Zach Newman
Oct 11, 2017 · 11 min read

Note: This article is not only meant to tell you how to improve fat loss/muscle gain but to give you a deeper understanding of how it works. If you want the TL;DR version, skip to “The Solution” at the bottom of the page. If you care to know why I’m not just blowing smoke up your ass, keep reading.

In an ideal world, when we decide to diet all of the weight lost would come straight from fat cells, sparing our precious muscle tissue. Also, in this utopian universe, when we decide to bulk (or overfeed as I’ll refer to it in this article) all of the extra calories we ate would be used solely for the building of muscle tissue. We would also be able to slam a tall stack of IHOP Pumpkin Spice pancakes and wash it down with a large Dunkin Donuts iced coffee, everyday and it would somehow make us leaner and stronger.

I don’t know where that universe is, but it sure as hell ain’t the one we’re living in.

The above is an extreme, and highly idealistic, example of calorie partitioning. Calorie Partitioning in basic terms refers to where calories go when we eat too many (overfeed) and where they come from when we diet.

In other words, what percentage of the extra calories we eat is used for muscle growth and what percentage is stored as fat?

Conversely, during a diet, where will our body seek to make up the missing calories we remove from our diet — mostly fat or mostly protein (muscle)?

When we diet the goal is to maintain as much lean mass as possible as we aim to shed fat. On the opposite end, the goal in overfeeding is to supply the body with a surplus of calories optimize muscle growth, but at the same time we pray we don’t put on too much fat. Calorie partitioning plays an enormous role in how well we accomplish these goals.

The more efficient partitioners of calories our bodies are the more easily we can achieve these desired results. But what determines our ability to partition calories efficiently, is it all genetic, and if not how can we control them?

How To Optimize Calorie Partitioning

Optimizing calorie partitioning has a lot to do with hormones — mainly insulin and leptin. Let’s explore what they are and why they matter. PAY ATTENTION! — They’re going to come up later in this article.

Insulin & Insulin Sensitivity — What and Why?

Insulin is a hormone secreted by the body whenever we eat carbs. Insulin is known as the “storage hormone” because it controls the storage and usage of carbohydrates. When we eat carbs they’re broken down into a sugar called glucose and this glucose enters the bloodstream and is either stored in places like muscle tissue and the liver as glycogen to be used as fuel for activity or it’s dumped off into fat cells.

Now insulin’s job is to direct the glucose upon entering the bloodstream. This is where insulin sensitvity comes into play. ‘Insulin sensitive’ meaning the tissue will more readily accept the insulin and the glucose into the tissue whereas ‘insulin resistant’, on the other hand, would mean the tissue would more often try to reject the insulin and glucose from entering.

Ideally we could flip a switch and control which tissues were insulin sensitive and which were insulin resistant. During a diet we would want our muscle tissue to be insulin resistant. This would cut off glucose as an available energy source and mobilize fatty acids to be used as muscle fuel thus accomplishing two things — 1. Provide energy to the muscle to maintain itself and 2. Burn off fat.

The opposite would be true when we’re overfeeding and trying to gain muscle. We’d want fat cells to be insulin resistant as to reject the storage of glucose and muscle tissue to remain insulin sensitive as to take in all that glucose and use it as fuel to build muscle.

Those with poor insulin sensitivity tend to store less glucose as glycogen for fuel and end up pouring more into fat.

What Controls Insulin Sensitivity?

Again genetics is a huge factor. Not much we can do there. However, our diet offers some room to improve our insulin sensitivity.

Diets high in refined carbs, saturated fats, and low in fiber tend to impair insulin sensitivity. On the other hand, diets that swap more refined carbs for complex carbs, more saturated fats for healthier fats (fish oils and monounsaturated fats like olive oil), and higher in fiber improve insulin sensitivity.

Exercise is a major component of controlling insulin sensitivity as well. Muscular contraction itself (through resistance training) can actually improve insulin sensitivity by facilitating glucose uptake into the muscle. Also, glycogen (the stored form of glucose) depletion improves insulin sensitivity as well. This is huge because glycogen is the body’s most rapidly available energy source and the first place it goes to when it needs a large dose of fuel at a moment’s notice like during heavy weight lifting for example.


Leptin is a protein released from fat cells (and muscle cells to a lesser degree) that is directly correlate to body fat percentage — the higher your body fat percentage, the more fat you have, thus the more leptin you have. This is important to note because keeping leptin at appropriate levels promotes using fat as fuel and promotes insulin resistance in fat cells (meaning you won’t store fat as easily). The problem lies when we’re losing body fat. Being in a caloric deficit and losing body fat naturally decreases leptin levels.

