What's Going On with Stubborn Fat? Part 1

One of the most frustrating experiences when leaning out is to find areas on your body that seem to take forever to lose fat from. Sometimes people even experience weight loss without much, if any, measurement losses for a period of time.  Additionally, men and women see rates of fat loss and area-specific fat loss occur on different levels.  All of this can lead to frustration, bewilderment and poor adherence long-term.

To briefly review, fat loss occurs when the triglycerides stored within the fat cell are mobilized, or released.  Glycerol plus three fatty acids are released from the fat cell into the area around the fat cell.  In low energy states between meals fatty acids will be mobilized from fat cells and in high-energy states fatty acids will be stored in fat cells.  Storage can occur after a meal of pretty much any size so it isn't so much the size of the meal as the overall calorie balance that determines if you ultimately lose fat. The result of the daily storage and release will result in a net surplus, deficit or maintenance and that is determined by your total calorie intake, not just the size of the meal.

You'll likely hear or have heard that insulin prevents fat loss from occuring and while that is true, it is only in the acute process.  Insulin released after a meal blunts fatty acid release and promotes fat storage but just like with low-energy states between meals, low-insulin states provide a window for fatt acids to be released into the bloodstream. Going back to the previous point however, is that even if you are spiking insulin often with high intakes of protein and carbohydrates, it is the energy balance (calorie total) that will determine loss or gain.  Looking at insulin like this helps us to not be as concerned with it's effects on a daily basis or even a per-meal basis and we can simply focus on eating enough protein, choosing good food sources, controlling calories and getting adequate fiber for most cases.  Complete meals, whole foods and controlled calories will all help to control wild insulin surges or falls anyway so things tend to work themselves out in the end.

The primary hormone that stimulates fat loss is Hormone Sensitivie Lipase or HSL.  HSL mobilizes fatty acids out of the fat cell and into circulation.  HSL is ultimately and largely controlled by a few other key hormones in the body.

Hormones that Enhance Fat Mobilization

  • Catecholamines: Adrenaline and noradrenaline.  These hormones are released into the blood stream and nerve synapses during times of stress (which can also be low-calorie times) and enhance the activity of HSL.  Exercise is one of the most potent drivers of these hormones
  • Atrial Natriuretic Peptiide (ANP): Released from the heart, involved in water and sodium balance but also enhances HSL.  Interestingly enough, ANP can work even when insulin is higher.
  • Cortisol: Does not have a direct increase on HSL but can mobilize fat on it's own in short pulses, such as between meals or during exercise.  Chronic cortisol elevation though (think chronically stress out, under recovered and under-sleeping people) will actually cause MORE fat storage
  • Growth Hormone: Has independent effects on fat loss

Hormones that Inhibit Fat Mobilization

  • Insulin: Obviously already discusses but it is important to drive home that insulin blunts HSL activity which will obviously blunt fat loss.  Now, consider that all of the above hormones (catecholamines, ANP, cortisol, GH) and generally occur in low-insulin states.  So, we can look at insulin as directly opposing HSL release which will blunt fat loss and driving up catecholamines and cortisol will increase fat loss.  A significant note though is that insulin essentially blunts all of the above fat-mobilizing hormones.  Aside from ANP, catecholamines, cortisol and GH will all be suppressed in high insulin states.

Mobilized vs Transported


Above you'll note that all of these hormones simply blunt or enhance fat mobilization.  This is another reason we cannot look at insulin as the boogey man because it helps with energy storage, suppressing stress hormones (which can be a good thing of course) and reducing protein (or muscle) breakdown. It doesn't stop fat LOSS, it simply reduces fat MOBILIZATION. Once again, if insulin is lower as it would be in any well-designed fat loss program then the overall shift will fall in favor of the fat mobilizing hormones and away from the fat storing hormones. But we musn't think that insulin is actually inhibiting the ability of the muscle to burn fat for fuel it simply makes less fat available in the bloodstream and preferentially drives nutrients to fat, muscle and liver cells to reduce their presence in the bloodstream.

