The concept of intermittent fasting has taken the world by storm these last couple years, mostly due to the popularity of the ketogenic diet.

As a nutritionist, I don’t necessarily love or hate keto; I think it definitely has its place in the therapeutic, food-as-medicine world, and I think most Americans in general could stand to eat way less carbohydrates than they currently do (ESPECIALLY refined and processed carbs with added inflammatory vegetable oils).

That’s not to say that everyone needs to be aiming for ketogenic levels of carb vs. fat intake, but finding the right kinds of carbohydrates and consuming them in appropriate amounts is important for all of us (and this goes for fats and proteins too — which is why it can be helpful to seek assistance from a professional. Navigating the world of macronutrient balance is confusing and, honestly, personal to your body’s needs).

The problem with the explosive popularity of the ketogenic diet is that everyone and their third cousin thinks they have it nailed down to a science and that “THEIR WAY IS THE ONLY WAY THAT WORKS!!” or that you have to only eat bacon and butter to do it right. Oh, and practice fasting.

First of all, no. Just no. Please do not listen to these people.

Secondly, fasting can be a great tool in your metabolic toolbox, but there are different ways to do it and you should make sure you’re practicing it safely. It probably wouldn’t hurt to get professional assistance on this, too.

It has been shown to be supportive of body fat loss (which is why it’s so popular), and is more effective than just reducing caloric intake (which is only supportive short-term anyway). Fasting also provides brain and organ support for those looking to practice it for other reasons or don’t have body fat loss goals. 

Let’s break down the different ways you can intermittently fast, why each option may or may not be right for you, and what I favor as a nutritionist.

I want to lovingly remind you that this list is not an actual recommendation for you. I can’t make sweeping generalizations for all people without having actually worked one-on-one with them. That’s neither wise nor fair to you, as someone looking for answers. You deserve tailored goals. If you have any questions about this, please reach out and let me know.

1. Actual intermittent fasting (a specific eating and fasting window)

I want to emphasize right from the beginning that you should be getting in all of your calories during this scheduled eating window. You do not want to begin fasting for long periods of time AND decreasing your total calories. That’s a stressful recipe for bodily disaster.

The daily window-style fasting could look like:

• 12:12 — finish eating by 7 PM and eat again at 7 AM, having fasted for 12 total hours. This is usually a good place to start, as most people have trouble adjusting to fasting in the beginning. Twelve hours should be pretty easy since you’re hopefully sleeping for more than half the time.

• 14:10 — finish eating by 7 PM and eat again at 9 AM, having fasted for 14 total hours — again, most done while asleep.

• 16:8 — finish eating by 7 PM and eat again at 11 AM. You get the idea.

The times to stop and start consuming calories will be up to you and your work/life schedule, sleep needs, etc. The times I provided above are just examples.

I normally have my interested clients start on the 12:12 window, because as I mentioned, this is the easiest place to begin and is doable for most people. Keep in mind, the average American has an eating window of 15 hours (or more!) on a regular basis, so taking it down to 12 is a great way to slowly and safely transition your body’s hormone signals and expectations. Once you get this window down and you’re feeling good, you can try the next step up in lengthening the fasting window.

Pros: It’s adaptable to your work schedule and lifestyle, you can usually get your body into ketosis during the fasting window, and it provides your digestive system a well-deserved break from breaking down food. If a client ever expresses interest in trying fasting, we start here.

Cons: It’s not as beneficial for autophagy as an extended fast would be, as we will address and explain below. Stay with me here!

2. Full-day fasting (24 hours) — also known as “Eat-Stop-Eat”

Similar to the “window” method, here you would, for example, stop eating after you finish dinner — say, 6 PM — and not eat again until 6 PM the following day. This is obviously harder, so I don’t recommend just doing this right away or without professional guidance.

Pros: This longer fast can keep you in ketosis while ramping up autophagy, and you can choose to do it as needed. Some people do it on Sundays if they tend to have an easier schedule, etc. — others choose to only do this once every few months. Again, it’s adaptable. Interesting point to research: full-day fasting (or as close as possible given the parameters of someone’s life) has been shown to reduce symptoms of chemotherapy treatment if done properly. I’m not a doctor nor am I making a medical recommendation, but it’s super interesting and something to do personal inquiry on or ask your physician.

Cons: A lot harder and is usually only easier when you’ve been eating high-quality fats in larger proportions — not necessarily ketogenic levels but still lower-carb, higher-fat. It also can mess with your stress response if you already have dysregulated cortisol or HPA-axis issues, so it’s not recommended for people trying to manage their life stress.

3. Alternate day fasting (sometimes called 4:3)

This takes the 24-hour fasting up a notch by incorporating it more often, literally as it sounds in the description — you could fast for 24 hours on Monday, eat normally Tuesday, and fast again on Wednesday, etc. The “4:3” title comes from the off-on cycle of eating in this method during the 7-day week.

Some people do this in what’s called a “5:2” ratio, where you eat normally for five days of the week, and do a fast for two days of the week — but the proportion is up to the individual. It can be two 24-hour fasts, spread throughout the week, or one longer 48-hour fast (which is obviously more intense).