It’s a paradox; the more leptin you have the easier it is to burn fat and the harder it is to store it. Yet when we lose the fat our leptin levels go down thus making it harder to then lose more fat without losing muscle tissue.

Body Fat Percentage — The Unlock To Better Calorie Partitioning

Body fat percentage is the greatest influencer of how well we partition calories because it tends to correlate with insulin sensitivity and leptin levels — the two key hormones we just covered.

For insulin, the fatter you are the more insulin resistant you become (you store more glucose as fat, use less for fuel) and the leaner you are the more insulin sensitive you become (you use more glucose for fuel, store less as fat).

With leptin, the higher your body fat percentage the higher your levels of leptin. This is conducive for fat loss and muscle gain. The lower your body fat percentage is the lower your leptin levels and the harder it is to burn fat and retain muscle.

How this relates to fat loss and muscle gain is as follows.

Beginning A Fat Loss Phase

  • Start with a higher body fat percentage — lose more fat, retain more muscle.
  • Start with a lower body fat percentage — lose more muscle, lose less fat.

At a higher body fat percentage we have higher levels of leptin. Higher levels of leptin promotes using fat as fuel

On the other hand when body fat is low and leptin is low, fatty acids aren’t as easily mobilized to be used as fuel. This increases your body’s reliance on amino acids and glucose for fuel. All of this creates an environment that is very difficult to lose weight in.

Beginning A Muscle Gain Phase

  • Start with a higher body fat percentage — more calories stored as fat than used to build muscle.
  • Start with a lower body fat percentage —more calories used to build muscle than stored as fat.

This ties back into insulin sensitivity. Because our muscle mass is high and body fat is low our body as a whole becomes more insulin sensitive so it does a better job of utilizing excess calories/glucose for fuel rather than storing them as fat.

As our body fat percentage rises, our bodies start to become more insulin resistant and so rather than using glucose for fuel it stores more of it as fat.

The Best Times To Lose Fat and Gain Muscle

For these reasons, it is best to begin your fat loss phase when your body fat is higher (for men — 18%–22%; for women — 28%-32%) & begin your muscle gain phase when your body fat is lower (for men — 12%-13% body fat or lower; for women — 22%-23% for women).

The Solution

We now know that our body fat percentage is the main determinant for what our bodies do with extra calories/carbs — a higher body fat percentage will leave us more insulin resistant and more likely to store carbs/glucose as fat; a lower body fat percentage will leave us more insulin sensitive thus using extra calories/carbs more for building muscle rather than storing them as fat. This is why when it comes to eating more calories/carbs in an effort to gain muscle its best to start at a lower body fat.

But a higher body fat means better leptin levels and better leptin levels means an easier time burning fat and retaining muscle during a fat loss stage. This is why it’s best to begin a fat loss stage at a higher body fat percentage rather than a lower one because it becomes harder to mobilize fatty acids for fuel as our body fat decreases and our leptin levels drop.

But body fat percentage isn’t the only factor in hormone levels. Diet is very important as well. It’s also about surplus and deficits and how they affect hormones. So what if you’re at a particular BF% and you want to know how to eat to affect your hormones in the right way?

Eating For Fat Loss (Caloric Deficits)

It shouldn’t be a surprise to you by now that fat loss (and weight loss in general) requires a caloric deficit net calories (calories consumed - calories expended) < calories needed to maintain weight. There is both good and bad that comes from being in a steady caloric deficit that we need to know.

The Good

  • Blood Glucose + Insulin levels drop — Improves insulin resistance
  • Improved insulin resistance mobilizes fatty acids as a source of fuel — fat is burned more often

The Bad

  • Testosterone levels drop — Less glucose uptake into the muscle
  • The hormones leptin and ghrelin (the satiety hormone) drop — hunger increases
  • The body limits non-essential life functions to conserve calories — includes muscle protein synthesis which is responsibile for building and maintaining muscle thus hurting ability to maintain muscle mass
  • Fat accumulation is accelerated upon return to normal caloric intake

How To Limit ‘The Bad’

So the biggest downsides from a caloric deficit are lost muscle mass and increased hunger — two things nobody wants to deal with. However, with a little diligence and the right strategy we can limit them and possibly neutralize them.

