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Today we’re taking a peek under the hood and looking at some of the hormones involved in hunger and satiety, a.k.a. appetite hormones.
You might think of hunger as a gnawing feeling in your stomach and satiety as that feeling of fullness when you’ve eaten enough… or maybe too much. That’s how we experience the feelings we call hunger and satiety, true; but I’m talking today about the physiological drives to eat or stop eating that is driven by hormones.
Eating behavior is coordinated mostly in the brain by the hypothalamus, which acts as the control center for appetite. Hunger and satiety hormones deliver information from the body about how much energy you are taking in and whether you need more. The overarching goal here is energy homeostasis—balancing the energy coming in (via food) with the energy needed for the everyday functions of being alive.
When you have sufficient energy, your body is free to invest in growth, repair, and reproduction. Taking in more energy than you need can lead to excess fat storage and issues like hyperinsulinemia, insulin resistance, and metabolic syndrome. Energy deficits result in adaptations designed to conserve energy. In the long run, energy deficits might increase longevity, but they can also seriously undermine health and, for example, impair fertility.
Today I’m going to cover some of the key hormones that are involved in this delicate dance. This is by no means a complete list. Let me know in the comments if you have a burning desire to learn more about one of the hormones not covered here.
Ghrelin: the Hunger Hormone
Ghrelin is usually called “the hunger hormone” because it directly stimulates your drive to eat. In fact, it is the only known peripheral (outside the central nervous system) hormone that has this effect. Other peripheral appetite hormones all act to suppress hunger and reduce food intake. I always use the mnemonic “ghrelin gets your stomach growlin’” to keep it straight. I’m sure the endocrinologists in the crowd are groaning at that one.
Ghrelin is released primarily by cells in the stomach. Levels rise before meals and correlate with subjective feelings of hunger.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4443295/‘>2
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Should I Just Take a Ghrelin Blocker?
After it was discovered in 1999, ghrelin became a target for drug companies hoping to cash in by developing ghrelin inhibitors as a treatment for obesity. These efforts haven’t panned out for several reasons. First, ghrelin doesn’t stimulate overeating in normal physiological conditions. If you administer ghrelin to a human or lab rat, they will eat more, even to the point of becoming obese in the case of rodents. Normally, though, ghrelin levels don’t stay consistently high. They rise and fall to reflect energy balance. After you eat, ghrelin levels fall in proportion to the number of calories you ingest,https://pubmed.ncbi.nlm.nih.gov/15528308/‘>4
Ghrelin doesn’t stimulate eating just for the heck of it. Its main job seems to be preventing a negative energy balance. Obese individuals actually have chronically lower ghrelin than their lighter counterparts.https://www.ncbi.nlm.nih.gov/pubmed/15713718‘>6
Drug trials have also been stymied because ghrelin has wide-reaching effects on other aspects of health besides eating behavior. Some of the known activities of ghrelin include:https://www.ncbi.nlm.nih.gov/pmc/articles/4443295/‘>8 https://pubmed.ncbi.nlm.nih.gov/21785007/‘>10
In other words, suppressing ghrelin could be very costly indeed. You can focus on metabolic flexibility instead. More on that later.
Leptin: the Satiety Hormone
Leptin’s main job is to signal to the brain when you have sufficient energy available. It is produced by adipose (body fat) cells. More body fat means more circulating leptin. Leptin is also released after you eat. Carbohydrate intake prompts a particularly strong leptin response, protein less so, and fat probably only minimally.
Sometime leptin is characterized as ghrelin’s counterbalance. Whereas ghrelin is “the hunger hormone,” leptin is “the satiety hormone” (although in truth there are many, as you’ll see). If ghrelin tells the brain GO, leptin tells the brain STOP. I think that characterization isn’t exactly correct, though.
It seems to me that both leptin and ghrelin prevent negative energy balance. If you think about it, for most of human history, energy shortage—which, in the extreme, means starvation and death—was a much bigger problem than energy abundance. Consuming too much food is a thoroughly modern problem. We should be more strongly attuned to shortages.
Elevated ghrelin levels signal to the brain that it’s in danger of going into the red; low levels of leptin do the same. This explains why low leptin is particularly problematic from a health perspective. It’s associated with mood disturbances and infertility, among other issues.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4454393/‘>12 Low leptin and high ghrelin both put the body in an energy conservation state. Leptin decreases, and ghrelin increases, in response to dieting and weight loss.https://pubmed.ncbi.nlm.nih.gov/15181038/‘>14 In fact, leptin decreases more than you’d expect just based on how much body fat is lost while dieting. It’s one of the reasons hunger increases and can become unbearable when you’re on a diet. Presumably, these hormonal changes reflect the body’s efforts to defend its energy stores and restore homeostasis.
