As a lifestyle-leaning research doctor, I needed to understand the science. The Obesity Code seemed the most evidence-based summary resource, and I loved it. Fung successfully combines plenty of research, his clinical experience, and sensible nutrition advice, and also addresses the socioeconomic forces conspiring to make us fat. He is very clear that we should eat more fruits and veggies, fiber, healthy protein, and fats, and avoid sugar, refined grains, processed foods, and for God’s sake, stop snacking. Check, check, check, I agree. The only part that was still questionable in my mind was the intermittent fasting part.
There are MUCH bigger fish to fry with regards to getting healthy than a few calories here and there during a fast. 80% adherence that you stick with for a year is better than 100% adherence that you abandon after a month because it was too restrictive. If you’re trying to get to a minimum bodyfat percentage, you’ll need to be more strict – until then, however, do what allows you to stay compliant!
When the female body senses it’s headed towards famine, it will increase the production of the hunger hormones, ghrelin and leptin, which signal the body that you’re hungry and need to eat (2). Additionally, if there’s not enough food for you to survive, your body is going to shut down the system that would allow you to create another human. This is the body’s natural way of protecting a potential pregnancy, even if you’re not actually pregnant or trying to conceive.
And while this may sound difficult, it’s really not. After all, the reasons our bodies store fat in the first place is because we, as a species, aren't really designed for constant eating. The three-square-meals (or more) eating plan is a relatively new phenomenon in human history; for much of our past, feast and famine were the order of the day. Our bodies know how to handle long stretches without food, and they know how to make good use of the “feasts” when they come along.
There are many different variations of intermittent fasting as well. Dr. Dom D’Agostino, the well-known ketogenic diet researcher, suggests doing a longer intermittent fast for 3 days, 3 times a year. This means not eating for 3 days, and eating normally until the next fast. Daily intermittent fasts are recommended as well. He says that it is ideal to have one to two meals after fasting for most of the day to reap the benefits of intermittent fasting every day.
Whichever option you choose, there's enough evidence to show that intermittent fasting has many health benefits. Dr. Palanisamy sums it up best by saying, "The final caveat is that some fasting is better than none. So if having a regular or even bulletproof coffee is the only way that you can stick with the practice of intermittent fasting, then it's probably worth it."

So, if your goal is ketosis, intermittent fasting can help you get into ketosis even faster. Simultaneously, the keto diet makes intermittent fasting more doable because your body is already adapted to fasting with ketones. In addition, most people naturally eat less frequently on keto because of the high satiety level, so you’re likely already used to bigger windows without food.


Keep these studies in mind as your body tries to play tricks on you during your first day of fasting.  Even after three days of fasting, health complications are highly unlikely. However, it is important to know about the possible issues that can be caused by fasting. If you choose to incorporate fasting into your daily diet, you typically want to eat every day as well. Occasionally going on a longer period of fasting.
One monk, for example, set out to do a 40 day fast with medical supervision while maintaining his daily activities in the monastery. After 36 days, the medical professionals had to step in due to “profound weakness” and low blood pressure when standing. Although the monk fasted for 15 days longer than Ghandi, the medical professionals were able to stop the fast in time so that he could recover.

Perhaps most importantly, intermittent fasting is one of the simplest strategies we have for taking bad weight off while keeping good weight on because it requires very little behavior change. This is a very good thing because it means intermittent fasting falls into the category of “simple enough that you'll actually do it, but meaningful enough that it will actually make a difference.”


You’re consuming less food and thus spending less money. Rather than overeating to put on 1 pound of muscle and 4 pounds of fat in a week or two, you’re aiming to eat exactly enough to put on 1 pound of muscle without adding much fat on top of it.  Yeah, it’s a delicate balance, but there’s far less swing involved. You are just slowly, steadily, and consistently building muscle and strength over many months.
This is excellent, thank you! One thing I would love to see added to this research is the keto effect of just water over those 120 minutes, and THEN the keto effect of adding a tad bit of protein, such as collagen powder (I use the green tub great lakes powder; it dissolves great in coffee). I feel like that might put your test even more into an annals of science, and for us folks who don’t have the finger prick blood testers, it would be fun to know. Also, sugar free sweeteners like splenda (!!) or stevia–do they have any effect? Anyway–great read, exactly what I was looking for when I googled my question.

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Surprisingly, since I've started intermittent fasting I've increased muscle mass (up 10 pounds from 205 to 215), decreased body fat (down 3% from 14% to 11%), increased explosiveness (set a personal best with a clean and jerk of 253 pounds a few months back), and decreased the amount of time I've spent training (down from 7.5 hours per week to 2.5 hours per week).


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.
There are different types of intermittent fasting, but the most common involves only eating within a certain window of time each day. For example, you might only eat between 12pm and 6pm each day, giving you a 6-hour “feeding” window when you eat all of your calories for the day. That means you’ll be fasting for 18 hours in between. Your intermittent fasting ratio would then be 18/6.
An intermittent fast is a brief fast where, for 12–16 hours or more, you don’t eat anything except water (a few exceptions apply). And while that may sound incredibly difficult to achieve, you might already be fasting without knowing it if you eat dinner at, say, 7 p.m. and break your fast in the morning between 7—10 a.m. — and if you only have water and black coffee or tea between. 
There’s a ton of incredibly promising intermittent fasting (IF) research done on fat rats. They lose weight, their blood pressure, cholesterol, and blood sugars improve… but they’re rats. Studies in humans, almost across the board, have shown that IF is safe and incredibly effective, but really no more effective than any other diet. In addition, many people find it difficult to fast.
This process can be used as a way to get you into ketosis more quickly, so you can transition gracefully into a ketogenic lifestyle or as a way to stimulate autophagy and fat loss. If you can’t go without fat for the full 3 day fast — it’s okay — you will still illicit many of the benefits of fasting by limiting your protein and carbohydrate intake.

It doesn't matter when you start your 8–hour eating period. You can start at 8am and stop at 4pm. Or you start at 2pm and stop at 10pm. Do whatever works for you. I tend to find that eating around 1pm and 8pm works well because those times allow me to eat lunch and dinner with friends and family. Breakfast is typically a meal that I eat on my own, so skipping it isn't a big deal.
Mackenzie has worked in several branches of a very popular national chain of coffee shops and has experience with customers trying to comply with a variety of diets. Keto, Whole30, Vegan, and many more. She says that she and her staff have learned a number of tricks to help customers who struggle with switching to black coffee after drinking their favorite “Large Caramel Cappuccino with Whipped Cream” for years!
As a lifestyle-leaning research doctor, I needed to understand the science. The Obesity Code seemed the most evidence-based summary resource, and I loved it. Fung successfully combines plenty of research, his clinical experience, and sensible nutrition advice, and also addresses the socioeconomic forces conspiring to make us fat. He is very clear that we should eat more fruits and veggies, fiber, healthy protein, and fats, and avoid sugar, refined grains, processed foods, and for God’s sake, stop snacking. Check, check, check, I agree. The only part that was still questionable in my mind was the intermittent fasting part.
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