When fat is released from the cell it needs to get to the muscle to be burned off as energy.  The bloodstream is a tightly controlled and regulated system which is why these hormones are so effective at mobilizing and storing nutrients: we need tightly managed nutrients in the blood.  You've heard of blood sugar, right?  Between meals the amount of glucose (blood sugar) in all 5 liters of your blood is about 4 grams, or a teaspoon.  It is that tightly controlled and regulated.!Insulin can drive nutrients into the muscle just like it can in fat cells which is why you've heard so much about "insulin sensitivity". Having muscle sensitive to insulin means when insulin is present in the bloodstream your muscle cells will happily grab both glucose and fatty acids up to store and eventually burn off as energy preferentially over fat cells. 

So insulin can push nutrients to muscle just like it can to fat - the caveat is that insulin simply prevents more fat from being released from fat cells while it is present in the blood.


By now you can see that all the hormones discussed above have an effect on whether fat is mobilized from the fat cell. 

Mobilization still requires transport and that is largely determined by the amount of blood flow past the fat cell.  Higher rates of blood flow means higher fat mobilization and a greater likelihood that the fat will reach the muscle to be burned off as energy.  Interestingly enough, the catecholamines and ANP which both work to mobilize fat also increase blood flow which means they increase it's transport too!

We can quickly see that areas higher in blood flow will have an easier time mobilizing fat away from storage, into the bloodstream and to the muscle to be used as energy. Areas with lower blood flow will have a harder time transporting fat away from the fat cell.

Fat stored around the internal organs (visceral fat) has some of the most potent detriments to your health BUT it also has very high blood flow.  Since testosterone tends to enhance visceral fat storage in the presence of excess calories, men see greater visceral fat storage than women do.  But becase visceral fat has very high blood flow, it is quite easily mobilized and transported in a calorie deficit.  Men often see faster initial fat loss progress because a higher percentage of fat is stored here than women (who will store more on the lowe body).

*It is important to note that women who are obese, have PCOS or are post-menopausealhave a shift in hormone activity that increases testosterone because estrogen and progesterone are lower.  The reasons for this are different in each case but the end result is somewhat similar: fat storage resulting in a more male pattern with greater abdominal fat storage and less on the limbs.  In women, higher testosterone decreases insulin sensitivity which means higher carb diets (especially in PCOS) won't be as effective and will make fat loss more difficult.  It may mean a greater ability to put on muscle though, so this time can be taken advantage of by strength training to add muscle mass combined with a lower-carb diet to help with the poor insulin sensitivity.

One thing to note about the often-experienced weight loss with no measurement change, which I have witnessed in many clients, is that a loss in visceral fat will not necessarily change measurements because the fat is stored so deep in the body.  People will often become frustrated at this phenomena, losing perhaps 3-5lbs and seeing not visual or measurement changes.  Men will see larger initial weight losses in most cases and women will often be frustrated by the lack of initial measurement change and comparing their rate of weight loss to men.  In both cases, fat IS being lost and the body is trying to use the stored fat that poses the greatest health risk first.  Since men store more here, they'll also lose more initially as well.

To recap Part 1 and make sure we understand the basic here, lets look at some bulletpoints:

  • Fat need to be mobilized first before it can be transported and burned off
  • HSL is the primary hormone in fat mobilization.  Certain hormones enhance it like the catecholamines while insulin directly opposes it
  • Mobilization is not enough, fat also needs to be transported away from the fat cell
  • Blood flow has a direct impact on how well fat is mobilized away from the cell
  • The hormones that help primarily with mobilization ALSO increase blood flow which helps with transport
  • Visceral fat has the highest blood flow and will be mobilized first but may not result in much change in appearance or measurements despite being burned off
  • Men and women store bodyfat in different patterns: men have more visceral fat and will usually see faster initial weight loss simply because of where the fat is stored and the blood flow to that area

Understanding something, even in a basic way can greatly improve our success.  If you can grasp and understand the above bulletpoints you have a firm basis for applying logic and reason to your fat loss nutrition. It can also clear the confusion about demonizing insulin or the misrepresentation of these hormones' effects on the body and fat loss/storage. If you see the bigger picture you are much more likely to be adherent and be able to adjust your nutrition using informed decisions rather than reacting emotionally.

Next week we will discuss how fat is burned and a few strategies for working on the fat this is most stubborn.