None of the coffee additives caused a significant drop in our blood ketone levels. At 120 minutes, my, (Becky’s), ketone readings increased after drinking black coffee, coffee with cream, coffee with MCT oil, and coffee with butter. At 120 minutes, Keith’s ketone readings dropped by 0.1 mmol/L after drinking only black coffee. His ketone readings rose slightly after consuming coffee with cream, MCT oil, and butter.
This is the same as the 8-to-6 window plan, but you are extending your fasting time an extra four hours. I personally practice this plan during the workweek. I'm not a breakfast person, so I just enjoy a few cups of herbal tea to start my day. With this plan you will be eating only between the hours of 12 p.m. and 6 p.m. for a full 18 hours of fasting within a 24-hour period.

Forms of intermittent fasting exist in religious practices in various groups across the world.[12] Religious fasting regimens include, but are not limited to, Vrata in Hinduism, Ramadan fasting (Islam), Yom Kippur fasting (Judaism), Orthodox Christian fasting, Fast Sunday (The Church of Jesus Christ of Latter-day Saints), and Buddhist fasting.[12] Certain religious fasting practices, like Buddhist fasting, only require abstinence from certain foods, while others, like the Jewish fast on Yom Kippur, last for a short period of time and would cause negligible effects on the body.[12]
Based on this, researchers from the University of Alabama conducted a study with a small group of obese men with prediabetes. They compared a form of intermittent fasting called “early time-restricted feeding,” where all meals were fit into an early eight-hour period of the day (7 am to 3 pm), or spread out over 12 hours (between 7 am and 7 pm). Both groups maintained their weight (did not gain or lose) but after five weeks, the eight-hours group had dramatically lower insulin levels and significantly improved insulin sensitivity, as well as significantly lower blood pressure. The best part? The eight-hours group also had significantly decreased appetite. They weren’t starving.
The four-hour eating window — which Hofmekler refers to as the “overeating” phase — is at night in order to maximize the Parasympathetic Nervous System’s ability to help the body recuperate, promoting calm, relaxation and digestion, while also allowing the body to use the nutrients consumed for repair and growth. Eating at night may also help the body produce hormones and burn fat during the day, according to Hofmekler. During these four hours, the order in which you eat specific food groups matters, too. Hofmelker says to start with veggies, protein and fat. After finishing those groups, only if you are still hungry should you tack on some carbohydrates.
So what’s the first step in getting started? Each method has its own guidelines for how long to fast and what to eat during the “feeding” phase. Below, you’ll find the five most popular methods and the basics of how they work. Keep in mind, intermittent fasting isn’t for everyone. Those with health conditions of any kind should check with their doctor before changing up their usual routine. Note that personal goals and lifestyle are key factors to consider when choosing a fasting method.
Because of the massive amount of sugar that Americans eat on average, most people have become dependent on glucose, instead of fatty acids, for energy. Every supermarket, grocery store and coffee shop sells an abundance of sugary foods and drinks. When you eat a lot of sugar, and that sugar isn't utilized for energy, your body breaks it down and eventually stores it as body fat.
Put a coffee filter or your cheesecloth (you can even use a paper towel if you don’t have a coffee filter/cheesecloth) into the mesh strainer and place it over another glass container. Gently pour the filtered coffee through the filter and let it slowly drip into the glass container below. If the filter fills up, just wait and let it drip naturally (this could take up to 10 minutes).
Fasting on keto can be incredibly beneficial, especially if you’ve reached a plateau and aren’t seeing results from the ketogenic diet alone. While it’s not required, keto intermittent fasting can bring the benefits of your diet to the next level and help optimize your health. It is also thought to speed up ketosis by helping your body burn through glycogen stores more quickly, which can help sidestep symptoms of the keto flu to get faster results.

Since all of your hormones are so deeply interconnected, when one hormone is thrown off balance, the rest are also negatively impacted. It’s like a domino effect. As the “messengers” that regulate nearly every function in your body — from energy production to digestion, metabolism, and blood pressure — you don’t want to disrupt their natural rhythm.


Although there's no specific dietary recommendation when intermittent fasting, many people choose to combine it with a low-carb, ketogenic diet. When it's time to eat, include foods that are high in good fats and low in carbohydrates. That means eating nuts, seeds, vegetables, avocado, olives, meat and fish, while avoiding whole grains, fruits, starchy vegetables, sugary drinks and anything processed.

