Well first if you want to increase your chances of me answering your question don’t mention Lyle McDonald 
I get along with absolutely everybody in the strength training community but for some reason Lyle hates me and has resorted to personal attacks in the past (even though we used to be “friends”). So when I read his name I normally stop reading.
He is a actually a very smart guy and does a lot of research. But sometimes he is more of a theorist.
What is the possible fate of ingested nutrients?
- Stored as energy (glycogen or fat)
- Used to build and repair structures (muscle, organs)
- Used to build hormones
- Burn off a fuel or heat
- Pissed out
Carbs can obviously be stored as glycogen either in the muscles or liver. And while Lyle argue against it (he likes to argue against everything) carbs CAN be stored as fat. They can also be burned off to produce energy or heat.
But carbs cannot be used to build muscle or organs… well to be fair “energy” is needed to fuel the repair processes so carbs can be useful but they are not building material.
And only protein (peptide hormones like GH, insulin, IGF-1) and fats, or more precisely cholesterol (steroid hormones like testosterone, estrogen, cortisol, DHEA, etc.) are used th -build hormones.
So basically when it comes to carbs they are either:
- Stored as energy (glycogen or fat)
- Used for energy (by the brain, muscles or organs)
- Burned off as heat
- Pissed out
Let’s assume that your glycogen stores are full. Then the fate of carbs is either…
- Stored as fat
- Used for energy
- Burned off as heat
- Pissed out
Now unless you suddenly have a sharp increase in caloric expenditure from carbs (which means a VERY important increase in high intensity exercise) there is only so much energy you use per day. To paraphrase Dr.Serrano (who I trust a lot more than Lyle since he has tons of experience helping patients ranging from average Joes up to Mr.Olympia competitors and pro athletes) on top of having an amazing amount of knowledge; doing a workout like 10 sets of 10 reps on squats will “burn” around 250 calories (the caloric estimation on the threadmill are bullshit to quote him). Even if that was 100% from carbs (which is not the case, it’s about 60-70%) it would account for about 60g of carbs… so let’s say that a high volume workout can burn around 100g of carbs; since you aren’t burning a lot of carbs during the rest of the day (unless you work a physical labor job) it is unlikely that you will burn all of the excess carbs.
You can also use carbs to produce heat. Now, if you work outside in Canada, in the winter, it might make you burn off some additional carbs due to the need to elevate body temperature. But if you work inside or in a hot climate the only spikes in heat production will be for a short period immediately after a meal. Is that enough to prevent the excess carbs to be stored as fat? Highly improbable.
As for pissing it out, it happens. There is actually a new drug to prevent diabetes that basically makes your piss a large amount of the sugar you eat. But in a normal adult it’s only a few grams per day. A high amount of daily glucose in the urine might be a sign of a kidney issue. But I could see how someone with a very high carbs intake could be healthy and pee 50g or so of glucose per day. But it begs the question “why eat those extra carbs if you are going to pee them out?” … is it just to satisfy your carbs cravings?
Now if you add up all these elements it might mean that you wont store all the extra carbs as fat. But if you overconsume carbs when your muscle glycogen stores are full you will still store a good proportion of it as fat.
And also remember something… let’s say that your muscles have a storage capacity of 500-600g. Well that doesn’t mean that you can/should eat 500-600g of carbs per day since you are unlikely to use up all the stored glycogen in a day, especially if you are on a muscle-building phase consuming calories at or above maintenance.
Let’s say that you use 100g of carbs during your workout (which is likely an overestimation), you are pissing out 50g per day (again, unlikely but I’m going with the highest numbers), your brain uses around 150g per day and if you are sedentary you will likely use around 100-150g to fuel other metabolic processes.
So that comes up to AT THE MOST 400g per day BUT MOST LIKELY AROUND 300 or even 250. The carbs above that will be stored as fat. It might not be enormous, but it can add up pretty quickly.
No to mention that consuming carbs throughout the day will spike insulin throughout the day too (if you eat 20g or more in one sitting it is likely to spike it). The problem is that insulin greatly inhibits fat mobilization. In other words as long as insulin is elevated you are less efficient at mobilizing fat to use for fuel. So if you eat carbs all day long you might not store all of them as fat (maybe not even a large amount either) BUT the fact that you are greatly reducing fat mobilization lead to the same result: more fat cell growth. It’s like a bank account: if you only deposit a small amount each day but you don’t take anything out, the account will still grow.
“Yeah but many bodybuilders eat rice 4-5 times a day”…sure, but taking thyroid hormones, growth hormone and clenbuterol (some even use DNP… with DNP the more carbs you eat the more effective it is) changes everything when it comes to carbs and fat loss.
My opinion is that carbs are not evil and muscle growth does occur faster when there are carbs in the diet… BUT you don’t need a huge amount to get the benefits and you CAN get fat from eating too many carbs (even if it were strictly due to an indirect effect, which it isn’t, the result is still the same).
Again if someone is not natural it changes many things. I am friends with a two guys, a pro boybuilder and a strongman and they eats TONS of carbs. But they also use steroids, growth hormone and peptides (bodybuilder uses fat loss drugs). They don’t get TOO fat, but they don’t stay as lean either.
Hope this helps.
