How Much is it Worth Controlling Minutiae?
The concept of the average trainee manipulating their macronutrient intake to correspond in accordance with their exercise duration and intensity is either largely a waste of time or the discovery of some unlocked potential.
Tomes of research on substrate (glucose, fatty acids or amino acids) utilization during exercise have shed light on the varying degrees of fuel usage depending on the mode and intensity of exercise. However, for almost everyone looking to add muscle, lean out and get stronger, the 3,000 foot view works just fine.
I say this because the metabolic processes of deriving energy do not operate in black or white as we wish they did. Let’s take fatty acid usage for example.
Fat for Fuel
In a low intensity exercise state, 25% of maximal O2 intake or walking at 3 miles an hour, fatty acid usage accounts for most of the fuel used for energy. I’ve covered before why walking is a great exercise addition because it takes almost nothing from you in terms of recovery but uses almost exclusively fat for fuel, albeit a small amount.
Where does this fat come from though? We have fat stored in fat cells of course but also in our muscles, as intramuscular triglycerides. About 85% comes from plasma, meaning fat released by our fat tissue into the blood, to be taken up by our muscles and oxidized for energy.
As we approach exercise intensity of about 65%, the amount of fat used from fat cells via our blood declines, while usage of fat stored in our muscles increases, to about a 50/50 split.
However, at this level of intensity, fat cannot be oxidized (burned) at a fast enough rate to provide all the energy needed so about half of total energy at this intensity level comes from stored carbohydrate, either in our muscles or released from the liver. Using the “talk test”, an exercise intensity of 65% means you can carry on a conversation with someone in
At a moderate exercise intensity you are already using:
- 50% energy from fat – with half coming from fat cells and half coming from intramuscular triglycerides
- 50% energy from carbohydrate – with a mix coming from stored carbohydrate in muscle and that released by the liver into the bloodstream
Once you reach an exercise intensity of about 85% (think doing a hard set of weight lifting or fast run) nearly two thirds of energy is coming from stored carbohydrate in the muscles (glycogen), with a slight increase in reliance on blood glucose and then perhaps 20% coming from fatty acids derived from both fat cells and intramuscular triglycerides.
All carbs, no fat?
A logical conclusion then, is that exercising at a high intensity such as lifting weights uses mostly carbohydrates as fuel and fat is not important. This leads to many very low-fat bodybuilding style diets which do lend themselves to productive training sessions (through an abundance of the necessary fuel, carbs) but they do not take into account the need for fat for energy.
Not only do fatty acids spare both glucose (carbs) to be used for training but also amino acids (protein) for the synthesis and repair of muscle tissue. Having sufficient fat intake helps direct other nutrients towards more useful and productive pathways. In addition, when you eat carbohydrates they are broken down into glucose, processed in the liver and released into the bloodstream. When glucose reaches the muscle it needs to be stored as glycogen. The process of converting glucose to glycogen is energy costly and the body EXPENDS energy to actually make usable energy from carbohydrates…huh.
Rather than use energy from carbohydrate just to get energy from carbohydrate, the body can utilize energy from fat to fuel the process of converting glucose to glycogen. Many coaches might see this as an opportunity to use a very low-fat diet so more energy from fat cells is used to fuel these processes. Unfortunately, the amount of fat we can free into the bloodstream is limited and the liver can produce fatty acids to meet demand. Remember that a high-carbohydrate diet will produce more insulin so in a fed state that insulin will suppress fatty acid release from fat cells.
A low-fat diet can make it easier for some trainees to lean out and/or have more productive training sessions but it does not mean that fat is not an important factor. In fact, there is an essential requirement for fat intake to cover essential body fat storage (that around the organs) and hormone production. Falling below that for extended periods will certainly have negative consequences.
When we take into consideration that essential fat intake is around .4g/lb, a 150lb client shouldn’t drop below 60g fat per day for weeks on end, yet time and again many large trainees weighing over 150lbs are trying to eat 50g or less. Not only is this not very palatable but it is also self-limiting because ingested carbohydrate will have to be used to produce fatty acids in the liver.
