1. Skipping Breakfast is NOT Intermittent Fasting
The original intermittent fasting approach was based on human cycles:
- The sympathetic or active phase – Don't eat
- The parasympathetic or rest/recover phase – Eat
Simple. Basically, it means not eating during the day when you're active and then eating in the evening when you have time to recover. You used food (or the lack of food) to help put yourself in the physiological/neurological state where you needed to be.
Nowadays, many people do an easy (but less logical) version of intermittent fasting: they count the time they're sleeping as fasting. For example, they stop eating at 8 PM and start eating again at noon the next day – a 16 hour "fast."
This is simply "skipping breakfast," which, by the look of most people doing it, doesn't really work. Here's why:
- You aren't really "fasted" for 16 hours; you're just "not eating" for 16 hours. Big difference! You see, your last meal might take 3 to 6 hours to fully digest and be absorbed (depending on the meal). Only THEN are you fasted.
- Fasting during the night doesn't have the same impact as fasting during the day. Fasting during the day when you're active leads to a much larger AMPK activation, which is what drives most of the benefits of fasting.
- Eating from noon to 8 PM goes against the natural circadian rhythm of your body. If you claim to use intermittent fasting to optimize your health and function, then go all-in with your logic. Fast when you need to be active and feast when you need to recover, not the other way around.
Sure, not eating from 8 PM to noon is much easier and more comfortable, but it's not intermittent fasting. It actually goes against the logic of true intermittent fasting. The only benefit you get from it? Feeling like you belong to the cool gang.
If you want to do intermittent fasting, go for it! But at least go for the real thing. Don't eat from sunrise to sundown (or close to it) and feast at day's end to get into parasympathetic mode.
2. Ketosis is a Last-Ditch Survival Mechanism, Not a Lifestyle
Mathieu Bouchard, N.D., said it best: "Nutritional ketosis is an essential survival mechanism that ensures metabolic flexibility during prolonged fasting or lack of carbohydrate ingestion." (1)
That's something people fail to understand. It means that the purpose of ketosis is to safeguard against starvation when energy intake is insufficient.
The body really doesn't want to be in ketosis. Think about it. If ketosis were a favored energy system, it would be the primary system we use all the time. Rather, glycolysis and fat oxidation are the primary energy systems. Ketosis is only there to help you survive when you can't fuel your body properly for a brief period.
Ketosis is like the spare tire of your car. It can "work," but it's not optimal for long-term use.
This is evidenced by several studies establishing that work capacity (especially in intense activities) goes down when using a ketogenic diet.
As for building muscle, well, you can't build muscle optimally while running on a last-ditch survival mechanism. This is supported by a review of the literature. The gist? While a keto diet can work well for fat loss, it's suboptimal for muscle and strength gains. (2)
Now, before you get your panties twisted in a bunch... Wait, can we still say that these days? How about this: Before getting your unisex underwear twisted in a bunch, make sure your reading comprehension is up to par: keto is not OPTIMAL for muscle growth and strength gains.
I'm not saying it's completely ineffective or that you can't build muscle or strength on a keto diet. It's just suboptimal. There's a difference between suboptimal and "not effective."
Stay objective. Don't let emotions drive your judgment.
3. Ketosis and Using Fat for Fuel Are Not the Same Thing
You can use fat for fuel without being in ketosis. In fact, you could eat 1000 grams of carbs per day and still use fat for fuel.
Remember, ketosis is a safety mechanism triggered to provide fuel for your brain in case of a glucose shortage. Yes, the body uses fatty acids to produce ketones. So, technically, ketosis does use fat for fuel. But not all of the fat usage for fuel is done through ketosis.
Most tissues requiring energy can use fat oxidation or glycolysis for fuel. The main exception is the brain. The brain can only use glucose or ketones for fuel, not fatty acids directly.
As long as the brain has enough glucose to work properly, there's no real need to resort to ketosis, which is more complex than using glucose. Glucose can come from the carbs you eat, but it can also be produced by breaking down protein into amino acids. The liver turns some of them into glucose.
That's why if your protein intake is really high, even if your carbs are close to zero, you might not get into ketosis: you have enough amino acids to produce glucose to fuel the brain.
The body will start producing ketone bodies significantly when carbs and protein intake are insufficient to produce the glucose required for the brain to work. That's why it's a survival mechanism. It happens when you don't ingest the nutrients required to fuel the brain. And having a functional brain is kinda important.
A lot of people claiming to be doing a "keto diet" might not actually be doing a keto diet. True keto recommendations normally include consuming at least 60-70% of your calories from fat.
Ketosis is NOT being "fat-adapted" (although it's a catchy concept). You can use fat for fuel just fine. What they call "fat-adapted" is simply your body producing enough ketones to fully fuel the brain – not having to break down muscle tissue to make some glucose to make up for the insufficient ketones.
In a nutshell, you can function on a backup generator, but it's not optimal.
4. Low Carb Means High Cortisol
I'm not going to make any friends here, but facts are facts. Keto and other low-carb diet approaches lead to higher cortisol levels, especially in response to training.
