Should I Eat Less Than My Resting Metabolic Rate (RMR)? The Risks of Extreme Calorie Restriction

October 14, 2025 •

5 min read

According to a study published in the journal Obesity, contestants from a popular weight loss show experienced a significant, long-term metabolic slowdown years after extreme calorie restriction. This highlights a crucial question for anyone pursuing weight loss: should I eat less than my resting metabolic rate? The answer from most health experts is a resounding no, as this can trigger a defensive response from your body that undermines your efforts and jeopardizes your long-term health.

Quick Summary

Eating below your resting metabolic rate (RMR) for prolonged periods can harm your health by causing metabolic slowdown, muscle loss, and nutrient deficiencies. A safe and sustainable weight loss strategy focuses on a moderate calorie deficit based on your total daily energy expenditure (TDEE), not the bare minimum your body needs at rest.

Key Points

Avoid Extreme Restriction: Do not intentionally eat fewer calories than your Resting Metabolic Rate (RMR), as this is the minimum needed for basic bodily functions.
Focus on TDEE: For weight loss, create a moderate calorie deficit (typically 300-500 calories) below your Total Daily Energy Expenditure (TDEE), which accounts for all your daily activity.
Risk of Metabolic Slowdown: Severe calorie restriction can cause your body to enter 'survival mode,' slowing your metabolism and making weight loss harder in the long run.
Prevent Muscle Loss: Consistently eating below your RMR forces your body to burn muscle tissue for energy, which further lowers your metabolic rate.
Prioritize Nutrient-Dense Foods: Ensure you meet your nutritional needs by eating a diet rich in protein, fruits, and vegetables to support metabolism and overall health.
Combine Diet with Exercise: Pair a smart calorie deficit with regular physical activity, including strength training, to preserve muscle mass and boost your metabolism.
Long-Term Strategy: Sustainable weight loss focuses on building healthy habits for the long term, avoiding the metabolic damage and rebound weight gain associated with crash diets.

Understanding Resting Metabolic Rate (RMR)

Before you can decide how to structure your diet, it's essential to understand what your Resting Metabolic Rate (RMR) truly represents. RMR, often used interchangeably with Basal Metabolic Rate (BMR), is the minimum number of calories your body needs to perform fundamental, life-sustaining functions while at rest. This includes things you don't even think about, like breathing, blood circulation, cell production, and brain function. It’s the energy your body needs just to keep the lights on.

Your Total Daily Energy Expenditure (TDEE), on the other hand, is the total number of calories you burn throughout the day, including your RMR, the calories burned during digestion (the thermic effect of food), and the calories expended during all physical activity (exercise and non-exercise activity thermogenesis, or NEAT). For safe and sustainable weight loss, the goal is to consume fewer calories than your TDEE, not fewer than your RMR.

The Risks of Eating Below Your RMR

When you consistently eat below your RMR, your body interprets this as a sign of starvation, a primal survival mechanism designed to help you endure periods of food scarcity. This triggers a series of physiological responses that can be detrimental to your health and counterproductive to your weight loss goals.

Metabolic Slowdown

Your body's primary response to severe calorie restriction is to conserve energy by slowing down your metabolism. This process, known as metabolic adaptation, means your body will burn fewer calories at rest in an effort to stretch its limited energy supply. What might have seemed like a fast track to weight loss becomes a frustrating plateau, where you struggle to lose weight even on very low calories. This slowdown can persist long after the diet is over, making weight maintenance difficult and increasing the likelihood of rebound weight gain.

Muscle Loss

Your body is an efficient machine, and when it doesn't get enough energy from food, it starts breaking down tissue for fuel. Unfortunately, it doesn't prioritize fat; it also consumes precious muscle mass. Since muscle tissue is more metabolically active than fat, losing muscle further decreases your RMR, exacerbating the metabolic slowdown. This can leave you with a higher body fat percentage and a weaker physique, even if the number on the scale has dropped. Over time, this includes the potential for loss of heart muscle, as well as skeletal muscle.

Hormonal and Health Disruptions

Severe and prolonged calorie restriction can throw your entire hormonal system into disarray. For women, this can lead to menstrual irregularities or amenorrhea (the absence of a menstrual period), decreased fertility, and increased risk of osteoporosis due to hormonal imbalances. For everyone, it can cause fatigue, lethargy, increased hunger (driven by fluctuations in hormones like ghrelin and leptin), poor sleep, and a compromised immune system.