As with ghrelin, leptin’s functions extend well beyond appetite. Leptin has a hand in bone and cardiovascular health, insulin sensitivity, regulating thyroid hormones, insulin sensitivity, and glucose metabolism.
How to Increase Leptin Levels
It is possible to increase your leptin levels naturally, without medication. Here’s how to do it.
- Eat enough food. If you are severely depriving yourself, leptin will be suppressed and ghrelin will take over. That’s no way to live.
- Be sure to get healthy fats. Fats signal to your body that you’ve consumed enough calories, and they take longer to break down than carbs do. Some of my favorite sources of healthy fats include avocado oil, coconut butter, ghee, and macadamia nuts, among others.
- Restrict carbs for a time. Carbs need to be constantly replenished. Once you get past the “low-carb flu,” you’ll find that you have energy without constantly having to reach for snacks.
- Cycle in carbs. To optimize your leptin and ghrelin balance, you’ll want to achieve metabolic flexibility.
For more details on leptin and how to control it, read this article.
Neuropeptide Y, or NPY, is the most abundant peptide in the central nervous system. Found mostly in the hypothalamus, it acts as a hormone and neurotransmitter. It’s involved in a host of actions locally in the brain and throughout the body.
Most importantly for the present purposes, NPY is considered the most potent appetite-stimulating compound in the human body. Each of the other hormones discussed in this post regulates food intake by acting on NPY in the hypothalamus. For example, ghrelin increases NPY activity, while leptin suppresses it. Elevated NPY strongly increases the drive to eat, especially carbohydrates.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2668104/‘>16 It’s also expressed by fat cells, and research suggests that NPY promotes fat storage.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4830398/‘>18, and it has known neuroprotective effects. There are a number of reasons to think that NPY is the key that explains how caloric restriction extends lifespan.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2775646/‘>20 This may be one reason you don’t stay full for long after eating high-carb meals.
Cholecystokinin (CCK) was the first known satiety hormone. It is secreted in the gastrointestinal tract, especially in the small intestine. CCK rises quickly after eating, especially in response to fat and protein in the meal, and it triggers the initial release of PYY.
Like PYY, CCK is involved in various processes related to digestion, especially the digestion of fat. CCK also has interesting effects in the brain. The hippocampus contains a large concentration of CCK receptors, indicating that CCK plays an important role in learning and memory, though it’s still not well understood.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3005241‘>22
Abbreviated GLP-1, this hormone is secreted by the ileum and colon in response to nutrient intake. It acts as a satiety hormone, but researchers are especially interested in how it stimulates insulin secretion, improves insulin sensitivity, and helps regulate blood glucose.https://www.ncbi.nlm.nih.gov/pubmed/16478824‘>24 which can persist for decades after the procedure.https://pubmed.ncbi.nlm.nih.gov/25673670/‘>26
Let’s end with a familiar one. You probably know that the pancreas releases insulin after you eat, especially following carbohydrate intake. Insulin is sometimes called the “storage hormone” because one of its main jobs is to “unlock” adipose cells in order to store fat for future use. In healthy individuals, it also supports energy homeostasis by inhibiting lipolysis (fat burning) when there is sufficient glucose in the bloodstream to supply energy.
As with the other hormones discussed here, insulin also acts as an energy barometer for the brain. It crosses the blood-brain barrier, where it regulates NPY expression and suppresses appetite.
Can You Control Your Hunger Hormones?
It’s tempting to think that if we understood these hormones’ actions, we could learn to control hunger and eating behavior and solve all the problems related to overeating. As great as that sounds, we’re a long way off.
As you can see, energy homeostasis depends on the coordination of many different signaling pathways within the body. Too often, people try to hone in on the effects of just one variable—leptin or ghrelin, say—hoping to manipulate hunger and satiety. None of these hormones works in isolation, though. There is still a lot to learn about the physiological significance of each of these hormones individually, not to mention how they work in tandem with one another.
Furthermore, in human studies, hormone levels don’t consistently map on to our actual eating behavior as you’d expect. This might be because scientists haven’t uncovered the whole picture and don’t understand how all the various pieces work together to produce hunger. Probably, it’s also because we humans are complicated creatures who eat for a lot of reasons other than pure physiological hunger.