Neutralizing Muscle Loss

  • Increase protein and carb intake — Your body is burning up fat, but it’s having a hard time delivering glucose (carbs) to the muscle. This is troublesome because glycogen, the stored form of carbs, is essential fuel for intense exercise. It’s also key in repairing and rebuilding the muscle (muscle protein syntheis) after a hard workout along with protein. Supplying the body with more of the two nutrients necessary in maintaining muscle mass at a time when the body has made doing that harder is essential.
  • Decrease fat intake — We can’t consume more protein can carbs and still maintain a caloric deficit without reducing fat. Fat isn’t essential to maintaining muscle mass, which is the goal here. If we’re looking to burn up as many fatty acids as possible, why consume more?
  • Lift heavy — If the food we eat is the ‘electricity’ that powers muscle protein synthesis then heavy weightlifting is the ‘power switch’. Muscle contraction and glycogen depletion evoke a reaction by the body that says “HEY! Our muscle tissue is weak. We must rebuild it, pronto!”. Heavy weight lifting is essential here. Don’t ignore it.

Defeating Hunger Pains

  • Eat Water Dense Foods — Foods with high water content like fruits and veggies take up more space in our stomach and cause us to feel fuller without packing on a bunch of calories.
  • Protein and Complex Carbs — Protein takes the longest time to digest compared to carbs and fat so it does wonders for keeping us full. Complex carbs, compared to refined carbs, take longer to digest as well and thus providing the same benefit.
  • Casein Protein Supplements — The two major protein supplements are whey and casein. Both just as good, but whey is a rapid-digesting protein whereas casein is a slow-digesting protein. As a result, casein is the better snack option when the goal is to stay satisfied for longer.
  • Drink More Water — This is the same idea as eating water dense foods. The more space taken up in your stomach, the greater sense of fullness you have.

Eating For Muscle Gain (Caloric Surplus)

On the opposite end, if you’re looking to gain muscle/strength than you need to create the most conducive enviroment in your body to do just that and for that you need to be in a caloric surplus — net calories (calories consumed — calories expended) > calories needed to maintain weight.

The Good

  • Blood Glucose & Insulin Levels Increase — insuling sensitivity improves which increases glucose uptake into the muscle which means more glycogen and greater energy stores for your workouts which, in turn, improves muscle growth.
  • Hormone Profile Improves — Cortisol decreases, testosterone increases, ghrelin (the hunger hormone) decreases, leptin increases. Essentially, you’re less hungry/more satisfied, muscle breakdown halts, muscle growth improves, and insulin sensitivity improves.

The Bad

  • You Store More Fat — You’re gaining weight. You thought it was just all gonna result in lean, sexy muscle?
  • You May Get Lax On Your Diet — There’s more room for fun foods and extra calories in a surplus, but this isn’t an excuse for abandoning common sense.

Limiting ‘The Bad’

  • Accept The Fat — You’re gonna gain some fat. Accept it. You can always cut later on.
  • Keep Training Intensity High — This should be obvious because the goal is to build muscle during a surplus. Without heavy weightlifiting not only will we not do that, but more calories will be left to be stored as fat since there’s no intense activity requiring them to be used as fuel.

The End

I’ve covered a lot in this article. Thank you for making it to the end. Also, it’s only right you have questions. Comment below and I’ll answer anything you got for me.



| Want quick, easy to read nutrition and fitness info on the go? My Instagram has you covered. Take a peek. — Instagram |

If you enjoyed what you just read, clap this article up and/or leave me a comment! Your feedback is insanely important to me — I read and reply to all of it.

About The Author: I’m Zach Newman — Personal Trainer/Physical Therapy Student/a guy who just love learn and write about fitness, and nutrition. Conversation is insanely important to me. It’s why I love creating things because creation sparks discussion and discussion is the best way to learn from each other and create community. So please, hop in the comments and respond to the article, ask a question, or simply tell me what you had for lunch today — seriously, I’m curious. What DID you have for lunch today?


Gradual change approach toward getting healthy, with personal weight loss stories, thoughts on diet, diabetes, chronic pain, high blood pressure, coping with debilitating conditions, sleep apnea, meditation, and healthy food choices.

Zach Newman

Written by

Personal Trainer and Physical Therapy student. These are my thoughts and ideas around health and fitness. Check out my Instagram — @FitnessByThePhoto


Gradual change approach toward getting healthy, with personal weight loss stories, thoughts on diet, diabetes, chronic pain, high blood pressure, coping with debilitating conditions, sleep apnea, meditation, and healthy food choices.

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