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.
I’ve read several places that adding gelatin or collagen to coffee breaks the fast, but I don’t understand why since there are no carbs, only protein, and fewer than 50 calories per tablespoon. Have you tested this? It would be great to be able to add protein to my morning coffee so I would love to know. Would also love to know if one tablespoon of coconut cream affects ketones and glucose.

You’ll run out of energy. When you don’t have anything in your system for several hours, your blood sugar will eventually drop below baseline. If you’ve ever had a blood sugar crash, you know how this state feels. Sleepiness, trouble focusing, lightheadedness, intense cravings, and the occasional mood swing typically accompany low blood sugar. Your cells run low on fuel and they start demanding that you give them more carbs.[13]
Also, be aware that when you exercise, your body directly burns away glycogen (a form of glucose stored in the muscles). Fasting depletes these stores, which can mean less available energy for the muscles to use when they need it. This can lead to extreme fatigue and decreased performance. The best fasting tips for athletes are to precede each workout with a low-calorie protein shake designed to deliver creatine, BCAAs, beta-alanine, and other amino acids directly to the muscles as they work them, and then to follow each workout with a whey-protein supplement to replenish depleted nutrient stores in order to speed up the recovery process. These workout supplements won’t add much to your overall calorie count, and will help ensure that your intermittent fasting schedule and your workout regimen aren’t getting in each other’s way.
So how long does it take to go into ketosis when fasting? On a standard keto diet, it typically takes around 2–3 days to reach ketosis, although it can take up to seven days in some cases. However, many people find that keto adaptation intermittent fasting can speed up the process and help your body burn through glycogen stores more quickly to help enter ketosis.
Worried about losing muscle if you fast? Maybe this will put your concerns to rest: a single 24-hour fast increased human growth hormone (HGH) by 2000% in men and 1300% in women.[2]  HGH plays an integral role in building muscle. Boosting your levels this high will have huge effect on your physique. Research shows that higher levels of HGH leads to lower levels of body fat, higher lean body mass and improved bone mass.[3]

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.
Of course, fasting — regardless of the method — isn’t for everyone. If you have any medical conditions or special dietary requirements, it’s smart to consult a doctor before giving intermittent fasting a shot. Anyone who tries it should also plan to be highly self-aware while fasting. If it’s not agreeing with you, or if you need to eat a little something to hold you over, that’s just fine. It takes our bodies time to adjust, and some require more than others. Keep in mind that hormones can make it harder for women to follow a fasting plan than for men. “Be cautious at first, and start slowly [with a shorter fast],” Shanks recommends. If it doesn’t make you feel better, try something different, or accept the fact that maybe fasting isn’t for you.
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.
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.
When you eat a meal, your body spends a few hours processing that food, burning what it can from what you just consumed.  Because it has all of this readily-available, easy to burn energy (thanks to the food you ate), your body will choose to use that as energy rather than the fat you have stored.  This is especially true if you just consumed carbohydrates/sugar, as your body prefers to burn sugar as energy before any other source.
×