For Dr. Cecily Clark-Ganheart, a board certified physician in Maternal-Fetal medicine, obstetrics, and gynecology,  losing weight was not easy. She had attempted and succeeded before, only to gain it all back. But after she discovered intermittent fasting, she realized she had finally found a sustainable way to lose weight and keep it off. 

She lost over 55 lbs in 18 months by fasting everyday for 18 hours and doing a 36-hour fast once a week. When she hit a 3-month plateau, she focused on nutrition to get the scale moving again. She now fasts for 16 hours a day to keep her weight down. To stay motivated, she kept track of things other than the number on the scale:  Am I feeling more energy? Is my health improving? Are my clothes fitting better? Am I losing inches? “Look at the whole picture because there is more than one marker of health,” she says. 

Dr. Cecily A. Clark-Ganheart, in her office.

We invited Dr. Clark-Ganheart for a live webinar to answer all your questions related to fasting as a way to shed those extra pounds. We spoke about how to fast safely, what constitutes breaking a fast, what to eat when you’re not fasting, and how and when to practice extended fasting. 

Her responses were edited for brevity and clarity.

Webinar highlights

On the precautions people with certain conditions should take

In general, most people can fast. However, there are certain groups of people that should exercise caution and make sure to speak with their healthcare provider:

If you’re taking medications: Some meds are safe to take on an empty stomach and some are not. For example, NSAIDs like ibuprofen have to be taken with food because they’re hard on the lining of the stomach and can cause GI bleeding. Metformin can cause GI distress if you take it on an empty stomach. A lot of times the [medication] bottle will tell you whether or not you should take it on an empty stomach. It’s always important to read your prescriptions.

If you are pregnant, lactating or breastfeeding:  You should not fast for weight loss, but you can still fast overnight for gut rest (<14 hours).

If you’re trying to conceive: Be careful about extended fasting (>18 hours) because you don’t want the body to think that there aren’t adequate resources around for reproduction. 

If you have type 1 diabetes: Talk to your endocrinologist or primary care doctor so that they can monitor your sugars and help you adjust your insulin.

If you have type 2 diabetes: You can fast provided that your medications have been adjusted appropriately. For instance, if you take insulin and you haven’t eaten, you could become dramatically hypoglycemic. Let your doctor know what your fasting window is so they can decide whether you need to take your meds in the morning or at night.

if you have gallbladder stones: Sometimes people notice rapid weight loss with intermittent fasting. This can cause gallstones [because] rapid weight loss is associated with increased risk of gallstones. 

if you have polycystic kidney disease: You can fast, but make sure to stay hydrated.

If you have heart disease: You can fast but if you have congestive heart failure or some of the more serious conditions, you probably shouldn’t start off with a three-day fast. if you have heart issues, even fasting just from sunset to sunrise, and getting a 12 hour period of gut rest on a regular basis is beneficial.

On what breaks a fast

Technically, anything but water breaks a fast if you’re looking at fasting in its purest definition. If [your coffee and tea] are truly plain, they shouldn’t inhibit autophagy or spike your insulin, and you’re still getting all the benefits of fasting. I recommend that people stay away from sugar substitutes and heavy creams. If you have a significant amount of weight to lose, you will probably still notice some initial weight loss even if you do have cream in your coffee during your fasting window. But eventually what I see happen is that people get into plateaus and the ‘dirty fast’ no longer works . Your best bet is going to be water, or your black coffee and your plain tea. If you don’t like black coffee, delay your cup of coffee [with milk or creamer] until you open your eating window. 

Photo by Kira auf der Heide on Unsplash

Does X break a fast?

This highly depends on your definition of ‘breaking a fast’. If you consider anything that interrupts gut rest as breaking a fast, anything other than water would break a fast. If you’re just worried about staying in ketosis, a few calories coming from drinking coffee or tea with flavors or additives like butter, MCT oil, or skim milk won’t reduce your ketosis levels and they might help you during longer fasts. If you are worried something is kicking you out of ketosis, the best to do is to measure your ketone levels, either in blood or in your breath.

Do medicines and over-the-counter medications break my fast?: No. You still need to take your medicines as prescribed, but make sure you can take them on an empty stomach. 

Vitamins and supplements such as coenzyme Q 10: Yes, they interfere with the low-nutrient environment needed to achieve autophagy. Vitamins and other supplements are best absorbed when you take them with food, so save them for your eating window.

Water with lemon or apple cider vinegar: Yes, because of the flavor. But it won’t make a difference for weight loss. 

Skim milk, MCT oil, butter, heavy cream, coconut oil, artificial or natural sweeteners in your coffee? They break a fast for gut rest. If they’re not interfering with your weight loss or ketosis levels, you can use them. Switch to plain coffee if you stop losing weight. 

Celery juice? Yes. 

Gum? Yes, even if it’s sugar free. Most gum has a sweetness to it. Gum starts a cephalic response when you’re anticipating food which could spike insulin.

Bone broth? Yes. But if you’re new to fasting and you need something to prevent you from eating, you can do it. Eventually, you’re going to want to move away from drinking it regularly during fasting.

On what to eat to break a fast 

I recommend breaking your fast with whole foods. You don’t want to overwhelm your system with a lot of processed foods. When you do extended fasting, be careful not to break your fast with a huge, heavy meal. Break your fast over a couple hours [to avoid] upsetting your GI. I usually break extended fasts (>24 hours) with fermented food (I make my own fermented vegetables) to reseed my gut with healthy gut bacteria and probiotics. I wait about 30 minutes and then I’ll have a small, low-fat meal with vegetables and a low-fat cut of fish or chicken. 

