Keto and Intermittent Fasting: A Beginner’s Guide
The ketogenic diet and intermittent fasting have more in common than you may believe. When combining the two practices, they may be able to synergistically work together toward common goals of fat loss and improved metabolic health.
Despite the differences in the diets, they have two big similarities: both increase ketone production and can also burn the body’s fat stores. In tandem, they may help to expedite your weight loss goals.
But where do they fit in together? Practicers of intermittent fasting are using the technique to improve weight loss, insulin sensitivity and other health biomarkers.1 The keto diet targets many of the same goals, like helping to reshape metabolism and improve body composition.
If you’re trying to decide between one or the other, why not try both at the same time? Let’s look at some of the benefits of each and how they can work together to encourage a healthy lifestyle.
The ketogenic diet has been around for several decades, but has gained increasing popularity over the last several years. While some diets encourage consumption of fewer calories, the ketogenic diet is based on low carbohydrate intake rather than focusing on calorie intake. Keto can be described as a low-carb, high-fat diet which induces production of ketones from fat, leading to a state of ketosis: the presence of ketones in the blood at greater than 0.5mM. This is much different than the traditional western high-carb diet.
Our bodies are biologically programed to run on a mix of carbohydrate and fat depending on what’s available.
Dietary carbohydrate gets taken up and used as energy via blood glucose (blood sugar), or it is stored as a molecule called glycogen in the liver. Glycogen is slowly released between meals to keep blood glucose energy levels stable. Once carbs are removed from the equation, the body eventually learns to use alternative fuel sources for energy as glycogen stores are depleted.
There are two ways to induce ketosis. The first, called endogenous ketosis, is when ketosis is triggered through diet or fasting. In this case, the body is making its own ketones, meaning the body is ketogenic. It can take days of fasting or weeks of dieting to achieve endogenous ketosis.
The ketogenic diet is often misconstrued by the masses as a high-fat diet that features bacon, butter, and oil as its main components. While you may choose to indulge in these particular types of foods, the main attribute of keto is that it requires dieters to consume little to no net carbs. If you’re on keto, you should aim for a carb intake around 50g per day—a really low amount.
The second was to induce ketosis is called exogenous ketosis. This means that ketones are introduced to the body from an external source, from ketone supplements. This body is still in ketosis (because its blood ketone levels are elevated), but it’s not ketogenic (because the body isn’t producing its own ketones).
Increasing Ketone Levels
Several supplements exist on the market to raise blood ketones through exogenous means. The goal with these types of products is to spur a faster, deeper ketosis without the need to diet or fast.
There are medium chain triglycerides, or MCT oils, which are a special type of fat found naturally in coconut oil, palm kernel oil, and butterfat. They do not contain ketones, instead possessing a fat that’s readily converted to ketones. While there are many MCTs on the market, it’s best to find one without artificial ingredients, and one that’s low-carb (to help you maintain ketosis).
Then there are ketone salts. Ketone levels rise marginally after using salts, from about 0.6mM – 1mm. And often, a high mineral intake is necessary to raise ketone levels, leading to GI issues and concern around the safety of long term high salt intake.
The choice between relying on exogenous or endogenous ketosis depends on your health and performance goals.
Although endogenous ketosis from the keto diet is a great recipe for weight loss, there are several other potential benefits of ketosis as well. Other benefits include:
- Improved mental focus
- Better satiation
- Better cholesterol readings
Interestingly, the body and brain can both use ketones as energy (like glucose). That’s why there are subjective reports of increased focus and less brain fog from keto dieters and people using exogenous ketones.
These are also some of the subjective feelings reported by intermittent fasters, likely due to the increased ketone levels from carb-depletion.
Intermittent fasting is exactly what it sounds like: not eating for a certain period of time. On the surface, cutting out meals for a set period of time seems beautifully simple. But new research is advancing our knowledge of the best timing for meals and the helpful changes to our biology that occur during fasting.
Science Behind Intermittent Fasting
When you consume carbohydrates, the pancreas begins to release insulin-triggering carb uptake and storage.
Virtually every meal we eat triggers a metabolic response in our body.
Carbohydrates in our food (and to a lesser extent, protein) trigger the release of the hormone. The insulin, in turn, tells the body to store any excess energy as glycogen or as fat for later use. Some of the fat is stored in the liver, but most of it becomes fat deposits in the body. Insulin also switches off the processes that release fat from fat deposits, meaning that fat is going into storage and not used as fuel.
When you practice intermittent fasting on the other hand, energy intake is lower; insulin levels begin to fall and fat burning increases.
By increasing the amount of time the body is in a fasted state, there will be more time for the body to tap into stored energy. Across evolution, most species would regularly enter a fasted state. Predators tend to eat larger portions at one given time and may not consume food for several days. There is nothing wrong with occasionally fasting for longer periods of time, and it actually has several health benefits (but of course, consult your doctor before doing this).
