How to (and How to Not) Integrate Cardio for Fat Loss

Introduction:

Cardio is often seen as a necessary and magical factor for fat loss, but its role is more nuanced. This article will outline its impact on fat loss, appetite, and recovery, and how to use it strategically. Please note that this will primarily be looking at cardio through the lens of fat loss, not general health and wellness. 

1: Metabolic Rate and Its Components:

Before going mentioning cardio, it’s important to understand exactly where the “energy out” side of the energy balance equation is coming from. We use Total Daily Energy Expenditure (TDEE) to guesstimate the total amount of calories you burn throughout a day — this is synonymous with your maintenance calories. TDEE is made up of four key components: Basal Metabolic Rate (BMR), the Thermic Effect of Food (TEF), Non-Exercise Activity Thermogenesis (NEAT), and Exercise Activity Thermogenesis (EAT).

• BMR[1] accounts for the majority of your TDEE (~60-70%) and represents the calories needed to maintain basic physiological functions, such as breathing, circulating blood, and maintaining body temperature. While BMR depends on factors like age, sex, weight, and body composition, it remains largely beyond your control, apart from small changes related to muscle mass or significant weight changes
• TEF contributes roughly 10% of TDEE and represents the energy required to digest and metabolize food. The TEF varies slightly based on macronutrient composition: protein has the highest TEF (20-30%), followed by carbohydrates (5-10%), and fats (0-3%). However, the overall contribution is relatively small and not easily influenced by dietary changes.
• NEAT is highly variable between individuals and includes all the energy expended during non-exercise activities like walking, fidgeting, standing, or performing daily tasks. For some, NEAT can differ by up to 2,000 calories per day[2], making it a significant, yet unpredictable, contributor to TDEE. NEAT tends to decrease when in a calorie deficit or after exercise, as the body seeks to conserve energy.
• EAT, or deliberate exercise, is the only component of TDEE we can truly control on a daily basis. However, its contribution to total calorie burn is relatively modest. Even intense cardio sessions may only burn 200-500 calories, which is small compared to TDEE as a whole.

With those figures in mind, it’s important to be cognizant that our metabolic rate is incredibly dynamic, and can have massive changes day-to-day — this is why I strongly believe aiming for perfection with calorie/macro tracking isn’t worthwhile, as your energy requirements on any given day can change significantly. And while we’re technically able to change our body composition, the outcome is surprisingly insignificant (and often misreported!). 1 pound of skeletal muscle actually only burns around 6 calories per day, and interestingly enough, 1 pound of adipose tissue burns around 2 calories per day[3] (which is why it’s common to require a calorie reduction after you’ve lost a considerable amount of weight to stay in a deficit).

It’s worth emphasizing that while cardio does burn calories, its impact on your overall TDEE is relatively small. This underscores the truth behind the saying, “you can’t out-train a bad diet,” particularly when it comes to fat loss. Cardio doesn’t possess any special properties that make it inherently beneficial for fat loss beyond the calories it burns. Instead, it should be viewed as a strategic tool: it allows you to increase calorie expenditure to either create a larger deficit or maintain a current deficit while eating more. Understanding this distinction ensures cardio is used effectively, without overestimating its role in your fat loss journey.

2: Cardio’s Impact on Hunger, NEAT, and Adaptation:

Cardio, like any form of physical activity, doesn’t exist in isolation. Its influence extends beyond simply burning calories, as it also affects your hunger, NEAT (Non-Exercise Activity Thermogenesis), and your body’s ability to adapt to exercise. Understanding these factors is key to using cardio effectively within a fat loss strategy.

Hunger:
One of the body’s primary mechanisms for regulating weight is by adjusting hunger levels—decreasing hunger when consuming excess calories and increasing it in a calorie deficit. Unfortunately for fat loss, our bodies are more sensitive to calorie deficits than surpluses. This evolutionary survival mechanism explains why weight gain often occurs more easily than weight loss.

Looking at the research, we can see two consistent trends — 1: very high intensity cardio (HIIT) tends temporarily reduce hunger, but increases it above baseline afterwards, and 2: moderate and low intensity cardio has a lot of variance between individuals.