What does it all mean? I think it means don’t look for a magic pill that will allow you to control appetite and hunger. If you struggle with unwanted hunger, the first thing to ask is whether you are eating enough to meet your energy needs. Are sending your brain scarcity signals by not eating enough, or perhaps not often enough? That’s an easy fix.
Next, you can try manipulating your macros. One of the advantages of low-carb, high-fat (LCHF) diets over low-fat, high-carb (LFHC) diets is that appetite is managed much better on LCHF.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2775646/‘>28 If you go very low-carb, you might experience the appetite suppressing effects of ketosis as well.
Check in with your stress levels and sleep habits. Too much of the former and not enough of the latter can drive up appetite.
If none of those is the answer, it might be time to make an appointment with an endocrinologist or functional medicine practitioner who can help you dig deeper.
Hunger isn’t something to be avoided, though. Hunger and satiety are normal physiological signals. Their job is to keep us alive and thriving. Rather than trying to manipulate or hack hunger, it’s useful to understand where it comes from so that we can respond appropriately and have the energy we need to be active and healthy.
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Intermittent fasting has taken the world by storm. No longer is it the province of fitness freaks. No longer do you get weird looks because you skipped the break room donuts. Now you’ve got grandmothers trying it and doctors recommending it. It’s here, the benefits are legion, and you’re interested. But how should you do it? Are there different types of intermittent fasting? Are there different benefits associated with the various flavors of IF?
Thinking about fasting, reading about fasting, and reciting the benefits of fasting are all pointless if you don’t know how to go about doing it.
First, the most fundamental concept central to all the flavors of intermittent fasting is not eating. Skipping meals, skipping entire days of meals, letting yourself get a little hungry. There’s no getting around that. It will happen. let’s go over the different variations of fasting. I’ll give a quick rundown. Each involves not eating for a period of time, unsurprisingly.
A couple other rules that apply to all the given methods:
- Sleeping hours (provided you don’t sleep-eat) count as fasting hours.
- Eat well regardless. While some fasting plans tout their adherents’ ability to eat crappy food and still lose weight, I’m not interested in fasting solely as a weight loss method. Keep your food Primal as possible.
Okay, on to the variations.
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12:12, 16:8, 18:6, or 20:4 Intermittent Fasting
As the names suggest, these breakdowns of intermittent fasting involves fasting for either 12, 16, 18, or 20 hours and taking in all of your food for the day over the remaining window of hours.
How to find out which fasting length is the the best one for you? There’s only one way. You have to experiment.
You can start with a 12:12 intermittent fast, which comes with the benefits of intermittent fasting and is easy to do for most people. You stop eating a couple of hours before bedtime, and delay breakfast a couple of hours after waking. If that works well, extend your fasting period the next day, and repeat until you find the eating and fasting pattern that feels good.
Lots of diets have added more detail to the intermittent fasting model, but bare-bones intermittent fasting is simply a shorter feeding period.
If you’ve heard of Leangains, Martin Berkhan’s incredibly popular fasting protocol, you’ve heard of 16:8 intermittent fasting. How does it work?
- A daily 16 hour fast during which you eat nothing containing calories. Coffee, tea, and other non-caloric fluids are fine. Some people get away with a little cream in their drink.
- A daily 8 hour eating window.
- Three days of weight training, ideally performed at the tail end of the fasting period. To improve performance and muscle protein synthesis, you have the option of consuming 10 grams of branched chain amino acids 10 minutes before the workout.
- Always eat high protein.
- On training days, eat more carbs and less fat.
- On rest days, eat more fat, fewer carbs, and slightly reduce calories.
- Most people begin their fast after dinner (say, 9 PM), workout in the afternoon (at around 12 PM), and break their fast immediately post-workout (at around 1 PM), but you can use any schedule you prefer as long as you hit the 16 hours of fasting.
- Your post-workout meal should have about 50% of your day’s caloric allotment (a real feast).
Who should try it?
12 or 16 hours isn’t a long time to wait for a meal, which makes intermittent fasting a great model for anyone who wants to experiment with fasting. One benefit of fasting this way is that it’s not that long a fast – you eat every day. It is totally doable. Whether you add the detailed lifting days and carb days is up to you.
Women may have better success with slightly shorter fasting windows—12-14 hours long instead of 16 hours. To understand why, check out my post on women and fasting.
People with steady eating schedules will have more success than people with erratic schedules. A huge benefit of intermittent fasting is the hormonal entrainment induced by regular feeding times. Once you get locked into your routine, your hunger hormones will adapt to the schedule, and the fasting should get easier, or even effortless. For this reason, it’s a good idea to get a feeding schedule and stick to it.