Alternate-day fasting. Go back and forth between feasting days and fasting days. Eat like a king or queen one day, then eat nothing the next. This will probably be the most challenging fasting option for most people. If you try it, make sure you’re eating a ton on your feast days, otherwise you’ll fall into a major calorie deficit and you’ll likely feel miserable.
Conversely, a 2013 study completed by researchers at Washington University School of Medicine, presented the exact opposite, showing increased reactions in receptors on the tongue, when participants were given artificial sweeteners. Their study concluded that if the receptors are capable of detecting sweetness, even though calories aren’t present, a hormonal response (insulin release) is likely.
Black coffee won't break your fast or take you out of ketosis. In fact, according to a report published in the Journal of Basic and Clinical Physiology and Pharmacology in 2017, caffeine may even increase your metabolism, which will help promote weight loss. Black coffee also helps curb your appetite, which can make getting through your morning fast much more manageable.

Most of us have contemplated going on a diet. When we find a diet that appeals to us, it seems as if it will be a breeze to do. But when we get into the nitty gritty of it, it becomes tough. For example, I stay on a low–carb diet almost all the time. But if I think about going on a low–fat diet, it looks easy. I think about bagels, whole wheat bread and jelly, mashed potatoes, corn, bananas by the dozen, etc. — all of which sound appealing. But were I to embark on such a low–fat diet I would soon tire of it and wish I could have meat and eggs. So a diet is easy in contemplation, but not so easy in the long–term execution.

No cravings. Fat doesn’t spike your blood sugar levels. In fact, a keto diet is so effective at stabilizing blood sugar that it got type II diabetics off their medication entirely, according to a recent study.[15] If you pair a keto diet with fasting, your blood sugar will stay stable and low (but not too low) all day. Say goodbye to the cravings, fatigue, and mood swings that make high-carb fasting so difficult.
Islam is the only major religion that engages in a fasting practice reflective of intermittent fasting in terms of both food consumption and diet consistency.[12] The duration of the Ramadan fast is between 28 and 30 days, depending on the year, and consists of not eating or drinking from sunrise until sunset.[12] During the holiday, Muslims eat twice per day: once in the morning before dawn and once in the evening after dusk.[12] A meta-analysis on the health of Muslims during Ramadan shows significant weight loss during the fasting period of up to 1.51 kilograms (3.3 lb), but this weight was regained within about two weeks of Ramadan ending.[13] The analysis concluded that "Ramadan provides an opportunity to lose weight, but structured and consistent lifestyle modifications are necessary to achieve lasting weight loss."[13] Negative effects of Ramadan fasting include increased risk of hypoglycemia in diabetics as well as inadequate levels of certain nutrients.[12]
Cons: Going 24 hours without any calories may be too difficult for some — especially at first. Many people struggle with going extended periods of time with no food, citing annoying symptoms including headaches, fatigue, or feeling cranky or anxious (though these side effects can dimish over time). The long fasting period can also make it more tempting to binge after a fast. This can be easily fixed… but it takes a lot of self-control, which some people lack.
Eating all your meals in an 8-hour window (say, eating between noon and 8PM, and fasting the other 16 hours a day) causes significant weight loss without counting calories.[1]  While this type of intermittent fasting causes weight loss no matter what people eat, research shows that people who do it in a healthy manner lose twice as much weight (7% vs. 3% of their body weight) as those who fast while still eating junk. So it’s still important to follow a high-performance diet like the Bulletproof Diet while you fast.
As a functional medicine practitioner, I see a wide range of health problems that all stem from chronic inflammation. And while acute inflammation is a natural and healthy response to help fight off pathogenic bacteria and infections, long-term chronic inflammation that doesn’t subside when the threat is gone can contribute to everything from autoimmune conditions to cancer.
The problem is that we tend to spend so much time in the fed state, fueling our bodies exclusively with glucose, that we become addicted. Once the flow of glucose stops and our insulin levels drop, we start getting hunger pains. This is one of the reasons that overweight individuals — people with more than adequate energy stores in their fat cells — often have such a difficult time cutting back on food intake. They’re not starving, but they’re not getting the glucose their bodies are used to.

Cons: Even though it’s nice to eat a few snacks rather than go without any food for 20-plus hours, the guidelines for what you need to eat (and when) can be hard to follow long-term. The strict schedule and meal plan may also interfere with social gatherings. Additionally, eating one main meal at night — while following strict guidelines of what to eat, and in what order — can be tough. It’s especially hard for those who prefer not to eat large meals late in the day.
AN IMPORTANT CAVEAT: Intermittent Fasting can be more complex for people who have issues with blood sugar regulation, suffer from hypoglycemia, have diabetes, etc. If you fit into this category, check with your doctor or dietitian before adjusting your eating schedule. It also affects women differently (there’s a whole section dedicated to that below)
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