• Chen et al., 2022: HIIT training causes short-term appetite suppression. (PMID: 35162760)
• Afrasyabi et al., 2019: HIIT training suppresses appetite short-term for lean individuals, but increases it in obese individuals (PMID: 31275881)
• Poon et al., 2018: HIIT and LISS training didn’t influence appetite or ad libitum energy intake in sedentary adults (PMID: 30279345)
• Blundell et al., 1999: Meta-analysis which shows 20% of studies show increased energy intake from exercise, 65% showed no change in energy intake, and 16% showed a decrease in energy intake (PMID: 10593531)
• Laan et al., 2010: Cardio had a small reduction in appetite post-workout, but it rose above baseline (and above the control) (PMID: 21164556)

The main takeaway here is to be mindful of your hunger levels and appetite for cardio days and non-cardio days — if you feel like you’re excessively hunger, cardio may not be beneficial for your fat loss in totality.

NEAT & Exercise Adaptation: 

The other frustrating mechanisms how our bodies regulate weight is from decreasing energy expenditure. When you increase physical activity, your body compensates in two ways: 1) Decreasing NEAT, where subconscious movements like fidgeting or casually walking around are reduced, and 2) Becoming more energy-efficient, meaning you burn fewer calories performing the same cardio over time. These natural adaptations, while evolutionary mechanisms for survival, can undermine your efforts to create a calorie deficit.

• Reduction in NEAT[4]: Of all the factors which make up TDEE, NEAT has the most variance between individuals, with a study reporting as much as a 2000 calorie difference in NEAT energy expenditure for individuals with a similar size.
  • When you engage in structured cardio, your body may compensate by subconsciously reducing other movements throughout the day. 
    
• Exercise Adaptation[5]: The more you perform a specific cardio activity, the more efficient your body becomes at it. Over time, this adaptation reduces the calories burned for the same activity. While this is a natural and expected physiological response, it means the initial energy expenditure from cardio may decline as you repeat the same workouts.

Together, these factors highlight why the calories burned from cardio shouldn’t be viewed in isolation. While cardio may provide an initial boost to energy expenditure, the impact can diminish over time due to both decreased NEAT and exercise adaptation. While far from perfect, tracking your daily step count independently of cardio to monitor overall movement can give you a very loose idea of how cardio is impacting NEAT. Additionally, varying your cardio modalities or taking periodic breaks can help reduce adaptation and keep energy expenditure from dropping too drastically.

3: Cardio and Recovery:

While it doesn’t directly impact energy expenditure, it’s important to look at cardio through the lens of how it impacts your lifting itself. Increasing physical activity, particularly with higher intensity cardio, will impact your performance in the gym in terms of strength, and can also reduce hypertrophy. When done excessively or without strategic planning, cardio can negatively impact your workouts in several ways:

Impaired Recovery and Fatigue:

• High-Intensity Interval Training (HIIT): can place significant demands on your body’s recovery systems, especially while in a calorie deficit. Recovery time and resources that could be allocated to repairing muscle tissue from resistance training may instead be used to recover from cardio.
• Takeaway: Use HIIT cardio sparingly, especially if you’re not well-adapted to general cardio, and/or if you’re newer to lifting. 
  

Diminished Gym Performance:

• Cardio performed too close to lifting sessions—either immediately before or on the same day—can leave you fatigued and reduce your ability to train at high efforts. This not only hinders strength development but also leads to fewer calories burned during resistance training.
• Takeaway: If you’re doing cardio, do it after your lifting sessions, and ideally space it out a few hours apart to minimize interference.  

Potential Reduction in Hypertrophy:

• As you’re all aware of with Booty by Bret, progressive overload is a key component to stimulating muscle growth. Excessive cardio may blunt these adaptations by creating too much fatigue, reducing training volume or intensity, and interfering with anabolic signaling itself.
• Takeaway: Don’t rely on cardio excessively for fat loss if you’re wanting to optimize muscle growth.  

You don’t actually lose all that much skeletal muscle when you’re consuming adequate protein and resistance training regularly. Strength loss, particularly with upper body lifts, is common just from being in a calorie deficit (and therefore, fat loss) even without cardio, but cardio can make it worse if not used strategically. However, your strength relative to your body weight should be increasing, so if you’re noticing your relative strength is dipping while you’re doing cardio, you might be overdoing it (and alternatively, if your relative strength is dropping significantly even without cardio, you might be in too large of a deficit, assuming you’re losing weight rapidly).

4: Cardio Modalities:

Now that we’ve laid out the foundation of how cardio interacts with energy balance and recovery, let’s look at the 3 main modalities of cardio, LISS, MISS, and HIIT, and how they fit into the factors discussed.