OMAD — One Meal a Day
Ori Hofmekler’s plan is based on the feast-and-fast concept:
- Eat one meal a day, at night, and make it a big one. A real feast. You have three or four hours to eat until full. So it’s basically 20/4 hours.
- You can occasionally snack on low-calorie raw fruit and vegetables during the day, but try to limit protein as much as possible until the feast.
- Exercise during the day, in a fasted state.
Who should try it?
People who have trouble sticking to a stricter fast will do better on the OMAD, as it allows light eating during the time leading up to the feast, but I wonder if you’d be squandering some of the benefits by eating.
Alternate Day Fasting
Researchers often use this method in lab studies:
- Eat normally one day (last meal at, say, 9 PM Monday).
- Don’t eat the next day.
- Resume eating the day after that (at, say, 9 AM Wednesday).
- It works out to a 36-ish hour fast, although there’s plenty of wiggle room. You could eat at 10 PM Monday and break the fast at 6 AM Wednesday for a “mere” 32 hour fast.
Who should try it?
People who have no trouble going to bed hungry. With other intermittent fasting methods, you can always manage to get to bed with a full belly; with ADF, you will be going to bed on an empty stomach several times a week. That can be tough.
That said, the therapeutic benefits to serious conditions will most likely really be pronounced with this way of fasting. The casual 20-something Primal eater who lifts heavy things and enjoys going out with friends? Probably not ideal. The older Primal eater interested in generating some autophagy and maybe staving off neurodegeneration? It might just work out. And while I’m not able to tell a cancer patient undergoing chemotherapy what to do, I’d guess that the longer fasts will be more beneficial in that regard, too.
Eat Stop Eat
Put together by Brad Pilon, Eat Stop Eat is really basic:
- Once or twice a week, don’t eat for 24 hours.
- Start your fast in the morning, at lunch, or at dinner. It doesn’t matter as long as you don’t eat for 24 hours.
- Break your fast with a “normal-sized meal.” Don’t try to make up for the lost calories by feasting.
- Exercise regularly.
Who should try it?
People interesting in fasting for the therapeutic benefits (cancer protection, autophagy, life extension, etc.) would probably get a lot out of this method, as opposed to people interested in the body composition benefits.
Going a full 24 hours without food is a much tougher slog than going for 16 hours. In my experience, going lower-carb and higher-fat makes longer fasts easier, so I’d have to say a low-carb Primal eater would do better than most.
But my personal favorite way of implementing fasting?
WHEN — When Hunger Ensues Naturally
I’m not going to put any bullet points here, because none are required. Instead, I’ll give a few scenarios:
I wake up bright and early on a Saturday morning. It’s about 65 degrees, the sun’s out, my dog is walking around with the leash in his mouth, and Red Rock Canyon is kinda calling my name. I’ve got my coffee already and I’m actually not all that hungry from dinner. You know what? I’ll go on that hike, skip breakfast, and really work up an appetite for lunch. Or not. If I’m hungry afterwards, I’ll eat. It’s a fast, but not really.
I hit the gym, put in a light workout, then swing by the beach for some sand sprints. I’m toast by the end and have to stagger back to my car, but I’m not hungry. Even when I get home and smell the grilled salmon, I have no desire for it. I might eat later that night, but only if my appetite returns. I’m fasting post-workout only because it doesn’t occur to me to eat, not because I’m following a plan.
I’m away on business, stuck on a layover that’s turned into a delay that’s turned into an overnighter. The only food available is a Kudos candy bar – I mean, healthy granola bar (they seriously still make these?) from the mini fridge, a greasy pizza joint on the corner across the street from the hotel, a Chinese takeout place next to the pizza joint, and a slew of fast food restaurants some ways down the road. It’s late, I’m tired, I had a Big Ass Salad before I left for LAX… you know what? I’m just going to skip the “meal.” I’ll figure out something at the airport in the morning (20 hour fast) or once I land (24 hour fast). And I’ll be okay either way.
That’s eating When Hunger Ensues Naturally.
This is the most natural, most effortless way of “fasting,” at least for me, because it allows a person to eat intuitively. Although most people will eventually acclimate to more regimented fasting schedules, and many may even need and thrive with that structure, I prefer a more fractal, loose, random pattern of “missing” (in quotations because I don’t feel like I’m missing anything, and that’s the whole point!) meals. I have no data on whether it’s as effective or more effective than the more popular methods, but I do know that I’ll often fast for 16 hours and eat for eight, or skip an entire day of eating, or sometimes (but very, very rarely) even approach a full 30 hours, and it seems likely that this random pattern of eating characterized the eating “schedules” of our ancestors.
