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Body Fat Primer: Everything You Wanted to Know (But Were Afraid to Ask)

By Paul Kriegler, RD

The human body has an amazing capacity to store energy.

Throughout childhood and adolescence, we accumulate a certain number of fat cells (adipose tissue) that will remain relatively constant for the rest of our lives. How many of these cells, you ask? Estimates are anywhere from 20 to 400 BILLION!

The size of the fat cells and energy content housed within them can be manipulated, but the number is somewhat set unfortunately. Although we often use “weight loss” and “fat loss” interchangeably as we talk about body transformation goals, the actual processes end up looking quite different in execution – and outcome.

Just what is the physiological story of fat, and what should it mean for our transformation journeys? Read on for a full body fat primer with everything you need to know for your fat loss goals.

How much energy-stored-as-fat do we have, and where is it? 

Think about a lean male athlete weighing 175 pounds with 8% body fat. He would be carrying around 2000 calories readily available in his muscle and liver as glycogen (carbohydrate chains, which can quickly be broken down into glucose for energy). On top of that fuel tank, he’s carting around an astonishing 49,000 accessible calories as stored fat!

If need be, someone like this could also sacrifice several thousand calories worth of muscle tissue (amino acids) into usable energy to survive. When all is said and done, this guy could walk for well over 200 hours at just above 3 miles per hour before his fuel reserves were empty (however unlikely it is that this would actually happen).

Most of the fat we store (when we’re relatively healthy) is found in subcutaneous fat tissue, intermixed between the deepest layer of skin and our muscle and fascia. The fat contained here acts as more than just energy deposits, however. It helps insulate our bodies from temperature extremes and physical injury. In short, it’s a sort of padding. A much smaller portion of fat can be found in and amongst our skeletal muscle tissue (intra-muscular triglycerides is the fancy name) and near our vital organs.

A typical American weighing the same as the lean athlete above may have about 35% body fat, amounting to just under 215,000 calories of fat storage, far less muscle protein, and therefore close to half the amount of stored glycogen (maybe just over 1000 calories of stored carbohydrate).

How much walking would it take to drain these tanks, you ask? By calculations on paper, it would take roughly four times as many hours (assuming the same ~200 calories per hour at 3.2 mph equaling 1,075 hours). Ouch. As you can see, some of us have more of an uphill battle than others.

When our health drifts off the optimal path and slants towards chronic disease, we’re much more likely to store fat in and among our vital organs, too. This is called VAT or visceral adipose tissue. It’s generally regarded as much more than an idle fuel tank, as scientists have identified an entire class of hormones and chemical signals made in this type of fat tissue. Yup, fat is a living, breathing, disruptive endocrine “organ,” which can act in ways that ironically make it more difficult (but not impossible) to tilt back toward optimal health.

Which way are you slanted, and what does it take to tip the “scales”?

It’s rather well understood that fat loss requires a few changes in our external and internal environments as well as consistency and time. (Oh, time!) Internally, a few things need to happen….

Our bodies need certain energy-storing signals to go away or get quieter. Namely, we need to lower our total need for the hormone insulin – not constantly and forever, but most of the time. Less insulin leads to much more efficient activity in our fat cells to break down fat droplets (packaged as triglycerides) into free fatty acids that can be taken up and oxidized (i.e. burned) by active skeletal muscle.

We also need to create an environment of tissues and organs that are eager to burn more energy. In other words, we need to get moving! Active muscles that move frequently (at a variety of intensities) are muscles that can use more fatty acids than sedentary muscles. Even frequent walks can get a sedentary person tilting in the fat loss direction initially. When this is done consistently under slightly less insulin load, we even begin to prefer fat as a fuel source!

Muscle-building hormones need to be stimulated, and more muscle needs to be developed (if we want to continue or maintain fat loss). Growth hormones are released when our activity choices overload our existing muscle tissue – when we lift significantly more weight than we previously could and then rest to recover. More muscle tissue means a bigger “engine” that’s oxidizing fat. Around. The. Clock.

The key fact is, we need an overall energy slant away from energy storage – NOT an all-out assault to create a continuous caloric deficit.

We can’t let the body believe it’s starving of any one nutrient, or it will actually get stingy with its fat stores. As an instinctual physiological response, it will conserve energy, down-shift metabolism, and possibly sacrifice muscle.

To successfully slant your body toward fat burning, you need to:

  • Eat mostly plants – primarily the colorful, non-starchy kind because they require the LEAST amount of insulin to be released (versus starchy veggies like potatoes). Remember, lowering insulin is the first step to releasing fat from storage.
  • Eat enough protein to maintain the muscle you have (and more protein if you need to build more muscle). Without it, you’ll have a bear of a time repairing from your higher activity patterns. You’ll also be mighty hungry.
  • Push yourself to challenge your strength, speed, or total activity until you’re pretty spent. Then sleep hard. And when your energy returns, challenge your body again. This is called training. Overload the body and then let it adequately repair. Over time, the body becomes adept at doing more work with less effort or damage.
  • In between challenging sessions, move frequently and consistently at slow paces to ensure your body seldom gets the urge to slow its energy use. In other words, walk more.
  • Avoid environments that combine energy-rich/nutrient-poor food choices with sedentary behavior (i.e. happy hour, anyone?) at least as a regular pastime. Be wary of your food environment influences, and try to surround yourself with healthy people and healthy food choices. Be the change you would like to see.

