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).
Make sure you still eat enough. Intermittent fasting does help you naturally eat less during the day, but be sure you’re still eating nutritious ketogenic foods to avoid any deficiencies or metabolic issues. Use a website or app to calculate ideal caloric intake and your ketogenic macros for each day, then track them to make sure you’re getting sufficient nutrition.
Third, you've probably already fasted many times, even though you don't know it. Have you ever slept in late on the weekends and then had a late brunch? Some people do this every weekend. In situations like these, we often eat dinner the night before and then don't eat until 11am or noon or even later. There's your 16–hour fast and you didn't even think about it.
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.
I am a 65-year-old male who started IF seven weeks ago. I only eat between noon and 8pm. I am obese, but losing about a pound a week so far. Notably, except for time, I have not changed what I eat at all. My diet was never terrible or great, and now it is the same, a mix of raw fruit sometimes and a donut another time. But I only eat it during the appointed hours. Remarkably, I do not feel hungry. I used to eat comfort breakfasts like pancakes or waffles, and I thought I would miss them. But no, I truly am not hungry in the mornings. I often delay lunch, but I still stop eating at 8. That alone probably has cut many calories of desserts. Bottom line: works for me so far.
Yes, by cutting out an entire meal each day, you are consuming fewer calories per week – even if your two meals per day are slightly bigger than before. Overall, you’re still consuming fewer calories per day. This is highlighted in a recent JAMA study[b] in which both calorie restricted dieters and intermittent fasters lost similar amounts of weight over a year period.