One study found a large cortisol increase in the first two days of low-carb eating. It became "less bad" after two weeks, but it was still higher than the higher-carb diet. (3)
Why? Well, the two key functions of cortisol are:
- Mobilizing stored energy for fuel
- Elevating blood glucose when it's too low
While number one is more dependent on caloric intake, number two is heavily influenced by carb intake. A diet leading to low blood glucose levels (any low-carb plan) will lead to higher cortisol and glucagon to mobilize stored glucose (as glycogen), or to break down muscle tissue into amino acids to have the liver convert them to glucose.
Why does it matter?
- Because high cortisol makes it harder to build muscle.
- High cortisol, over time, decreases the conversion of T4 (precursor of thyroid hormone) into T3 (active thyroid hormone), thus decreasing metabolic rate.
- High cortisol can lead to lower testosterone and estrogen levels.
Not to mention, a low-carb diet leads to a lower work capacity during intense workouts. And, of course, keto dieting is inferior for muscle growth. I suspect that the higher cortisol is part of the reason, but not the only one.
"Yeah, but keto works great for me, bro!"
I'm not saying it can't work. And it's certainly better than how many people are eating. But don't let personal bias, emotional bias, or recency bias cloud your objectivity!
5. It's Not Just Calories-In, Calories-Out
Sure, eating a caloric deficit will lead to weight loss, and – provided your protein intake is high and you train hard – most of that will be fat loss. But that's not all there is to it.
I understand where the calories-in vs. calories-out approach comes from. It was to show that you didn't need a special diet (keto, vegan, intermittent fasting, paleo, photosynthesis, etc.) to lose fat. I get that.
It also provided relief from overly strict diets by allowing people to eat a variety of foods. I'm all for that. Rigidity can lead to lower adherence.
But this has led many people to claim that food choices don't matter as long as you're in a calorie deficit. That might have some truth to it when it comes to fat loss, but fat loss isn't the only thing affected by what you put into your mouth.
Blood lipids, blood pressure, blood sugar, low-grade systemic inflammation, gut health, etc., are all things that can have a significant impact on your health. And they're all impacted by nutrition. Not to mention, food choices can affect neurotransmitter levels, which will affect your mood, well-being, resiliency, and sleep.
Eating should never be just about losing (or gaining) weight. Health and well-being should actually come first. Remember, losing fat is NOT the sole purpose of your nutrition plan!
6. Carbs Are Actually Kinda Essential
Here's one argument we often hear to support using a ketogenic or low-carb diet:
"You have essential fatty acids and essential amino acids, but there are no essential carbohydrates!"
This is a classic case of something not meaning what keto proponents think it means. In their minds, it means that carbs are not needed in a diet; they're an inferior class of nutrient.
That's NOT what "non-essential" means in nutritional science:
- Non-essential means the body can make something by converting other nutrients into it.
- Essential means your body can't make it on its own from other nutrients. And because your body can't make it, you need to supply it via nutrition.
As for carbs (glucose), the body can make them by converting some amino acids into glucose – gluconeogenesis. The body can also convert lactate (lactic acid) into glucose.
That's why they're called "non-essential." It has nothing to do with how important they are.
"Yeah, but I'll just let my body produce its own glucose from protein! No need to eat those nasty carbs; I'll just make up what I need!"
Sure, good luck with that.
The body converts amino acids to glucose at a 30% efficiency rate (or less). To make it simple, to make up 160 grams of glucose – the daily amount necessary for the proper function of organs, not counting physical activity – you'd need to convert 530 grams of protein, or more, into glucose.
Good luck adding muscle if you need 530 grams of protein just to support glucose production!
The point? Yes, you can produce glucose from other substances, and that makes it non-essential. But it doesn't mean that carbs aren't necessary, especially if we're talking about a hard-training individual who wants to build muscle or perform at a high level.
This also doesn't account for the fact that carbs have physiological effects outside of simply providing energy: physiological effects (increases in IGF-1, mTOR activation, reduction in cortisol, etc.) that will not be present to a significant extent by converting other substances into carbs.
In short, carbs being "non-essential" does not make them a less important macronutrient.
- Pilla R (2018) The Ketogenic Diet and its Clinical Applications in Type I and II Diabetes. Int J Diabetes Clin Res 5:092.
- Source: Valenzuela PL, Castillo-García A, Lucia A, Naclerio F. Effects of Combining a Ketogenic Diet with Resistance Training on Body Composition, Strength, and Mechanical Power in Trained Individuals: A Narrative Review. Nutrients. 2021; 13(9):3083
- Terink R, Witkamp RF, Hopman MTE, Siebelink E, Savelkoul HFJ, Mensink M. A 2 Week Cross-over Intervention with a Low Carbohydrate, High Fat Diet Compared to a High Carbohydrate Diet Attenuates Exercise-Induced Cortisol Response, but Not the Reduction of Exercise Capacity, in Recreational Athletes. Nutrients. 2021; 13(1):157