyle and activity level, rather than relying on BMR alone.

Example

If your BMR is 1,210 calories (as in the previous example), your actual daily needs may increase depending on lifestyle demands such as:

• Regular exercise

• High stress levels

• Poor sleep quality

• Increased mental or physical workload

  
  

It is reasonable to recognize that these variables collectively increase energy needs to different degrees.

A simplified approach is to adjust intake upward depending on overall daily demands.

For example, in a more demanding day, total caloric needs may rise from 1,210 kcal to approximately 1,600 kcal or more, depending on overall activity and stress load.

Clinical Insight

This dynamic variation reflects what is known physiologically as Total Daily Energy Expenditure (TDEE) — the sum of all energy used throughout the day, not only at rest.

Understanding this helps reduce the risk of chronic under-eating, which is one of the factors that may contribute to metabolic adaptation over time.

Correcting Nutritional Imbalances

In addition to total caloric intake, the quality of the diet plays a fundamental role in overall health. This includes ensuring an adequate balance of macronutrients and micronutrients that meet individual nutritional needs.

Rather than focusing on eliminating specific foods as “inflammatory,” a more evidence-based approach emphasizes dietary patterns that support metabolic health and reduce chronic low-grade inflammation.

In upcoming articles, I will cover:

• How to select macronutrients and determine their appropriate ratios

• How to ensure adequate micronutrient intake

• Can we trust the RDAs (Recommended Dietary Allowances)?

• Nutrient bioavailability and absorption

• Dietary patterns associated with inflammation and metabolic health

  
  

Remember: there is no one-size-fits-all approach. The best way is to personalize your diet according to your age, sex, lifestyle, and health goals.

Conclusion: Balance and Metabolic Resilience Are Key

As discussed above, extreme caloric restriction, without proper guidance may:

•  Reduced energy availability.

• Contribute to hormonal imbalance

• Lead to unintended weight plateau and weight gain over time

  
  

Then, the goal should not be focused solely on weight loss, but rather on restoring metabolic adaptability, while maintaining energy balance, vitality, and overall well-being.

Practical tip: Calculate your BMR, adjust caloric and nutrient intake accordingly, and prioritize long-term sustainable habits rather than short-term results.

Have you ever wondered why you can’t lose weight even while dieting? Or experienced a weight-loss plateau? Please, share your comment with us in the link below.

See you soon!

References

• Mifflin MD, St Jeor ST, et al. (1990). American Journal of Clinical Nutrition.

• Müller MJ, et al. (2015). American Journal of Clinical Nutrition.

• Most J, Redman LM. (2020). Experimental Gerontology.

• Leibel RL, Rosenbaum M, Hirsch J. (1995). New England Journal of Medicine.

• CALERIE Study – Calorie restriction and energy metabolism.

Important Disclaimer:

This article is for educational and informational purposes only and does nor replace evaluation, diagnosis, or treatment by a qualified healthcare professional.

I am trained in Traditional Chinese Medicine and have studied Functional Medicine, but the information presented here should not be considered individualized medical advice.

Always consult a qualified healthcare professional before starting, stopping, or changing any treatment, including medications or supplements.