In short, we’re all doing the same thing, chasing the same goals. We’re all skipping meals, reducing calories, staying active, and all the while we’re doing this without feeling miserable and restricted. It just so happens that because we’re efficient Primal fat-burning beasts, switching over to burning our own body fat reserves for energy during a fast is a natural, seamless transition. We often don’t even notice it. There’s no effort involved.
That’s the key: lack of stress. If any or all of these fasting methods stress you out, make you irritable, kill your performance, make you feel restricted, or reduce your ability to enjoy life, and these feelings persist beyond the first five fasts you attempt (when some adaptation difficulties are totally expected), you shouldn’t employ them. You should shelve fasting for a while and come back to it later, or never. It’s not a “requirement” or anything. It’s just a tool you can wield if your situation warrants it. In fact, this is the perfect opportunity to conduct an informal experiment of one. Try one style for a week or two, then throw in a a different style once or twice a week for a bit, then try another method. Compare and contrast. How did you feel? How did you perform at work, at home, and in the gym? Take some waist measurements perhaps, or analyze your favorite barometer of body composition to see how the different fasting methods worked – or didn’t work – for you.
Now, I’d like to hear from you. What’s your favorite fasting method? Do you have one, or you just kinda go with the flow? Be sure to review the previous installments below and if you have any questions about any of the stuff I’ve covered in this series, leave them in the comment section and I’ll try to get them answered for you next week. Thanks for reading!
The post How to Intermittent Fast and Which Type of Fasting Is Right For You appeared first on Mark’s Daily Apple.
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At this point, intermittent fasting isn’t a new concept, nor is it a difficult one. You take in all of your calories for the day within a limited window of time, and the rest of the day, you stick with water, maybe a cup of coffee, or tea in the morning if you feel so inclined. The idea is that giving your body a period of time “off” from digesting food allows your cells to heal and renew in other ways.
A Practice Born Because Calorie Restriction is Unpleasant
Intermittent fasting became popular because calorie restriction was found to contribute to healthy aging. A few mouse and worm studies seem to show that drastic reductions in food intake over a long period of time could prolong your life.
The research is compelling, but I’m not convinced actively restricting your calorie intake through sheer will is the true path to enjoyable longevity. I don’t want to be thin, frail, distractible, or preoccupied with food. I’d rather be vibrant and full of zest. I want to eat big strapping meals of steak and veggies smothered in butter without worrying about calories. I want to maintain muscle mass and have enough energy to go on long hikes and have the legs to still leap for high passes (over the young guys) at the end of Ultimate games. And as I appreciate the neuroprotective and autophagy-promoting qualities of calorie restriction, I’d rather not expend the mental energy and fortitude required to maintain such a regimen day-in and day-out.
Intermittent fasting is the workaround. Pushing off breakfast for a few hours gives me all of the benefits of calorie restriction, without all the misery.
Fasting is the way to have your cake and eat it too. Beyond the already proven benefits of a Primal Blueprint low-carb lifestyle, fasting once in a while seems to offer many of the same benefits of calorie restriction – you know, stuff like increased longevity, neuroprotection, increased insulin sensitivity, stronger resistance to stress, some cool effects on endogenous hormone production, increased mental clarity, plus more – but without the active, agonizing restriction.
You just eat Primally, focusing on meat and vegetables with plenty of animal fat, and skip meals on occasion. A sixteen-hour fast is on the low-but-still-effective end, or you could opt for longer, more intermittent fasts – say, a full twenty-four hours once or twice a week. Women may need to time fasts a little differently than men. More on that here.
When you’re done with the fast, eat as much as you want (which usually isn’t an issue, once you’re keto-adapted). It essentially turns into “eat when you’re hungry,” because let’s face it: eating the types of foods we evolved eating induces powerful satiety and makes eating the right amount of food a subconscious act. Fasting becomes a whole lot easier (and intuitive) when you’ve got your food quality dialed in. And I’ll come back to that little caveat at the end here.
“Fasting” was the top search term for MDA last week, and I hadn’t done a big post on it in a while, so I thought I’d do a comprehensive rundown of all the benefits (some conclusive, others prospective) you can expect to obtain from IF.
