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Is Diet Really 80% of the Fat Loss Equation?

Is Diet Really 80% of the Fat Loss Equation?

There has been a long standing cliche in the fitness business.

No doubt you’ve heard the cliche saying that ‘diet is 80% of fat loss’ or maybe you’ve heard that, ‘diet is 80% of muscle mass gain.’

I read it posted in dozens of quora answers nearly every time I answer a question about fat loss or muscle mass gain.

It’s a nice thought…

I know it has good intentions, it’s an attempt to focus people’s energy towards things that seemingly matter more.

It’s far easier to create the necessary energy (caloric…) deficit with diet than it is to create a caloric deficit with exercise.


A grande Starbucks pumpkin spice latte can pretty much completely ruin an hour’s worth of exercise in minutes.

What if, bear with me, for a moment I told you to stop even thinking about calories.

What if the energy output of exercise was almost completely irrelevant to it’s benefits to fat loss (or muscle mass gain for that matter)??

What if I said thinking of exercise as energy out is frivolous?

Now I’m not disputing the laws of thermodynamics because of course energy matters, but the thing is, there is more to the closed energy system than just energy in and energy out.

There is previously available energy in the system you have to consider.

You cannot lose fat without some sort of energy loss, and you cannot gain muscle without some sort of energy excess.

Notice however, that I tend to use energy in and energy out, rather than the common vernacular: “calories in and calories out.”

That’s because there is a difference between the calories you’re likely to read on the back of a package, or in the latest and greatest fitness app, and the ACTUAL energy you’re putting into your body.

Or vice versa, the number of calories you see on the treadmill isn’t the actual number of calories you burned, actually more often than not, it includes what you would have normally burned had you just been sitting around doing nothing (assuming 2000 kcal of actual energy output at rest per day, you burn about 1.3 kcal a minute doing nothing…).

Neither are necessarily the actual amount of energy you took in or burned off.

You see you can utilize stored glycogen (the storage form of glucose a simple carb/sugar), you can utilize stored fat as energy, and you can even use stored protein as energy.

Theoretically though your body is predominantly water, but you can still utilize other existing tissues as energy under certain circumstances.

Hence there is more going on that just energy in and energy out.

Furthermore, though not related to this post directly, energy in these forms is typically tied up with water:

  • Fat stores appear to be are anywhere from about 7-47% water depending on location (a lot less than muscle mass).
  • Muscle (though not the only protein source in the body) is about 78% water, give or take
  • Bone is about 67% water (another protein and mineral source…)
  • Glycogen (at least in the liver and at least in rodents) appears to be anywhere from 0-80% water (typically about 1-4 grams of water with every gram of glycogen, 3.8 apparently on average)

Why mention that?

Well it gives you an understanding of water weight, how and why you might lose weight even without the required ‘caloric’ balance.

Fat loss and weight loss are NOT the same thing.

That’s why I use energy balance instead, because a pound of fat isn’t necessarily pure fat, so losing a pound of weight doesn’t always translate exactly as a certain number of calories.

I heard someone, I think it was Yoni Freedhoff or David Katz refer to this as ‘true calories.’


What does that have to do with diet and why shouldn’t you assume that 80% of the equation is diet related?

Well because although diet is generally more effective than exercise alone (i.e. no dietary intervention), that doesn’t mean it’s more than twice as effective.

Furthermore, dietary changes alone leave a lot on the table that contribute significantly not only to keeping weight off (or on!) and by themselves do not necessarily lead to a lot of the health benefits that one might expect.

A huge 66-study meta-analysis that was published in March 2015, reveals some very interesting facts that should make you question whether or not diet really is 80% of the equation and not more like the logical 50% of the equation as you might assume.

Here’s what they found:

First, hypocaloric balance is necessary for changing body composition, but the effectiveness for establishing imbalance does not equate with the effectiveness for body compositional changes, or any biomarkers associated with metabolic issues. With analysis showing that there is a necessity to include exercise in combination with diet effectively elicit changes in body composition and biomarkers of metabolic issues.

More importantly, the combination, resistance training (RT) was more effective than endurance training (ET) or combination of RT and ET, particularly when progressive training volume of 2-to-3 sets for 6-to-10 reps at an intensity of ≥75% 1RM, utilizing whole body and free-weight exercises, at altering body compositional measures (ES of 0.47, 0.30, and 0.40 for loss of BM, FM, and retention of FFM respectively) and reducing total cholesterol (ES = 0.85), triglycerides (ES = 0.86) and low-density lipoproteins (ES = 0.60). Additionally RT was more effective at reducing fasting insulin levels (ES = 3.5) than ET or ET and RT.

Now that last bit just reinforces why I highly encourage people to strength train, but the interesting thing about this in general are some of the other statements and observations of the data.

Things like:

  • More effective at altering body composition measures, especially fat free mass (FFM) — You may want to lose weight, but surely you want to lose the right kind of weight and maintain the right kind of weight too?
  • Improving health markers like cholesterol, triglycerides and LDL (cholesterol — typically called ‘bad cholesterol’) and insulin sensitivity

Basically resistance training in particular — though exercise + dietary changes produced better results than diet alone too — was far more effective at changing not only weight and body composition, but factors that likely influence your ability to keep weight off.

All of that despite (in many instances) not having much of an apparently overall caloric deficit, most likely because a lot of that energy was being displaced in the body via energy utilizing from fatty tissue and the reformation of fat free tissues like muscle and/or bone.

The lesson?

Though diet on it’s own might be more effective than exercise, it isn’t 80% more effective, at least not over the right kind of exercise used in combination with dietary changes.

Changing how you look and feel is about a lot more than just weight.

The next time someone tells you that diet is 80% of equation, kindly tell them they can go fly a kite.

It’s WAY more effective if you focus on diet AND exercise.