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The Weight Loss Paradox: Why Shedding Pounds Can Make Burning Calories Harder

In the previous part of this blog series, we explored the concept of metabolism and its role in daily energy expenditure. We broke down the three main components – Resting Energy Expenditure (REE), Activity Energy Expenditure (AEE), and Thermic Effect of Feeding (TEF) – and how they contribute to the total number of calories you burn each day.

Now, let's delve deeper into a crucial aspect of weight management: how our bodies respond to weight loss in terms of energy expenditure.

Weight Loss and the Calorie Burn Challenge

Imagine this: you've embarked on a weight loss journey, ditched sugary drinks, started hitting the gym, and the numbers on the scale are reflecting your hard work. Fantastic! But here's a catch – as you lose weight, your body also becomes more metabolically efficient. This means it might start burning fewer calories overall, even at rest.

The Science Behind the Slowdown

In animal studies [1], food restriction and weight loss lead to a decrease in REE. However, animals tend to compensate by increasing their activity levels in search of food. This doesn't necessarily translate directly to humans. While weight loss will undoubtedly decrease your energy expenditure simply because you have less mass to move around, the bigger question is: how much does it decrease?

The Adaptive Thermogenesis Mystery: A Case of Conflicting Numbers

Ideally, the decrease in calorie burning would be proportional to the weight lost. However, a phenomenon called adaptive thermogenesis  throws a curveball. This theory suggests the body adapts to weight loss by becoming more efficient, burning fewer calories for the same functions (both at rest and during activity).

Imagine an individual, Sarah who is embarking on a 12-week weight loss program. She manages to lose 15 pounds. Here's how her energy expenditure might be affected according to adaptive thermogenesis:

Scenario 1: Proportional Decrease (No Adaptive Thermogenesis)

  • Before Weight Loss:

  • Sarah: 150 lbs, burns 150 lbs * 10 calories/lb/day = 1500 calories/day (assuming 10 calories/lb/day baseline)

  • After Weight Loss (15 lbs lost):

  • Sarah: 135 lbs

  • Estimated calorie burn = 135 lbs * 10 calories/lb/day = 1350 calories/day (based on new weight and baseline rate)

  • Reduction in calorie burn: 1500 calories/day (before) - 1350 calories/day (after) = 150 calories/day

Scenario 2: Adaptive Thermogenesis

  • Before Weight Loss: (same as Scenario 1)

  • Sarah: 150 lbs, burns 1500 calories/day

  • After Weight Loss (15 lbs lost):

  • Sarah: 135 lbs

  • Estimated calorie burn (without adaptive thermogenesis) = 1350 calories/day (same as Scenario 1)

  • Due to adaptive thermogenesis, Sarah's body burns slightly fewer calories than expected for her new weight (e.g., 50 calories/day less)

  • Actual calorie burn = 1350 calories/day (estimated) - 50 calories/day (adaptive thermogenesis adjustment) = 1300 calories/day



Before Weight Loss (150 lbs)

After Weight Loss (135 lbs)

Scenario 1: Proportional Decrease (No Adaptive Thermogenesis)

Calorie burning decreases proportionally to weight loss.

1500 calories/day (150 lbs * 10 calories/lb)

1350 calories/day (135 lbs * 10 calories/lb)

Reduction in Calorie Burn

150 calories/day (1500 calories - 1350 calories)

Scenario 2: Adaptive Thermogenesis

Body becomes slightly more efficient, burning fewer calories than expected for the new weight.

1500 calories/day (same as Scenario 1)

Estimated burn: 1350 calories/day (same as Scenario 1)

Actual Calorie Burn (with Adaptive Thermogenesis)

May be slightly lower than estimated burn due to increased efficiency.

Example: 1330 calories/day (1350 calories - 50 calories)

Reduction due to Adaptive Thermogenesis (Example)

Example: 50 calories/day

Additional Notes:

  • The 10 calories/lb baseline rate is an estimate for basal metabolic rate (BMR). Actual BMR can vary significantly due to factors like age, sex, muscle mass, and genetics.

  • Scenario 1 reflects a proportional decrease in calorie burning based solely on weight loss (150 calories/day due to losing 15 lbs).

  • Scenario 2 highlights adaptive thermogenesis, where Sarah's body might burn slightly less (e.g., 50 calories/day in this example) than the estimated value due to increased efficiency.

  • The 50-calorie reduction for adaptive thermogenesis is also an example. The extent of adaptive thermogenesis can vary depending on the individual and the severity of calorie restriction.