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Intermittent Fasting and Longevity
Everyone wants to live longer, but I find longevity pointless if you’re not enjoying yourself. Otherwise, life becomes dreary.
The popular c. elegans worm enjoys increased longevity with both twenty-four and forty-eight hour IFs via signaling through a gene that we all have.full PDF) from the 1940s found that varying amounts of twenty-four hour IFs (every other day, every fourth day, every eighth day, etc) prolonged the lifespan of rats without retarding or stunting the growth (as occurred with calorie restricting them). Female rats responded best to every eight day fasts, while males responded best to every other day fasts.
Reductions in brain insulin signaling have been shown to increase lifespan in animals, either by calorie restricting or actively knocking out brain insulin receptors.http://www.ncbi.nlm.nih.gov/pubmed/21244426‘>3
Going in and pharmaceutically manhandling your cholesterol synthesizing equipment is one thing; eating real food and exercising, resulting in possible alterations to your lipid profile, is another. We don’t set out to force your blood lipids into submission, but lifestyle changes that happen to change them for “the better” are usually a good thing. Fasting brings potent changes to blood lipids in an “organic” way – you’re just letting your machinery do its thing on its own – and this is probably a very good thing.
Intermittent fasting is as effective or even more effective than calorie restriction in improving metabolic syndrome markers in overweight women, and it’s a whole lot easier to stick with.http://www.ncbi.nlm.nih.gov/pubmed/20300080‘>5
I discussed this last week, but it can’t hurt to mention that short-term alternate day fasting wrought improvements in LDL particle size and distribution in obese adults.http://www.ncbi.nlm.nih.gov/pubmed/20815899‘>7
Heck, intermittent fasting even helped cocaine addicts stick to their treatment and rehab program.http://www.ncbi.nlm.nih.gov/pubmed/18184721‘>9 In fact, here’s a review of most of the animal anti-cancer evidence.http://www.ncbi.nlm.nih.gov/pubmed/19135806‘>11 This is refreshing news. A preliminary studyhttp://ajpregu.physiology.org/content/296/1/R29.full‘>13 I’ve found this to be the case for me. If the body “needs” food right after a workout, why would hunger be blunted? This is why I tend to hold off on the eating post-workout. Every little bit helps, especially as you age.
Fasting doesn’t cause your brain tissue to waste away, contrary to what some people will tell you. It’s actually good for brain health. Any dietary restriction tends to increase neuronal plasticity and promote neurogenesis, but it was IF that had the greatest effect (with the fewest downsides).http://onlinelibrary.wiley.com/doi/10.1046/j.1471-4159.2003.01586.x/full‘>15 That is, mice who ate larger meals more infrequently saw greater increases in brain and overall bodily health. Still another study found that IF was beneficial for peripheral nerve function in mice by promoting the maintenance of the neuronal pathways responsible for locomotor performance.http://www.ncbi.nlm.nih.gov/pubmed/21106691‘>17), which is the process by which cells recycle waste material, eliminate or downregulate wasteful processes, and repair themselves. Why is autophagy so important? It’s required to maintain muscle masshttp://www.ncbi.nlm.nih.gov/pubmed/20104028‘>19 It reduces the negative effects of aginghttp://www.ncbi.nlm.nih.gov/pubmed/17934054‘>21
Without the autophagy that fasting provides, you would get very few of the benefits. Fasting even increases neuronal autophagy,http://www.ncbi.nlm.nih.gov/pubmed/21051570‘>23 (which mean better performance down the line), improved muscle protein synthesis,http://www.ncbi.nlm.nih.gov/pubmed/20187284‘>25 (you’ll earn your meal and make more muscle out of it if you train on an empty stomach). Studies on Muslim athletes during Ramadan show no effect on performance while fasting,http://www.ncbi.nlm.nih.gov/pubmed/19787180‘>27 in those who exercise and fast rather than just fast. When you train in a fasted state, glycogen breakdown is blunted28 and more fat is burned, leaving you more glycolytic energy in the tank for when you really need it and less body fat. Those are just a sampling of the benefits to fasted training; there are dozens more.
Mental Well-being and Clarity
A lot of health influencers will tell you that failure to eat something every few hours will cause mental fog and sluggishness, so keep a banana or a granola bar on your person at all times. Of course, this is all based on an assumption that we need to supply exogenous carbs on a regular basis to properly fuel the brain. This notion that fasting is only the province of anorexics or “caveman” has kept many people from experiencing the vast array of benefits.