A Comparison: Safe vs. Unsafe Weight Loss

To highlight the difference between a sustainable approach and a risky one, let's compare two scenarios:


Feature	Safe and Sustainable Weight Loss	Risky (Eating Below RMR)
Calorie Deficit Strategy	Consume 300-500 calories less than your Total Daily Energy Expenditure (TDEE).	Drastically cut calories to fall below your Resting Metabolic Rate (RMR).
Metabolic Impact	Creates a manageable deficit that encourages fat burning while minimizing metabolic slowdown.	Triggers metabolic adaptation, causing the body to burn fewer calories at rest and making future weight loss more difficult.
Body Composition	Prioritizes fat loss while preserving lean muscle mass, especially with adequate protein intake and strength training.	Leads to significant muscle loss alongside fat loss, decreasing your overall metabolic rate.
Energy & Hunger	Supports stable energy levels and helps control hunger and cravings, making it easier to stick to the plan.	Causes intense fatigue, listlessness, and increased hunger due to hormonal shifts, leading to binge-restrict cycles.
Nutritional Adequacy	Easier to meet daily nutritional needs for vitamins and minerals, supporting overall health.	Increases the risk of nutrient deficiencies (e.g., iron, B12, calcium), which can lead to complications like anemia, brittle hair, and weakened bones.
Long-Term Success	Focuses on sustainable lifestyle changes, leading to better long-term weight maintenance and a healthier relationship with food.	Often results in rebound weight gain due to metabolic damage and poor habits, restarting the cycle.

The Healthy Alternative: Creating a Smart Calorie Deficit

Instead of aiming for an unsustainably low calorie intake, a more intelligent and effective approach is to create a moderate calorie deficit relative to your TDEE. Here’s how you can achieve this safely:

Calculate Your TDEE: Start by estimating your TDEE using an online calculator that factors in your RMR and your daily activity level.
Create a Moderate Deficit: For most people, a deficit of 300–500 calories below your TDEE is a safe and effective starting point, leading to a steady, sustainable weight loss of about 0.5–1 pound per week. For those with more significant weight to lose, a larger deficit may be appropriate under medical supervision, but it should still prioritize nutritional intake.
Prioritize Protein: Ensure your diet is rich in protein, as this helps preserve muscle mass while dieting. Protein also has a higher thermic effect than carbohydrates or fats, meaning your body burns more calories digesting it.
Incorporate Strength Training: Building and maintaining muscle mass is one of the best ways to keep your RMR from dropping during weight loss. Aim for resistance training at least twice per week to boost your metabolism and improve body composition.
Don't Forget NEAT: Increase your Non-Exercise Activity Thermogenesis (NEAT) by simply moving more throughout the day. Take the stairs, walk to the store, or pace while on a phone call. These small bursts of activity add up and can significantly increase your daily calorie burn.
Stay Hydrated and Sleep Well: Proper hydration and adequate sleep are vital for a healthy metabolism and hormone regulation. Aim for 7–9 hours of sleep per night to regulate hunger hormones and support your body's recovery.

Conclusion

While the concept of eating below your Resting Metabolic Rate might seem like a shortcut to fast weight loss, the science and health risks tell a different story. The human body is designed for survival, and extreme calorie restriction triggers a defensive metabolic slowdown, muscle loss, and hormonal chaos that is not only detrimental to your health but also sabotages your long-term success. A balanced, informed approach that focuses on a moderate calorie deficit relative to your Total Daily Energy Expenditure, combined with regular exercise and a nutrient-dense diet, is the far more sustainable and effective path to achieving your weight loss goals and maintaining a healthy body for years to come. Consult a healthcare professional or registered dietitian for a personalized plan that is right for you.

Visit the Academy of Nutrition and Dietetics for guidance on finding a registered dietitian.

Frequently Asked Questions

RMR (Resting Metabolic Rate) is the minimum amount of energy your body needs to function at rest, including breathing and circulation. TDEE (Total Daily Energy Expenditure) is the total calories you burn throughout the day, including your RMR, physical activity, and food digestion.

For most individuals, a healthy and sustainable calorie deficit is around 300–500 calories below your TDEE per day. This typically leads to a steady weight loss of about 0.5–1 pound per week.

Eating below your RMR can trigger metabolic adaptation, where your body conserves energy by slowing your metabolism. This makes weight loss more difficult over time and increases the risk of weight regain.

Yes, severe calorie restriction can cause your body to break down muscle tissue for energy, especially if protein intake is insufficient. Losing muscle mass is counterproductive as it lowers your overall metabolic rate.

If you eat at your RMR, you will likely maintain your current weight if you are sedentary. To lose weight, you must create a deficit by either eating slightly less than your TDEE or increasing your activity level.

You can increase your RMR by building muscle mass through strength training, as muscle tissue burns more calories at rest. Other strategies include eating enough protein, getting adequate sleep, and staying hydrated.

Long-term consequences of severe calorie restriction include metabolic damage, hormonal imbalances (such as those affecting fertility), nutrient deficiencies, increased risk of osteoporosis, and a difficult cycle of weight loss and regain.