Simply put, restricting the amount of calories you consume will put the body into a fasted state.
There is a common belief that skipping a meal is bad for your metabolism or overall health. The truth is, we see more data support the idea of restricted eating. The three-meals-a-day convention has been standard in American diets for decades. But obesity has increased. Diabetes and pre-diabetes have also increased.
Obviously, something isn’t working.
In studies performed on animals, those in a fasted state had longer lifespans compared to those that did not fast. It seems the benefits of fasting can not only be seen short term, but over the course of a lifetime as well.
An interesting diet that mimics fasting is called the Prolon Diet. The idea is to really decrease insulin release while still providing nutrients. It’s a low-protein, low-carbohydrate, high-fat diet with calorie intake ranging from 770 – 1,100 calories per day. Studies have shown a fast-mimicking diet can improve biomarkers for ageing, diabetes and cardiovascular disease.15,16
Advantages of Intermittent Fasting
Besides benefits for body composition or weight loss, there are a number of advantages that accompany intermittent fasting.
- Easier to manage than traditional dieting: Preparing a single (or a couple, depending on your feeding window) meals per day is logistically easier than preparing several meals from a time management standpoint. Plus, intermittent fasting saves you the headache of rigorous meal prepping, or finding foods that comply with a specific diet
- Decrease in fat mass: Individuals who practiced intermittent fasting showed a decrease in fat mass while maintaining muscle mass and strength.
- Longevity: Studies have shown that populations who fast on a regular basis can appear to have increased longevity. A study was performed on rats that ate only once per day and it found that compared to other groups, those rats had a longer lifespan regardless of the amount of food consumed.
- Improved health and metabolism: Metabolic health may be improved with fasting by way of circadian biology, the gut microbiome, and modifiable lifestyle behaviors, such as sleep. Research has shown that intermittent fasting may help improve blood lipids, glycemic control, control insulin levels, decrease blood pressure, and decrease inflammation.
- Boost brain health: Fasting robustly is a strong trigger for neurogenesis and beta-hydroxybutyrate (or BHB, one of the three ketone bodies), which can trigger the release of brain growth factors.
- Speed up endurance adaptation: Fasting promotes pathways involved in fat metabolism, which may help endurance performance—for example, growth of new mitochondria.
- Reduced risk of diabetes: Through intermittent fasting, reduced insulin resistance can help those with type 2 diabetes lower blood glucose levels and improve blood sugar. Intermittent fasting can also decrease inflammation.
- Late dinners interfere with our circadian clocks (circadian rhythms), and everything gets out of synchronisation, especially sleep and recovery. It is recommended to eat 4 hours before bed to maintain healthy sleep.
Unlike many other diets, intermittent fasting deals not with what you eat, but rather when you eat.
This dietary convention is all about timing rather than eating certain varieties of food. When you choose to partake in intermittent fasting, you are eating within a certain window of time. By forcing the body to stay in a fasted state for a longer period of time, the body will turn to fat stores to use for energy (since it doesn’t have carbs).
The body stores way more fat than carbohydrates, and will eventually learn to tap into those fat stores for energy. Simply choosing to eat in certain windows of time can have a positive long term effect on your body composition and overall health. Your body fat can decrease as well.
There are different variations of intermittent fasting, so it is not a one size fits all type of practice.
The most common method of intermittent fasting is choosing a certain time for food intake (sometimes called “feeding hours”).
You may choose to eat over a four, six, or eight-hour window. This means you only eat during this particular timeframe, and the remaining hours of the day are spent fasting.
Some people fast for 16-hour periods, eating only between the hours of 12pm – 8pm, and not eating outside of that timeframe. Some do a 24-hour fast every week. Some of the most dedicated intermittent fasters will do a 36-hour fast every week.
Here are a couple of ways to work eating windows and fasting windows into your normal eating schedule:
- Four-hour window: First meal of the day at 3:00pm and the last meal of the day is consumed by 7:00pm
- Six-hour window: First meal of the day at 2:00pm and the last meal of the day is eaten by 8:00pm
- Eight-hour window: First meal of the day is at 12:00pm and the last meal is enjoyed by 8:00pm
Some people may take their fasts a step further and may choose to only eat once per day. This becomes a 24-hour (or near 24-hour) fast. You should use your sleeping hours to your advantage, almost like free fasting time (unless you’re sleep-eating). A common way to do this is to consume your last meal at 8pm, then wait to eat until 8pm the following day. Often, this is referred to as one-meal-a-day or OMAD fasting.
Regardless of the eating window, the total caloric intake for the day should remain the same.
Some may argue that there are advantages to having a longer period of fasting, but your choice of eating window is entirely up to you. The best fasting protocol is the one that you stick to. Find a way to work this into your everyday schedule for the best, most consistent results.
