The What, How, Why… and WOW of Carb Cycling

Is eating keto all the time really optimal? Or should you carb cycle? What even is carb cycling and what are its presumed advantages? And if you carb cycle, how should you do it? And finally, can you mimic carb cycling but without the carbs? These are some of the tantalizing questions we will address in this video, but first, fair warning, this video will be dense. Denser than the caloric concentration of this 2,310-calorie, 303-gram-of-carb Heath Bar Milkshake from Baskin-Robbins. Yes, that's a real thing, you can Google it, but hopefully it's not on your diet plan. But hopefully you will leave this video with a better understanding of human physiology and practical knowledge to implement in your own life, rather than with a scary case of refeeding syndrome, which could happen if you had that milkshake after a prolonged fast. And it could actually kill you. I'm not joking, I'll explain that later. It's real physiology and real medicine. But first, let's quickly define carb cycling. Carb cycling refers to an eating pattern where one eats a mostly low-carb or very low-carb ketogenic diet, but on occasion carb refeeds. This can follow a daily pattern such as intermittent fasting or time-restricted feeding, but without the backdrop of a low-carbohydrate diet. Or it can involve refeeds over longer timescales, say 1 day of carbs per week, 1 month of carbs every 4 months, or 1 season of carbs per year. The time course is not specific, but the central thesis underlying its presumed metabolic benefits can be summed up in 3 words: cyclic metabolic switching. The cyclic metabolic switching theory posits that extended fasting or very low carbohydrate diets sufficient to trigger the metabolic state of ketosis, for which ketogenic diets are named, leads to the activation of adaptive cellular stress response pathways. We'll get into more specifics later. And during this time, cell growth pathways, including those stimulated by the growth hormone insulin and a key metabolic regulator called mTOR, they're inhibited. And then during refeeding, pathways that promote cell growth, like those downstream of insulin and mTOR, are activated. And this creates cycles of activation between stress response pathways and growth and development pathways. It's the metabolic equivalent, if you'll indulge me in an analogy, of a good weightlifting program. You stress your muscles to trigger adaptation. Then you need to rest and recover. And it's during that rest and recovery period when you're eating and sleeping that growth occurs. But if you spend too much time in either phase, so too much exercise with too little recovery or too much eating and sleeping with not enough stress to your body, your health will suffer. So in general, and this is a high-level truth in biology and human physiology, Biology and human physiology operate in ebbs and flows. So that's the big picture idea here, that forcing the body to cycle between states of ketosis and refeeding is optimal for stimulating metabolic resilience, adaptive growth, and development. Now, the literature is admittedly a bit skinny on data comparing chronic low-carb ketogenic diets to those incorporating carb cycling in healthy people. I wish there were more data on this specific topic. Unfortunately, there aren't, but we can gain insights from the literature on intermittent fasting that doesn't come with carb restriction and ask, is there an advantage to this form of cyclic metabolic switching with carb refeeds versus simple continuous caloric restriction? And the answer to this question is an unequivocal yes. For example, in a 6-month randomized controlled trial with 107 women with overweight or obesity, women received either a continuous caloric restriction diet with 75% of their estimated caloric needs or an intermittent caloric restriction diet with 2 days per week where they were eating very low calories, basically fasting, 650 calories per day, and then the other 5 days of the week they were not calorically restricted at all. This is metabolically similar to intermittent fasting, and in the paper they call this diet the intermittent energy restriction diet, IER. You'll see that in a table in a moment, but I'm just going to call it the 5:2 group because they're basically fasting 2 days and then eating the other 5 without caloric restriction. Now, while both groups lost similar amounts of weight, 5.7 kilograms in the 5:2 eating group versus 4.5 kilograms in the continuous caloric restriction group, insulin sensitivity improved significantly more in the 5:2 fasting group, suggesting additional benefits of intermittent fasting beyond caloric restriction. And here's an additional finding from the study that you need to look closely for to truly perceive. If you want to play a little game of nerdy I Spy, pause the video here and look at this table and see if you can see what I see. Okay, you unpaused, you want the answer? The decrease in waist circumference in the 5:2 group was 6.1 centimeters versus only 3.9 centimeters in the the continuous caloric restriction group. In a study of this size, don't get hung up on the p-value of 0.13. To me, there's a pretty clear trend here, and the actual size of the difference between groups was pretty large. I think with a larger sample size, it's highly likely that the result would have been statistically significant. So the main point here, at least according to me, in my opinion, there did appear to be preferential reduction in abdominal fat and possibly visceral fat within the abdomen, which is the most dangerous type of fat as compared to fat on the hips and thighs. That's kind of interesting. It's definitely speculative. I'd love to see this trial done again at larger scale over longer time courses. But anyway, combined with the significantly greater improvements in insulin sensitivity which was seen in the 5:2 group, this all supports the idea there's a metabolic advantage of fasting that goes beyond caloric restriction. Bottom line, the scale does not tell the whole story. Duh, right? And