Pros: You quite literally become a “pro” at cleaning out your cellular waste and normalizing your hunger and satiety hormones on a regular basis, provided that you’re not chronically stressed or have other contraindications. You can also try “fasting-mimicking” (see next option) during your fasted days on this method, if you choose, to get you acclimated.

Cons: This can again be stressful on your body over time if you haven’t dealt with your chronic stress issues. This is also difficult if you’re someone who trains or exercises intensely multiple times per week — this type of fasting would likely be way too much for your body and you risk nutrient deficiencies and burning muscle for energy due to extreme need. This is more for people who’ve been practicing fasting safely for longer periods of time.

4. Fasting-mimicking

This is almost like fasting for 24-hours except that instead of abstaining entirely from all food, you eat 20-25% of your normal caloric intake, so for someone who typically eats 2,000 calories in a normal day (note: please be eating more than this), you’d have 400-500 calories total for the day, from nutrient dense foods (not Fritos or donuts).

Pros: A good way to focus on nutrient density in your foods. This has also been studied for weight loss and shown to be effective, but…

Cons: ...my take on that specific finding is that it’s just like eating in a caloric deficit, which is always shown to be good for weight loss. That whole “calories in < calories out” adage — it sounds awesome on paper but a lot of problems can develop from chronic undereating and this is a slippery slope, in my opinion. Plus it can confuse your hunger hormones and your body’s feelings of safety. I don’t normally recommend this to clients. Either fast or don’t, but this in-between stuff is not for most people.

5. Fat fasting

This is as plain as it sounds — you consume calories but all almost entirely from fat. Sources could include coconut, avocado, olives, high-fat meats and seafood like salmon or sardines, whole eggs, properly-oiled condiments like mayonnaise and mustard, and nuts and nut butters.

I’ve never done this personally, and it basically sounds just like eating a ketogenic diet, so… again, my opinion is either fast or don’t.

*Caveat -- if you wanted to start your fasting window or day with a fatty coffee, this is technically a fat fast also, and can have TONS of benefits. This is one of the more popular fasting ideas. I will include more details on this in a future post, but feel free to contact me if you have questions in the meantime!

Pros: It helps get you into ketosis, because you’re consuming fat for fuel.

Cons: ...it isn’t really “fasting” as much as it is shifting your macronutrient intake, unless you’re sticking to something like a fatty coffee.

6. Bone broth fasting

This is one of my personal favorites mostly because it’s so delicious while being efficacious. Again, it’s as simple as it sounds — you fast from all food and calories except for water, your caffeine of choice (plain only), and bone broth.

Now I’m not talking the regular chicken broths or stocks you can buy for 99 cents at the grocery store. I mean the good stuff — the quality bone broth that comes from organically raised animals and has been simmered longer than 24 hours to get all the good stuff. It should be gelatinous in nature when not warm or hot.

You just sip on it throughout the day to provide your body sodium and nutrients while maintaining the benefits of fasting. I personally will sip eight ounces every time I feel a pang of hunger coming on while fasting, because it helps control the blood sugar response. I also add high-quality sea salt and herbs/spices to mine -- like turmeric, rosemary, pepper, etc.

It’s the perfect time of year right now to be sipping on warm mugs of this immune-boosting superfood!

Pros: Satiating, nourishing, comforting, and delicious. Doesn’t stress your digestive system and actually supports its healing.

Cons: This would be extremely difficult for vegans, obviously. It’s also technically consuming calories, albeit small (~40-60 calories per cup), and mostly from protein. Otherwise I can’t think of any downsides -- biased and not sorry at all.

7. Water fasting

Again, plain as day… all you’d consume is water, preferably with tons of salt and electrolytes.

This is what’s known to be 100% fully true “fasting” — because you’re literally taking in only hydration and nutrients, and abstaining from all forms of calories. While bone broth fasting is great, there are still calories there.

Technically speaking… a “dry” fast is true fasting, where you don’t consume ANYTHING… but never in a million years would I attempt nor recommend this method. Just figured I’d clarify in case someone had questions about the difference between the two.

Pros: Truly getting into ketosis, burning stored body fat for fuel, and promoting autophagy at the highest level.

Cons: Extremely difficult to do if you’re not used to it or prepared, and can be dangerous if not done properly. What I mean by that is if you’re not hydrating and taking in electrolytes in the right proportions, you can through off your osmotic balance and cause issues. I don’t recommend anyone do this without professional help.

8. One meal a day (OMAD)

Self-explanatory, as usual, but this is an extension of the full-day/24-hour fast example above. Folks practicing OMAD have been honing in their expertise with fasting longer-term (usually for years) and consume all their daily caloric needs (yes, you read that right — ALL of their calories) within one meal (or a small eating window of 2-3 hours).

Pros: You don’t have to: worry about food, constantly think about it, always be in the kitchen prepping, etc. 

Cons: You need to be practicing safe fasting for a while to cozy into this sweet spot, and many people fail to get 2,000+ calories in this small window (it’s just hard to eat that much that quickly for most people). Again, I don’t ever recommend it.

The Bottom Line

Fasting can be a great adjunct to a healthy diet and lifestyle but, literally, the “healthy” part is a requirement. I caution against fasting for the general public for a lot of reasons, which will be forthcoming in the next post. Make sure you know what’s right for you before you dive into it, as with trying anything new. I’ll see you shortly for the second part of this series.