Why is it that low carbers frequently experience shockingly rapid weight loss at the beginning of their diets, then appear to “plateau”?
Does going on a ketogenic diet mean you have to stay on it forever?
Why do many folks experience a few days of low-energy moodiness (“low carb flu”) at the beginning of ketogenic diets?
The answer to all of these queries can be found in understanding our body’s relationship with glycogen.
Glycogen is the way the body processes and stores glucose as energy, chiefly in the liver and the muscles. High intensity activities like sprinting draw upon the glycogen tucked away in our muscles for fuel, which is why you hear about marathoners “carb-loading” in the days before a big race.
The glycogen stored in the liver is what keeps specific systems running all day, including the brain, kidney cells, and red blood cells. For anyone not low-carbing, the body needs a minimum of 100g of glucose each day in order to meet the basic demands of the brain.
So — what if a person consumes significantly less than 100g of carbohydrates in a day? What happens when the body runs out of glycogen stores?
The hierarchy of energy sources
Your body’s just as lazy as you are on Sunday afternoon eating chips on the couch, and it will get energy from the easiest sources possible as long as they’re available. The zippiest energy comes from carbohydrates in the diet, especially simple carbs quickly converted into sugars (think white bread, sweets, fructose, etc.), with more complex carbs following shortly after.
For a person following SAD (Standard American Diet) — we’re talking easily over 300g carbohydrates a day on average — the body may not ever burn through this ingested potential energy. Instead, it simply sweeps it away under the rug — you know, the one bulging around your waist — where no one will ever notice.
When you cut ingested carbs down to below that 100g/day mark, however, something quite interesting happens. The body burns through those consumed carbs first, then turns to the glycogen stores in the liver to maintain its basic system functions. When those stores run out — usually after about a day of carb deprivation — is where the magic really happens.
Gluconeogenesis: the body’s back-up plan
The body may be a lazy bastard, but it keeps a few tricks up its sleeves. If there’s no more glucose nor glycogen to be had, a process called gluconeogenesis begins in the liver (long one, but break it down: “gluco” = glucose, “neo” = new, “genesis” = to make).
Gluconeogenesis is the reason why you don’t actually need any dietary carbohydrates whatsoever to keep rattling down the street. When faced with low carbohydrate intake in the diet, the liver will kick into gluconeogenesis gear, generating the glucose necessary for brain function from glycerol in lipids and amino acids in proteins.
Hitting the wall: low carb flu and fat burning mode
However, getting your glucose through gluconeogenesis is also is a much longer process, and rather shocking for your lazy punk of a body to switch to all of a sudden. Consider those marathon athletes — the condition known as “hitting the wall,” when total exhaustion just suddenly takes over and no more energy is to be had, is the direct result of glycogen depletion in the muscles.
For non-marathoners, glycogen depletion is generally brought on by switching to a diet low in carbs, and the first few days eating this way often brings on similar feelings of running into a wall. It’s a beast known by many names – the Atkins flu, Induction flu, keto flu, low carb flu — and is marked by 2-3 days of nausea, headache, low-energy, and irritability. The body’s been so used to getting its energy from quick-n-easy carb-cheezies; the low carb flu is the bummer of a side effect as it switches over to other sources of fuel.
What lies on the other side of the flu is excellent news for anyone looking to ditch the jiggle, however — the best alternative energy source for the newly adjusted body is its fat stores. Congratulations: you have now entered fat-burning mode!
Is it really fat? Losing water weight
It’s very common for those new to low-carbing to lose a significant amount of weight very quickly at the beginning of their carb restriction. We could be talking four pounds, or even ten or twelve, depending on how overweight the person is to begin with. Why is this? Isn’t this a dangerously fast rate of weight loss?
It’s all about the glycogen stores — as it turns out, each gram of glycogen is bound to 3-4 hefty grams of water. So, as your body burns its way through the reduced dietary carbs and into the glycogen stores, the water attached to the glycogen flushes away as well — resulting in the phenomenon commonly known as “water weight.” There’s no fat loss here, yet — the glycogen and accompanying water’s simply been squeezed out of your muscles and liver.
This also explains why plenty of folks experience an alarming weight gain in the day just following a cheat meal. Even if the ingested carbs are at a moderate level (i.e. consumption of a grilled cheese sammie, not an entire deep-fried birthday cake), your greedy liver and muscles snatch up as much glucose as they can take, and up to four grams of weighty water accompany each grabbed gram of glycogen. Bam! Instant significant weight gain.
Water weight: easy come, easy go, neither cause for panic nor glee. Truly incinerating the nasty fat requires sticking to a low carb diet for a while, taking advantage of fat burning mode over time.
Will all the fat burned during ketosis return with a vengeance?
One of the most persistent warnings low-carb naysayers have regarding losing weight in a ketogenic state is that “you’ll just gain it all back once you go off the diet.” The horror!
Also, completely untrue. The “water weight” resulting from glycogen stores will return almost immediately as soon as you switch back to ingesting more than 100g/carbs a day — that’s just the nature of glycogen storage. Any weight gain beyond that is as a result of caloric surplus, not anything having to do with coming off ketosis.
The bottom line
Glycogen is a way the body stores glucose as energyUnder 100g/carbs/day will begin to deplete glycogen storesSwitching away from glycogen as your principal energy source causes the “low carb flu”Glycogen binds with water molecules; flushing it away results in loss of “water weight”
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