Muscle or Fat?: Part 1
A common misconception with changing your body composition or weight is that there's a "culprit" for the way you look. Typical culprits in the nutrition lineup are carbohydrates, gluten, dairy, eating past 7PM, combining fats and carbs or overeating protein. There's a lot more but we simply don't have time to round them all up.
Somewhere along the way these past few decades, the common scientific knowledge of calorie balance has been overlooked. Not by the scientific community of course, but by companies and programs looking to sell you a product as well as the consumer looking for the simplest and lowest-effort solution.
What drives me batty is that oftentimes consumers will put in MORE work trying to fast and then time their post-workout meal correctly, go Keto, avoid anything non-Paleo or take a slew of vitamins and supplements that even Keith Richards would think twice about (he did a lot of drugs, if you didn't know!). In fact simply eating enough protein and managing calories is so much simpler, cost effective and results-driven yet it's really hard to sell; so of course it makes sense that companies wouldn't.
Our nutrition world is coming around and for as many absolutely bonkers claims and products out there, we're getting many more people looking to what the science says and trying to manage the absolute basics that affect our physiology in the most bang-for-your-buck way. This would be eating optimal protein, balancing calories, consuming enough fiber and then doing those things consistently over the long-term. Hard to make it sexy, but effective.
In this new age of scientific-driven nutrition there are a lot of people and clients, so fed up with being led around by their wallet and manipulated into ridiculous diet programs that they've abandoned nuance. If It Fits Your Macros (IIFYM) was a Godsend to many people who were like "you're telling me if I just eat X amount of calories and protein I can eat whatever foods I want? Um, OK I am doing that until I die". The relief of being able to get most of your results from managing a few simple things started to pick up some traction. And, as it always does, this created zealots on both sides.
There are groups of people who stick to the camp of "only calories matter" and while that is a Titanic-sinking sized icberg of truth, it's not the whole truth.
Understanding Energy Storage
For me, the understanding of different energy storage sites is fascinating. The when we look at how nuanced, complex and redundant our physiology is, it doesn't make sense to make a claim that is so widespread. If you take supplements as an example, creatine is THE most researched sport supplement and is pretty much the only researched supplement that science can make some pretty hard and fast statements on. There are a ton of other supplements researched, with lots of data on many of them and yet we can only still conclusively agree on creatine.
So to make conclusive statements on nutrition is also hasty and short-sighted.
Most people think of energy storage as fat cells. Essentially, if you overeat at a meal you store fat and if you only eat a little you burn fat. From the 10,000 foot view that holds a lot of truth but it's not actually what's happening meal to meal or sometimes even day to day.
Ready for a whopper? No, not the burger but a hard truth: most fat storage comes from dietary fat. Yikes! I thought we were told that wasn't true? Dietary fat very closely resembles body fat and is the most efficiently stored nutrient as body fat. After pretty much any meal, unless it's absolutely tiny or possibly contains no fat, you will store some of the fat from the meal as body fat. Yes, even on a diet.
Most dietary fat contains long-chain fatty acids and these cannot transport across the intestinal lumen into the bloodstream the way smaller carbohydrate or proteins can. Instead they are packeged into something called a chylomicron, enter the lymph tissue and must travel in the lymph before emptying into the heart through the subclavian artery, then pumped into general blood circulation. This takes on average 3-5 hours. By the time you've ingested a meal you've already used the proteins and carbohydrates from that meal for any energy needs or protein turnover, fat is late to the game.
Some dietary fat can be picked up by muscle cells after it enters general circulation by for the most part, that dietary fat will be stored as body fat.
Ok, OK then should be just cut all dietary fat then so we NEVER store it? Aside from being nearly impossible and miserable, we don't need to do that. Our energy balance and carbohydrate intake determines what happens with our stored fat tissue. Since protein is used for rebuilding and creating new muscle and organ tissue we won't store that, in fact we store very little protein in our body which is why regular protein consumption is essential for maintaining a positive protein balance overall.
Carbohydrates are the preferred fuel source for your muscles, nervous system and brain, in the form of glucose. Your body will always preferentially burn carbohydrates for energy.