complementary results have been observed in other randomized controlled trials. For example, in a controlled crossover feeding trial, now in men, time-restricted feeding in a 6-hour window improved insulin sensitivity, improved blood pressure, and improved markers of oxidative stress as compared to eating in a 12-hour window. The authors of this trial concluded that the benefits of intermittent fasting are not solely due to caloric restriction, and that quoting, "Intermittent fasting can improve health even in the absence of weight loss." Now, relevantly, the diet compositions of both these studies included 45-50% of calories from carbs, making these studies representative of a form of daily carb cycling. I could go on. There are many randomized controlled trials that echo similar conclusions. But bottom line, when it comes to calories and carbs, It's important to ask when, not just how much. But that's only the tip of the iceberg, for two reasons. First, many trials are limited by resources available to conduct them. For example, if the earlier study that we went over had a larger sample size, I'm pretty confident the difference in waist circumference would have been significant. The 5:2 fasting group would have had a smaller waist circumference or a larger decrease in waist circumference than the continuous caloric restriction group. Second, and more importantly, we can only draw conclusions from what we can measure. Let me clarify that point with an example because it's important. If eating the same calories and same foods in a different pattern, say eating pattern A versus eating pattern B, resulted in differences in, say, brain health, such as more neuroplasticity, and better Alzheimer's disease protection, how would we know for sure? Studies to test this are nearly impossible to conduct. So would we conclude that Pattern A and Pattern B are equal eating patterns? No, we couldn't conclude that. We just haven't collected the data to prove they are not equal. So as a community of critical thinkers, and that's what we are here on this channel, we must discuss mechanisms and speculate intelligently because sometimes that's all we have. We do know, for example, that fasting activates repair and renewal pathways, increases the expression of antioxidant enzymes, and clears cellular waste. Maybe you heard of autophagy. It stimulates DNA repair, activates anti-aging proteins like the sirtuins, raises levels of hormones like adiponectin that boost muscle resilience and brain function, and fasting suppresses inflammation, in part through the generation of ketone bodies like beta-hydroxybutyrate. The point is this: carbohydrate restriction and fasting promote metabolic resilience pathways. We know this. But then what? Do we want those pathways stimulated 24/7? Maybe not. Just like you need to rest after a workout, cells need a growth phase. And refeeding does this. Carbs, along with protein, stimulate growth pathways. And carbs especially spike insulin, a growth hormone. And yeah, it's easier to grow with pasta on the menu than without. But this isn't necessarily bad. It's not good or bad. It's only bad if there's too much growth signal and not enough renew and repair signal. They operate as a couple, renew and repair and growth. They're the yin yang of metabolic health. So it's possible that keto-carb cycling is optimal for brain health, muscle development, and resilience all things being equal. It's possible, and if that practice works for you in any form, great! I'm happy for you and I want to enable you to play around and find what works for you. That said, if you want my candid opinion, I actually don't think carb cycling is necessary. What? Did I just flip-flop? No, I did not, and I'll explain why shortly. But before I do that, I want to review how to break a fast and how to carb cycle. These things are kind of entwined. So let's start with how to break a fast. If you fast for more than 24 hours, your gastrointestinal system slows down. That makes sense, right? You're not eating, so your body stops spending energy on maintaining your gastrointestinal system. Thus, you basically need to warm it up. You need to warm up your gut. And here's a cautionary tale to make the point. My first prolonged fast was about 48 hours, after which I broke it with, get this, 3 slices of pecan pie. And I quickly regretted that nutty decision. Admittedly, this was after a colonoscopy, so not exactly a voluntary fast, and back then I wasn't really into metabolic health. But honestly, I preferred the procedure, the colonoscopy, to the aftermath of what happened with that pie. Super uncomfortable. So, rule number 1: Do not eat a lot when you're breaking a fast. Start with a light pre-meal, like bone broth or 2 to 3 hard-boiled eggs or a small full-fat Greek yogurt. Those will all do just fine. Try to avoid nuts, seeds, and fibrous vegetables, especially raw vegetables, which are harder to digest. Then wait an hour or two or three before having a full meal. Also, if you've fasted for 3 days or more, or followed a very low carbohydrate diet for a long time, be extra careful. You're at risk for refeeding syndrome. This occurs when your body experiences a large spike in insulin that drives a dangerous shift in electrolytes: phosphate, magnesium, and potassium. Levels of these electrolytes drop, which can cause cardiac arrhythmias, irregular heartbeats, rhabdomyolysis, seizures. And even death. Moral of the story: remember that 300g of carb milkshake from earlier? Well, it could literally kill you. That's sort of a joke, but also an accurate statement under the wrong physiologic conditions. So be careful when breaking a prolonged fast. Now, how to carb cycle. I can kind of break this up into 3 main strategies: First, daily carb cycling. This includes intermittent fasting and time-restricted eating, generally with a 6-hour or shorter eating window to allow time for mild ketosis. I would still keep your carbs moderate, maybe 100 to 150 grams per day depending on your body size, to ensure you dip into ketosis. Also, with this strategy, carbs