Okay, so if I do my best to fix what’s around me and what’s going on inside of me, how fast can I lose fat?

Great question. The knee-jerk tendency is to calculate possible fat loss rates on paper and expect it to happen that way in real life.

We’ve all heard the old adage that to lose a pound on the scale you need to create a 3500 calorie deficit (or 500 calories per day for a week). For two pounds, it would seem to be a 7000 calorie deficit (or 1000 calories per day for a week). But is losing weight the same as losing fat? Nope.

Most weight loss studies using calorie math as the main intervention (whether it’s a reduction in calories eaten, an increase in calories burned or a combo of the two) show that when people create these deficits and see weight loss, it comes from a mix of the body’s tissues. A simple reduction in calories eaten can lead to weight loss, but that loss usually involves the loss of much more than just fat.

For example, if a person cuts calories by 500 per day and does nothing different, he/she may lose about a pound a week on average for a couple weeks. The first place from which the body loses energy and weight would be muscle and liver glycogen. From the typical American example above, this depletion of “sugar stores” would take roughly 36 to 48 hours depending on lifestyle energy demands (how much energy this person burns at rest, burns with high-level brain function, etc.). The 1000 calories of glycogen burned in this case would be a loss of about 250 grams of stored carbohydrate (~0.55 lb).

Lesser known fact: when we lose sugar stores, we lose about 3 to 4 grams of water for every gram of glycogen. That means this person may see an additional 1.6 pounds (on the low end) reduction on the scale (now totaling about 2.15 pounds of “weight loss”) without hardly touching his/her fat stores. Uh oh. Now this person is lighter, motivated, and really, really sluggish and weak. And hungry.

In this example, the next week or so of reduced calorie intake is forced through willpower, hopes and dreams (with a hint of irritability and a splash of hunger). Nonetheless, our “hangry” (combination of hungry/angry) weight loss crusader presses on, and the body scrambles to find ways to make up the energy deficit. The body unlocks some energy from fat (good) and also breaks down some skeletal muscle into amino acids to convert to sugar (a not-so-good but natural occurrence anytime the body’s energy needs are not met for more than a few days). Weight loss over these 7-10 days typically shows up as another 1-3 pounds, maybe more if the encouraged individual is now combining his/her low calorie intake with some extra walking to further drive the energy deficit.

However, only about 75% of the weight loss (best case scenario) will be body fat. The rest will be precious lean tissue. To boot, in NO way has this weight loss effort stimulated growth hormones or demand for stronger, more developed muscles! If body composition were being measured at day 1 and day 14, this hypothetical person would likely see body fat percentage either stay the same or even go up! There’s nothing more defeating than that.

The scenario is all too common unfortunately. This typical case may yield fat loss at an initial rate of about 1.5-2 pounds per MONTH, then slow down (despite weight loss of 5 pounds) when the initial calorie math fueled dreams of 1.5 to 2 pounds per WEEK! Translate the initial monthly progress here into body fat percentage change, and this person just went from 35% body fat at 175 lbs to 34.7% body fat at 170 lbs (after losing glycogen, water, fat, and muscle).

With less muscle and less energy, this story is usually followed by a gradual regain of weight – most of it fat. Oops.

On the flip side, it’s possible to lose 2-4% body fat per month, which means the amount of weight lost will vary greatly. In this more positive scenario, the 175 lb person with 35% body fat could achieve a body fat percentage of about 31% in a month if a different mindset and plan were followed, although he/she may only lose 1-4 pounds on the scale. Run the numbers, and that means our subject may end up at 172 to 173 pounds but would have lost nearly 8 pounds of fat mass. This individual would also be in great position to accelerate or at very least maintain that pace in subsequent months.

The “body fat focused” plan would emphasize lowering energy-storing signals (like insulin) most days, ramping up other growth hormones (through heavy lifting and sufficient rest), and feeding the body adequately enough to maintain or even gain lean tissue (using very little if any consciously-created calorie deficits through low-calorie approaches). If the aim is building lean muscle tissue through proper overload and rest, frequent low-intensity movement, and nourishing (rather than restrictive) eating patterns, this person could achieve a slight weight loss but an impressive fat loss!

It’s true that this plan feels and even appears slower for weight loss (on the scale), but it does more to transform internal energy partitioning and external appearance than any reduced calorie diet strategy could ever hope to achieve. Finally, it’s built to create momentum and to maintain results.

Which plan sounds better to you? Are you interested in learning more about how you can apply fat loss principles to your transformation? Talk with one of our registered dietitians today.

Are you ready for a new perspective on nutrition and exercise? Be sure to

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Thanks for reading.


The posts on this blog are not intended to suggest or recommend the diagnosis, treatment, cure, or prevention of any disease, nor to substitute for medical treatment, nor to be an alternative to medical advice. The use of the suggestions and recommendations on this blog post is at the choice and risk of the reader.
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