In this case, if you eat a lot of carbs you'll burn more carbs and store more fat. If you eat a lot of fat (but few carbs) you'll store more fat but BURN more fat. The major decider here is how many total calories you eat. On a low-carb diet you are both storing and burning more fat, whether you lean out or not is determined by how many total calories from fat you consume. On a high carb and low fat diet you'll burn more carbs and store more fat but you WILL pull energy needs from fat cells if you are in a deficit - the decider here is how many total calories from carbohydrates you consume.
In either case, you body will always preferentially use carbohydrates for fuel and store dietary fat as body fat. This is because stored carbohydrate (glycogen) is our primary fuel source, fuels our highest intensity activity which is what we do best and we have a much smaller storage capacity for them. Since we can almost endlessly store body fat, we need to prioritze refilling muscle glycogen - it's a finite fuel source.
Fat Keeps Us Alive and Kicking
We also need a certain amount of fat to ensure our physiology runs properly. Fat tissue is not metabolically inactive, in fact it produces multiple hormones that have major implications for our health and well-being. Leptin is a major one and fat cells produce leptin which tells our hypothalamus how much energy storage we have. It's basically a system of saying "hey, this much leptin produced means we have this much stored energy". If we produced enough leptin (because we have a certain amount of body fat), our physiology runs smoothly. We have normal hunger/satiety cues and for women, adequate leptin levels help start the menstrual cycle.
When leptin goes down we see decreases in thyroid, follicle stimulating hormone and leutenizing hormone. These cause drops in testosterone, growth hormone and sympathetic hormones like adrenaline. With lowered sympathetic hormones and thyroid, metabolism goes down. Cortisol goes up, hunger goes up, appetite goes up and you'll feel pretty lousy.
Not only does fat impact so much of our physiology but it is a kick-ass energy storage site too. Fat cells are about 90% lipids, compared to muscle cells which are in fact mostly water. Fat cells can store a huge amount of energy in a small space and weight which ensures that if we don't have enough calories, we can survive for quite a long time.
Looking at all this, it makes so much sense why dietary fat is preferentially stored while glucose is preferentially burned. If we could easily burn off as much body fat as we wanted there would be massive amounts of people starving themselves to death to get to 5% bodyfat. It's actually a good thing it's not that easy.
Now this is the storage component the general public doesn't really know about. Muscle, just like fat, is active tissue. It's not just the "stuff" that helps us lift weights. Muscle is our primary storage site of glycogen (stored carbohydrate) and we can also store a small amount of fat in the muscle (intra-muscular triglycerides) along with a lot of water. A pound of fat contains somewhere around 3,500 calories where a pound of muscle only contains about 600.
It takes a lot more energy to build new muscle tissue and muscle itself is much more matabolically active than fat in terms of expending calories. Fat cells do not contain mitochondira, the cellular machinery to turn nutrients into energy. Muscle does however which is why muscle expends more energy, since we need the mitochondria to produce energy for the muscle to contract and move us around.
Since muscle tissue is energy costly and building new muscle tissue is even more metabolically costly, it's much harder to gain muscle than it is fat. Again, in terms of survival this makes a lot of sense: in a world where resources are scarce, having a ton of muscle means you need more calories to stay alive. Even in many modern countries, where average protein intakes are low, you'll find people to be smaller. If protein is a finite commodity in your diet, you probably won't put on a ton of muscle. This certainly helps keep energy expenditure lower.
When we consume protein, the proteins are broken down into amino acids which go to protein turnover. Protein turnover is basically the process of breaking down and rebuilding proteins. It happens constantly and is a normal process - if protein synthesis exceeds protein breakdown, we'll build more muscle tissue. If protein breakdown exceeds protein synthesis, we'll lose muscle tissue. Most people, without weight training, can maintain their genetically set muscle mass pretty easily, at least until they hit their 40s and above.
Weight training kickstarts anabolism, the building of new muscle tissue, but you must consume adequate protein to actually have the materials needed to build the muscle. If not, protein turnover will settle back to where you started. Since protein turnover is constantly happening, you can see why we wouldn't store protein as fat; it's too precious a nutrient to waste on fat storage and building new muscle tissue is so energy-costly that there wouldn't be a lot of excess protein to turn into fat tissue.
Phew! We'll take a break here and pick up next week on carbohydrat storage as well as some strategies for optimizing storing energy in muscle vs fat.
If you made through all of the above you know more about fat and muscle physiology than 99% of the population. You rock!