Getting off the no-fat bandwagon
What do you tell someone who is seeking advice for a more sustainable and balanced nutrition approach after coming off a very low-fat approach?
Using .4-.7g fat per pound as a window, we can come up with a decent range that should fit just about anyone’s preferences. Personally, I am not a fan of very high-fat diets because they limit carbohydrate intake and there is very little evidence that ketones are a superior fuel; at best they are similar, at worst they inhibit performance. That’s not much of an endorsement.
In addition, dietary fat is the primary nutrient stored as body fat. Contrary to pop-culture belief, carbohydrates are rarely stored as body fat. In fact, it usually takes 7 days of ingesting 500-700g daily of carbohydrates before the liver converts glucose to fatty acids (denovolipogenesis).
Bummer Alert: Eating more fat doesn’t mean more fat burned
Unlike carbohydrates, the use of fat for fuel in a mixed diet does not increase as fat intake increases. The amount of fat burned for energy daily is more closely tied to how much body fat you have, so fat overfeeding long-term will need to be met with an increase in body fat before they are equalized. For instance, an estimate according to Schutz et al 1992 shows that it takes about 22lbs of increased fat mass to equalize a 20g per day increase in fat intake over baseline. Essentially, eating more dietary fat won’t burn more fat UNTIL you gain more body fat.
Operate within windows
No, not Windows 10, Windows 10 sucks. Instead of trying to fine tune every gram of carbohydrate, fat and protein, getting into the ballpark and then adjusting based on preference and performance is much more feasible and practical. After all, if a trainee is ingesting 300g carbs per day, will an increase of 10g make all that much of a difference aside from the fact that it’s simply more calories?
It is impossible to factor in the fat utilization from glycogen synthesis, liver production of fatty acids and the breakdown of fuel usage during exercise like lifting weights. How do you determine the fuel usage? Lifting is primarily carbohydrate fueled while rest between sets relies on fatty acids ; are you doing that math?
We know that there is an obligatory requirement for carbohydrates for organs and the nervous system. We know there is a minimum threshold for fat intake. We also know there is a limit on the amount of dietary fat we can use for energy.
It isn’t that complicated then to find a small window of acceptable fat intake, assign protein based on solid research (1.8-2.2g/kg) and make up the rest of the calories via carbs. We spend far too much time stressing about carbohydrate intake in the realm of insulin sensitivity when losing body fat is the fastest way to regain insulin sensitivity. Please remember that you can become insulin resistant by over-eating dietary fat in the absence of carbohydrates. In fact this is how scientists get rodents obese in short periods of time: over-feed them with fat.
Let go of the control you never had
The system is very complex with redundant pathways to ensure we have energy available to keep us alive and ticking. Rather than suppose we have a magic formula for muscle gain, fat loss or recomposition we should remember that calorie intake is steering the ship. We can help facilitate processes by assigning science-based nutrition recommendations but we truly operate on the 3,000 foot view.'
The secret that most successful nutrition coaches will tell you (but no one listens) is that when you begin working with a client, everything is an informed guess. Once you know what they are eating in terms of quantity and you can track of their weight changes, you have a good idea of their calorie needs. Once those numbers are elucidated, assigning very practical macronutrient breakdowns helps give you some runway to work with. Any tinkering along the way in terms of 5g here and 10g there is more an adjustment of calories through practical means than anything else. I love the hope that a 5g change in carbohydrates from 295 to 300g is even registered at the cellular level in terms of changing homeostasis. Ha!
You might think you have your 317g of daily carbs dialed in perfectly but between nutrition labels having a margin of error, carbohydrate density of foods differing and substrate utilization during exercise changing, you’re always operating at best-guess. Success comes from controlling as much as is practical without devoting unnecessary energy to minutiae you do not understand (myself included).
If you read through most practical sport-science practitioners operating in the real world, their recommendations begin to look similar and unexciting. Know your parameters, know you operate within nutritional bumper lanes and maybe we can all stop thinking we’ve found a metabolic “hack” that shortcuts a process we have no business worrying about in the first place.