What is most efficient way to burn fat?

Not the fastest. I want to know how to target fat specifically if possible or just calories in general if not for the least effort output. Time spent exercising or the activity doesn't matter as much as long as total energy used is less (or maybe... perceived to be less).

I've read all about how HIIT will blast fat off - even after you are done working out, but that slow running will target fat specifically - and you can do that for a longer time.

1 hour of slow running generally seems easier to me than 20 minutes HIIT. At least psychologically. But is it really more efficient fat burn? You can (and should?) feel like death after a good HIIT session, and pretty fine after a pretty long run.

The math I tried:

HIIT feels like 100 effort

Easy Jog feels like 20 effort


100 effort expended over 20 minutes & 500 fat-based-calories burned

HIIT_EFFORT = 100 * 20 = 2000

Easy Jog

20 effort expended over 60 minutes & 500 fat-based-calories burned

JOG_EFFORT = 20 * 60 = 1200


HIIT: 500 calories / HIIT_EFFORT = 0.25 calories burned per effort

Jog: 500 calories / JOG_EFFORT = 0.42 calories burned per effort

In this case the easy jog is more efficient at fat burning than hiit.

  • Perhaps by maximizing brown fat? But, not sure if brown fat reduces white fat...
    – ManRow
    Commented Oct 20, 2017 at 23:46

2 Answers 2


Your "perception" of energy/effort used is strictly personal opinion. Taking the HIIT vs Jogging example. If both burns the same amount of calories, which is better? Whatever you like better is the answer. Why do people say HIIT is better for losing fat? Because of what you mentioned. It only takes 20 minutes compared to 60 minutes of jogging for the same result. In the end though, if you'd rather jog longer for less effort, that's what you should do. In the end, the only way to lose fat is a caloric deficit. How you reach that deficit, in the end, doesn't matter much (strictly in terms of losing fat).

Of course, if you simply starve yourself and eat nothing, you'll be at the maximum deficit, but you're not only going to lose fat. You'll lose muscle and suffer health issues. So to answer the primary question, the most efficient way to lose fat is to not eat. That comes with the possibility of death due to starvation, or severe health issues and malnutrition at least.

If you want to lose fat efficiently, while maintaining muscle and health, I would suggest aiming for a 750 calorie deficit per day while doing some weight training and supplementing with protein and BCAAs. BCAAs have been proven to help reduce the amount of muscle lost when cutting. For general diet, keep your protein high while keeping fat and carbs relatively low. When eating fats and carbs, try to get good fats (avacados, olives, olive oil, almonds) and good carbs (black beans, brown rice, oatmeal). With a 750 calorie daily deficit, you should burn about 1-2 pounds of fat per week.

You'll likely lose some muscle too, but that's what the weight training is for. You weight train to help you reach your caloric deficit, minimize muscle loss, and maximize fat loss. Doing cardio is ultimately not necessary for minimizing muscle loss, nor is it necessary to reduce your caloric deficit. But, If you feel like you're hungry and want to eat more, you can, for example, eat 600 more calories per day and jog at 5mph for 1 hour per day. 1 hour of 5mph jogging will burn about 600 calories (on average), so in the end, your deficit remains the same.

  • Yes all good concepts to consider for personal health and fitness. I would never exercise to be allowed to be allowed to eat more, but I suppose that's just me, and I currently still want to lose about 10 lbs, and so looking for that maximum calorie deficit that you are talking about. My go to exercise seems to be a higher intensity steady state cardio, not quite as long as a slower cardio, and not as intense as hiit. But for general health you should probably mix in some hiit and longer runs as well to keep body guessing.
    – Andrew
    Commented Oct 20, 2017 at 16:36
  • Yea, the extra exercise for extra eating is just a suggestion for those people who would prefer to eat more. Personal preference. I personally would also not exercise more to eat more. If you're aiming for a maximum deficit, most studies suggest that 1000 calories is the highest you should aim for, but it's suggested to take multivitamins and other supplements like fish oil when you aim for a deficit that high as malnutrition is likely. And thats a good point. Your body adjusts to exercise, and will burn less calories with exercises you do regularly. So "mixing it up" is a great suggestion.
    – Jun Kang
    Commented Oct 20, 2017 at 16:47

As your question states you're not concerned with how long your workout takes.

Steady state will burn the highest % of fat.

NOTE: As you keep saying efficient in your post. I'm not taking efficiency into account here, just workload and substrate utilization.


Definition: achieving maximum productivity with minimum wasted effort or expense.

The graph shows exercise intensity related to the % of fat used as a fuel source.

CHO = Carbohydrates
SNS = Sympathetic Nervous System

enter image description here

Image Source: http://leanitup.com


The point on the graph where the lines intersect is where you switch the primary substrate utilized (from carbs to fat or vice versa) - this corresponds roughly with the lactate threshold. This point is not fixed and can change with proper training as you become more conditioned the onset of this threshold is delayed (you can exercise harder longer).

It’s a misleading chart so it’s easy to draw the wrong conclusion. All the chart shows is the % of calories burned by “fat” based on intensity. To apply the chart to a workout plan, It’s key to understand the difference between relative and absolute intensity.

Here is an over simplistic way to think of it…

Person A is jogging at 25% intensity for 10 minutes. Person B is running at 75% intensity for 10 minutes.

Person A burns 100 total calories during their workout, 75% from fat and 25% from carbs. Person B burns a total of 400 calories 25% from fat, 75% from carbs

Person A at is burning more REALTIVE calories from fat (75%) However the ABSOULTE number of fat calories burned is only 75 calories out of the 100 total calories.

Person B was only burring 25% of his calories from fat (this being the RELATIVE amount) The ABSOULTE number of calories from fat burned is 100 calories out of the 400 total calories.

So you’re burning a higher % of your calories from fat at lower intensities, but you’re also burning less overall calories.

If we made this more realistic (and had person B do intervals – as they would need the recovery) they’d still be burring more ABSOLUTE calories and fat and therefore lose more weight (but tough to show this on a graph….)

  • So it looks like about 65% is the best "aerobic power" to be working at. How would one determine that, perhaps 65% of maximum heart rate?
    – Andrew
    Commented Oct 20, 2017 at 16:32
  • There is a lot of research that suggests the target heart rate for burning fat is between 60% and 70% of your maximum heart rate. At 25 years old, that suggests a target heart rate of around 127. Personally, I feel like that's low. I would probably hit a heart rate of 127 by jogging at like 4mph for a couple minutes. But then again, I'm not a health scientist, so what do I know.
    – Jun Kang
    Commented Oct 20, 2017 at 16:56
  • Please see above - the chart is not saying 65% is ideal, it's just providing a example of what fuel is being used at various intensities... And you would be correct 127 is too low if you want to most efficiently lose weight. The original question did not ask that it said "What is most efficient way to burn fat? Not the fastest. I want to know how to target fat specifically" that is why I defined efficient as these two sentences conflict.
    – Mike-DHSc
    Commented Oct 20, 2017 at 19:51
  • @Andrew see this: fitness.stackexchange.com/questions/36238/…
    – Mike-DHSc
    Commented Oct 20, 2017 at 20:05

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