Photo by Brooke Lark on Unsplash

On getting enough nutrients while fasting

What I find helps to combat under eating with fasting is to switch up your fasting schedule. For example,  a common thing I see people do is they’ll do one meal a day on Monday, Wednesday, and Friday, but then the other days, they’ll do a 16 hour fast. That variation still gives you the benefits of fasting but you’re making sure you have days where you’re getting 1200 calories or more.

On combining fasting with diet plans

You can combine intermittent fasting with a low-carb diet, a plant-based diet, or paleo for weight loss.  I think the key with all of these different diets is that you eat real foods and cut down on processed sugars. Intermittent fasting will work with whichever nutritional plan you choose to follow. But it should be a whole foods lifestyle for sustainability long term.

On the best fasting method to lose weight and how to overcome plateaus

There’s not necessarily going to be one fasting method that works for everyone. You may see someone have great success with one, and then you try it and you don’t like it because it’s not sustainable for you. So, don’t be afraid to play around with it. In general, it is easier to lose weight with intermittent fasting the more weight you have to lose. If you need to lose a hundred pounds, you [will lose weight quickly] by fasting for 18+ hours, for example. As you drop the weight, you may find that you need to switch it up more. What I generally recommend for weight loss [and overcoming plateaus] is schedule variation. Whatever you do for too long, your body adapts to. So 18:6 is a great place to start. But if you don’t find that you’re losing the weight you want with 18 hours of fasting, that’s when I would  throw in a few days of one meal a day and alternate.

[When thinking about how to get out of a plateau,] don’t forget about the other things in life that can cause weight gain or stress. If you’re sleeping less than six to seven hours a day, that’s associated with weight gain. If you have a lot of emotional stress going on, that can also affect your ability to lose weight. Alcohol is another reason for a plateau. Pick one day a week to drink alcohol and practice moderation. And if you can’t moderate, it’s probably best to cut it out or only have it once or twice a month until you hit your goal weight.

Photo by i yunmai on Unsplash

On how to reduce cravings during your eating window

Limiting processed foods helps to reduce hunger. If you’re used to drinking sweet tea or pop or if you usually have a dessert or something processed, I would try to cut that out for the last meal of your day to reduce cravings. Make sure your last meal of the day is filling. I’ll sometimes add olive oil or avocado oil to my meal because they [help you feel full]. Protein is thought to help suppress hunger longer than carbohydrates. If you’re plant-based, add more plant based proteins like lentils or beans.  And if you’re doing low carb, look for wild-caught produce or grass-fed meats.

On fasting and having a ‘cheat’ day

Once a week, fast for 12 hours rather than your usual 16 or 18 or your one meal a day. In that time, you can incorporate some other things that you were lacking before while still being mindful about what you’re eating. I wouldn’t do it more than once a week because that can induce cravings and make it harder to get back into the habit of fasting.

On extended fasting

I really like the seasonal approach to extended fasting where you close out or enter each season with an extended fast. And then after that, you go back to your regular fasting pattern. That would give you a nice, extended fast for autophagy four times a year. The point of extended fasting, contrary to popular belief, is not to lose weight. It is to either tap into autophagy or sometimes to break a set point if you have a plateau. Whenever someone says they want to do extended fasting, my first question is: What’s your goal with this extended fast? If it’s to wear a dress by Saturday, that’s not a good reason to use extended fasting. Extended fasts (3-5 days) can be a stressor on the body. Just like with anything in life, more is not always better.

If you do alternate day fasting, keep your fasting period under 36 hours and don’t restrict calories on your non-fasting days. Once you hit your goal weight, fast for 16 hours for maintenance.

If you like doing fasts between 36-48 hours, do them once a week. The shorter fasts can still help get your results. Keep up on your calories to get adequate nutrition.

On exercise during fasting

If you’re fasting under 36 hours, most times you don’t have to change your exercise regimen. You might just have to get used to working out without your pre-meal snack, which is why I think those type of fasts are more sustainable longterm because you really don’t have to alter your life that much.

[You can] work out during extended fasts, but  pay attention to hydration and electrolyte supplementation. At the start of a three day fast, work out in a fasted state the first day. Once you get further into your fast, you may decide to not do anything hardcore and just go walk for a couple of miles.

On fasting and the female cycle

I’ve seen a lot of people blame extended fasting on why their menstrual cycle became irregular, but then they’re also working out two or three hours a day and they’ve cut their calories when they’re not fasting. And so they’re putting a lot of different stressors all at once on their body, so of course their menstrual cycle is going to go crazy. That’s the other reason why you don’t need to do the extended fasts too often. You can do regular intermittent fasting and a seasonal extended fast and you’re not going to mess up your your cycle. If you’re doing extended fasts several times a month, initially your body may keep up, but eventually that’s not a good idea.

On fasting when you work the night shift

I recommend fasting through your shift and having your meals at home. Eat at home before you go to night shift. While you work, you may use bone broth or coffee while you adjust. When you get off in the morning, have your breakfast at home and go to sleep. This way you get in 12 hour periods of fasting and avoid eating during the night when digestion is slowest and the insulin responses are the highest. Another alternative is going to sleep immediately after you get home. And then when you wake up, have your first meal and then eat again before your night shift.

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