Low-Intensity Steady-State (LISS):

• Duration: 30-60 minutes, 1-5 times a week
• Pros:
  • Minimal gym performance impairment
  • Generally easier on joints
  • Unlikely to significantly alter hunger long-term
• Cons:
  • Time demanding
  • Boring
  • Fairly little energy expenditure 
• Examples: Walking, low-resistance cardio machine (stationary bike, elliptical, treadmill, etc.). Any activity where you’re moving but you’re still able to hold a conversation. 

Medium-Intensity Steady-State (MISS):

• Duration: 15-45 minutes, 1-3 times a week
• Pros:
  • Minimal gym performance impairment
  • Generally easier on joints
  • Unlikely to significantly alter hunger long-term
• Cons:
  • Can start to impair performance
  • Still takes a fair amount of time to burn calories
• Examples: Recreational sport, hiking, swimming, medium resistance cardio machines. You shouldn’t be gasping for air or have your lungs burning, but you shouldn’t be able to hold a consistent conversation.

High-Intensity Interval Training (HIIT):

• Duration: Alternating short (5-20 seconds) bursts of maximal effort, with low-intensity recovery intervals of 30-90 seconds
• Pros:
  • Very time efficient
  • Burns a significant amount of calories
  • May improve metabolic health more than less intense forms

• Cons:
  • Extremely recovery demanding
  • Higher injury risk
  • Not suitable for beginners
• Examples: Sprints, prowler sprints/sled drags. These should leave you almost entirely out of breath, barely able to sustain movement during the rest phases.

No single modality is universally “better” than another—it depends on your goals, recovery capacity, and preferences. Consider how each type of cardio fits into your overall training and energy balance strategy:

• If you’re prioritizing recovery and minimizing interference, LISS is a safe choice.
• If you want to balance time efficiency and calorie burn, MISS is a versatile option.
• If you’re looking to maximize calorie burn in less time and can handle the recovery demands, HIIT may be appropriate, but it should be used with caution.

Practical Takeaway: 

There’s a lot of variables which factor into how cardio fits into the puzzle, a lot of which are conflicting. To start, I think there’s value in pointing out that in Bret’s vast experience as a coach, he just about never has anyone start fat loss phases out with cardio programmed in. As fat loss inevitably becomes harder, and reducing calories more no longer becomes a viable option, he will encourage for a higher daily step count (which is in the gray area of being NEAT and EAT) rather than deliberate and designated cardio. If you’re wanting to incorporate cardio into your fat loss routine, I would consider the following key points:

1. Understand Cardio’s Contribution to a Calorie Deficit:
   1. Cardio burns calories, but its overall contribution to fat loss is modest.
   2. Cardio doesn’t have any unique fat burning properties, it’s a tool for increasing energy expenditure.
2. Start Small And Gradually Build: 
   1. Begin with 1-2 low-impact sessions per week for 10-20 minutes.
   2. Let your body adapt before increasing duration, intensity, or frequency.
3. Choose the Appropriate Intensity: 
   
   1. Start with LISS, then progress to MISS; only use HIIT sparingly to avoid recovery issues.
   2. If cardio makes you hungrier, stick with much lower effort modalities to manage appetite
4. Monitor Hunger And Movement:
   1. Pay attention to your hunger 24-hours after cardio. Avoid “eating back” the calories burned.
   2. Track daily step count (excluding cardio) to ensure NEAT doesn’t decrease significantly.
5. Strategic Timing:
   1. Perform cardio after lifting to minimize interference for strength and hypertrophy.
   2. Be mindful of signs of overtraining / under-recovering.
6. Adapt and Adjust Over Time:
   
   1. Your body will become more efficient, burning fewer calories for the same task over time.
   2. Reassess our cardio plan regularly and vary modalities to counteract adaptation.
7. Deload Cardio as Needed:
   
   1. Take breaks or reduce cardio duration and/or intensity when fatigue starts to accumulate to minimize energy adaptation.

Closing Thoughts: 

Cardio is a valuable tool, but it’s not a magic solution for fat loss. Its primary role is to help sustain a calorie deficit over time, but it must be approached strategically due to its potential impact on hunger, non-exercise energy expenditure, and gym performance. For some, cardio can be an incredibly effective addition to their routine, while for others, it may become a frustrating roadblock that stalls progress.

The key is to implement cardio gradually and mindfully. If you’re struggling to maintain a calorie deficit with your current intake, try introducing small doses of cardio and monitor how it affects your hunger, daily activity levels, energy, and mood. Remember, there’s no one-size-fits-all solution—adjust your approach as needed to ensure it complements your lifting, recovery, and overall goals.