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It seems that in recent years the health and fitness industry has slowly shifted in favor of high-intensity interval training (HIIT) as opposed to traditional low-intensity, steady-state (LISS) cardio. Why though? Well, research contends that HIIT is indeed a highly efficient way to enhance the fat-loss process, and is less likely to make you lose muscle tissue (as compared to LISS). Read on as we take a look at which form of cardio is best for your fat-loss plan.
What is HIIT?
Essentially, HIIT is any form of cardiovascular exercise where you exert yourself as hard as you can until exhaustion kicks in (e.g. sprinting for 15-20 seconds). This forces your body to rely on anaerobic metabolism (since oxygen is depleted) and you end up taxing a variety of energy systems in the body. In turn, HIIT elicits a variety of metabolic adaptations that traditional LISS cardio does not.
Here’s an example High-Intensity Interval Training (HIIT) routine:
- Warm up with 5-10 minutes of light jogging
- Sprint for 15-20 seconds
- Walk for 60-90 seconds until you are fully recovered
- Repeat 5-10 times (aim to improve your capacity over time)
HIIT Vs. LISS for Fat Loss
HIIT is an anaerobic form of exercise and thus relies heavily on glycolytic (carbohydrate) metabolism for energy. Thus, most traditional “fitness experts” contend that LISS cardio is the better option for weight loss since it relies primarily on fat for fuel. While LISS may seem better for fat-loss in the short-term, literature actually suggests that HIIT is superior for sustained, long-term fat loss.  Moreover, HIIT also enhances muscle gain in active individuals, whereas LISS cardio can actually be detrimental to muscle building (and retention). 
To put it more simply, LISS cardio is essentially just a way to burn extra calories throughout the day, but it doesn’t do much beyond that. HIIT, on the other hand, is a form of exercise that promotes the fat-loss process over a period of time even after exercise has ceased.
HIIT induces a multitude of physiological effects that traditional LISS cardio does not. Literature suggests that these metabolic adaptations incurred by HIIT include things like: reduced appetite, increased excess post-exercise oxygen uptake (EPOC), improved blood lipids, enhanced VO2 max output, better heart health, and more efficient endocrine activity. Very few of these metabolic adaptations occur after performing LISS cardio. [3, 4, 5] Specifically as it relates to insulin and leptin, research shows that HIIT improves insulin sensitivity (a good thing!) and improves leptin sensitivity which helps reduce appetite and increase your metabolism.
In fact, research suggests that doing a few HIIT sessions per week (and watching your diet) can even help prevent/reverse type-2 diabetes.  Intuitively then, you can see why HIIT would be preferable for someone looking to be healthy and lean.
Moreover, HIIT is the best way to shred fat and keep it off.  This appears to be because HIIT stimulates a process in cells called mitochondrial biogenesis. The reason that process is so crucial is because it increases metabolism—your body essentially requires more energy to perform daily functions.
So let’s recap the top 5 benefits of HIIT:
- Promotes sustainable fat loss
- Improves insulin sensitivity
- Increases resting metabolic rate (for a period of time)
- Improves cholesterol levels and blood pressure
- Helps keep your heart healthy
The Case for LISS Cardio
Now don’t get too ahead of yourself just yet and assume that HIIT should be the only form of cardio you do for the rest of your years. LISS cardio still has its place in most anyone’s fitness regimen, but HIIT should take precedence over it.
LISS cardio comes in handy when you just need a way to burn calories without taxing yourself too much physically. That being said, be cautious of overdoing the amount of LISS cardio you do, especially when trying to lose fat. Most people get carried away with the amount of LISS cardio they perform, and this in turn causes their metabolic rate to drop, making fat loss much harder (not only that, they start to lose a lot of their hard-earned muscle).
Another thing to consider is that you should make LISS cardio something you enjoy. Go for a walk outside if it’s a nice day, or go on a bike ride. There are many more options than going to the gym and staring into space while you mindlessly walk in place on a treadmill.
Is Fasted Cardio More Effective for Fat Loss?
Fasted cardio is another topic in and of itself, but the main thing to know is that there is little-to-no research suggesting it is better for fat-loss (in the long term). While fasted cardio (specifically at low intensity) may be a good way to use fat for energy, it fails to provide more fat loss than people who do cardio after eating a meal. In fact, individuals who eat something before doing cardio actually burn more fat and lose less muscle than those who do cardio fasted. Main thing to remember – eat something before you do cardio; you’ll be happy you did when all’s said and done.
As a starting point for your fat-loss cardio regimen, incorporate at least 2-3 HIIT sessions every week and LISS cardio should be as minimal as possible while sustaining continuous fat loss. Once fat loss stalls or slows down, add a few LISS cardio sessions throughout the week.
Remember to continually push yourself further/harder when you do HIIT since your body will eventually adapt and need more of a challenge than it’s used to. If you’re regularly weight training your HIIT sessions should stay within the 2-4 times per week range (any more than that and you’ll likely get burned out very quickly).
Hopefully this article has given you some insights into how to incorporate both HIIT and LISS cardio in an efficacious manner. Push yourself, stay consistent and watch the fat melt off!
As always if you have any questions about this article and or anything else related to Working Out, Nutrition or Supplementation please feel free to email me at Tom@topsecretnutrition.com.
Good Luck with meeting your Fitness Goals!
- Gaesser, G. A., & Angadi, S. S. (2011). High-intensity interval training for health and fitness: can less be more?. Journal of Applied Physiology, 111(6), 1540-1541.
- Davis, W. J., Wood, D. T., Andrews, R. G., Elkind, L. M., & Davis, W. B. (2008). Concurrent training enhances athletes’ strength, muscle endurance, and other measures. The Journal of Strength & Conditioning Research, 22(5), 1487-1502.
- Shiraev, T., & Barclay, G. (2012). Evidence based exercise: Clinical benefits of high intensity interval training. Australian family physician, 41(12), 960.
- Wisløff, U., Støylen, A., Loennechen, J. P., Bruvold, M., Rognmo, Ø., Haram, P. M., … & Skjærpe, T. (2007). Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients a randomized study. Circulation, 115(24), 3086-3094.
- Alkahtani, S. A., Byrne, N. M., Hills, A. P., & King, N. A. (2014). Interval training intensity affects energy intake compensation in obese men.International Journal of Sport Nutrition & Exercise Metabolism, 24(6).
- Mendes, R., Sousa, N., Garrido, N., Rocha, P., José, L. T. B., & Victor, M. R. (2013). EFFICACY OF ACUTE HIGH-INTENSITY INTERVAL TRAINING IN LOWERING GLYCEMIA IN PATIENTS WITH TYPE 2 DIABETES: DIABETES EM MOVIMENTO® PILOT STUDY. British journal of sports medicine, 47(10), e3-e3.
- Gibala, M. J., & McGee, S. L. (2008). Metabolic adaptations to short-term high-intensity interval training: a little pain for a lot of gain?. Exercise and sport sciences reviews, 36(2), 58-63.