can be targeted after a workout when your muscles are basically glucose sponges. The glucose transporters are transported to the surface of the muscle when you exercise. And for some people, this can help with performance. And if you do this, it's actually one of the few times where fast-digesting carbs might be more useful, like a banana or a baked sweet potato, which is a higher glycemic index than a boiled sweet potato. Fun fact there. Okay. Two, weekly carb cycling. This is usually one carb refeed day per week. If you go with this pattern, choose slower-digesting carbs from whole foods, something like a boiled, not baked, sweet potato, berries, maybe homemade pasta with buckwheat or semolina flour. There's a lot on the buffet with this pattern. And this pattern is also perfect to build in a nice sushi date night to, if that floats your boat. Sounds pretty nice to me. And 3, seasonal or long-term carb cycling. Now, this pattern is pretty flexible. That's its main advantage, life flexibility. You can pair it with vacations or, if you're an athlete, high-load training phases. Again, I would stick with slow-digesting carbs on balance, but there are no rigid rules. So, have fun with that one if you practice it. I'll also note the only way to truly know how changing your eating patterns is actually affecting your physiology, your body, your biology and your biomarkers is to test it. That's the n=1 scientific approach that I'm always talking about. And the great news is that access to self-testing tools is better than ever. You can get your own continuous glucose monitors and run these experiments yourself. One company that offers this is Levels Health, and they have a great app that helps you interpret the data, annotate the glycemic curves. It's really cool. I'll link to them with a discount code below if you want to check it out. Or if you want a broader view of your metabolic health? A company with which I'm affiliated called SiPhox offers easy at-home testing kits with over 17 biomarkers, and we're currently continuing a metabolic health awareness promotion together with actually no or minimal benefits to the company by way of, and thanks to, a 50% discount on 2 testing kits for you. They just want to get the word out about metabolic health, and like me, they believe in getting your data into your hands, empowering you to be the captain of your own health ship. Just check out the video notes for details on these products. Alright, with those relevant plugs behind us, now for another question: Do you need to carb cycle if you're keto? Do you need to carb cycle to be metabolically optimal? In my opinion, the answer is no, no you don't, and that's not contradictory with what I've said thus far. Let me explain. I believe you can, for lack of a better term, hack the cyclic metabolic switch. Remember, refeeding refers to giving your body a growth stimulus, and while growth pathways are complex, one could argue that insulin is the most relevant growth hormone. And you don't need carbs to spike insulin. Protein also spikes insulin. In fact, some proteins like dairy protein and especially whey protein can spike insulin so much that in some people it spikes more than bread. But don't expect to see the same jump in blood sugar when eating whey protein as compared to eating, say, bread. Because protein doesn't have sugar. No duh, right? And protein also increases other hormones like glucagon which have distinct metabolic effects, like promoting fat release. So while protein won't burn fat off your body just by itself, the hormonal profile and impact is distinct from eating protein vs. eating carbs. Kind of obviously. Hopefully. And yet you do get the growth signal and the insulin spike from protein. Especially whey protein. And this is why I don't think you need to carb cycle to activate this cyclic metabolic switch. Having large enough protein boluses can spike insulin and signal growth pathways. And in case you're wondering, yes, it's true, a large enough insulin spike from protein can kick you out of ketosis. But because you're not topping off your liver glycogen stores, you typically return to ketosis quite quickly. When I last tested this on myself, and I have, in the 4-hour window after having whey protein mixed into my omelette, my ketones went from 2.5 millimoles to 0.3 millimoles, which is a much, much larger dip than if I have just the eggs alone. But by the 8-hour mark, my ketones were drifting back up: 1.5 millimole, 2 millimole, and so on. So you can carb cycle and use it as a tool to reap the rewards of cyclic metabolic switching if you want. Building carb cycling into your daily, weekly, or yearly routines could have benefits—metabolically, in terms of life flexibility, and otherwise. And you may also be able to hack this cyclic metabolic switch without carbs by having exposures to large enough boluses of protein. And there may be particular advantages to whey protein and dairy protein for this specific purpose. Although I'm not saying you should supplement whey protein, I think steak, eggs, fish are generally sufficient. But the biohackers out there will probably like that as well. So whether you use carbs strategically or lean on protein to mimic the same effects, the real key here, the real takeaway, is understanding how to cycle between stress and growth, repair and rebuild, just like your body was designed to do. And the best part, you don't need to guess about all of this. You can test, adapt, and discover what works best for you. That is the beauty of n=1 experimentation, especially in a world where personalization is power. This is all about you, how it works for you. And if this helped you rethink carbs or keto in a new way, please hit that subscribe button. It really helps. And if you found this video fun, check out other new videos—this masterclass on the microbiome video and a fun experiment I did with kale and chocolate to prove glycemic index and carbs don't reveal all. Your metabolism deserves more than just one-size-fits-all dietary advice. So stay curious and have a lovely day.