I’ll share some of my experiences, now doing heavy strength training for 3 years in a fasted state: For my first “fasted” workout or two after starting an IF protocol, it was very weird to not eat before training. However, after a few sessions, I learned that my body could certainly function (and even thrive) during my training sessions despite not eating a pre-workout meal.


Fill your plate with plenty of healthy fats, such as coconut oil, avocados, olive oil, ghee and grass-fed butter as well as moderate amounts of protein foods like grass-fed meat, free-range poultry, fatty fish and eggs. Non-starchy vegetables, fresh herbs, nuts, seeds and healthy beverages like water, bone broth and green tea can all be enjoyed as well.
In practice, however, I would be concerned with eating enough. Based on my experience, teaching yourself to consistently eat more is one of the harder parts of intermittent fasting. You might be able to feast for a meal, but learning to do so every day of the week takes a little bit of planning, a lot of cooking, and consistent eating. The end result is that most people who try intermittent fasting end up losing some weight because the size of their meals remains similar even though a few meals are being cut out each week.
In addition, the refined sugar found in most beverages digests quickly, spiking both your blood sugar and your insulin levels. It's also highly addictive. Your body doesn't just want more, it needs more. In fact, according to a review published in Current Opinion in Clinical Nutrition and Metabolic Care in 2013, sugar and sweetened beverages and foods induce reward and craving responses in the brain that are comparable to the responses triggered by addictive drugs, which continue the cycle.
Finally, note that fasting to induce ketosis can also trigger a set of symptoms often known as the “keto flu.” Fasting ketosis symptoms may include decreased energy levels, increased cravings, digestive issues, muscle aches and dizziness. These symptoms can last between a few days to a few weeks when starting the ketogenic diet, but they typically subside once your body enters ketosis and begins to adapt.
Intermittent fasting is hard in the contemplation, of that there is no doubt. “You go without food for 24 hours?” people would ask, incredulously when we explained what we were doing. “I could never do that.” But once started, it’s a snap. No worries about what and where to eat for one or two out of the three meals per day. It’s a great liberation. Your food expenditures plummet. And you’re not particularly hungry. … Although it’s tough to overcome the idea of going without food, once you begin the regimen, nothing could be easier.”

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.
After determining your preferred protocol of intermittent fasting, you should start planning out your diet for the days that you do eat. On a standard keto diet, 75 percent of total calories should come from fat, 20 percent should be from protein and 5 percent should come from carbs. When getting started, however, you can start with a modified keto diet instead, which is often considered more flexible and easy-to-follow. With this diet plan, about 40–60 percent of calories should come from healthy keto fats with 20–30 percent from protein foods and 15–25 percent from carbohydrates.
In animal studies, after two weeks of intermittent fasting, female rats stopped having menstrual cycles and their ovaries shrunk while experiencing more insomnia than their male counterparts (though the male rats did experience lower testosterone production). (6) Unfortunately, there are very few human studies looking at the differences between intermittent fasting for men and women, but the animal studies confirm our suspicion: Intermittent fasting for long periods of time can sometimes throw off a woman’s hormonal balance, cause fertility problems and exacerbate eating disorders like anorexia, bulimia and binge eating disorder.
Although some of the intermittent fasting methods online seem more intense than others (some can last upwards of 48 hours), the beauty of intermittent fasting is that you get to choose and experiment with how long you fast. This not only allows you to determine how intermittent fasting can fit in within your lifestyle, but to discover the fasting sweet spot that helps you feel best physically.
The benefits of intermittent fasting translate to untrained overweight and obese individuals as well. One study published in Obesity Reviews found that eating fewer calories is effective for fat loss, but it does come with some muscle loss. However, if the subjects fasted for 24 hours and ate as much as they wanted on the next day for a period of 12 weeks, they lost significantly less muscle mass.

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.
If you have an addictive relationship with food and you struggle with portion control, track your calorie intake in your meals to make sure you’re not overeating. If you skip breakfast, you might be so hungry from this that you OVEREAT for lunch and this can lead to weight gain. Again, the important thing here is that with intermittent fasting you’re eating fewer calories than normal because you’re skipping a meal every day.
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