Key Points:

  • Weight loss can lead to a decrease in calorie burning due to a lower body weight.

  • Adaptive thermogenesis can further reduce calorie expenditure as the body becomes more efficient.

  • These scenarios provide a simplified illustration, and individual results may vary.

The Challenge: The True Picture

The real challenge lies in determining which scenario, or somewhere in between, represents what happens in real-world weight loss for a particular individual.

Conflicting Evidence: The Weight Loss Research Rollercoaster

Unfortunately, research on adaptive thermogenesis in humans is conflicting. Some studies show a greater decrease in energy expenditure than expected with weight loss, supporting the theory. However, other studies haven't been able to replicate these findings.

Why the Confusion? Unraveling the Mystery

There are several reasons why research might be conflicting. One potential culprit is the method used to measure energy expenditure in free-living people. These studies often rely on techniques like the doubly-labeled water technique, which assumes participants are weight stable. However, even slight, undetected weight gain can skew the results, making someone appear more metabolically efficient than they truly are.

The Bottom Line: Weight Loss is a Complex Equation

The relationship between weight loss and energy expenditure is complex. While some degree of metabolic adaptation is likely, the extent to which it occurs in humans remains unclear.

Weighted Vests: The Jury's Still Out

The idea of using weighted vests for increased calorie burning is intriguing. The theory goes like this: if you wear a 15-pound weighted vest, your body perceives itself as being 150 pounds instead of your actual weight of 135 pounds. This, in turn, might lead your body to burn more calories to cope with the perceived increase in weight, similar to how a heavier person burns more calories at rest.

The Gravitostat: Fact or Fiction?

This potential mechanism hinges on the existence of a theorized system called the gravitastat. The gravitostat is a proposed regulatory system within the body that might sense changes in gravitational load on our bones. According to this theory, the gravitostat communicates with the body's metabolism, potentially influencing calorie expenditure and hunger levels.

Intriguing Theory with Emerging Evidence

There's limited scientific evidence to definitively confirm the gravitostat's existence and effectiveness. However, a recent study published in PNAS [2] offered some intriguing insights. Researchers observed that increased loading on rodents through weighted capsules led to a decrease in body weight and fat mass. Importantly, this effect was independent of leptin, a hormone known to regulate appetite. This suggests the existence of a separate system for body weight regulation, potentially linked to the gravitostat.

Weighted Vests and NEAT: Maintaining Your Calorie-Burning Engine

Non-exercise activity thermogenesis (NEAT) refers to the calories you burn through everyday activities like walking around, fidgeting, and maintaining posture. It contributes significantly to your overall daily energy expenditure. As you lose weight, NEAT naturally declines because you simply have less body mass to move around, as we saw in the example of Sarah's weight loss adaptations. This can hinder your weight loss efforts.

Weighted vests might help counteract this NEAT decline. By adding weight, they essentially replace the lost body weight, forcing your body to exert more energy during daily activities. This can help you maintain a higher NEAT level and burn more calories throughout the day, even without increasing your exercise volume.

Weighted Vests and Total Daily Energy Expenditure: A Potential Advantage

Similar to NEAT, your total daily energy expenditure (TDEE), which includes your resting metabolic rate, activity level, and the thermic effect of feeding (calories burned digesting food), also dips as you lose weight. Weighted vests might help mitigate this decline in TDEE by keeping your body working a little harder throughout the day.

Quantifying NEAT: With vs. Without a Weighted Vest

Let's consider an example to illustrate the potential impact of weighted vests on NEAT. Let's go back to Sarah, a 150-pound woman with an active job that requires her to walk around frequently throughout the day. Here's a simplified breakdown of her NEAT:

  • Activities: Throughout the day, Sarah walks for a total of 60 minutes, fidgets moderately for 90 minutes, and stands for brief periods throughout the day which adds up to 30 minutes.

  • Energy Expenditure per Minute: We can estimate the calorie expenditure per minute for each activity using METs (Metabolic Equivalents). You can find METs charts online for various activities. Here are some general estimates:

  • Walking (moderate pace): 3.3 METs

  • Fidgeting: 1.5 METs

  • Standing: 1.2 METs NEAT Calculation:

  • Walking: 60 minutes  3.3 METs  (1 calorie per minute per MET) = 198 calories

  • Fidgeting: 90 minutes  1.5 METs  (1 calorie per minute per MET) = 135 calories

  • Standing: 30 minutes  1.2 METs  (1 calorie per minute per MET) = 36 calories

  • Total NEAT (without weighted vest): 198 calories + 135 calories + 36 calories = 369 calories

Impact of Weighted Vest:

Now, let's say Sarah adds a 10-pound weighted vest. Here's how it might affect her NEAT:

The energy expenditure per minute for each activity (walking, fidgeting, standing) would increase slightly because she's carrying more weight. We can estimate a 10% increase for simplicity.