I maintain that one’s comfort in handling intermittent fasting effortlessly does increase dramatically when you’ve reprogrammed those cells (and genes) to predispose your body to derive most of your day-to-day energy from fat, as opposed to constantly dipping into glycogen stores (as happens when we rely so much on refeeding carbs every few hours).
Overall, fasting just seems right. It’s like a reset button for your entire body, presumably across a large spectrum of maladies and dysfunctions. It puts your body into repair mode – at the cellular level – and it can restore normal hormonal function in the obese or overweight. Now, you don’t have to fast, but it’s definitely something to consider.
Have you tried intermittent fasting yet? Let me know how intermittent fasting has worked – or hasn’t – with your lifestyle in the comment section!
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Fasting is a great tool for so many things. You can use it to regulate food intake and lose body fat. Fasting can help you shift body composition, normalize your appetite, and gain control over your relationship to food. Many people report cognitive enhancements from fasting, and it’s a surefire way to speed up the transition into ketosis and full-blown fat adaptation. There’s strong evidence that we look, feel, and perform best skipping the occasional meal—that it’s the evolutionary norm for humans not to have constant, unceasing access to food. After all, we didn’t always have 24 hour grocery stores and fast food restaurants. But what about fasting with a cold?
And what about intermittent fasting and the immune system? Should you fast at all when you’re sick? What about fasting with the flu? Or how about bacterial infections—can fasting help with those? These are actually some of the most common questions I receive. Because intermittent fasting seems to help with so many other conditions, it makes sense to wonder about its relationship to the immune response.
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There are two main types of infections that most people worry over: viral infections and bacterial infections.
- Viral infections include influenza (flu), the common cold, viral gastroenteritis, and the various coronaviruses. There are also things like measles, chickenpox, and viral meningitis, but most people aren’t very worried about catching those these days.
- Bacterial infections include pneumonia (most pneumonias are bacterial in origin, though some can be viral), bacterial gastroenteritis, food poisoning, and bacterial sinus infections.
Fasting With a Cold – Viral Infections
In general, fasting doesn’t look like a great idea if you’re dealing with a viral infection like the flu or common cold. Why?
Studies on Fasting and Viruses
Animal studies show that mice who fast have a worse response to subsequent viral infections. In one paper, mice were either fasted every other day or placed a normal diet, then exposed to a “viral mimetic” (a type of chemical that replicates a viral infection). The mice who fasted ended up with higher cortisol, a more inflammatory immune response, more severe symptoms, and acted sicker than the mice who ate.1
Another mouse study found that in animals exposed to an infectious virus, a fat-based (fasting) metabolism was detrimental to survival and a glucose-based (fed) metabolism was beneficial.2
Viruses Deplete Nutrients
Viruses are much smaller than bacteria and generally cause trouble by hijacking cells and using your body’s machinery to replicate. To do so, they often steal nutrients from the host. One example is selenium, a crucial nutrient for viral replication. Studies show that viral infections can induce selenium deficiencies and that correcting those deficiencies by, well, eating selenium-rich foods can improve the outcome of infections.3
Most viruses will deplete nutrients and you need to eat to replenish them.
Fasting Inhibits MTOR, Which is Good and Bad
Blocking MTOR (mammalian target of rapamycin) through fasting reduces expression of another major immune component: the interferon-inducible transmembrane protein (IFITM). 4 Think of the IFITM as a barrier preventing some viruses from gaining a foothold in your body, including influenza, Ebola, SARS, MERS, Marburg, Dengue, and hepatitis C. These are IFITM-sensitive viruses, but there are also IFITM-resistant viruses, like the common cold.
In fact, one study found that increasing IFITM levels increased vulnerability to infection by the common cold virus.5 Using fasting to reduce mTOR and lower IFITM expression could conceivably increase resistance to the common cold while increasing vulnerability to flu (and the others like Ebola and so on). Double edged-blade.
Or perhaps it’s triple-edged.
Part of dealing with an infection is learning from it. Our immune systems have to seroconvert antibodies so that when we encounter the infection again, our immune system is better equipped to head it off at the pass. This is the concept behind vaccination—a measured dose of the infective agent that trains our immune system to defeat the real thing in the future. As it turns out, inhibiting mTOR through fasting could affect our ability to seroconvert antibodies in response to viral infections.
In studies of older adults, higher levels of mTOR predict lower rates of seroconversion, and giving them an mTOR inhibitor improves seroconversion after a flu vaccine. If fasting reduces mTOR (and it does), it should in theory improve the antibody response to a vaccine or infection.