It’s supremely important to stay hydrated while you fast. Though, some fasters consume only water during both shorter and longer fasts. Another popular beverage choice during a fast is black coffee, but this can be seen as a crutch because it reduces appetite.
Alternate day fasting (ADF) is a form of intermittent fasting, but takes a bit more of an extreme approach: no food for 24 hours every other day. However, alternate schedules allow for 500 calories to be consumed on fasting days, which have shown to be easier to stick with.
No matter the protocol, ADF diets have shown positive results for weight loss.Interestingly, studies in animals showed that ADF may modulate risk factors for chronic disease, and can help retain muscle mass in humans (something of a concern with fasting).
Longer water fasts can last anywhere from 36 hours to several days.
Studies in both animals and humans have suggested water fasts can have health benefits.
Most cited benefits include stimulating autophagy and reducing the risk for chronic disease. With these longer fasts—and really, fasting in general—always consult your doctor.
Bringing Keto and Intermittent Fasting Together
The ketogenic diet and intermittent fasting tap into similar metabolic pathways, and so they should be able to work together synergistically
The obvious juxtaposition: a keto is a form of long-term dieting with a specific macronutrient target, that therefore restricts what types of foods you eat. Intermittent fasting occurs in the short term and restricts only when you can eat—with no macro-rules in the eating windows.
However, as explored earlier with low-protein, high-fat, low-carb diets, focusing on keto during the eating windows may prolong the helpful metabolic pathways invoked by fasting. An interesting application is Peter Attia’s “Nothingburger,” in which he conducted a week-long fast between two weeks of nutritional ketosis.
Both dieting methods can work toward the same goal: use fat stores for energy and put the body in a state of ketosis. Both deplete the body of glucose. If you’re intermittent fasting, it may be able to put you into a state of ketosis more quickly than dieting alone.
Very few studies look at the keto and intermittent fasting together. However, as our understanding of the biology supporting both deepens, we can see clear synergies; this illustrates the two together can be a good combination.
Starting a Keto and Intermittent Fasting Hybrid Diet
Although starting a hybrid type of diet sounds complicated, it can be simplified very easily. Here’s a look at what a single day might look like if you’re on keto and intermittent fasting. Follow these steps for an example keto meal plan that could be employed while intermittent fasting.
6:00am: Wake up, drink water and/or black coffee.
9:00am: Drink another cup of coffee if you’re feeling especially hungry or low on energy.
12:00pm: Begin eating window with eight ounces of chicken breast and a salad with olive oil dressing and feta cheese. Other lunch additions include hard-boiled eggs, salmon, and avocado.
3:00pm: Snack on a handful of almonds and some blueberries.
6:00pm: Eat eight ounces of fish accompanied by vegetables like Brussels sprouts, string beans or asparagus.
8:00pm: Blueberries or nuts as dessert, for the final food consumed of the day.
If you’re considering a week of intermittent fasting interspersed with your keto diet, here’s what that week might look like.
Monday: Feeding hours between noon – 8pm. If you exercise on Mondays, try a midday workout when you’re fully fueled. Enjoy your last meal at 8pm. Keto meals might include a smoked salmon and avocado plate, or a steak and sweet potato dinner.
Tuesday: Fasting day. No calories consumed until 8pm.
Wednesday: Try a fasted workout in the morning. Begin eating at noon—you’ll probably be hungry. Reward yourself with a big chicken BLT salad for lunch and cheese omelette for dinner.
Thursday: No workouts, no all-day fasting. Since energy requirements are less on these days, begin eating at noon and try a turkey, cheese and avocado wrap for lunch, then salmon and asparagus for dinner.
Friday: Maybe the fasted workout didn’t go your way. Today, try a workout later in the day, planning your last 8pm meal as one high in protein. Try roasted chicken paired with creamy broccoli.
Saturday and Sunday: Here is another opportunity to try an extended fast, if you’re feeling up for it. But if you’re working out, ensure to properly fuel until you fully become fat-adapted. Maybe a nice long run outside is an option here. And use Sundays to meal prep, making the rest of the week easier!
This is an extremely simplified version, but starting this style of diet does not have to be complicated. Eat keto-friendly foods in a predetermined window. In this case, the standard eight-hour eating window was followed, however, you may choose to follow a shorter eating window if so desired.
Tying it All Together
Keto dieting and intermittent fasting can go hand-in-hand when done correctly. Both should encourage the body to enter a state of endogenous ketosis, and hopefully, boost the results.
But remember—this is a process. It’ll take a bit of time to find out the best schedule that fits your lifestyle. Don’t be afraid to experiment and adapt. The best diet plan is the one that you’re able to stick to.
Have you tried intermittent fasting combined with keto? Share your experience in the comments.
This arcticle was originally published on HVMN by Ryan Rodal
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