Baseline Minutes

Baseline Calories

New Calories (10% Increase)




217.8 (198 * 1.1)




148.5 (135 * 1.1)




39.6 (36 * 1.1)

Total NEAT




NEAT Difference

36.9 (405.9 - 369)

NEAT Difference: By wearing a weighted vest (10lbs), Sarah's NEAT could potentially increase by:

405.9 calories - 369 calories = 36.9 calories

This may seem like a small difference, but over time, these extra calories burned can contribute to weight loss or weight management efforts, without having to do much, especially if you can progressively increase the weight of the weighted vest.

Important Note: This is a simplified example, and actual NEAT calculations can be more complex. However, it provides a general idea of how weighted vests might influence daily calorie expenditure through NEAT. It also shows how losing weight can lead to a decrease in metabolic rate!

Weighted Apparel During Contest Prep: Lending Support

A study published on Weightology [3] adds another layer of interest to the potential benefits of weighted vests. This study examined the use of weighted apparel by a bodybuilder during his contest preparation. The athlete wore a weighted vest and other weighted clothing throughout his prep phase. Interestingly, he reported experiencing phenomenal results, including achieving his lowest ever body fat percentage while feeling less hungry and finding the prep process to be easier overall.

While anecdotal, this case study suggests that weighted apparel might:

  • Help maintain NEAT (Non-exercise activity thermogenesis): This refers to the calories burned through everyday activities like fidgeting or walking throughout the day. Weighted clothing could increase NEAT by requiring the body to exert more energy for simple movements.

  • Reduce appetite: The study suggests the athlete experienced decreased hunger, potentially due to the body's response to the increased load (The added weight, is negating the decline in leptin levels, which would normally increase appetite).

  • Allow for fat loss in a state of high energy flux: Traditionally, calorie restriction is a key component of contest prep. However, this study suggests that adding weight (through weighted clothing) might allow for fat loss while maintaining a higher calorie intake, potentially leading to a more sustainable and less stressful approach.

Cutting Calories vs. Addressing the Gravitostat?

The study also challenges the traditional approach of calorie restriction for weight loss. While reducing calorie intake can lead to weight loss, it may not be the most sustainable or healthy approach in the long run. The gravitostat theory suggests that addressing the body's perception of weight through increased loading could be a more effective strategy, particularly for those who struggle with excessive sitting or a sedentary lifestyle.

Impact of Calorie Restriction on NEAT: Why Weighted Vests Can Be an Advantage

The concept of NEAT highlights a potential drawback of relying solely on calorie restriction for weight loss. The traditional mantra of "eat less to lose weight" can be effective, but it often leads to a decrease in NEAT as your body mass shrinks. This means you're burning fewer calories overall, even at rest.

Weighted vests offer a potential solution to this issue. By adding weight, you can counteract the NEAT decline associated with calorie restriction and potentially maintain a higher total daily energy expenditure. This may allow for a more sustainable approach to weight loss, where you're burning more calories without feeling excessively restricted or forced to significantly increase exercise volume.

Remember, a balanced approach is key. While weighted vests might be a helpful tool, they shouldn't replace a healthy diet and exercise routine. Consult with a healthcare professional before starting any new weight loss program, especially if you have any underlying health conditions.

The Bottom Line on Weighted Vests

Weighted vests may add a bit of intensity to your workouts, potentially leading to a greater calorie burn during the exercise itself. Additionally, the emerging research on the gravitostat suggests they might offer long-term benefits for weight management by influencing the body's perception of weight and potentially reducing hunger levels.

However, more research is needed to fully understand the effectiveness of weighted vests for boosting metabolism and promoting fat loss. If you're considering using a weighted vest, it's wise to start light and gradually increase the weight to avoid injury. Remember, consistency with exercise and a healthy diet are still the cornerstones of weight management.

We'll be keeping an eye on future research developments regarding the gravitostat and its potential impact on metabolism and weight management strategies. Stay tuned for updates!


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