Weird, right? Fasting reduces mTOR, which could impair your short term response to an infectious insult (or improve it if it’s the common cold) while improving your long term response. You might still get sick but at least your chances of developing longterm immunity should increase.
Fasting With a Cold – Bacterial Infections
In general, fasting looks like a better idea when you’re sick with a bacterial infection.
Research on Fasting and Bacteria
Animal models of bacterial infections find that mice tolerate them much better in a fasted, ketogenic state. In fact, the ketone body beta-hydroxybutyrate is able to directly nullify some of the oxidative stress associated with bacterial infections;6 while “ketogenesis was required for survival in bacterial inflammation, it was dispensable in the case of viral inflammation.”
Bacterial Infections Reduce Appetite Naturally
One indicator is that your appetite often falls off a cliff when you have a bacterial infection. The last you want to do when you’re dealing a bout of food poisoning is eat. This doesn’t usually happen with viral infections, and I believe that’s important. In those “base” states of survival, what you crave is a good indicator of what you need.
Fasting Improves Phagocytosis (and Sugar Inhibits It)
A key component of the innate immune system’s ability to deal with bacterial infections is phagocytosis: When a class of immune cells called neutrophils surrounds, engulfs, and destroys individual bacteria. The phagocytic index describes the number of bacterial cells a neutrophil is able to engulf and nullify in a set time. Generally speaking, higher phagocytic activity means you have a better response to bacterial infections.
Luckily, we know pretty well how to increase and decrease phagocytic activity in people. To decrease phagocytic activity (make neutrophils worse at engulfing and destroying pathogenic bacterial cells), you simply feed a person sugar.7 It could be orange juice, honey, sucrose, fructose, or glucose—any simple source of sugars—and if you give 100 grams to a person, their phagocytic capacity drops for at least five hours. Give the person nothing—let them fast—and their phagocytic capacity climbs. Even at 5 hours after eating the sugar, the phagocytosis still hasn’t caught up to that of the fasting person.
Later studies confirm that low fasting blood glucose is a strong predictor of a strong neutrophil:leukocyte ratio8. Lower glucose, more neutrophils available to take on bacterial pathogens. Fasting is a reliable way to drop your blood glucose.
Phagocytosis doesn’t work so well against viral infections because a virus sequesters itself in the host’s cells. Neutrophils can’t engulf and kill the host cells; that’d just be counterproductive and probably quite dangerous. However, there’s evidence both ways: that neutrophils can enhance the immune response to viral infections but they can also exacerbate the damage done to host tissues. It isn’t clear what role they play so I’d advise against consciously manipulating them through fasting.
Intermittent Fasting While Sick: Making Sense of it All
There are no easy, straightforward rules governing the optimal fasting strategy for infections, whether viral or bacterial. Each virus is different. Every bacteria is separate. Nothing in biology is simple. What we do know:
- If fasting stresses you out, it will be bad for your immunity. Cortisol depresses the immune system.
- If fasting ruins your sleep, it will be bad for your immunity. Proper sleep is absolutely essential for an optimal immune response.
- If you’re hungry, let that be your guide. Eat. Don’t force the issue.
- If you’re not hungry, skip the meal. Again, let your body’s signals be your guide.
- When faced with an immune insult, or if something’s “going around,” cut back on the fasting or at least keep it shorter than normal. 16 hours instead of 30. 20 instead of 48.
- Realize that fasting is not a panacea. It’s not the answer to everything.
- Understand that bacterial and viral infections often tag along with each other. A virus will weaken the host enough to allow bacterial pathogens to flourish. You’ll often be dealing with both at once. I’d imagine that something that allows you to stay fed while also enjoying a fat-based metabolism—like a lazy ketogenic diet—could work well here.
- Fasting can prune damaged parts of your immune system and replace them with renewed components.9 This is good for long term immune health, but if an infectious agent happens to catch you in the middle of an extended fast while you’re doing the pruning, your risk of infection probably goes up. There’s always a give and a take.
There are no magic bullets, but it cuts both ways. You are resilient. While most of the humans throughout history didn’t make it through hundreds of thousands of years of death, destruction, famine, and disease, your gene line did. So don’t think you have to pick one or the other—fasting or feeding—in response to illness. Go with what feels best, don’t get dogmatic, and just take it easy.
What’s your go-to feeding strategy for dealing with sickness? Do you differentiate between viral and bacterial illnesses? Let me know down below!
The post Fasting with a Cold: How Does Fasting Impact Viral and Bacterial Infections appeared first on Mark’s Daily Apple.
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